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    Subject[ 133/171] rbd: return errors for mapped but deleted snapshot
    Date
    3.4-stable review patch.  If anyone has any objections, please let me know.

    ------------------


    From: Josh Durgin <josh.durgin@inktank.com>

    When a snapshot is deleted, the OSD will return ENOENT when reading
    from it. This is normally interpreted as a hole by rbd, which will
    return zeroes. To minimize the time in which this can happen, stop
    requests early when we are notified that our snapshot no longer
    exists.

    [elder@inktank.com: updated __rbd_init_snaps_header() logic]

    Signed-off-by: Josh Durgin <josh.durgin@inktank.com>
    Reviewed-by: Alex Elder <elder@inktank.com>
    (cherry picked from commit e88a36ec961b8c1899c59c5e4ae35a318c0209d3)
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

    Conflicts:

    drivers/block/rbd.c
    ---
    drivers/block/rbd.c | 32 ++++++++++++++++++++++++++++++--
    1 file changed, 30 insertions(+), 2 deletions(-)

    --- a/drivers/block/rbd.c
    +++ b/drivers/block/rbd.c
    @@ -174,9 +174,13 @@ struct rbd_device {

    /* protects updating the header */
    struct rw_semaphore header_rwsem;
    + /* name of the snapshot this device reads from */
    char snap_name[RBD_MAX_SNAP_NAME_LEN];
    + /* id of the snapshot this device reads from */
    u64 snap_id; /* current snapshot id */
    - int read_only;
    + /* whether the snap_id this device reads from still exists */
    + bool snap_exists;
    + int read_only;

    struct list_head node;

    @@ -590,6 +594,7 @@ static int rbd_header_set_snap(struct rb
    else
    snapc->seq = 0;
    dev->snap_id = CEPH_NOSNAP;
    + dev->snap_exists = false;
    dev->read_only = 0;
    if (size)
    *size = header->image_size;
    @@ -598,6 +603,7 @@ static int rbd_header_set_snap(struct rb
    if (ret < 0)
    goto done;
    dev->snap_id = snapc->seq;
    + dev->snap_exists = true;
    dev->read_only = 1;
    }

    @@ -1466,6 +1472,21 @@ static void rbd_rq_fn(struct request_que

    spin_unlock_irq(q->queue_lock);

    + if (rbd_dev->snap_id != CEPH_NOSNAP) {
    + bool snap_exists;
    +
    + down_read(&rbd_dev->header_rwsem);
    + snap_exists = rbd_dev->snap_exists;
    + up_read(&rbd_dev->header_rwsem);
    +
    + if (!snap_exists) {
    + dout("request for non-existent snapshot");
    + spin_lock_irq(q->queue_lock);
    + __blk_end_request_all(rq, -ENXIO);
    + continue;
    + }
    + }
    +
    dout("%s 0x%x bytes at 0x%llx\n",
    do_write ? "write" : "read",
    size, blk_rq_pos(rq) * SECTOR_SIZE);
    @@ -2069,7 +2090,14 @@ static int __rbd_init_snaps_header(struc
    cur_id = rbd_dev->header.snapc->snaps[i - 1];

    if (!i || old_snap->id < cur_id) {
    - /* old_snap->id was skipped, thus was removed */
    + /*
    + * old_snap->id was skipped, thus was
    + * removed. If this rbd_dev is mapped to
    + * the removed snapshot, record that it no
    + * longer exists, to prevent further I/O.
    + */
    + if (rbd_dev->snap_id == old_snap->id)
    + rbd_dev->snap_exists = false;
    __rbd_remove_snap_dev(rbd_dev, old_snap);
    continue;
    }



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