vfs: add d_prune dentry operation

This adds a d_prune dentry operation that is called by the VFS prior to
pruning (i.e. unhashing and killing) a hashed dentry from the dcache.
Wrap dentry_lru_del() and use the new _prune() helper in the cases where we
are about to unhash and kill the dentry.

This will be used by Ceph to maintain a flag indicating whether the
complete contents of a directory are contained in the dcache, allowing it
to satisfy lookups and readdir without addition server communication.

Renumber a few DCACHE_* #defines to group DCACHE_OP_PRUNE with the other
DCACHE_OP_ bits.

Signed-off-by: Sage Weil <sage@newdream.net>
Signed-off-by: Christoph Hellwig <hch@lst.de>

diff --git a/Documentation/filesystems/Locking b/Documentation/filesystems/Locking
index 6533807..d819ba1 100644 (file)
--- a/Documentation/filesystems/Locking
+++ b/Documentation/filesystems/Locking
@@ -29,6 +29,7 @@ d_hash                no              no              no              maybe
 d_compare:     yes             no              no              maybe
 d_delete:      no              yes             no              no
 d_release:     no              no              yes             no
+d_prune:        no              yes             no              no
 d_iput:                no              no              yes             no
 d_dname:       no              no              no              no
 d_automount:   no              no              yes             no

diff --git a/fs/dcache.c b/fs/dcache.c
index a88948b..274f13e 100644 (file)
--- a/fs/dcache.c
+++ b/fs/dcache.c
@@ -225,7 +225,7 @@ static void dentry_unlink_inode(struct dentry * dentry)
 }
 
 /*
- * dentry_lru_(add|del|move_tail) must be called with d_lock held.
+ * dentry_lru_(add|del|prune|move_tail) must be called with d_lock held.
  */
 static void dentry_lru_add(struct dentry *dentry)
 {
@@ -245,6 +245,9 @@ static void __dentry_lru_del(struct dentry *dentry)
        dentry_stat.nr_unused--;
 }
 
+/*
+ * Remove a dentry with references from the LRU.
+ */
 static void dentry_lru_del(struct dentry *dentry)
 {
        if (!list_empty(&dentry->d_lru)) {
@@ -254,6 +257,23 @@ static void dentry_lru_del(struct dentry *dentry)
        }
 }
 
+/*
+ * Remove a dentry that is unreferenced and about to be pruned
+ * (unhashed and destroyed) from the LRU, and inform the file system.
+ * This wrapper should be called _prior_ to unhashing a victim dentry.
+ */
+static void dentry_lru_prune(struct dentry *dentry)
+{
+       if (!list_empty(&dentry->d_lru)) {
+               if (dentry->d_flags & DCACHE_OP_PRUNE)
+                       dentry->d_op->d_prune(dentry);
+
+               spin_lock(&dcache_lru_lock);
+               __dentry_lru_del(dentry);
+               spin_unlock(&dcache_lru_lock);
+       }
+}
+
 static void dentry_lru_move_tail(struct dentry *dentry)
 {
        spin_lock(&dcache_lru_lock);
@@ -403,8 +423,12 @@ relock:
 
        if (ref)
                dentry->d_count--;
-       /* if dentry was on the d_lru list delete it from there */
-       dentry_lru_del(dentry);
+       /*
+        * if dentry was on the d_lru list delete it from there.
+        * inform the fs via d_prune that this dentry is about to be
+        * unhashed and destroyed.
+        */
+       dentry_lru_prune(dentry);
        /* if it was on the hash then remove it */
        __d_drop(dentry);
        return d_kill(dentry, parent);
@@ -854,8 +878,12 @@ static void shrink_dcache_for_umount_subtree(struct dentry *dentry)
                do {
                        struct inode *inode;
 
-                       /* detach from the system */
-                       dentry_lru_del(dentry);
+                       /*
+                        * remove the dentry from the lru, and inform
+                        * the fs that this dentry is about to be
+                        * unhashed and destroyed.
+                        */
+                       dentry_lru_prune(dentry);
                        __d_shrink(dentry);
 
                        if (dentry->d_count != 0) {
@@ -1283,6 +1311,8 @@ void d_set_d_op(struct dentry *dentry, const struct dentry_operations *op)
                dentry->d_flags |= DCACHE_OP_REVALIDATE;
        if (op->d_delete)
                dentry->d_flags |= DCACHE_OP_DELETE;
+       if (op->d_prune)
+               dentry->d_flags |= DCACHE_OP_PRUNE;
 
 }
 EXPORT_SYMBOL(d_set_d_op);

diff --git a/include/linux/dcache.h b/include/linux/dcache.h
index 62157c0..4df9261 100644 (file)
--- a/include/linux/dcache.h
+++ b/include/linux/dcache.h
@@ -165,6 +165,7 @@ struct dentry_operations {
                        unsigned int, const char *, const struct qstr *);
        int (*d_delete)(const struct dentry *);
        void (*d_release)(struct dentry *);
+       void (*d_prune)(struct dentry *);
        void (*d_iput)(struct dentry *, struct inode *);
        char *(*d_dname)(struct dentry *, char *, int);
        struct vfsmount *(*d_automount)(struct path *);
@@ -184,8 +185,9 @@ struct dentry_operations {
 #define DCACHE_OP_COMPARE      0x0002
 #define DCACHE_OP_REVALIDATE   0x0004
 #define DCACHE_OP_DELETE       0x0008
+#define DCACHE_OP_PRUNE         0x0010
 
-#define        DCACHE_DISCONNECTED     0x0010
+#define        DCACHE_DISCONNECTED     0x0020
      /* This dentry is possibly not currently connected to the dcache tree, in
       * which case its parent will either be itself, or will have this flag as
       * well.  nfsd will not use a dentry with this bit set, but will first
@@ -196,8 +198,8 @@ struct dentry_operations {
       * dentry into place and return that dentry rather than the passed one,
       * typically using d_splice_alias. */
 
-#define DCACHE_REFERENCED      0x0020  /* Recently used, don't discard. */
-#define DCACHE_RCUACCESS       0x0040  /* Entry has ever been RCU-visible */
+#define DCACHE_REFERENCED      0x0040  /* Recently used, don't discard. */
+#define DCACHE_RCUACCESS       0x0080  /* Entry has ever been RCU-visible */
 
 #define DCACHE_CANT_MOUNT      0x0100
 #define DCACHE_GENOCIDE                0x0200