[Xen-changelog] [qemu-xen master] block: Return -ENOTSUP rather than assert on unaligned discards

[patchbot@xxxxxxx]

commit 49228d1e95e1be879c57f5dbccb44405670e343d
Author:     Eric Blake <eblake@xxxxxxxxxx>
AuthorDate: Thu Nov 17 14:13:57 2016 -0600
Commit:     Kevin Wolf <kwolf@xxxxxxxxxx>
CommitDate: Tue Nov 22 15:59:22 2016 +0100

    block: Return -ENOTSUP rather than assert on unaligned discards
    
    Right now, the block layer rounds discard requests, so that
    individual drivers are able to assert that discard requests
    will never be unaligned.  But there are some ISCSI devices
    that track and coalesce multiple unaligned requests, turning it
    into an actual discard if the requests eventually cover an
    entire page, which implies that it is better to always pass
    discard requests as low down the stack as possible.
    
    In isolation, this patch has no semantic effect, since the
    block layer currently never passes an unaligned request through.
    But the block layer already has code that silently ignores
    drivers that return -ENOTSUP for a discard request that cannot
    be honored (as well as drivers that return 0 even when nothing
    was done).  But the next patch will update the block layer to
    fragment discard requests, so that clients are guaranteed that
    they are either dealing with an unaligned head or tail, or an
    aligned core, making it similar to the block layer semantics of
    write zero fragmentation.
    
    CC: qemu-stable@xxxxxxxxxx
    Signed-off-by: Eric Blake <eblake@xxxxxxxxxx>
    Reviewed-by: Max Reitz <mreitz@xxxxxxxxxx>
    Signed-off-by: Kevin Wolf <kwolf@xxxxxxxxxx>
---
 block/iscsi.c    | 4 +++-
 block/qcow2.c    | 5 +++++
 block/sheepdog.c | 5 +++--
 3 files changed, 11 insertions(+), 3 deletions(-)

diff --git a/block/iscsi.c b/block/iscsi.c
index 71bd523..0960929 100644
--- a/block/iscsi.c
+++ b/block/iscsi.c
@@ -1083,7 +1083,9 @@ coroutine_fn iscsi_co_pdiscard(BlockDriverState *bs, 
int64_t offset, int count)
     struct IscsiTask iTask;
     struct unmap_list list;
 
-    assert(is_byte_request_lun_aligned(offset, count, iscsilun));
+    if (!is_byte_request_lun_aligned(offset, count, iscsilun)) {
+        return -ENOTSUP;
+    }
 
     if (!iscsilun->lbp.lbpu) {
         /* UNMAP is not supported by the target */
diff --git a/block/qcow2.c b/block/qcow2.c
index e22f6dc..7cfcd84 100644
--- a/block/qcow2.c
+++ b/block/qcow2.c
@@ -2491,6 +2491,11 @@ static coroutine_fn int 
qcow2_co_pdiscard(BlockDriverState *bs,
     int ret;
     BDRVQcow2State *s = bs->opaque;
 
+    if (!QEMU_IS_ALIGNED(offset | count, s->cluster_size)) {
+        assert(count < s->cluster_size);
+        return -ENOTSUP;
+    }
+
     qemu_co_mutex_lock(&s->lock);
     ret = qcow2_discard_clusters(bs, offset, count >> BDRV_SECTOR_BITS,
                                  QCOW2_DISCARD_REQUEST, false);
diff --git a/block/sheepdog.c b/block/sheepdog.c
index 1fb9173..4c9af89 100644
--- a/block/sheepdog.c
+++ b/block/sheepdog.c
@@ -2829,8 +2829,9 @@ static coroutine_fn int sd_co_pdiscard(BlockDriverState 
*bs, int64_t offset,
     iov.iov_len = sizeof(zero);
     discard_iov.iov = &iov;
     discard_iov.niov = 1;
-    assert((offset & (BDRV_SECTOR_SIZE - 1)) == 0);
-    assert((count & (BDRV_SECTOR_SIZE - 1)) == 0);
+    if (!QEMU_IS_ALIGNED(offset | count, BDRV_SECTOR_SIZE)) {
+        return -ENOTSUP;
+    }
     acb = sd_aio_setup(bs, &discard_iov, offset >> BDRV_SECTOR_BITS,
                        count >> BDRV_SECTOR_BITS);
     acb->aiocb_type = AIOCB_DISCARD_OBJ;
--
generated by git-patchbot for /home/xen/git/qemu-xen.git#master

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