ceph: move generic flushing code into helper

[pandora-kernel.git] / fs / ceph / caps.c

#include "ceph_debug.h"

#include <linux/fs.h>
#include <linux/kernel.h>
#include <linux/sched.h>
#include <linux/vmalloc.h>
#include <linux/wait.h>

#include "super.h"
#include "decode.h"
#include "messenger.h"

/*
 * Capability management
 *
 * The Ceph metadata servers control client access to inode metadata
 * and file data by issuing capabilities, granting clients permission
 * to read and/or write both inode field and file data to OSDs
 * (storage nodes).  Each capability consists of a set of bits
 * indicating which operations are allowed.
 *
 * If the client holds a *_SHARED cap, the client has a coherent value
 * that can be safely read from the cached inode.
 *
 * In the case of a *_EXCL (exclusive) or FILE_WR capabilities, the
 * client is allowed to change inode attributes (e.g., file size,
 * mtime), note its dirty state in the ceph_cap, and asynchronously
 * flush that metadata change to the MDS.
 *
 * In the event of a conflicting operation (perhaps by another
 * client), the MDS will revoke the conflicting client capabilities.
 *
 * In order for a client to cache an inode, it must hold a capability
 * with at least one MDS server.  When inodes are released, release
 * notifications are batched and periodically sent en masse to the MDS
 * cluster to release server state.
 */


/*
 * Generate readable cap strings for debugging output.
 */
#define MAX_CAP_STR 20
static char cap_str[MAX_CAP_STR][40];
static DEFINE_SPINLOCK(cap_str_lock);
static int last_cap_str;

static char *gcap_string(char *s, int c)
{
        if (c & CEPH_CAP_GSHARED)
                *s++ = 's';
        if (c & CEPH_CAP_GEXCL)
                *s++ = 'x';
        if (c & CEPH_CAP_GCACHE)
                *s++ = 'c';
        if (c & CEPH_CAP_GRD)
                *s++ = 'r';
        if (c & CEPH_CAP_GWR)
                *s++ = 'w';
        if (c & CEPH_CAP_GBUFFER)
                *s++ = 'b';
        if (c & CEPH_CAP_GLAZYIO)
                *s++ = 'l';
        return s;
}

const char *ceph_cap_string(int caps)
{
        int i;
        char *s;
        int c;

        spin_lock(&cap_str_lock);
        i = last_cap_str++;
        if (last_cap_str == MAX_CAP_STR)
                last_cap_str = 0;
        spin_unlock(&cap_str_lock);

        s = cap_str[i];

        if (caps & CEPH_CAP_PIN)
                *s++ = 'p';

        c = (caps >> CEPH_CAP_SAUTH) & 3;
        if (c) {
                *s++ = 'A';
                s = gcap_string(s, c);
        }

        c = (caps >> CEPH_CAP_SLINK) & 3;
        if (c) {
                *s++ = 'L';
                s = gcap_string(s, c);
        }

        c = (caps >> CEPH_CAP_SXATTR) & 3;
        if (c) {
                *s++ = 'X';
                s = gcap_string(s, c);
        }

        c = caps >> CEPH_CAP_SFILE;
        if (c) {
                *s++ = 'F';
                s = gcap_string(s, c);
        }

        if (s == cap_str[i])
                *s++ = '-';
        *s = 0;
        return cap_str[i];
}

/*
 * Cap reservations
 *
 * Maintain a global pool of preallocated struct ceph_caps, referenced
 * by struct ceph_caps_reservations.  This ensures that we preallocate
 * memory needed to successfully process an MDS response.  (If an MDS
 * sends us cap information and we fail to process it, we will have
 * problems due to the client and MDS being out of sync.)
 *
 * Reservations are 'owned' by a ceph_cap_reservation context.
 */
static spinlock_t caps_list_lock;
static struct list_head caps_list;  /* unused (reserved or unreserved) */
static int caps_total_count;        /* total caps allocated */
static int caps_use_count;          /* in use */
static int caps_reserve_count;      /* unused, reserved */
static int caps_avail_count;        /* unused, unreserved */

void __init ceph_caps_init(void)
{
        INIT_LIST_HEAD(&caps_list);
        spin_lock_init(&caps_list_lock);
}

void ceph_caps_finalize(void)
{
        struct ceph_cap *cap;

        spin_lock(&caps_list_lock);
        while (!list_empty(&caps_list)) {
                cap = list_first_entry(&caps_list, struct ceph_cap, caps_item);
                list_del(&cap->caps_item);
                kmem_cache_free(ceph_cap_cachep, cap);
        }
        caps_total_count = 0;
        caps_avail_count = 0;
        caps_use_count = 0;
        caps_reserve_count = 0;
        spin_unlock(&caps_list_lock);
}

int ceph_reserve_caps(struct ceph_cap_reservation *ctx, int need)
{
        int i;
        struct ceph_cap *cap;
        int have;
        int alloc = 0;
        LIST_HEAD(newcaps);
        int ret = 0;

        dout("reserve caps ctx=%p need=%d\n", ctx, need);

        /* first reserve any caps that are already allocated */
        spin_lock(&caps_list_lock);
        if (caps_avail_count >= need)
                have = need;
        else
                have = caps_avail_count;
        caps_avail_count -= have;
        caps_reserve_count += have;
        BUG_ON(caps_total_count != caps_use_count + caps_reserve_count +
               caps_avail_count);
        spin_unlock(&caps_list_lock);

        for (i = have; i < need; i++) {
                cap = kmem_cache_alloc(ceph_cap_cachep, GFP_NOFS);
                if (!cap) {
                        ret = -ENOMEM;
                        goto out_alloc_count;
                }
                list_add(&cap->caps_item, &newcaps);
                alloc++;
        }
        BUG_ON(have + alloc != need);

        spin_lock(&caps_list_lock);
        caps_total_count += alloc;
        caps_reserve_count += alloc;
        list_splice(&newcaps, &caps_list);

        BUG_ON(caps_total_count != caps_use_count + caps_reserve_count +
               caps_avail_count);
        spin_unlock(&caps_list_lock);

        ctx->count = need;
        dout("reserve caps ctx=%p %d = %d used + %d resv + %d avail\n",
             ctx, caps_total_count, caps_use_count, caps_reserve_count,
             caps_avail_count);
        return 0;

out_alloc_count:
        /* we didn't manage to reserve as much as we needed */
        pr_warning("reserve caps ctx=%p ENOMEM need=%d got=%d\n",
                   ctx, need, have);
        return ret;
}

int ceph_unreserve_caps(struct ceph_cap_reservation *ctx)
{
        dout("unreserve caps ctx=%p count=%d\n", ctx, ctx->count);
        if (ctx->count) {
                spin_lock(&caps_list_lock);
                BUG_ON(caps_reserve_count < ctx->count);
                caps_reserve_count -= ctx->count;
                caps_avail_count += ctx->count;
                ctx->count = 0;
                dout("unreserve caps %d = %d used + %d resv + %d avail\n",
                     caps_total_count, caps_use_count, caps_reserve_count,
                     caps_avail_count);
                BUG_ON(caps_total_count != caps_use_count + caps_reserve_count +
                       caps_avail_count);
                spin_unlock(&caps_list_lock);
        }
        return 0;
}

static struct ceph_cap *get_cap(struct ceph_cap_reservation *ctx)
{
        struct ceph_cap *cap = NULL;

        /* temporary, until we do something about cap import/export */
        if (!ctx)
                return kmem_cache_alloc(ceph_cap_cachep, GFP_NOFS);

        spin_lock(&caps_list_lock);
        dout("get_cap ctx=%p (%d) %d = %d used + %d resv + %d avail\n",
             ctx, ctx->count, caps_total_count, caps_use_count,
             caps_reserve_count, caps_avail_count);
        BUG_ON(!ctx->count);
        BUG_ON(ctx->count > caps_reserve_count);
        BUG_ON(list_empty(&caps_list));

        ctx->count--;
        caps_reserve_count--;
        caps_use_count++;

        cap = list_first_entry(&caps_list, struct ceph_cap, caps_item);
        list_del(&cap->caps_item);

        BUG_ON(caps_total_count != caps_use_count + caps_reserve_count +
               caps_avail_count);
        spin_unlock(&caps_list_lock);
        return cap;
}

static void put_cap(struct ceph_cap *cap,
                    struct ceph_cap_reservation *ctx)
{
        spin_lock(&caps_list_lock);
        dout("put_cap ctx=%p (%d) %d = %d used + %d resv + %d avail\n",
             ctx, ctx ? ctx->count : 0, caps_total_count, caps_use_count,
             caps_reserve_count, caps_avail_count);
        caps_use_count--;
        /*
         * Keep some preallocated caps around, at least enough to do a
         * readdir (which needs to preallocate lots of them), to avoid
         * lots of free/alloc churn.
         */
        if (caps_avail_count >= caps_reserve_count +
            ceph_client(cap->ci->vfs_inode.i_sb)->mount_args.max_readdir) {
                caps_total_count--;
                kmem_cache_free(ceph_cap_cachep, cap);
        } else {
                if (ctx) {
                        ctx->count++;
                        caps_reserve_count++;
                } else {
                        caps_avail_count++;
                }
                list_add(&cap->caps_item, &caps_list);
        }

        BUG_ON(caps_total_count != caps_use_count + caps_reserve_count +
               caps_avail_count);
        spin_unlock(&caps_list_lock);
}

void ceph_reservation_status(struct ceph_client *client,
                             int *total, int *avail, int *used, int *reserved)
{
        if (total)
                *total = caps_total_count;
        if (avail)
                *avail = caps_avail_count;
        if (used)
                *used = caps_use_count;
        if (reserved)
                *reserved = caps_reserve_count;
}

/*
 * Find ceph_cap for given mds, if any.
 *
 * Called with i_lock held.
 */
static struct ceph_cap *__get_cap_for_mds(struct ceph_inode_info *ci, int mds)
{
        struct ceph_cap *cap;
        struct rb_node *n = ci->i_caps.rb_node;

        while (n) {
                cap = rb_entry(n, struct ceph_cap, ci_node);
                if (mds < cap->mds)
                        n = n->rb_left;
                else if (mds > cap->mds)
                        n = n->rb_right;
                else
                        return cap;
        }
        return NULL;
}

/*
 * Return id of any MDS with a cap, preferably FILE_WR|WRBUFFER|EXCL, else
 * -1.
 */
static int __ceph_get_cap_mds(struct ceph_inode_info *ci, u32 *mseq)
{
        struct ceph_cap *cap;
        int mds = -1;
        struct rb_node *p;

        /* prefer mds with WR|WRBUFFER|EXCL caps */
        for (p = rb_first(&ci->i_caps); p; p = rb_next(p)) {
                cap = rb_entry(p, struct ceph_cap, ci_node);
                mds = cap->mds;
                if (mseq)
                        *mseq = cap->mseq;
                if (cap->issued & (CEPH_CAP_FILE_WR |
                                   CEPH_CAP_FILE_BUFFER |
                                   CEPH_CAP_FILE_EXCL))
                        break;
        }
        return mds;
}

int ceph_get_cap_mds(struct inode *inode)
{
        int mds;
        spin_lock(&inode->i_lock);
        mds = __ceph_get_cap_mds(ceph_inode(inode), NULL);
        spin_unlock(&inode->i_lock);
        return mds;
}

/*
 * Called under i_lock.
 */
static void __insert_cap_node(struct ceph_inode_info *ci,
                              struct ceph_cap *new)
{
        struct rb_node **p = &ci->i_caps.rb_node;
        struct rb_node *parent = NULL;
        struct ceph_cap *cap = NULL;

        while (*p) {
                parent = *p;
                cap = rb_entry(parent, struct ceph_cap, ci_node);
                if (new->mds < cap->mds)
                        p = &(*p)->rb_left;
                else if (new->mds > cap->mds)
                        p = &(*p)->rb_right;
                else
                        BUG();
        }

        rb_link_node(&new->ci_node, parent, p);
        rb_insert_color(&new->ci_node, &ci->i_caps);
}

/*
 * (re)set cap hold timeouts, which control the delayed release
 * of unused caps back to the MDS.  Should be called on cap use.
 */
static void __cap_set_timeouts(struct ceph_mds_client *mdsc,
                               struct ceph_inode_info *ci)
{
        struct ceph_mount_args *ma = &mdsc->client->mount_args;

        ci->i_hold_caps_min = round_jiffies(jiffies +
                                            ma->caps_wanted_delay_min * HZ);
        ci->i_hold_caps_max = round_jiffies(jiffies +
                                            ma->caps_wanted_delay_max * HZ);
        dout("__cap_set_timeouts %p min %lu max %lu\n", &ci->vfs_inode,
             ci->i_hold_caps_min - jiffies, ci->i_hold_caps_max - jiffies);
}

/*
 * (Re)queue cap at the end of the delayed cap release list.
 *
 * If I_FLUSH is set, leave the inode at the front of the list.
 *
 * Caller holds i_lock
 *    -> we take mdsc->cap_delay_lock
 */
static void __cap_delay_requeue(struct ceph_mds_client *mdsc,
                                struct ceph_inode_info *ci)
{
        __cap_set_timeouts(mdsc, ci);
        dout("__cap_delay_requeue %p flags %d at %lu\n", &ci->vfs_inode,
             ci->i_ceph_flags, ci->i_hold_caps_max);
        if (!mdsc->stopping) {
                spin_lock(&mdsc->cap_delay_lock);
                if (!list_empty(&ci->i_cap_delay_list)) {
                        if (ci->i_ceph_flags & CEPH_I_FLUSH)
                                goto no_change;
                        list_del_init(&ci->i_cap_delay_list);
                }
                list_add_tail(&ci->i_cap_delay_list, &mdsc->cap_delay_list);
no_change:
                spin_unlock(&mdsc->cap_delay_lock);
        }
}

/*
 * Queue an inode for immediate writeback.  Mark inode with I_FLUSH,
 * indicating we should send a cap message to flush dirty metadata
 * asap, and move to the front of the delayed cap list.
 */
static void __cap_delay_requeue_front(struct ceph_mds_client *mdsc,
                                      struct ceph_inode_info *ci)
{
        dout("__cap_delay_requeue_front %p\n", &ci->vfs_inode);
        spin_lock(&mdsc->cap_delay_lock);
        ci->i_ceph_flags |= CEPH_I_FLUSH;
        if (!list_empty(&ci->i_cap_delay_list))
                list_del_init(&ci->i_cap_delay_list);
        list_add(&ci->i_cap_delay_list, &mdsc->cap_delay_list);
        spin_unlock(&mdsc->cap_delay_lock);
}

/*
 * Cancel delayed work on cap.
 *
 * Caller must hold i_lock.
 */
static void __cap_delay_cancel(struct ceph_mds_client *mdsc,
                               struct ceph_inode_info *ci)
{
        dout("__cap_delay_cancel %p\n", &ci->vfs_inode);
        if (list_empty(&ci->i_cap_delay_list))
                return;
        spin_lock(&mdsc->cap_delay_lock);
        list_del_init(&ci->i_cap_delay_list);
        spin_unlock(&mdsc->cap_delay_lock);
}

/*
 * Common issue checks for add_cap, handle_cap_grant.
 */
static void __check_cap_issue(struct ceph_inode_info *ci, struct ceph_cap *cap,
                              unsigned issued)
{
        unsigned had = __ceph_caps_issued(ci, NULL);

        /*
         * Each time we receive FILE_CACHE anew, we increment
         * i_rdcache_gen.
         */
        if ((issued & CEPH_CAP_FILE_CACHE) &&
            (had & CEPH_CAP_FILE_CACHE) == 0)
                ci->i_rdcache_gen++;

        /*
         * if we are newly issued FILE_SHARED, clear I_COMPLETE; we
         * don't know what happened to this directory while we didn't
         * have the cap.
         */
        if ((issued & CEPH_CAP_FILE_SHARED) &&
            (had & CEPH_CAP_FILE_SHARED) == 0) {
                ci->i_shared_gen++;
                if (S_ISDIR(ci->vfs_inode.i_mode)) {
                        dout(" marking %p NOT complete\n", &ci->vfs_inode);
                        ci->i_ceph_flags &= ~CEPH_I_COMPLETE;
                }
        }
}

/*
 * Add a capability under the given MDS session.
 *
 * Caller should hold session snap_rwsem (read) and s_mutex.
 *
 * @fmode is the open file mode, if we are opening a file, otherwise
 * it is < 0.  (This is so we can atomically add the cap and add an
 * open file reference to it.)
 */
int ceph_add_cap(struct inode *inode,
                 struct ceph_mds_session *session, u64 cap_id,
                 int fmode, unsigned issued, unsigned wanted,
                 unsigned seq, unsigned mseq, u64 realmino, int flags,
                 struct ceph_cap_reservation *caps_reservation)
{
        struct ceph_mds_client *mdsc = &ceph_inode_to_client(inode)->mdsc;
        struct ceph_inode_info *ci = ceph_inode(inode);
        struct ceph_cap *new_cap = NULL;
        struct ceph_cap *cap;
        int mds = session->s_mds;
        int actual_wanted;

        dout("add_cap %p mds%d cap %llx %s seq %d\n", inode,
             session->s_mds, cap_id, ceph_cap_string(issued), seq);

        /*
         * If we are opening the file, include file mode wanted bits
         * in wanted.
         */
        if (fmode >= 0)
                wanted |= ceph_caps_for_mode(fmode);

retry:
        spin_lock(&inode->i_lock);
        cap = __get_cap_for_mds(ci, mds);
        if (!cap) {
                if (new_cap) {
                        cap = new_cap;
                        new_cap = NULL;
                } else {
                        spin_unlock(&inode->i_lock);
                        new_cap = get_cap(caps_reservation);
                        if (new_cap == NULL)
                                return -ENOMEM;
                        goto retry;
                }

                cap->issued = 0;
                cap->implemented = 0;
                cap->mds = mds;
                cap->mds_wanted = 0;

                cap->ci = ci;
                __insert_cap_node(ci, cap);

                /* clear out old exporting info?  (i.e. on cap import) */
                if (ci->i_cap_exporting_mds == mds) {
                        ci->i_cap_exporting_issued = 0;
                        ci->i_cap_exporting_mseq = 0;
                        ci->i_cap_exporting_mds = -1;
                }

                /* add to session cap list */
                cap->session = session;
                spin_lock(&session->s_cap_lock);
                list_add_tail(&cap->session_caps, &session->s_caps);
                session->s_nr_caps++;
                spin_unlock(&session->s_cap_lock);
        }

        if (!ci->i_snap_realm) {
                /*
                 * add this inode to the appropriate snap realm
                 */
                struct ceph_snap_realm *realm = ceph_lookup_snap_realm(mdsc,
                                                               realmino);
                if (realm) {
                        ceph_get_snap_realm(mdsc, realm);
                        spin_lock(&realm->inodes_with_caps_lock);
                        ci->i_snap_realm = realm;
                        list_add(&ci->i_snap_realm_item,
                                 &realm->inodes_with_caps);
                        spin_unlock(&realm->inodes_with_caps_lock);
                } else {
                        pr_err("ceph_add_cap: couldn't find snap realm %llx\n",
                               realmino);
                }
        }

        __check_cap_issue(ci, cap, issued);

        /*
         * If we are issued caps we don't want, or the mds' wanted
         * value appears to be off, queue a check so we'll release
         * later and/or update the mds wanted value.
         */
        actual_wanted = __ceph_caps_wanted(ci);
        if ((wanted & ~actual_wanted) ||
            (issued & ~actual_wanted & CEPH_CAP_ANY_WR)) {
                dout(" issued %s, mds wanted %s, actual %s, queueing\n",
                     ceph_cap_string(issued), ceph_cap_string(wanted),
                     ceph_cap_string(actual_wanted));
                __cap_delay_requeue(mdsc, ci);
        }

        if (flags & CEPH_CAP_FLAG_AUTH)
                ci->i_auth_cap = cap;
        else if (ci->i_auth_cap == cap)
                ci->i_auth_cap = NULL;

        dout("add_cap inode %p (%llx.%llx) cap %p %s now %s seq %d mds%d\n",
             inode, ceph_vinop(inode), cap, ceph_cap_string(issued),
             ceph_cap_string(issued|cap->issued), seq, mds);
        cap->cap_id = cap_id;
        cap->issued = issued;
        cap->implemented |= issued;
        cap->mds_wanted |= wanted;
        cap->seq = seq;
        cap->issue_seq = seq;
        cap->mseq = mseq;
        cap->gen = session->s_cap_gen;

        if (fmode >= 0)
                __ceph_get_fmode(ci, fmode);
        spin_unlock(&inode->i_lock);
        wake_up(&ci->i_cap_wq);
        return 0;
}

/*
 * Return true if cap has not timed out and belongs to the current
 * generation of the MDS session (i.e. has not gone 'stale' due to
 * us losing touch with the mds).
 */
static int __cap_is_valid(struct ceph_cap *cap)
{
        unsigned long ttl;
        u32 gen;

        spin_lock(&cap->session->s_cap_lock);
        gen = cap->session->s_cap_gen;
        ttl = cap->session->s_cap_ttl;
        spin_unlock(&cap->session->s_cap_lock);

        if (cap->gen < gen || time_after_eq(jiffies, ttl)) {
                dout("__cap_is_valid %p cap %p issued %s "
                     "but STALE (gen %u vs %u)\n", &cap->ci->vfs_inode,
                     cap, ceph_cap_string(cap->issued), cap->gen, gen);
                return 0;
        }

        return 1;
}

/*
 * Return set of valid cap bits issued to us.  Note that caps time
 * out, and may be invalidated in bulk if the client session times out
 * and session->s_cap_gen is bumped.
 */
int __ceph_caps_issued(struct ceph_inode_info *ci, int *implemented)
{
        int have = ci->i_snap_caps;
        struct ceph_cap *cap;
        struct rb_node *p;

        if (implemented)
                *implemented = 0;
        for (p = rb_first(&ci->i_caps); p; p = rb_next(p)) {
                cap = rb_entry(p, struct ceph_cap, ci_node);
                if (!__cap_is_valid(cap))
                        continue;
                dout("__ceph_caps_issued %p cap %p issued %s\n",
                     &ci->vfs_inode, cap, ceph_cap_string(cap->issued));
                have |= cap->issued;
                if (implemented)
                        *implemented |= cap->implemented;
        }
        return have;
}

/*
 * Get cap bits issued by caps other than @ocap
 */
int __ceph_caps_issued_other(struct ceph_inode_info *ci, struct ceph_cap *ocap)
{
        int have = ci->i_snap_caps;
        struct ceph_cap *cap;
        struct rb_node *p;

        for (p = rb_first(&ci->i_caps); p; p = rb_next(p)) {
                cap = rb_entry(p, struct ceph_cap, ci_node);
                if (cap == ocap)
                        continue;
                if (!__cap_is_valid(cap))
                        continue;
                have |= cap->issued;
        }
        return have;
}

/*
 * Move a cap to the end of the LRU (oldest caps at list head, newest
 * at list tail).
 */
static void __touch_cap(struct ceph_cap *cap)
{
        struct ceph_mds_session *s = cap->session;

        dout("__touch_cap %p cap %p mds%d\n", &cap->ci->vfs_inode, cap,
             s->s_mds);
        spin_lock(&s->s_cap_lock);
        list_move_tail(&cap->session_caps, &s->s_caps);
        spin_unlock(&s->s_cap_lock);
}

/*
 * Check if we hold the given mask.  If so, move the cap(s) to the
 * front of their respective LRUs.  (This is the preferred way for
 * callers to check for caps they want.)
 */
int __ceph_caps_issued_mask(struct ceph_inode_info *ci, int mask, int touch)
{
        struct ceph_cap *cap;
        struct rb_node *p;
        int have = ci->i_snap_caps;

        if ((have & mask) == mask) {
                dout("__ceph_caps_issued_mask %p snap issued %s"
                     " (mask %s)\n", &ci->vfs_inode,
                     ceph_cap_string(have),
                     ceph_cap_string(mask));
                return 1;
        }

        for (p = rb_first(&ci->i_caps); p; p = rb_next(p)) {
                cap = rb_entry(p, struct ceph_cap, ci_node);
                if (!__cap_is_valid(cap))
                        continue;
                if ((cap->issued & mask) == mask) {
                        dout("__ceph_caps_issued_mask %p cap %p issued %s"
                             " (mask %s)\n", &ci->vfs_inode, cap,
                             ceph_cap_string(cap->issued),
                             ceph_cap_string(mask));
                        if (touch)
                                __touch_cap(cap);
                        return 1;
                }

                /* does a combination of caps satisfy mask? */
                have |= cap->issued;
                if ((have & mask) == mask) {
                        dout("__ceph_caps_issued_mask %p combo issued %s"
                             " (mask %s)\n", &ci->vfs_inode,
                             ceph_cap_string(cap->issued),
                             ceph_cap_string(mask));
                        if (touch) {
                                struct rb_node *q;

                                /* touch this + preceeding caps */
                                __touch_cap(cap);
                                for (q = rb_first(&ci->i_caps); q != p;
                                     q = rb_next(q)) {
                                        cap = rb_entry(q, struct ceph_cap,
                                                       ci_node);
                                        if (!__cap_is_valid(cap))
                                                continue;
                                        __touch_cap(cap);
                                }
                        }
                        return 1;
                }
        }

        return 0;
}

/*
 * Return true if mask caps are currently being revoked by an MDS.
 */
int ceph_caps_revoking(struct ceph_inode_info *ci, int mask)
{
        struct inode *inode = &ci->vfs_inode;
        struct ceph_cap *cap;
        struct rb_node *p;
        int ret = 0;

        spin_lock(&inode->i_lock);
        for (p = rb_first(&ci->i_caps); p; p = rb_next(p)) {
                cap = rb_entry(p, struct ceph_cap, ci_node);
                if (__cap_is_valid(cap) &&
                    (cap->implemented & ~cap->issued & mask)) {
                        ret = 1;
                        break;
                }
        }
        spin_unlock(&inode->i_lock);
        dout("ceph_caps_revoking %p %s = %d\n", inode,
             ceph_cap_string(mask), ret);
        return ret;
}

int __ceph_caps_used(struct ceph_inode_info *ci)
{
        int used = 0;
        if (ci->i_pin_ref)
                used |= CEPH_CAP_PIN;
        if (ci->i_rd_ref)
                used |= CEPH_CAP_FILE_RD;
        if (ci->i_rdcache_ref || ci->i_rdcache_gen)
                used |= CEPH_CAP_FILE_CACHE;
        if (ci->i_wr_ref)
                used |= CEPH_CAP_FILE_WR;
        if (ci->i_wrbuffer_ref)
                used |= CEPH_CAP_FILE_BUFFER;
        return used;
}

/*
 * wanted, by virtue of open file modes
 */
int __ceph_caps_file_wanted(struct ceph_inode_info *ci)
{
        int want = 0;
        int mode;
        for (mode = 0; mode < 4; mode++)
                if (ci->i_nr_by_mode[mode])
                        want |= ceph_caps_for_mode(mode);
        return want;
}

/*
 * Return caps we have registered with the MDS(s) as 'wanted'.
 */
int __ceph_caps_mds_wanted(struct ceph_inode_info *ci)
{
        struct ceph_cap *cap;
        struct rb_node *p;
        int mds_wanted = 0;

        for (p = rb_first(&ci->i_caps); p; p = rb_next(p)) {
                cap = rb_entry(p, struct ceph_cap, ci_node);
                if (!__cap_is_valid(cap))
                        continue;
                mds_wanted |= cap->mds_wanted;
        }
        return mds_wanted;
}

/*
 * called under i_lock
 */
static int __ceph_is_any_caps(struct ceph_inode_info *ci)
{
        return !RB_EMPTY_ROOT(&ci->i_caps) || ci->i_cap_exporting_mds >= 0;
}

/*
 * caller should hold i_lock, and session s_mutex.
 * returns true if this is the last cap.  if so, caller should iput.
 */
void __ceph_remove_cap(struct ceph_cap *cap,
                       struct ceph_cap_reservation *ctx)
{
        struct ceph_mds_session *session = cap->session;
        struct ceph_inode_info *ci = cap->ci;
        struct ceph_mds_client *mdsc = &ceph_client(ci->vfs_inode.i_sb)->mdsc;

        dout("__ceph_remove_cap %p from %p\n", cap, &ci->vfs_inode);

        /* remove from session list */
        spin_lock(&session->s_cap_lock);
        list_del_init(&cap->session_caps);
        session->s_nr_caps--;
        spin_unlock(&session->s_cap_lock);

        /* remove from inode list */
        rb_erase(&cap->ci_node, &ci->i_caps);
        cap->session = NULL;
        if (ci->i_auth_cap == cap)
                ci->i_auth_cap = NULL;

        put_cap(cap, ctx);

        if (!__ceph_is_any_caps(ci) && ci->i_snap_realm) {
                struct ceph_snap_realm *realm = ci->i_snap_realm;
                spin_lock(&realm->inodes_with_caps_lock);
                list_del_init(&ci->i_snap_realm_item);
                ci->i_snap_realm_counter++;
                ci->i_snap_realm = NULL;
                spin_unlock(&realm->inodes_with_caps_lock);
                ceph_put_snap_realm(mdsc, realm);
        }
        if (!__ceph_is_any_real_caps(ci))
                __cap_delay_cancel(mdsc, ci);
}

/*
 * Build and send a cap message to the given MDS.
 *
 * Caller should be holding s_mutex.
 */
static int send_cap_msg(struct ceph_mds_session *session,
                        u64 ino, u64 cid, int op,
                        int caps, int wanted, int dirty,
                        u32 seq, u64 flush_tid, u32 issue_seq, u32 mseq,
                        u64 size, u64 max_size,
                        struct timespec *mtime, struct timespec *atime,
                        u64 time_warp_seq,
                        uid_t uid, gid_t gid, mode_t mode,
                        u64 xattr_version,
                        struct ceph_buffer *xattrs_buf,
                        u64 follows)
{
        struct ceph_mds_caps *fc;
        struct ceph_msg *msg;

        dout("send_cap_msg %s %llx %llx caps %s wanted %s dirty %s"
             " seq %u/%u mseq %u follows %lld size %llu/%llu"
             " xattr_ver %llu xattr_len %d\n", ceph_cap_op_name(op),
             cid, ino, ceph_cap_string(caps), ceph_cap_string(wanted),
             ceph_cap_string(dirty),
             seq, issue_seq, mseq, follows, size, max_size,
             xattr_version, xattrs_buf ? (int)xattrs_buf->vec.iov_len : 0);

        msg = ceph_msg_new(CEPH_MSG_CLIENT_CAPS, sizeof(*fc), 0, 0, NULL);
        if (IS_ERR(msg))
                return PTR_ERR(msg);

        fc = msg->front.iov_base;

        memset(fc, 0, sizeof(*fc));

        fc->cap_id = cpu_to_le64(cid);
        fc->op = cpu_to_le32(op);
        fc->seq = cpu_to_le32(seq);
        fc->client_tid = cpu_to_le64(flush_tid);
        fc->issue_seq = cpu_to_le32(issue_seq);
        fc->migrate_seq = cpu_to_le32(mseq);
        fc->caps = cpu_to_le32(caps);
        fc->wanted = cpu_to_le32(wanted);
        fc->dirty = cpu_to_le32(dirty);
        fc->ino = cpu_to_le64(ino);
        fc->snap_follows = cpu_to_le64(follows);

        fc->size = cpu_to_le64(size);
        fc->max_size = cpu_to_le64(max_size);
        if (mtime)
                ceph_encode_timespec(&fc->mtime, mtime);
        if (atime)
                ceph_encode_timespec(&fc->atime, atime);
        fc->time_warp_seq = cpu_to_le32(time_warp_seq);

        fc->uid = cpu_to_le32(uid);
        fc->gid = cpu_to_le32(gid);
        fc->mode = cpu_to_le32(mode);

        fc->xattr_version = cpu_to_le64(xattr_version);
        if (xattrs_buf) {
                msg->middle = ceph_buffer_get(xattrs_buf);
                fc->xattr_len = cpu_to_le32(xattrs_buf->vec.iov_len);
                msg->hdr.middle_len = cpu_to_le32(xattrs_buf->vec.iov_len);
        }

        ceph_con_send(&session->s_con, msg);
        return 0;
}

/*
 * Queue cap releases when an inode is dropped from our
 * cache.
 */
void ceph_queue_caps_release(struct inode *inode)
{
        struct ceph_inode_info *ci = ceph_inode(inode);
        struct rb_node *p;

        spin_lock(&inode->i_lock);
        p = rb_first(&ci->i_caps);
        while (p) {
                struct ceph_cap *cap = rb_entry(p, struct ceph_cap, ci_node);
                struct ceph_mds_session *session = cap->session;
                struct ceph_msg *msg;
                struct ceph_mds_cap_release *head;
                struct ceph_mds_cap_item *item;

                spin_lock(&session->s_cap_lock);
                BUG_ON(!session->s_num_cap_releases);
                msg = list_first_entry(&session->s_cap_releases,
                                       struct ceph_msg, list_head);

                dout(" adding %p release to mds%d msg %p (%d left)\n",
                     inode, session->s_mds, msg, session->s_num_cap_releases);

                BUG_ON(msg->front.iov_len + sizeof(*item) > PAGE_CACHE_SIZE);
                head = msg->front.iov_base;
                head->num = cpu_to_le32(le32_to_cpu(head->num) + 1);
                item = msg->front.iov_base + msg->front.iov_len;
                item->ino = cpu_to_le64(ceph_ino(inode));
                item->cap_id = cpu_to_le64(cap->cap_id);
                item->migrate_seq = cpu_to_le32(cap->mseq);
                item->seq = cpu_to_le32(cap->issue_seq);

                session->s_num_cap_releases--;

                msg->front.iov_len += sizeof(*item);
                if (le32_to_cpu(head->num) == CEPH_CAPS_PER_RELEASE) {
                        dout(" release msg %p full\n", msg);
                        list_move_tail(&msg->list_head,
                                      &session->s_cap_releases_done);
                } else {
                        dout(" release msg %p at %d/%d (%d)\n", msg,
                             (int)le32_to_cpu(head->num),
                             (int)CEPH_CAPS_PER_RELEASE,
                             (int)msg->front.iov_len);
                }
                spin_unlock(&session->s_cap_lock);
                p = rb_next(p);
                __ceph_remove_cap(cap, NULL);

        }
        spin_unlock(&inode->i_lock);
}

/*
 * Send a cap msg on the given inode.  Update our caps state, then
 * drop i_lock and send the message.
 *
 * Make note of max_size reported/requested from mds, revoked caps
 * that have now been implemented.
 *
 * Make half-hearted attempt ot to invalidate page cache if we are
 * dropping RDCACHE.  Note that this will leave behind locked pages
 * that we'll then need to deal with elsewhere.
 *
 * Return non-zero if delayed release, or we experienced an error
 * such that the caller should requeue + retry later.
 *
 * called with i_lock, then drops it.
 * caller should hold snap_rwsem (read), s_mutex.
 */
static int __send_cap(struct ceph_mds_client *mdsc, struct ceph_cap *cap,
                      int op, int used, int want, int retain, int flushing,
                      unsigned *pflush_tid)
        __releases(cap->ci->vfs_inode->i_lock)
{
        struct ceph_inode_info *ci = cap->ci;
        struct inode *inode = &ci->vfs_inode;
        u64 cap_id = cap->cap_id;
        int held = cap->issued | cap->implemented;
        int revoking = cap->implemented & ~cap->issued;
        int dropping = cap->issued & ~retain;
        int keep;
        u64 seq, issue_seq, mseq, time_warp_seq, follows;
        u64 size, max_size;
        struct timespec mtime, atime;
        int wake = 0;
        mode_t mode;
        uid_t uid;
        gid_t gid;
        struct ceph_mds_session *session;
        u64 xattr_version = 0;
        int delayed = 0;
        u64 flush_tid = 0;
        int i;
        int ret;

        dout("__send_cap %p cap %p session %p %s -> %s (revoking %s)\n",
             inode, cap, cap->session,
             ceph_cap_string(held), ceph_cap_string(held & retain),
             ceph_cap_string(revoking));
        BUG_ON((retain & CEPH_CAP_PIN) == 0);

        session = cap->session;

        /* don't release wanted unless we've waited a bit. */
        if ((ci->i_ceph_flags & CEPH_I_NODELAY) == 0 &&
            time_before(jiffies, ci->i_hold_caps_min)) {
                dout(" delaying issued %s -> %s, wanted %s -> %s on send\n",
                     ceph_cap_string(cap->issued),
                     ceph_cap_string(cap->issued & retain),
                     ceph_cap_string(cap->mds_wanted),
                     ceph_cap_string(want));
                want |= cap->mds_wanted;
                retain |= cap->issued;
                delayed = 1;
        }
        ci->i_ceph_flags &= ~(CEPH_I_NODELAY | CEPH_I_FLUSH);

        cap->issued &= retain;  /* drop bits we don't want */
        if (cap->implemented & ~cap->issued) {
                /*
                 * Wake up any waiters on wanted -> needed transition.
                 * This is due to the weird transition from buffered
                 * to sync IO... we need to flush dirty pages _before_
                 * allowing sync writes to avoid reordering.
                 */
                wake = 1;
        }
        cap->implemented &= cap->issued | used;
        cap->mds_wanted = want;

        if (flushing) {
                /*
                 * assign a tid for flush operations so we can avoid
                 * flush1 -> dirty1 -> flush2 -> flushack1 -> mark
                 * clean type races.  track latest tid for every bit
                 * so we can handle flush AxFw, flush Fw, and have the
                 * first ack clean Ax.
                 */
                flush_tid = ++ci->i_cap_flush_last_tid;
                if (pflush_tid)
                        *pflush_tid = flush_tid;
                dout(" cap_flush_tid %d\n", (int)flush_tid);
                for (i = 0; i < CEPH_CAP_BITS; i++)
                        if (flushing & (1 << i))
                                ci->i_cap_flush_tid[i] = flush_tid;
        }

        keep = cap->implemented;
        seq = cap->seq;
        issue_seq = cap->issue_seq;
        mseq = cap->mseq;
        size = inode->i_size;
        ci->i_reported_size = size;
        max_size = ci->i_wanted_max_size;
        ci->i_requested_max_size = max_size;
        mtime = inode->i_mtime;
        atime = inode->i_atime;
        time_warp_seq = ci->i_time_warp_seq;
        follows = ci->i_snap_realm->cached_context->seq;
        uid = inode->i_uid;
        gid = inode->i_gid;
        mode = inode->i_mode;

        if (dropping & CEPH_CAP_XATTR_EXCL) {
                __ceph_build_xattrs_blob(ci);
                xattr_version = ci->i_xattrs.version + 1;
        }

        spin_unlock(&inode->i_lock);

        if (dropping & CEPH_CAP_FILE_CACHE) {
                /* invalidate what we can */
                dout("invalidating pages on %p\n", inode);
                invalidate_mapping_pages(&inode->i_data, 0, -1);
        }

        ret = send_cap_msg(session, ceph_vino(inode).ino, cap_id,
                op, keep, want, flushing, seq, flush_tid, issue_seq, mseq,
                size, max_size, &mtime, &atime, time_warp_seq,
                uid, gid, mode,
                xattr_version,
                (flushing & CEPH_CAP_XATTR_EXCL) ? ci->i_xattrs.blob : NULL,
                follows);
        if (ret < 0) {
                dout("error sending cap msg, must requeue %p\n", inode);
                delayed = 1;
        }

        if (wake)
                wake_up(&ci->i_cap_wq);

        return delayed;
}

/*
 * When a snapshot is taken, clients accumulate dirty metadata on
 * inodes with capabilities in ceph_cap_snaps to describe the file
 * state at the time the snapshot was taken.  This must be flushed
 * asynchronously back to the MDS once sync writes complete and dirty
 * data is written out.
 *
 * Called under i_lock.  Takes s_mutex as needed.
 */
void __ceph_flush_snaps(struct ceph_inode_info *ci,
                        struct ceph_mds_session **psession)
{
        struct inode *inode = &ci->vfs_inode;
        int mds;
        struct ceph_cap_snap *capsnap;
        u32 mseq;
        struct ceph_mds_client *mdsc = &ceph_inode_to_client(inode)->mdsc;
        struct ceph_mds_session *session = NULL; /* if session != NULL, we hold
                                                    session->s_mutex */
        u64 next_follows = 0;  /* keep track of how far we've gotten through the
                             i_cap_snaps list, and skip these entries next time
                             around to avoid an infinite loop */

        if (psession)
                session = *psession;

        dout("__flush_snaps %p\n", inode);
retry:
        list_for_each_entry(capsnap, &ci->i_cap_snaps, ci_item) {
                /* avoid an infiniute loop after retry */
                if (capsnap->follows < next_follows)
                        continue;
                /*
                 * we need to wait for sync writes to complete and for dirty
                 * pages to be written out.
                 */
                if (capsnap->dirty_pages || capsnap->writing)
                        continue;

                /* pick mds, take s_mutex */
                mds = __ceph_get_cap_mds(ci, &mseq);
                if (session && session->s_mds != mds) {
                        dout("oops, wrong session %p mutex\n", session);
                        mutex_unlock(&session->s_mutex);
                        ceph_put_mds_session(session);
                        session = NULL;
                }
                if (!session) {
                        spin_unlock(&inode->i_lock);
                        mutex_lock(&mdsc->mutex);
                        session = __ceph_lookup_mds_session(mdsc, mds);
                        mutex_unlock(&mdsc->mutex);
                        if (session) {
                                dout("inverting session/ino locks on %p\n",
                                     session);
                                mutex_lock(&session->s_mutex);
                        }
                        /*
                         * if session == NULL, we raced against a cap
                         * deletion.  retry, and we'll get a better
                         * @mds value next time.
                         */
                        spin_lock(&inode->i_lock);
                        goto retry;
                }

                capsnap->flush_tid = ++ci->i_cap_flush_last_tid;
                atomic_inc(&capsnap->nref);
                if (!list_empty(&capsnap->flushing_item))
                        list_del_init(&capsnap->flushing_item);
                list_add_tail(&capsnap->flushing_item,
                              &session->s_cap_snaps_flushing);
                spin_unlock(&inode->i_lock);

                dout("flush_snaps %p cap_snap %p follows %lld size %llu\n",
                     inode, capsnap, next_follows, capsnap->size);
                send_cap_msg(session, ceph_vino(inode).ino, 0,
                             CEPH_CAP_OP_FLUSHSNAP, capsnap->issued, 0,
                             capsnap->dirty, 0, capsnap->flush_tid, 0, mseq,
                             capsnap->size, 0,
                             &capsnap->mtime, &capsnap->atime,
                             capsnap->time_warp_seq,
                             capsnap->uid, capsnap->gid, capsnap->mode,
                             0, NULL,
                             capsnap->follows);

                next_follows = capsnap->follows + 1;
                ceph_put_cap_snap(capsnap);

                spin_lock(&inode->i_lock);
                goto retry;
        }

        /* we flushed them all; remove this inode from the queue */
        spin_lock(&mdsc->snap_flush_lock);
        list_del_init(&ci->i_snap_flush_item);
        spin_unlock(&mdsc->snap_flush_lock);

        if (psession)
                *psession = session;
        else if (session) {
                mutex_unlock(&session->s_mutex);
                ceph_put_mds_session(session);
        }
}

static void ceph_flush_snaps(struct ceph_inode_info *ci)
{
        struct inode *inode = &ci->vfs_inode;

        spin_lock(&inode->i_lock);
        __ceph_flush_snaps(ci, NULL);
        spin_unlock(&inode->i_lock);
}

/*
 * Add dirty inode to the flushing list.  Assigned a seq number so we
 * can wait for caps to flush without starving.
 *
 * Called under i_lock.
 */
static int __mark_caps_flushing(struct inode *inode,
                                 struct ceph_mds_session *session)
{
        struct ceph_mds_client *mdsc = &ceph_client(inode->i_sb)->mdsc;
        struct ceph_inode_info *ci = ceph_inode(inode);
        int flushing;
        
        BUG_ON(ci->i_dirty_caps == 0);
        BUG_ON(list_empty(&ci->i_dirty_item));

        flushing = ci->i_dirty_caps;
        dout("__mark_caps_flushing flushing %s, flushing_caps %s -> %s\n",
             ceph_cap_string(flushing),
             ceph_cap_string(ci->i_flushing_caps),
             ceph_cap_string(ci->i_flushing_caps | flushing));
        ci->i_flushing_caps |= flushing;
        ci->i_dirty_caps = 0;

        spin_lock(&mdsc->cap_dirty_lock);
        if (list_empty(&ci->i_flushing_item)) {
                list_del_init(&ci->i_dirty_item);
                list_add_tail(&ci->i_flushing_item, &session->s_cap_flushing);
                mdsc->num_cap_flushing++;
                ci->i_cap_flush_seq = ++mdsc->cap_flush_seq;
                dout(" inode %p now flushing seq %lld\n", &ci->vfs_inode,
                     ci->i_cap_flush_seq);
        }
        spin_unlock(&mdsc->cap_dirty_lock);

        return flushing;
}

/*
 * Swiss army knife function to examine currently used and wanted
 * versus held caps.  Release, flush, ack revoked caps to mds as
 * appropriate.
 *
 *  CHECK_CAPS_NODELAY - caller is delayed work and we should not delay
 *    cap release further.
 *  CHECK_CAPS_AUTHONLY - we should only check the auth cap
 *  CHECK_CAPS_FLUSH - we should flush any dirty caps immediately, without
 *    further delay.
 */
void ceph_check_caps(struct ceph_inode_info *ci, int flags,
                     struct ceph_mds_session *session)
{
        struct ceph_client *client = ceph_inode_to_client(&ci->vfs_inode);
        struct ceph_mds_client *mdsc = &client->mdsc;
        struct inode *inode = &ci->vfs_inode;
        struct ceph_cap *cap;
        int file_wanted, used;
        int took_snap_rwsem = 0;             /* true if mdsc->snap_rwsem held */
        int drop_session_lock = session ? 0 : 1;
        int want, retain, revoking, flushing = 0;
        int mds = -1;   /* keep track of how far we've gone through i_caps list
                           to avoid an infinite loop on retry */
        struct rb_node *p;
        int tried_invalidate = 0;
        int delayed = 0, sent = 0, force_requeue = 0, num;
        int is_delayed = flags & CHECK_CAPS_NODELAY;

        /* if we are unmounting, flush any unused caps immediately. */
        if (mdsc->stopping)
                is_delayed = 1;

        spin_lock(&inode->i_lock);

        if (ci->i_ceph_flags & CEPH_I_FLUSH)
                flags |= CHECK_CAPS_FLUSH;

        /* flush snaps first time around only */
        if (!list_empty(&ci->i_cap_snaps))
                __ceph_flush_snaps(ci, &session);
        goto retry_locked;
retry:
        spin_lock(&inode->i_lock);
retry_locked:
        file_wanted = __ceph_caps_file_wanted(ci);
        used = __ceph_caps_used(ci);
        want = file_wanted | used;

        retain = want | CEPH_CAP_PIN;
        if (!mdsc->stopping && inode->i_nlink > 0) {
                if (want) {
                        retain |= CEPH_CAP_ANY;       /* be greedy */
                } else {
                        retain |= CEPH_CAP_ANY_SHARED;
                        /*
                         * keep RD only if we didn't have the file open RW,
                         * because then the mds would revoke it anyway to
                         * journal max_size=0.
                         */
                        if (ci->i_max_size == 0)
                                retain |= CEPH_CAP_ANY_RD;
                }
        }

        dout("check_caps %p file_want %s used %s dirty %s flushing %s"
             " issued %s retain %s %s%s%s\n", inode,
             ceph_cap_string(file_wanted),
             ceph_cap_string(used), ceph_cap_string(ci->i_dirty_caps),
             ceph_cap_string(ci->i_flushing_caps),
             ceph_cap_string(__ceph_caps_issued(ci, NULL)),
             ceph_cap_string(retain),
             (flags & CHECK_CAPS_AUTHONLY) ? " AUTHONLY" : "",
             (flags & CHECK_CAPS_NODELAY) ? " NODELAY" : "",
             (flags & CHECK_CAPS_FLUSH) ? " FLUSH" : "");

        /*
         * If we no longer need to hold onto old our caps, and we may
         * have cached pages, but don't want them, then try to invalidate.
         * If we fail, it's because pages are locked.... try again later.
         */
        if ((!is_delayed || mdsc->stopping) &&
            ci->i_wrbuffer_ref == 0 &&               /* no dirty pages... */
            ci->i_rdcache_gen &&                     /* may have cached pages */
            file_wanted == 0 &&                      /* no open files */
            !ci->i_truncate_pending &&
            !tried_invalidate) {
                u32 invalidating_gen = ci->i_rdcache_gen;
                int ret;

                dout("check_caps trying to invalidate on %p\n", inode);
                spin_unlock(&inode->i_lock);
                ret = invalidate_inode_pages2(&inode->i_data);
                spin_lock(&inode->i_lock);
                if (ret == 0 && invalidating_gen == ci->i_rdcache_gen) {
                        /* success. */
                        ci->i_rdcache_gen = 0;
                        ci->i_rdcache_revoking = 0;
                } else {
                        dout("check_caps failed to invalidate pages\n");
                        /* we failed to invalidate pages.  check these
                           caps again later. */
                        force_requeue = 1;
                        __cap_set_timeouts(mdsc, ci);
                }
                tried_invalidate = 1;
                goto retry_locked;
        }

        num = 0;
        for (p = rb_first(&ci->i_caps); p; p = rb_next(p)) {
                cap = rb_entry(p, struct ceph_cap, ci_node);
                num++;

                /* avoid looping forever */
                if (mds >= cap->mds ||
                    ((flags & CHECK_CAPS_AUTHONLY) && cap != ci->i_auth_cap))
                        continue;

                /* NOTE: no side-effects allowed, until we take s_mutex */

                revoking = cap->implemented & ~cap->issued;
                if (revoking)
                        dout("mds%d revoking %s\n", cap->mds,
                             ceph_cap_string(revoking));

                if (cap == ci->i_auth_cap &&
                    (cap->issued & CEPH_CAP_FILE_WR)) {
                        /* request larger max_size from MDS? */
                        if (ci->i_wanted_max_size > ci->i_max_size &&
                            ci->i_wanted_max_size > ci->i_requested_max_size) {
                                dout("requesting new max_size\n");
                                goto ack;
                        }

                        /* approaching file_max? */
                        if ((inode->i_size << 1) >= ci->i_max_size &&
                            (ci->i_reported_size << 1) < ci->i_max_size) {
                                dout("i_size approaching max_size\n");
                                goto ack;
                        }
                }
                /* flush anything dirty? */
                if (cap == ci->i_auth_cap && (flags & CHECK_CAPS_FLUSH) &&
                    ci->i_dirty_caps) {
                        dout("flushing dirty caps\n");
                        goto ack;
                }

                /* completed revocation? going down and there are no caps? */
                if (revoking && (revoking & used) == 0) {
                        dout("completed revocation of %s\n",
                             ceph_cap_string(cap->implemented & ~cap->issued));
                        goto ack;
                }

                /* want more caps from mds? */
                if (want & ~(cap->mds_wanted | cap->issued))
                        goto ack;

                /* things we might delay */
                if ((cap->issued & ~retain) == 0 &&
                    cap->mds_wanted == want)
                        continue;     /* nope, all good */

                if (is_delayed)
                        goto ack;

                /* delay? */
                if ((ci->i_ceph_flags & CEPH_I_NODELAY) == 0 &&
                    time_before(jiffies, ci->i_hold_caps_max)) {
                        dout(" delaying issued %s -> %s, wanted %s -> %s\n",
                             ceph_cap_string(cap->issued),
                             ceph_cap_string(cap->issued & retain),
                             ceph_cap_string(cap->mds_wanted),
                             ceph_cap_string(want));
                        delayed++;
                        continue;
                }

ack:
                if (session && session != cap->session) {
                        dout("oops, wrong session %p mutex\n", session);
                        mutex_unlock(&session->s_mutex);
                        session = NULL;
                }
                if (!session) {
                        session = cap->session;
                        if (mutex_trylock(&session->s_mutex) == 0) {
                                dout("inverting session/ino locks on %p\n",
                                     session);
                                spin_unlock(&inode->i_lock);
                                if (took_snap_rwsem) {
                                        up_read(&mdsc->snap_rwsem);
                                        took_snap_rwsem = 0;
                                }
                                mutex_lock(&session->s_mutex);
                                goto retry;
                        }
                }
                /* take snap_rwsem after session mutex */
                if (!took_snap_rwsem) {
                        if (down_read_trylock(&mdsc->snap_rwsem) == 0) {
                                dout("inverting snap/in locks on %p\n",
                                     inode);
                                spin_unlock(&inode->i_lock);
                                down_read(&mdsc->snap_rwsem);
                                took_snap_rwsem = 1;
                                goto retry;
                        }
                        took_snap_rwsem = 1;
                }

                if (cap == ci->i_auth_cap && ci->i_dirty_caps)
                        flushing = __mark_caps_flushing(inode, session);

                mds = cap->mds;  /* remember mds, so we don't repeat */
                sent++;

                /* __send_cap drops i_lock */
                delayed += __send_cap(mdsc, cap, CEPH_CAP_OP_UPDATE, used, want,
                                      retain, flushing, NULL);
                goto retry; /* retake i_lock and restart our cap scan. */
        }

        /*
         * Reschedule delayed caps release if we delayed anything,
         * otherwise cancel.
         */
        if (delayed && is_delayed)
                force_requeue = 1;   /* __send_cap delayed release; requeue */
        if (!delayed && !is_delayed)
                __cap_delay_cancel(mdsc, ci);
        else if (!is_delayed || force_requeue)
                __cap_delay_requeue(mdsc, ci);

        spin_unlock(&inode->i_lock);

        if (session && drop_session_lock)
                mutex_unlock(&session->s_mutex);
        if (took_snap_rwsem)
                up_read(&mdsc->snap_rwsem);
}

/*
 * Mark caps dirty.  If inode is newly dirty, add to the global dirty
 * list.
 */
int __ceph_mark_dirty_caps(struct ceph_inode_info *ci, int mask)
{
        struct ceph_mds_client *mdsc = &ceph_client(ci->vfs_inode.i_sb)->mdsc;
        struct inode *inode = &ci->vfs_inode;
        int was = __ceph_caps_dirty(ci);
        int dirty = 0;

        dout("__mark_dirty_caps %p %s dirty %s -> %s\n", &ci->vfs_inode,
             ceph_cap_string(mask), ceph_cap_string(ci->i_dirty_caps),
             ceph_cap_string(ci->i_dirty_caps | mask));
        ci->i_dirty_caps |= mask;
        if (!was) {
                dout(" inode %p now dirty\n", &ci->vfs_inode);
                spin_lock(&mdsc->cap_dirty_lock);
                list_add(&ci->i_dirty_item, &mdsc->cap_dirty);
                spin_unlock(&mdsc->cap_dirty_lock);
                igrab(inode);
                dirty |= I_DIRTY_SYNC;
        }
        if ((was & CEPH_CAP_FILE_BUFFER) &&
            (mask & CEPH_CAP_FILE_BUFFER))
                dirty |= I_DIRTY_DATASYNC;
        if (dirty)
                __mark_inode_dirty(inode, dirty);
        __cap_delay_requeue(mdsc, ci);
        return was;
}

/*
 * Try to flush dirty caps back to the auth mds.
 */
static int try_flush_caps(struct inode *inode, struct ceph_mds_session *session,
                          unsigned *flush_tid)
{
        struct ceph_mds_client *mdsc = &ceph_client(inode->i_sb)->mdsc;
        struct ceph_inode_info *ci = ceph_inode(inode);
        int unlock_session = session ? 0 : 1;
        int flushing = 0;

retry:
        spin_lock(&inode->i_lock);
        if (ci->i_dirty_caps && ci->i_auth_cap) {
                struct ceph_cap *cap = ci->i_auth_cap;
                int used = __ceph_caps_used(ci);
                int want = __ceph_caps_wanted(ci);
                int delayed;

                if (!session) {
                        spin_unlock(&inode->i_lock);
                        session = cap->session;
                        mutex_lock(&session->s_mutex);
                        goto retry;
                }
                BUG_ON(session != cap->session);
                if (cap->session->s_state < CEPH_MDS_SESSION_OPEN)
                        goto out;

                flushing = __mark_caps_flushing(inode, session);

                /* __send_cap drops i_lock */
                delayed = __send_cap(mdsc, cap, CEPH_CAP_OP_FLUSH, used, want,
                                     cap->issued | cap->implemented, flushing,
                                     flush_tid);
                if (!delayed)
                        goto out_unlocked;

                spin_lock(&inode->i_lock);
                __cap_delay_requeue(mdsc, ci);
        }
out:
        spin_unlock(&inode->i_lock);
out_unlocked:
        if (session && unlock_session)
                mutex_unlock(&session->s_mutex);
        return flushing;
}

/*
 * Return true if we've flushed caps through the given flush_tid.
 */
static int caps_are_flushed(struct inode *inode, unsigned tid)
{
        struct ceph_inode_info *ci = ceph_inode(inode);
        int dirty, i, ret = 1;

        spin_lock(&inode->i_lock);
        dirty = __ceph_caps_dirty(ci);
        for (i = 0; i < CEPH_CAP_BITS; i++)
                if ((ci->i_flushing_caps & (1 << i)) &&
                    ci->i_cap_flush_tid[i] <= tid) {
                        /* still flushing this bit */
                        ret = 0;
                        break;
                }
        spin_unlock(&inode->i_lock);
        return ret;
}

/*
 * Wait on any unsafe replies for the given inode.  First wait on the
 * newest request, and make that the upper bound.  Then, if there are
 * more requests, keep waiting on the oldest as long as it is still older
 * than the original request.
 */
static void sync_write_wait(struct inode *inode)
{
        struct ceph_inode_info *ci = ceph_inode(inode);
        struct list_head *head = &ci->i_unsafe_writes;
        struct ceph_osd_request *req;
        u64 last_tid;

        spin_lock(&ci->i_unsafe_lock);
        if (list_empty(head))
                goto out;

        /* set upper bound as _last_ entry in chain */
        req = list_entry(head->prev, struct ceph_osd_request,
                         r_unsafe_item);
        last_tid = req->r_tid;

        do {
                ceph_osdc_get_request(req);
                spin_unlock(&ci->i_unsafe_lock);
                dout("sync_write_wait on tid %llu (until %llu)\n",
                     req->r_tid, last_tid);
                wait_for_completion(&req->r_safe_completion);
                spin_lock(&ci->i_unsafe_lock);
                ceph_osdc_put_request(req);

                /*
                 * from here on look at first entry in chain, since we
                 * only want to wait for anything older than last_tid
                 */
                if (list_empty(head))
                        break;
                req = list_entry(head->next, struct ceph_osd_request,
                                 r_unsafe_item);
        } while (req->r_tid < last_tid);
out:
        spin_unlock(&ci->i_unsafe_lock);
}

int ceph_fsync(struct file *file, struct dentry *dentry, int datasync)
{
        struct inode *inode = dentry->d_inode;
        struct ceph_inode_info *ci = ceph_inode(inode);
        unsigned flush_tid;
        int ret;
        int dirty;

        dout("fsync %p%s\n", inode, datasync ? " datasync" : "");
        sync_write_wait(inode);

        ret = filemap_write_and_wait(inode->i_mapping);
        if (ret < 0)
                return ret;

        dirty = try_flush_caps(inode, NULL, &flush_tid);
        dout("fsync dirty caps are %s\n", ceph_cap_string(dirty));

        /*
         * only wait on non-file metadata writeback (the mds
         * can recover size and mtime, so we don't need to
         * wait for that)
         */
        if (!datasync && (dirty & ~CEPH_CAP_ANY_FILE_WR)) {
                dout("fsync waiting for flush_tid %u\n", flush_tid);
                ret = wait_event_interruptible(ci->i_cap_wq,
                                       caps_are_flushed(inode, flush_tid));
        }

        dout("fsync %p%s done\n", inode, datasync ? " datasync" : "");
        return ret;
}

/*
 * Flush any dirty caps back to the mds.  If we aren't asked to wait,
 * queue inode for flush but don't do so immediately, because we can
 * get by with fewer MDS messages if we wait for data writeback to
 * complete first.
 */
int ceph_write_inode(struct inode *inode, int wait)
{
        struct ceph_inode_info *ci = ceph_inode(inode);
        unsigned flush_tid;
        int err = 0;
        int dirty;

        dout("write_inode %p wait=%d\n", inode, wait);
        if (wait) {
                dirty = try_flush_caps(inode, NULL, &flush_tid);
                if (dirty)
                        err = wait_event_interruptible(ci->i_cap_wq,
                                       caps_are_flushed(inode, flush_tid));
        } else {
                struct ceph_mds_client *mdsc = &ceph_client(inode->i_sb)->mdsc;

                spin_lock(&inode->i_lock);
                if (__ceph_caps_dirty(ci))
                        __cap_delay_requeue_front(mdsc, ci);
                spin_unlock(&inode->i_lock);
        }
        return err;
}

/*
 * After a recovering MDS goes active, we need to resend any caps
 * we were flushing.
 *
 * Caller holds session->s_mutex.
 */
static void kick_flushing_capsnaps(struct ceph_mds_client *mdsc,
                                   struct ceph_mds_session *session)
{
        struct ceph_cap_snap *capsnap;

        dout("kick_flushing_capsnaps mds%d\n", session->s_mds);
        list_for_each_entry(capsnap, &session->s_cap_snaps_flushing,
                            flushing_item) {
                struct ceph_inode_info *ci = capsnap->ci;
                struct inode *inode = &ci->vfs_inode;
                struct ceph_cap *cap;

                spin_lock(&inode->i_lock);
                cap = ci->i_auth_cap;
                if (cap && cap->session == session) {
                        dout("kick_flushing_caps %p cap %p capsnap %p\n", inode,
                             cap, capsnap);
                        __ceph_flush_snaps(ci, &session);
                } else {
                        pr_err("%p auth cap %p not mds%d ???\n", inode,
                               cap, session->s_mds);
                        spin_unlock(&inode->i_lock);
                }
        }
}

void ceph_kick_flushing_caps(struct ceph_mds_client *mdsc,
                             struct ceph_mds_session *session)
{
        struct ceph_inode_info *ci;

        kick_flushing_capsnaps(mdsc, session);

        dout("kick_flushing_caps mds%d\n", session->s_mds);
        list_for_each_entry(ci, &session->s_cap_flushing, i_flushing_item) {
                struct inode *inode = &ci->vfs_inode;
                struct ceph_cap *cap;
                int delayed = 0;

                spin_lock(&inode->i_lock);
                cap = ci->i_auth_cap;
                if (cap && cap->session == session) {
                        dout("kick_flushing_caps %p cap %p %s\n", inode,
                             cap, ceph_cap_string(ci->i_flushing_caps));
                        delayed = __send_cap(mdsc, cap, CEPH_CAP_OP_FLUSH,
                                             __ceph_caps_used(ci),
                                             __ceph_caps_wanted(ci),
                                             cap->issued | cap->implemented,
                                             ci->i_flushing_caps, NULL);
                        if (delayed) {
                                spin_lock(&inode->i_lock);
                                __cap_delay_requeue(mdsc, ci);
                                spin_unlock(&inode->i_lock);
                        }
                } else {
                        pr_err("%p auth cap %p not mds%d ???\n", inode,
                               cap, session->s_mds);
                        spin_unlock(&inode->i_lock);
                }
        }
}


/*
 * Take references to capabilities we hold, so that we don't release
 * them to the MDS prematurely.
 *
 * Protected by i_lock.
 */
static void __take_cap_refs(struct ceph_inode_info *ci, int got)
{
        if (got & CEPH_CAP_PIN)
                ci->i_pin_ref++;
        if (got & CEPH_CAP_FILE_RD)
                ci->i_rd_ref++;
        if (got & CEPH_CAP_FILE_CACHE)
                ci->i_rdcache_ref++;
        if (got & CEPH_CAP_FILE_WR)
                ci->i_wr_ref++;
        if (got & CEPH_CAP_FILE_BUFFER) {
                if (ci->i_wrbuffer_ref == 0)
                        igrab(&ci->vfs_inode);
                ci->i_wrbuffer_ref++;
                dout("__take_cap_refs %p wrbuffer %d -> %d (?)\n",
                     &ci->vfs_inode, ci->i_wrbuffer_ref-1, ci->i_wrbuffer_ref);
        }
}

/*
 * Try to grab cap references.  Specify those refs we @want, and the
 * minimal set we @need.  Also include the larger offset we are writing
 * to (when applicable), and check against max_size here as well.
 * Note that caller is responsible for ensuring max_size increases are
 * requested from the MDS.
 */
static int try_get_cap_refs(struct ceph_inode_info *ci, int need, int want,
                            int *got, loff_t endoff, int *check_max, int *err)
{
        struct inode *inode = &ci->vfs_inode;
        int ret = 0;
        int have, implemented;

        dout("get_cap_refs %p need %s want %s\n", inode,
             ceph_cap_string(need), ceph_cap_string(want));
        spin_lock(&inode->i_lock);

        /* make sure we _have_ some caps! */
        if (!__ceph_is_any_caps(ci)) {
                dout("get_cap_refs %p no real caps\n", inode);
                *err = -EBADF;
                ret = 1;
                goto out;
        }

        if (need & CEPH_CAP_FILE_WR) {
                if (endoff >= 0 && endoff > (loff_t)ci->i_max_size) {
                        dout("get_cap_refs %p endoff %llu > maxsize %llu\n",
                             inode, endoff, ci->i_max_size);
                        if (endoff > ci->i_wanted_max_size) {
                                *check_max = 1;
                                ret = 1;
                        }
                        goto out;
                }
                /*
                 * If a sync write is in progress, we must wait, so that we
                 * can get a final snapshot value for size+mtime.
                 */
                if (__ceph_have_pending_cap_snap(ci)) {
                        dout("get_cap_refs %p cap_snap_pending\n", inode);
                        goto out;
                }
        }
        have = __ceph_caps_issued(ci, &implemented);

        /*
         * disallow writes while a truncate is pending
         */
        if (ci->i_truncate_pending)
                have &= ~CEPH_CAP_FILE_WR;

        if ((have & need) == need) {
                /*
                 * Look at (implemented & ~have & not) so that we keep waiting
                 * on transition from wanted -> needed caps.  This is needed
                 * for WRBUFFER|WR -> WR to avoid a new WR sync write from
                 * going before a prior buffered writeback happens.
                 */
                int not = want & ~(have & need);
                int revoking = implemented & ~have;
                dout("get_cap_refs %p have %s but not %s (revoking %s)\n",
                     inode, ceph_cap_string(have), ceph_cap_string(not),
                     ceph_cap_string(revoking));
                if ((revoking & not) == 0) {
                        *got = need | (have & want);
                        __take_cap_refs(ci, *got);
                        ret = 1;
                }
        } else {
                dout("get_cap_refs %p have %s needed %s\n", inode,
                     ceph_cap_string(have), ceph_cap_string(need));
        }
out:
        spin_unlock(&inode->i_lock);
        dout("get_cap_refs %p ret %d got %s\n", inode,
             ret, ceph_cap_string(*got));
        return ret;
}

/*
 * Check the offset we are writing up to against our current
 * max_size.  If necessary, tell the MDS we want to write to
 * a larger offset.
 */
static void check_max_size(struct inode *inode, loff_t endoff)
{
        struct ceph_inode_info *ci = ceph_inode(inode);
        int check = 0;

        /* do we need to explicitly request a larger max_size? */
        spin_lock(&inode->i_lock);
        if ((endoff >= ci->i_max_size ||
             endoff > (inode->i_size << 1)) &&
            endoff > ci->i_wanted_max_size) {
                dout("write %p at large endoff %llu, req max_size\n",
                     inode, endoff);
                ci->i_wanted_max_size = endoff;
                check = 1;
        }
        spin_unlock(&inode->i_lock);
        if (check)
                ceph_check_caps(ci, CHECK_CAPS_AUTHONLY, NULL);
}

/*
 * Wait for caps, and take cap references.  If we can't get a WR cap
 * due to a small max_size, make sure we check_max_size (and possibly
 * ask the mds) so we don't get hung up indefinitely.
 */
int ceph_get_caps(struct ceph_inode_info *ci, int need, int want, int *got,
                  loff_t endoff)
{
        int check_max, ret, err;

retry:
        if (endoff > 0)
                check_max_size(&ci->vfs_inode, endoff);
        check_max = 0;
        err = 0;
        ret = wait_event_interruptible(ci->i_cap_wq,
                                       try_get_cap_refs(ci, need, want,
                                                        got, endoff,
                                                        &check_max, &err));
        if (err)
                ret = err;
        if (check_max)
                goto retry;
        return ret;
}

/*
 * Take cap refs.  Caller must already know we hold at least one ref
 * on the caps in question or we don't know this is safe.
 */
void ceph_get_cap_refs(struct ceph_inode_info *ci, int caps)
{
        spin_lock(&ci->vfs_inode.i_lock);
        __take_cap_refs(ci, caps);
        spin_unlock(&ci->vfs_inode.i_lock);
}

/*
 * Release cap refs.
 *
 * If we released the last ref on any given cap, call ceph_check_caps
 * to release (or schedule a release).
 *
 * If we are releasing a WR cap (from a sync write), finalize any affected
 * cap_snap, and wake up any waiters.
 */
void ceph_put_cap_refs(struct ceph_inode_info *ci, int had)
{
        struct inode *inode = &ci->vfs_inode;
        int last = 0, put = 0, flushsnaps = 0, wake = 0;
        struct ceph_cap_snap *capsnap;

        spin_lock(&inode->i_lock);
        if (had & CEPH_CAP_PIN)
                --ci->i_pin_ref;
        if (had & CEPH_CAP_FILE_RD)
                if (--ci->i_rd_ref == 0)
                        last++;
        if (had & CEPH_CAP_FILE_CACHE)
                if (--ci->i_rdcache_ref == 0)
                        last++;
        if (had & CEPH_CAP_FILE_BUFFER) {
                if (--ci->i_wrbuffer_ref == 0) {
                        last++;
                        put++;
                }
                dout("put_cap_refs %p wrbuffer %d -> %d (?)\n",
                     inode, ci->i_wrbuffer_ref+1, ci->i_wrbuffer_ref);
        }
        if (had & CEPH_CAP_FILE_WR)
                if (--ci->i_wr_ref == 0) {
                        last++;
                        if (!list_empty(&ci->i_cap_snaps)) {
                                capsnap = list_first_entry(&ci->i_cap_snaps,
                                                     struct ceph_cap_snap,
                                                     ci_item);
                                if (capsnap->writing) {
                                        capsnap->writing = 0;
                                        flushsnaps =
                                                __ceph_finish_cap_snap(ci,
                                                                       capsnap);
                                        wake = 1;
                                }
                        }
                }
        spin_unlock(&inode->i_lock);

        dout("put_cap_refs %p had %s %s\n", inode, ceph_cap_string(had),
             last ? "last" : "");

        if (last && !flushsnaps)
                ceph_check_caps(ci, 0, NULL);
        else if (flushsnaps)
                ceph_flush_snaps(ci);
        if (wake)
                wake_up(&ci->i_cap_wq);
        if (put)
                iput(inode);
}

/*
 * Release @nr WRBUFFER refs on dirty pages for the given @snapc snap
 * context.  Adjust per-snap dirty page accounting as appropriate.
 * Once all dirty data for a cap_snap is flushed, flush snapped file
 * metadata back to the MDS.  If we dropped the last ref, call
 * ceph_check_caps.
 */
void ceph_put_wrbuffer_cap_refs(struct ceph_inode_info *ci, int nr,
                                struct ceph_snap_context *snapc)
{
        struct inode *inode = &ci->vfs_inode;
        int last = 0;
        int last_snap = 0;
        int found = 0;
        struct ceph_cap_snap *capsnap = NULL;

        spin_lock(&inode->i_lock);
        ci->i_wrbuffer_ref -= nr;
        last = !ci->i_wrbuffer_ref;

        if (ci->i_head_snapc == snapc) {
                ci->i_wrbuffer_ref_head -= nr;
                if (!ci->i_wrbuffer_ref_head) {
                        ceph_put_snap_context(ci->i_head_snapc);
                        ci->i_head_snapc = NULL;
                }
                dout("put_wrbuffer_cap_refs on %p head %d/%d -> %d/%d %s\n",
                     inode,
                     ci->i_wrbuffer_ref+nr, ci->i_wrbuffer_ref_head+nr,
                     ci->i_wrbuffer_ref, ci->i_wrbuffer_ref_head,
                     last ? " LAST" : "");
        } else {
                list_for_each_entry(capsnap, &ci->i_cap_snaps, ci_item) {
                        if (capsnap->context == snapc) {
                                found = 1;
                                capsnap->dirty_pages -= nr;
                                last_snap = !capsnap->dirty_pages;
                                break;
                        }
                }
                BUG_ON(!found);
                dout("put_wrbuffer_cap_refs on %p cap_snap %p "
                     " snap %lld %d/%d -> %d/%d %s%s\n",
                     inode, capsnap, capsnap->context->seq,
                     ci->i_wrbuffer_ref+nr, capsnap->dirty_pages + nr,
                     ci->i_wrbuffer_ref, capsnap->dirty_pages,
                     last ? " (wrbuffer last)" : "",
                     last_snap ? " (capsnap last)" : "");
        }

        spin_unlock(&inode->i_lock);

        if (last) {
                ceph_check_caps(ci, CHECK_CAPS_AUTHONLY, NULL);
                iput(inode);
        } else if (last_snap) {
                ceph_flush_snaps(ci);
                wake_up(&ci->i_cap_wq);
        }
}

/*
 * Handle a cap GRANT message from the MDS.  (Note that a GRANT may
 * actually be a revocation if it specifies a smaller cap set.)
 *
 * caller holds s_mutex.
 * return value:
 *  0 - ok
 *  1 - check_caps on auth cap only (writeback)
 *  2 - check_caps (ack revoke)
 */
static int handle_cap_grant(struct inode *inode, struct ceph_mds_caps *grant,
                            struct ceph_mds_session *session,
                            struct ceph_cap *cap,
                            struct ceph_buffer *xattr_buf)
        __releases(inode->i_lock)

{
        struct ceph_inode_info *ci = ceph_inode(inode);
        int mds = session->s_mds;
        int seq = le32_to_cpu(grant->seq);
        int newcaps = le32_to_cpu(grant->caps);
        int issued, implemented, used, wanted, dirty;
        u64 size = le64_to_cpu(grant->size);
        u64 max_size = le64_to_cpu(grant->max_size);
        struct timespec mtime, atime, ctime;
        int reply = 0;
        int wake = 0;
        int writeback = 0;
        int revoked_rdcache = 0;
        int invalidate_async = 0;
        int tried_invalidate = 0;
        int ret;

        dout("handle_cap_grant inode %p cap %p mds%d seq %d %s\n",
             inode, cap, mds, seq, ceph_cap_string(newcaps));
        dout(" size %llu max_size %llu, i_size %llu\n", size, max_size,
                inode->i_size);

        /*
         * If CACHE is being revoked, and we have no dirty buffers,
         * try to invalidate (once).  (If there are dirty buffers, we
         * will invalidate _after_ writeback.)
         */
restart:
        if (((cap->issued & ~newcaps) & CEPH_CAP_FILE_CACHE) &&
            !ci->i_wrbuffer_ref && !tried_invalidate) {
                dout("CACHE invalidation\n");
                spin_unlock(&inode->i_lock);
                tried_invalidate = 1;

                ret = invalidate_inode_pages2(&inode->i_data);
                spin_lock(&inode->i_lock);
                if (ret < 0) {
                        /* there were locked pages.. invalidate later
                           in a separate thread. */
                        if (ci->i_rdcache_revoking != ci->i_rdcache_gen) {
                                invalidate_async = 1;
                                ci->i_rdcache_revoking = ci->i_rdcache_gen;
                        }
                } else {
                        /* we successfully invalidated those pages */
                        revoked_rdcache = 1;
                        ci->i_rdcache_gen = 0;
                        ci->i_rdcache_revoking = 0;
                }
                goto restart;
        }

        /* side effects now are allowed */

        issued = __ceph_caps_issued(ci, &implemented);
        issued |= implemented | __ceph_caps_dirty(ci);

        cap->gen = session->s_cap_gen;

        __check_cap_issue(ci, cap, newcaps);

        if ((issued & CEPH_CAP_AUTH_EXCL) == 0) {
                inode->i_mode = le32_to_cpu(grant->mode);
                inode->i_uid = le32_to_cpu(grant->uid);
                inode->i_gid = le32_to_cpu(grant->gid);
                dout("%p mode 0%o uid.gid %d.%d\n", inode, inode->i_mode,
                     inode->i_uid, inode->i_gid);
        }

        if ((issued & CEPH_CAP_LINK_EXCL) == 0)
                inode->i_nlink = le32_to_cpu(grant->nlink);

        if ((issued & CEPH_CAP_XATTR_EXCL) == 0 && grant->xattr_len) {
                int len = le32_to_cpu(grant->xattr_len);
                u64 version = le64_to_cpu(grant->xattr_version);

                if (version > ci->i_xattrs.version) {
                        dout(" got new xattrs v%llu on %p len %d\n",
                             version, inode, len);
                        if (ci->i_xattrs.blob)
                                ceph_buffer_put(ci->i_xattrs.blob);
                        ci->i_xattrs.blob = ceph_buffer_get(xattr_buf);
                        ci->i_xattrs.version = version;
                }
        }

        /* size/ctime/mtime/atime? */
        ceph_fill_file_size(inode, issued,
                            le32_to_cpu(grant->truncate_seq),
                            le64_to_cpu(grant->truncate_size), size);
        ceph_decode_timespec(&mtime, &grant->mtime);
        ceph_decode_timespec(&atime, &grant->atime);
        ceph_decode_timespec(&ctime, &grant->ctime);
        ceph_fill_file_time(inode, issued,
                            le32_to_cpu(grant->time_warp_seq), &ctime, &mtime,
                            &atime);

        /* max size increase? */
        if (max_size != ci->i_max_size) {
                dout("max_size %lld -> %llu\n", ci->i_max_size, max_size);
                ci->i_max_size = max_size;
                if (max_size >= ci->i_wanted_max_size) {
                        ci->i_wanted_max_size = 0;  /* reset */
                        ci->i_requested_max_size = 0;
                }
                wake = 1;
        }

        /* check cap bits */
        wanted = __ceph_caps_wanted(ci);
        used = __ceph_caps_used(ci);
        dirty = __ceph_caps_dirty(ci);
        dout(" my wanted = %s, used = %s, dirty %s\n",
             ceph_cap_string(wanted),
             ceph_cap_string(used),
             ceph_cap_string(dirty));
        if (wanted != le32_to_cpu(grant->wanted)) {
                dout("mds wanted %s -> %s\n",
                     ceph_cap_string(le32_to_cpu(grant->wanted)),
                     ceph_cap_string(wanted));
                grant->wanted = cpu_to_le32(wanted);
        }

        cap->seq = seq;

        /* file layout may have changed */
        ci->i_layout = grant->layout;

        /* revocation, grant, or no-op? */
        if (cap->issued & ~newcaps) {
                dout("revocation: %s -> %s\n", ceph_cap_string(cap->issued),
                     ceph_cap_string(newcaps));
                if ((used & ~newcaps) & CEPH_CAP_FILE_BUFFER)
                        writeback = 1; /* will delay ack */
                else if (dirty & ~newcaps)
                        reply = 1;     /* initiate writeback in check_caps */
                else if (((used & ~newcaps) & CEPH_CAP_FILE_CACHE) == 0 ||
                           revoked_rdcache)
                        reply = 2;     /* send revoke ack in check_caps */
                cap->issued = newcaps;
        } else if (cap->issued == newcaps) {
                dout("caps unchanged: %s -> %s\n",
                     ceph_cap_string(cap->issued), ceph_cap_string(newcaps));
        } else {
                dout("grant: %s -> %s\n", ceph_cap_string(cap->issued),
                     ceph_cap_string(newcaps));
                cap->issued = newcaps;
                cap->implemented |= newcaps; /* add bits only, to
                                              * avoid stepping on a
                                              * pending revocation */
                wake = 1;
        }

        spin_unlock(&inode->i_lock);
        if (writeback) {
                /*
                 * queue inode for writeback: we can't actually call
                 * filemap_write_and_wait, etc. from message handler
                 * context.
                 */
                dout("queueing %p for writeback\n", inode);
                if (ceph_queue_writeback(inode))
                        igrab(inode);
        }
        if (invalidate_async) {
                dout("queueing %p for page invalidation\n", inode);
                if (ceph_queue_page_invalidation(inode))
                        igrab(inode);
        }
        if (wake)
                wake_up(&ci->i_cap_wq);
        return reply;
}

/*
 * Handle FLUSH_ACK from MDS, indicating that metadata we sent to the
 * MDS has been safely committed.
 */
static void handle_cap_flush_ack(struct inode *inode,
                                 struct ceph_mds_caps *m,
                                 struct ceph_mds_session *session,
                                 struct ceph_cap *cap)
        __releases(inode->i_lock)
{
        struct ceph_inode_info *ci = ceph_inode(inode);
        struct ceph_mds_client *mdsc = &ceph_client(inode->i_sb)->mdsc;
        unsigned seq = le32_to_cpu(m->seq);
        int dirty = le32_to_cpu(m->dirty);
        int cleaned = 0;
        u64 flush_tid = le64_to_cpu(m->client_tid);
        int old_dirty = 0, new_dirty = 0;
        int i;

        for (i = 0; i < CEPH_CAP_BITS; i++)
                if ((dirty & (1 << i)) &&
                    flush_tid == ci->i_cap_flush_tid[i])
                        cleaned |= 1 << i;

        dout("handle_cap_flush_ack inode %p mds%d seq %d on %s cleaned %s,"
             " flushing %s -> %s\n",
             inode, session->s_mds, seq, ceph_cap_string(dirty),
             ceph_cap_string(cleaned), ceph_cap_string(ci->i_flushing_caps),
             ceph_cap_string(ci->i_flushing_caps & ~cleaned));

        if (ci->i_flushing_caps == (ci->i_flushing_caps & ~cleaned))
                goto out;

        old_dirty = ci->i_dirty_caps | ci->i_flushing_caps;
        ci->i_flushing_caps &= ~cleaned;
        new_dirty = ci->i_dirty_caps | ci->i_flushing_caps;

        spin_lock(&mdsc->cap_dirty_lock);
        if (ci->i_flushing_caps == 0) {
                list_del_init(&ci->i_flushing_item);
                if (!list_empty(&session->s_cap_flushing))
                        dout(" mds%d still flushing cap on %p\n",
                             session->s_mds,
                             &list_entry(session->s_cap_flushing.next,
                                         struct ceph_inode_info,
                                         i_flushing_item)->vfs_inode);
                mdsc->num_cap_flushing--;
                wake_up(&mdsc->cap_flushing_wq);
                dout(" inode %p now !flushing\n", inode);
        }
        if (old_dirty && !new_dirty) {
                dout(" inode %p now clean\n", inode);
                list_del_init(&ci->i_dirty_item);
        }
        spin_unlock(&mdsc->cap_dirty_lock);
        wake_up(&ci->i_cap_wq);

out:
        spin_unlock(&inode->i_lock);
        if (old_dirty && !new_dirty)
                iput(inode);
}

/*
 * Handle FLUSHSNAP_ACK.  MDS has flushed snap data to disk and we can
 * throw away our cap_snap.
 *
 * Caller hold s_mutex.
 */
static void handle_cap_flushsnap_ack(struct inode *inode,
                                     struct ceph_mds_caps *m,
                                     struct ceph_mds_session *session)
{
        struct ceph_inode_info *ci = ceph_inode(inode);
        u64 follows = le64_to_cpu(m->snap_follows);
        u64 flush_tid = le64_to_cpu(m->client_tid);
        struct ceph_cap_snap *capsnap;
        int drop = 0;

        dout("handle_cap_flushsnap_ack inode %p ci %p mds%d follows %lld\n",
             inode, ci, session->s_mds, follows);

        spin_lock(&inode->i_lock);
        list_for_each_entry(capsnap, &ci->i_cap_snaps, ci_item) {
                if (capsnap->follows == follows) {
                        if (capsnap->flush_tid != flush_tid) {
                                dout(" cap_snap %p follows %lld tid %lld !="
                                     " %lld\n", capsnap, follows,
                                     flush_tid, capsnap->flush_tid);
                                break;
                        }
                        WARN_ON(capsnap->dirty_pages || capsnap->writing);
                        dout(" removing cap_snap %p follows %lld\n",
                             capsnap, follows);
                        ceph_put_snap_context(capsnap->context);
                        list_del(&capsnap->ci_item);
                        list_del(&capsnap->flushing_item);
                        ceph_put_cap_snap(capsnap);
                        drop = 1;
                        break;
                } else {
                        dout(" skipping cap_snap %p follows %lld\n",
                             capsnap, capsnap->follows);
                }
        }
        spin_unlock(&inode->i_lock);
        if (drop)
                iput(inode);
}

/*
 * Handle TRUNC from MDS, indicating file truncation.
 *
 * caller hold s_mutex.
 */
static void handle_cap_trunc(struct inode *inode,
                             struct ceph_mds_caps *trunc,
                             struct ceph_mds_session *session)
        __releases(inode->i_lock)
{
        struct ceph_inode_info *ci = ceph_inode(inode);
        int mds = session->s_mds;
        int seq = le32_to_cpu(trunc->seq);
        u32 truncate_seq = le32_to_cpu(trunc->truncate_seq);
        u64 truncate_size = le64_to_cpu(trunc->truncate_size);
        u64 size = le64_to_cpu(trunc->size);
        int implemented = 0;
        int dirty = __ceph_caps_dirty(ci);
        int issued = __ceph_caps_issued(ceph_inode(inode), &implemented);
        int queue_trunc = 0;

        issued |= implemented | dirty;

        dout("handle_cap_trunc inode %p mds%d seq %d to %lld seq %d\n",
             inode, mds, seq, truncate_size, truncate_seq);
        queue_trunc = ceph_fill_file_size(inode, issued,
                                          truncate_seq, truncate_size, size);
        spin_unlock(&inode->i_lock);

        if (queue_trunc)
                if (queue_work(ceph_client(inode->i_sb)->trunc_wq,
                               &ci->i_vmtruncate_work))
                        igrab(inode);
}

/*
 * Handle EXPORT from MDS.  Cap is being migrated _from_ this mds to a
 * different one.  If we are the most recent migration we've seen (as
 * indicated by mseq), make note of the migrating cap bits for the
 * duration (until we see the corresponding IMPORT).
 *
 * caller holds s_mutex
 */
static void handle_cap_export(struct inode *inode, struct ceph_mds_caps *ex,
                              struct ceph_mds_session *session)
{
        struct ceph_inode_info *ci = ceph_inode(inode);
        int mds = session->s_mds;
        unsigned mseq = le32_to_cpu(ex->migrate_seq);
        struct ceph_cap *cap = NULL, *t;
        struct rb_node *p;
        int remember = 1;

        dout("handle_cap_export inode %p ci %p mds%d mseq %d\n",
             inode, ci, mds, mseq);

        spin_lock(&inode->i_lock);

        /* make sure we haven't seen a higher mseq */
        for (p = rb_first(&ci->i_caps); p; p = rb_next(p)) {
                t = rb_entry(p, struct ceph_cap, ci_node);
                if (ceph_seq_cmp(t->mseq, mseq) > 0) {
                        dout(" higher mseq on cap from mds%d\n",
                             t->session->s_mds);
                        remember = 0;
                }
                if (t->session->s_mds == mds)
                        cap = t;
        }

        if (cap) {
                if (remember) {
                        /* make note */
                        ci->i_cap_exporting_mds = mds;
                        ci->i_cap_exporting_mseq = mseq;
                        ci->i_cap_exporting_issued = cap->issued;
                }
                __ceph_remove_cap(cap, NULL);
        } else {
                WARN_ON(!cap);
        }

        spin_unlock(&inode->i_lock);
}

/*
 * Handle cap IMPORT.  If there are temp bits from an older EXPORT,
 * clean them up.
 *
 * caller holds s_mutex.
 */
static void handle_cap_import(struct ceph_mds_client *mdsc,
                              struct inode *inode, struct ceph_mds_caps *im,
                              struct ceph_mds_session *session,
                              void *snaptrace, int snaptrace_len)
{
        struct ceph_inode_info *ci = ceph_inode(inode);
        int mds = session->s_mds;
        unsigned issued = le32_to_cpu(im->caps);
        unsigned wanted = le32_to_cpu(im->wanted);
        unsigned seq = le32_to_cpu(im->seq);
        unsigned mseq = le32_to_cpu(im->migrate_seq);
        u64 realmino = le64_to_cpu(im->realm);
        u64 cap_id = le64_to_cpu(im->cap_id);

        if (ci->i_cap_exporting_mds >= 0 &&
            ceph_seq_cmp(ci->i_cap_exporting_mseq, mseq) < 0) {
                dout("handle_cap_import inode %p ci %p mds%d mseq %d"
                     " - cleared exporting from mds%d\n",
                     inode, ci, mds, mseq,
                     ci->i_cap_exporting_mds);
                ci->i_cap_exporting_issued = 0;
                ci->i_cap_exporting_mseq = 0;
                ci->i_cap_exporting_mds = -1;
        } else {
                dout("handle_cap_import inode %p ci %p mds%d mseq %d\n",
                     inode, ci, mds, mseq);
        }

        down_write(&mdsc->snap_rwsem);
        ceph_update_snap_trace(mdsc, snaptrace, snaptrace+snaptrace_len,
                               false);
        downgrade_write(&mdsc->snap_rwsem);
        ceph_add_cap(inode, session, cap_id, -1,
                     issued, wanted, seq, mseq, realmino, CEPH_CAP_FLAG_AUTH,
                     NULL /* no caps context */);
        try_flush_caps(inode, session, NULL);
        up_read(&mdsc->snap_rwsem);
}

/*
 * Handle a caps message from the MDS.
 *
 * Identify the appropriate session, inode, and call the right handler
 * based on the cap op.
 */
void ceph_handle_caps(struct ceph_mds_session *session,
                      struct ceph_msg *msg)
{
        struct ceph_mds_client *mdsc = session->s_mdsc;
        struct super_block *sb = mdsc->client->sb;
        struct inode *inode;
        struct ceph_cap *cap;
        struct ceph_mds_caps *h;
        int mds = le64_to_cpu(msg->hdr.src.name.num);
        int op;
        u32 seq;
        struct ceph_vino vino;
        u64 cap_id;
        u64 size, max_size;
        int check_caps = 0;
        int r;

        dout("handle_caps from mds%d\n", mds);

        /* decode */
        if (msg->front.iov_len < sizeof(*h))
                goto bad;
        h = msg->front.iov_base;
        op = le32_to_cpu(h->op);
        vino.ino = le64_to_cpu(h->ino);
        vino.snap = CEPH_NOSNAP;
        cap_id = le64_to_cpu(h->cap_id);
        seq = le32_to_cpu(h->seq);
        size = le64_to_cpu(h->size);
        max_size = le64_to_cpu(h->max_size);

        mutex_lock(&session->s_mutex);
        session->s_seq++;
        dout(" mds%d seq %lld cap seq %u\n", session->s_mds, session->s_seq,
             (unsigned)seq);

        /* lookup ino */
        inode = ceph_find_inode(sb, vino);
        dout(" op %s ino %llx.%llx inode %p\n", ceph_cap_op_name(op), vino.ino,
             vino.snap, inode);
        if (!inode) {
                dout(" i don't have ino %llx\n", vino.ino);
                goto done;
        }

        /* these will work even if we don't have a cap yet */
        switch (op) {
        case CEPH_CAP_OP_FLUSHSNAP_ACK:
                handle_cap_flushsnap_ack(inode, h, session);
                goto done;

        case CEPH_CAP_OP_EXPORT:
                handle_cap_export(inode, h, session);
                goto done;

        case CEPH_CAP_OP_IMPORT:
                handle_cap_import(mdsc, inode, h, session,
                                  msg->middle,
                                  le32_to_cpu(h->snap_trace_len));
                check_caps = 1; /* we may have sent a RELEASE to the old auth */
                goto done;
        }

        /* the rest require a cap */
        spin_lock(&inode->i_lock);
        cap = __get_cap_for_mds(ceph_inode(inode), mds);
        if (!cap) {
                dout("no cap on %p ino %llx.%llx from mds%d, releasing\n",
                     inode, ceph_ino(inode), ceph_snap(inode), mds);
                spin_unlock(&inode->i_lock);
                goto done;
        }

        /* note that each of these drops i_lock for us */
        switch (op) {
        case CEPH_CAP_OP_REVOKE:
        case CEPH_CAP_OP_GRANT:
                r = handle_cap_grant(inode, h, session, cap, msg->middle);
                if (r == 1)
                        ceph_check_caps(ceph_inode(inode),
                                        CHECK_CAPS_NODELAY|CHECK_CAPS_AUTHONLY,
                                        session);
                else if (r == 2)
                        ceph_check_caps(ceph_inode(inode),
                                        CHECK_CAPS_NODELAY,
                                        session);
                break;

        case CEPH_CAP_OP_FLUSH_ACK:
                handle_cap_flush_ack(inode, h, session, cap);
                break;

        case CEPH_CAP_OP_TRUNC:
                handle_cap_trunc(inode, h, session);
                break;

        default:
                spin_unlock(&inode->i_lock);
                pr_err("ceph_handle_caps: unknown cap op %d %s\n", op,
                       ceph_cap_op_name(op));
        }

done:
        mutex_unlock(&session->s_mutex);

        if (check_caps)
                ceph_check_caps(ceph_inode(inode), CHECK_CAPS_NODELAY, NULL);
        if (inode)
                iput(inode);
        return;

bad:
        pr_err("ceph_handle_caps: corrupt message\n");
        return;
}

/*
 * Delayed work handler to process end of delayed cap release LRU list.
 */
void ceph_check_delayed_caps(struct ceph_mds_client *mdsc, int flushdirty)
{
        struct ceph_inode_info *ci;
        int flags = CHECK_CAPS_NODELAY;

        if (flushdirty)
                flags |= CHECK_CAPS_FLUSH;

        dout("check_delayed_caps\n");
        while (1) {
                spin_lock(&mdsc->cap_delay_lock);
                if (list_empty(&mdsc->cap_delay_list))
                        break;
                ci = list_first_entry(&mdsc->cap_delay_list,
                                      struct ceph_inode_info,
                                      i_cap_delay_list);
                if ((ci->i_ceph_flags & CEPH_I_FLUSH) == 0 &&
                    time_before(jiffies, ci->i_hold_caps_max))
                        break;
                list_del_init(&ci->i_cap_delay_list);
                spin_unlock(&mdsc->cap_delay_lock);
                dout("check_delayed_caps on %p\n", &ci->vfs_inode);
                ceph_check_caps(ci, flags, NULL);
        }
        spin_unlock(&mdsc->cap_delay_lock);
}

/*
 * Drop open file reference.  If we were the last open file,
 * we may need to release capabilities to the MDS (or schedule
 * their delayed release).
 */
void ceph_put_fmode(struct ceph_inode_info *ci, int fmode)
{
        struct inode *inode = &ci->vfs_inode;
        int last = 0;

        spin_lock(&inode->i_lock);
        dout("put_fmode %p fmode %d %d -> %d\n", inode, fmode,
             ci->i_nr_by_mode[fmode], ci->i_nr_by_mode[fmode]-1);
        BUG_ON(ci->i_nr_by_mode[fmode] == 0);
        if (--ci->i_nr_by_mode[fmode] == 0)
                last++;
        spin_unlock(&inode->i_lock);

        if (last && ci->i_vino.snap == CEPH_NOSNAP)
                ceph_check_caps(ci, 0, NULL);
}

/*
 * Helpers for embedding cap and dentry lease releases into mds
 * requests.
 *
 * @force is used by dentry_release (below) to force inclusion of a
 * record for the directory inode, even when there aren't any caps to
 * drop.
 */
int ceph_encode_inode_release(void **p, struct inode *inode,
                              int mds, int drop, int unless, int force)
{
        struct ceph_inode_info *ci = ceph_inode(inode);
        struct ceph_cap *cap;
        struct ceph_mds_request_release *rel = *p;
        int ret = 0;

        dout("encode_inode_release %p mds%d drop %s unless %s\n", inode,
             mds, ceph_cap_string(drop), ceph_cap_string(unless));

        spin_lock(&inode->i_lock);
        cap = __get_cap_for_mds(ci, mds);
        if (cap && __cap_is_valid(cap)) {
                if (force ||
                    ((cap->issued & drop) &&
                     (cap->issued & unless) == 0)) {
                        if ((cap->issued & drop) &&
                            (cap->issued & unless) == 0) {
                                dout("encode_inode_release %p cap %p %s -> "
                                     "%s\n", inode, cap,
                                     ceph_cap_string(cap->issued),
                                     ceph_cap_string(cap->issued & ~drop));
                                cap->issued &= ~drop;
                                cap->implemented &= ~drop;
                                if (ci->i_ceph_flags & CEPH_I_NODELAY) {
                                        int wanted = __ceph_caps_wanted(ci);
                                        dout("  wanted %s -> %s (act %s)\n",
                                             ceph_cap_string(cap->mds_wanted),
                                             ceph_cap_string(cap->mds_wanted &
                                                             ~wanted),
                                             ceph_cap_string(wanted));
                                        cap->mds_wanted &= wanted;
                                }
                        } else {
                                dout("encode_inode_release %p cap %p %s"
                                     " (force)\n", inode, cap,
                                     ceph_cap_string(cap->issued));
                        }

                        rel->ino = cpu_to_le64(ceph_ino(inode));
                        rel->cap_id = cpu_to_le64(cap->cap_id);
                        rel->seq = cpu_to_le32(cap->seq);
                        rel->issue_seq = cpu_to_le32(cap->issue_seq),
                        rel->mseq = cpu_to_le32(cap->mseq);
                        rel->caps = cpu_to_le32(cap->issued);
                        rel->wanted = cpu_to_le32(cap->mds_wanted);
                        rel->dname_len = 0;
                        rel->dname_seq = 0;
                        *p += sizeof(*rel);
                        ret = 1;
                } else {
                        dout("encode_inode_release %p cap %p %s\n",
                             inode, cap, ceph_cap_string(cap->issued));
                }
        }
        spin_unlock(&inode->i_lock);
        return ret;
}

int ceph_encode_dentry_release(void **p, struct dentry *dentry,
                               int mds, int drop, int unless)
{
        struct inode *dir = dentry->d_parent->d_inode;
        struct ceph_mds_request_release *rel = *p;
        struct ceph_dentry_info *di = ceph_dentry(dentry);
        int force = 0;
        int ret;

        /*
         * force an record for the directory caps if we have a dentry lease.
         * this is racy (can't take i_lock and d_lock together), but it
         * doesn't have to be perfect; the mds will revoke anything we don't
         * release.
         */
        spin_lock(&dentry->d_lock);
        if (di->lease_session && di->lease_session->s_mds == mds)
                force = 1;
        spin_unlock(&dentry->d_lock);

        ret = ceph_encode_inode_release(p, dir, mds, drop, unless, force);

        spin_lock(&dentry->d_lock);
        if (ret && di->lease_session && di->lease_session->s_mds == mds) {
                dout("encode_dentry_release %p mds%d seq %d\n",
                     dentry, mds, (int)di->lease_seq);
                rel->dname_len = cpu_to_le32(dentry->d_name.len);
                memcpy(*p, dentry->d_name.name, dentry->d_name.len);
                *p += dentry->d_name.len;
                rel->dname_seq = cpu_to_le32(di->lease_seq);
        }
        spin_unlock(&dentry->d_lock);
        return ret;
}