rbd: move snap_rwsem to the device, rename to header_rwsem

A new temporary header is allocated each time the header changes, but
only the changed properties are copied over. We don't need a new
semaphore for each header update.

This addresses http://tracker.newdream.net/issues/2174

Signed-off-by: Josh Durgin <josh.durgin@dreamhost.com>
Reviewed-by: Alex Elder <elder@dreamhost.com>

diff --git a/drivers/block/rbd.c b/drivers/block/rbd.c
index 6bbd5af..013c7a5 100644 (file)
--- a/drivers/block/rbd.c
+++ b/drivers/block/rbd.c
@@ -82,7 +82,6 @@ struct rbd_image_header {
        __u8 obj_order;
        __u8 crypt_type;
        __u8 comp_type;
-       struct rw_semaphore snap_rwsem;
        struct ceph_snap_context *snapc;
        size_t snap_names_len;
        u64 snap_seq;
@@ -173,6 +172,8 @@ struct rbd_device {
        struct ceph_osd_event   *watch_event;
        struct ceph_osd_request *watch_request;
 
+       /* protects updating the header */
+       struct rw_semaphore     header_rwsem;
        char                    snap_name[RBD_MAX_SNAP_NAME_LEN];
        u32 cur_snap;   /* index+1 of current snapshot within snap context
                           0 - for the head */
@@ -502,7 +503,6 @@ static int rbd_header_from_disk(struct rbd_image_header *header,
        if (!header->snapc)
                return -ENOMEM;
 
-       init_rwsem(&header->snap_rwsem);
        header->snap_names_len = le64_to_cpu(ondisk->snap_names_len);
        if (snap_count) {
                header->snap_names = kmalloc(header->snap_names_len,
@@ -597,7 +597,7 @@ static int rbd_header_set_snap(struct rbd_device *dev, u64 *size)
 
        BUILD_BUG_ON(sizeof (dev->snap_name) < sizeof (RBD_SNAP_HEAD_NAME));
 
-       down_write(&header->snap_rwsem);
+       down_write(&dev->header_rwsem);
 
        if (!memcmp(dev->snap_name, RBD_SNAP_HEAD_NAME,
                    sizeof (RBD_SNAP_HEAD_NAME))) {
@@ -620,7 +620,7 @@ static int rbd_header_set_snap(struct rbd_device *dev, u64 *size)
 
        ret = 0;
 done:
-       up_write(&header->snap_rwsem);
+       up_write(&dev->header_rwsem);
        return ret;
 }
 
@@ -887,7 +887,6 @@ static int rbd_do_request(struct request *rq,
        struct timespec mtime = CURRENT_TIME;
        struct rbd_request *req_data;
        struct ceph_osd_request_head *reqhead;
-       struct rbd_image_header *header = &dev->header;
        struct ceph_osd_client *osdc;
 
        req_data = kzalloc(sizeof(*req_data), GFP_NOIO);
@@ -905,13 +904,13 @@ static int rbd_do_request(struct request *rq,
 
        dout("rbd_do_request obj=%s ofs=%lld len=%lld\n", obj, len, ofs);
 
-       down_read(&header->snap_rwsem);
+       down_read(&dev->header_rwsem);
 
        osdc = &dev->rbd_client->client->osdc;
        req = ceph_osdc_alloc_request(osdc, flags, snapc, ops,
                                        false, GFP_NOIO, pages, bio);
        if (!req) {
-               up_read(&header->snap_rwsem);
+               up_read(&dev->header_rwsem);
                ret = -ENOMEM;
                goto done_pages;
        }
@@ -946,7 +945,7 @@ static int rbd_do_request(struct request *rq,
                                snapc,
                                &mtime,
                                req->r_oid, req->r_oid_len);
-       up_read(&header->snap_rwsem);
+       up_read(&dev->header_rwsem);
 
        if (linger_req) {
                ceph_osdc_set_request_linger(osdc, req);
@@ -1718,7 +1717,7 @@ static int __rbd_update_snaps(struct rbd_device *rbd_dev)
        /* resized? */
        set_capacity(rbd_dev->disk, h.image_size / SECTOR_SIZE);
 
-       down_write(&rbd_dev->header.snap_rwsem);
+       down_write(&rbd_dev->header_rwsem);
 
        snap_seq = rbd_dev->header.snapc->seq;
        if (rbd_dev->header.total_snaps &&
@@ -1743,7 +1742,7 @@ static int __rbd_update_snaps(struct rbd_device *rbd_dev)
 
        ret = __rbd_init_snaps_header(rbd_dev);
 
-       up_write(&rbd_dev->header.snap_rwsem);
+       up_write(&rbd_dev->header_rwsem);
 
        return ret;
 }
@@ -2380,8 +2379,9 @@ static ssize_t rbd_add(struct bus_type *bus,
        spin_lock_init(&rbd_dev->lock);
        INIT_LIST_HEAD(&rbd_dev->node);
        INIT_LIST_HEAD(&rbd_dev->snaps);
+       init_rwsem(&rbd_dev->header_rwsem);
 
-       init_rwsem(&rbd_dev->header.snap_rwsem);
+       init_rwsem(&rbd_dev->header_rwsem);
 
        /* generate unique id: find highest unique id, add one */
        rbd_id_get(rbd_dev);