[Qemu-devel] [PATCH] block: Avoid bogus flags during mirroring

[Qemu-devel] [PATCH] block: Avoid bogus flags during mirroring

[Eric Blake]

Commit e253f4b8 converted mirroring from sector-based bdrv_aio_*
to byte-based blk_aio_*, but failed to account for the subtle
difference in signatures (the former takes a semi-redundant length,
the latter takes a flags parameter).  Since all of our flags are
currently smaller in size than BDRV_SECTOR_SIZE, it has no ill
effects until we either perform sub-sector mirroring, or we start
asserting that no unexpected flags are set.  I found it while
testing new asserts when qemu-iotests 132 started warning about an
unknown flag 0x200000.

Add an assert to help us catch any other improper flags.

Signed-off-by: Eric Blake <eblake@redhat.com>
---
 block/block-backend.c | 2 ++
 block/mirror.c        | 6 ++----
 2 files changed, 4 insertions(+), 4 deletions(-)

diff --git a/block/block-backend.c b/block/block-backend.c
index 34500e6..a5dc6e3 100644
--- a/block/block-backend.c
+++ b/block/block-backend.c
@@ -945,6 +945,8 @@ static BlockAIOCB *blk_aio_prwv(BlockBackend *blk, int64_t offset, int bytes,
     acb->bh = NULL;
     acb->has_returned = false;

+    assert(flags <= 0x1f);
+
     co = qemu_coroutine_create(co_entry);
     qemu_coroutine_enter(co, acb);

diff --git a/block/mirror.c b/block/mirror.c
index fbbc496..41848b2 100644
--- a/block/mirror.c
+++ b/block/mirror.c
@@ -157,8 +157,7 @@ static void mirror_read_complete(void *opaque, int ret)
         return;
     }
     blk_aio_pwritev(s->target, op->sector_num * BDRV_SECTOR_SIZE, &op->qiov,
-                    op->nb_sectors * BDRV_SECTOR_SIZE,
-                    mirror_write_complete, op);
+                    0, mirror_write_complete, op);
 }

 static inline void mirror_clip_sectors(MirrorBlockJob *s,
@@ -275,8 +274,7 @@ static int mirror_do_read(MirrorBlockJob *s, int64_t sector_num,
     s->sectors_in_flight += nb_sectors;
     trace_mirror_one_iteration(s, sector_num, nb_sectors);

-    blk_aio_preadv(source, sector_num * BDRV_SECTOR_SIZE, &op->qiov,
-                   nb_sectors * BDRV_SECTOR_SIZE,
+    blk_aio_preadv(source, sector_num * BDRV_SECTOR_SIZE, &op->qiov, 0,
                    mirror_read_complete, op);
     return ret;
 }
-- 
2.5.5

Re: [Qemu-devel] [PATCH] block: Avoid bogus flags during mirroring

[Fam Zheng]

On Sat, 06/11 19:18, Eric Blake wrote:
> Commit e253f4b8 converted mirroring from sector-based bdrv_aio_*
> to byte-based blk_aio_*, but failed to account for the subtle
> difference in signatures (the former takes a semi-redundant length,
> the latter takes a flags parameter).  Since all of our flags are
> currently smaller in size than BDRV_SECTOR_SIZE, it has no ill
> effects until we either perform sub-sector mirroring, or we start
> asserting that no unexpected flags are set.  I found it while
> testing new asserts when qemu-iotests 132 started warning about an
> unknown flag 0x200000.
> 
> Add an assert to help us catch any other improper flags.
> 
> Signed-off-by: Eric Blake <eblake@redhat.com>
> ---
>  block/block-backend.c | 2 ++
>  block/mirror.c        | 6 ++----
>  2 files changed, 4 insertions(+), 4 deletions(-)
> 
> diff --git a/block/block-backend.c b/block/block-backend.c
> index 34500e6..a5dc6e3 100644
> --- a/block/block-backend.c
> +++ b/block/block-backend.c
> @@ -945,6 +945,8 @@ static BlockAIOCB *blk_aio_prwv(BlockBackend *blk, int64_t offset, int bytes,
>      acb->bh = NULL;
>      acb->has_returned = false;
> 
> +    assert(flags <= 0x1f);
> +

Maybe define BDRV_REQ_FLAGS_MAX in include/block/block.h so it's easier to keep
this assertion valid when we introduce more flags in the future?

Otherwise the patch looks good.

Fam

>      co = qemu_coroutine_create(co_entry);
>      qemu_coroutine_enter(co, acb);
> 
> diff --git a/block/mirror.c b/block/mirror.c
> index fbbc496..41848b2 100644
> --- a/block/mirror.c
> +++ b/block/mirror.c
> @@ -157,8 +157,7 @@ static void mirror_read_complete(void *opaque, int ret)
>          return;
>      }
>      blk_aio_pwritev(s->target, op->sector_num * BDRV_SECTOR_SIZE, &op->qiov,
> -                    op->nb_sectors * BDRV_SECTOR_SIZE,
> -                    mirror_write_complete, op);
> +                    0, mirror_write_complete, op);
>  }
> 
>  static inline void mirror_clip_sectors(MirrorBlockJob *s,
> @@ -275,8 +274,7 @@ static int mirror_do_read(MirrorBlockJob *s, int64_t sector_num,
>      s->sectors_in_flight += nb_sectors;
>      trace_mirror_one_iteration(s, sector_num, nb_sectors);
> 
> -    blk_aio_preadv(source, sector_num * BDRV_SECTOR_SIZE, &op->qiov,
> -                   nb_sectors * BDRV_SECTOR_SIZE,
> +    blk_aio_preadv(source, sector_num * BDRV_SECTOR_SIZE, &op->qiov, 0,
>                     mirror_read_complete, op);
>      return ret;
>  }
> -- 
> 2.5.5
> 
> 

Re: [Qemu-devel] [PATCH] block: Avoid bogus flags during mirroring

[Eric Blake]

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On 06/11/2016 08:15 PM, Fam Zheng wrote:
> On Sat, 06/11 19:18, Eric Blake wrote:
>> Commit e253f4b8 converted mirroring from sector-based bdrv_aio_*
>> to byte-based blk_aio_*, but failed to account for the subtle
>> difference in signatures (the former takes a semi-redundant length,
>> the latter takes a flags parameter).  Since all of our flags are
>> currently smaller in size than BDRV_SECTOR_SIZE, it has no ill
>> effects until we either perform sub-sector mirroring, or we start
>> asserting that no unexpected flags are set.  I found it while
>> testing new asserts when qemu-iotests 132 started warning about an
>> unknown flag 0x200000.
>>
>> Add an assert to help us catch any other improper flags.
>>
>> Signed-off-by: Eric Blake <eblake@redhat.com>
>> ---
>>  block/block-backend.c | 2 ++
>>  block/mirror.c        | 6 ++----
>>  2 files changed, 4 insertions(+), 4 deletions(-)
>>
>> diff --git a/block/block-backend.c b/block/block-backend.c
>> index 34500e6..a5dc6e3 100644
>> --- a/block/block-backend.c
>> +++ b/block/block-backend.c
>> @@ -945,6 +945,8 @@ static BlockAIOCB *blk_aio_prwv(BlockBackend *blk, int64_t offset, int bytes,
>>      acb->bh = NULL;
>>      acb->has_returned = false;
>>
>> +    assert(flags <= 0x1f);
>> +
> 
> Maybe define BDRV_REQ_FLAGS_MAX in include/block/block.h so it's easier to keep
> this assertion valid when we introduce more flags in the future?

Oh, good idea.  And I also don't know if blk_aio_prwv() is really the
best place (it happened to be nicer for getting a good gdb backtrace of
the culprit caller prior to entering coroutines, since coroutines tend
to kill the call trace - but is too narrow in that it doesn't catch
non-aio entry into the block layer) - so I should probably make the
actual asserts live in better places like bdrv_driver_p*.  I'll split
the patch between bug fix and assertion additions, v2 coming up later today.

> 
> Otherwise the patch looks good.
> 


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


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