On Wed, Apr 18, 2012 at 7:41 AM, Alex Elder <elder@xxxxxxxxxxxxx> wrote:
> When a device was open at a snapshot, and snapshots were deleted or
> added, data from the wrong snapshot could be read. Instead of
> assuming the snap context is constant, store the actual snap id when
> the device is initialized, and rely on the OSDs to signal an error
> if we try reading from a snapshot that was deleted.
>
> Signed-off-by: Josh Durgin <josh.durgin@xxxxxxxxxxxxx>
> Reviewed-by: Alex Elder <elder@xxxxxxxxxxxxx>
> ---
> drivers/block/rbd.c | 27 +++++----------------------
> 1 file changed, 5 insertions(+), 22 deletions(-)
>
> Index: b/drivers/block/rbd.c
> ===================================================================
> --- a/drivers/block/rbd.c
> +++ b/drivers/block/rbd.c
> @@ -175,8 +175,7 @@
> /* 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 */
> + u64 snap_id; /* current snapshot id */
> int read_only;
>
> struct list_head node;
> @@ -554,21 +553,6 @@
> return -ENOMEM;
> }
>
> -static int snap_index(struct rbd_image_header *header, int snap_num)
> -{
> - return header->total_snaps - snap_num;
> -}
> -
> -static u64 cur_snap_id(struct rbd_device *rbd_dev)
> -{
> - struct rbd_image_header *header = &rbd_dev->header;
> -
> - if (!rbd_dev->cur_snap)
> - return 0;
> -
> - return header->snapc->snaps[snap_index(header, rbd_dev->cur_snap)];
> -}
> -
> static int snap_by_name(struct rbd_image_header *header, const char
> *snap_name,
> u64 *seq, u64 *size)
> {
> @@ -607,7 +591,7 @@
> snapc->seq = header->snap_seq;
> else
> snapc->seq = 0;
> - dev->cur_snap = 0;
> + dev->snap_id = CEPH_NOSNAP;
> dev->read_only = 0;
> if (size)
> *size = header->image_size;
> @@ -615,8 +599,7 @@
> ret = snap_by_name(header, dev->snap_name, &snapc->seq,
> size);
> if (ret < 0)
> goto done;
> -
> - dev->cur_snap = header->total_snaps - ret;
> + dev->snap_id = snapc->seq;
> dev->read_only = 1;
> }
>
> @@ -1523,7 +1506,7 @@
> coll, cur_seg);
> else
> rbd_req_read(rq, rbd_dev,
> - cur_snap_id(rbd_dev),
> + rbd_dev->snap_id,
> ofs,
> op_size, bio,
> coll, cur_seg);
> @@ -1658,7 +1641,7 @@
> struct ceph_mon_client *monc;
>
> /* we should create a snapshot only if we're pointing at the head */
> - if (dev->cur_snap)
> + if (dev->snap_id != CEPH_NOSNAP)
> return -EINVAL;
>
> monc = &dev->rbd_client->client->monc;
Reviewed-by: Yehuda Sadeh <yehuda@xxxxxxxxxxxxxxx>
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