[0/2] block: Let blockdev-create return 0 on success
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Message ID 20190823184733.18929-1-mreitz@redhat.com
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  • block: Let blockdev-create return 0 on success
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Max Reitz Aug. 23, 2019, 6:47 p.m. UTC
Jobs are expected to return 0 on success.  .bdrv_co_create() on the
other hand is a block layer function, and as such returns a non-negative
value on success.

blockdev_create_run() should translate between the two (patch 1).

Without patch 1, blockdev-create is likely to fail for VPC images.
Hence patch 2.


Max Reitz (2):
  block: Let blockdev-create return 0 on success
  iotests: Test blockdev-create for vpc

 block/create.c             |   3 +-
 tests/qemu-iotests/266     | 182 +++++++++++++++++++++++++++++++++++++
 tests/qemu-iotests/266.out | 107 ++++++++++++++++++++++
 tests/qemu-iotests/group   |   1 +
 4 files changed, 292 insertions(+), 1 deletion(-)
 create mode 100755 tests/qemu-iotests/266
 create mode 100644 tests/qemu-iotests/266.out

Comments

John Snow Aug. 27, 2019, 9:15 p.m. UTC | #1
On 8/23/19 2:47 PM, Max Reitz wrote:
> Jobs are expected to return 0 on success.  .bdrv_co_create() on the
> other hand is a block layer function, and as such returns a non-negative
> value on success.
> 
> blockdev_create_run() should translate between the two (patch 1).
> 
> Without patch 1, blockdev-create is likely to fail for VPC images.
> Hence patch 2.
> 
> 
> Max Reitz (2):
>   block: Let blockdev-create return 0 on success
>   iotests: Test blockdev-create for vpc
> 
>  block/create.c             |   3 +-
>  tests/qemu-iotests/266     | 182 +++++++++++++++++++++++++++++++++++++
>  tests/qemu-iotests/266.out | 107 ++++++++++++++++++++++
>  tests/qemu-iotests/group   |   1 +
>  4 files changed, 292 insertions(+), 1 deletion(-)
>  create mode 100755 tests/qemu-iotests/266
>  create mode 100644 tests/qemu-iotests/266.out
> 

Reviewed-by: John Snow <jsnow@redhat.com>
Kevin Wolf Sept. 2, 2019, 1:32 p.m. UTC | #2
Am 23.08.2019 um 20:47 hat Max Reitz geschrieben:
> Jobs are expected to return 0 on success.  .bdrv_co_create() on the
> other hand is a block layer function, and as such returns a
> non-negative value on success.

I don't agree that >= 0 is the block layer way. The block layer uses
0/-errno for the largest part of its interfaces; and I think the
BlockDriver callbacks might even be consistent in this. Of course, we
never documented this anywhere, maybe we should...

The only historical exceptions I'm aware of are blk/bdrv_pread/pwrite(),
which return the byte count instead of 0. They should be fixed
eventually, but it just never seemed important enough, even though it
did cause bugs every now and then.

> blockdev_create_run() should translate between the two (patch 1).
> 
> Without patch 1, blockdev-create is likely to fail for VPC images.
> Hence patch 2.

I'd argue this is a VPC bug. In the success path, it shouldn't return
ret as it happens to be at the end (it comes from bdrv_pwrite()), but
set it to 0 right before the 'fail:' label.

This is really a regression Jeff introduced in commit fef6070eff2,
though the bug was only latent then (five years ago).

Kevin