[Qemu-devel] [PATCH for-2.6 v2] block: Don't ignore flags in blk_{, co, aio}_write_zeroes()

[Qemu-devel] [PATCH for-2.6 v2] block: Don't ignore flags in blk_{, co, aio}_write_zeroes()

[Kevin Wolf]

Commit 57d6a428 neglected to pass the given flags to blk_aio_prwv(),
which broke discard by WRITE SAME for scsi-disk (the UNMAP bit would be
ignored).

Commit fc1453cd introduced the same bug for blk_write_zeroes(). This is
used for 'qemu-img convert' without has_zero_init (e.g. on a block
device) and for preallocation=falloc in parallels.

Commit 8896e088 is the version for blk_co_write_zeroes(). This function
is only used in qemu-io.

Reported-by: Max Reitz <mreitz@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
---

v2:
- There are two more places with exactly the same bug [Eric]

 block/block-backend.c | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/block/block-backend.c b/block/block-backend.c
index 140c3f7..16c9d5e 100644
--- a/block/block-backend.c
+++ b/block/block-backend.c
@@ -820,7 +820,7 @@ int blk_write_zeroes(BlockBackend *blk, int64_t sector_num,
                      int nb_sectors, BdrvRequestFlags flags)
 {
     return blk_rw(blk, sector_num, NULL, nb_sectors, blk_write_entry,
-                  BDRV_REQ_ZERO_WRITE);
+                  flags | BDRV_REQ_ZERO_WRITE);
 }
 
 static void error_callback_bh(void *opaque)
@@ -942,7 +942,8 @@ BlockAIOCB *blk_aio_write_zeroes(BlockBackend *blk, int64_t sector_num,
 
     return blk_aio_prwv(blk, sector_num << BDRV_SECTOR_BITS,
                         nb_sectors << BDRV_SECTOR_BITS, NULL,
-                        blk_aio_write_entry, BDRV_REQ_ZERO_WRITE, cb, opaque);
+                        blk_aio_write_entry, flags | BDRV_REQ_ZERO_WRITE,
+                        cb, opaque);
 }
 
 int blk_pread(BlockBackend *blk, int64_t offset, void *buf, int count)
@@ -1452,7 +1453,7 @@ int coroutine_fn blk_co_write_zeroes(BlockBackend *blk, int64_t sector_num,
 
     return blk_co_pwritev(blk, sector_num << BDRV_SECTOR_BITS,
                           nb_sectors << BDRV_SECTOR_BITS, NULL,
-                          BDRV_REQ_ZERO_WRITE);
+                          flags | BDRV_REQ_ZERO_WRITE);
 }
 
 int blk_write_compressed(BlockBackend *blk, int64_t sector_num,
-- 
1.8.3.1

Re: [Qemu-devel] [PATCH for-2.6 v2] block: Don't ignore flags in blk_{, co, aio}_write_zeroes()

[Eric Blake]

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On 04/15/2016 08:52 AM, Kevin Wolf wrote:
> Commit 57d6a428 neglected to pass the given flags to blk_aio_prwv(),
> which broke discard by WRITE SAME for scsi-disk (the UNMAP bit would be
> ignored).
> 
> Commit fc1453cd introduced the same bug for blk_write_zeroes(). This is
> used for 'qemu-img convert' without has_zero_init (e.g. on a block
> device) and for preallocation=falloc in parallels.
> 
> Commit 8896e088 is the version for blk_co_write_zeroes(). This function
> is only used in qemu-io.
> 
> Reported-by: Max Reitz <mreitz@redhat.com>
> Signed-off-by: Kevin Wolf <kwolf@redhat.com>
> ---
> 
> v2:
> - There are two more places with exactly the same bug [Eric]

Not just me; Pavel spotted it first:
https://lists.gnu.org/archive/html/qemu-devel/2016-04/msg01613.html

> 
>  block/block-backend.c | 7 ++++---
>  1 file changed, 4 insertions(+), 3 deletions(-)

Reviewed-by: Eric Blake <eblake@redhat.com>

-- 
Eric Blake   eblake redhat com    +1-919-301-3266
Libvirt virtualization library http://libvirt.org


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