[Qemu-devel] [PATCH v3 0/3] qemu-img: Allow rebase with no input base

Max Reitz posted 3 patches 4 years, 10 months ago
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git fetch https://github.com/patchew-project/qemu tags/patchew/20190509175237.19363-1-mreitz@redhat.com
Maintainers: Kevin Wolf <kwolf@redhat.com>, Max Reitz <mreitz@redhat.com>
qemu-img.c                 |  72 ++++++++++++---------
tests/qemu-iotests/252     | 124 +++++++++++++++++++++++++++++++++++++
tests/qemu-iotests/252.out |  39 ++++++++++++
tests/qemu-iotests/group   |   1 +
4 files changed, 207 insertions(+), 29 deletions(-)
create mode 100755 tests/qemu-iotests/252
create mode 100644 tests/qemu-iotests/252.out
[Qemu-devel] [PATCH v3 0/3] qemu-img: Allow rebase with no input base
Posted by Max Reitz 4 years, 10 months ago
This series allows using qemu-img rebase (without -u) on images that do
not have a backing file.  Right now, this fails with the rather cryptic
error message:

$ qemu-img rebase -b base.qcow2 foo.qcow2
qemu-img: Could not open old backing file '': The 'file' block driver requires a file name

Yeah, well, OK.

With how rebase currently works, this would lead to the overlay being
filled with zeroes, however.  This is where patch 2 comes in and instead
makes rebase use blk_pwrite_zeroes() whenever it handles an area past
the input’s backing file’s EOF.

(Note that additionally we could try to punch holes in the overlay
whenever it matches the new backing file, but that’s something I’ll put
off for later.  (We don’t even have a reliable method for punching holes
into an overlay yet, although I would like to have such because it could
make active commit more efficient.))


And patch 3 adds the usual test.


v3:
- Patch 3: Move test to own file so it doesn’t run for qed or qcow2 v2
  (because it can’t, it requires zero clusters)

git backport-diff against v2:

Key:
[----] : patches are identical
[####] : number of functional differences between upstream/downstream patch
[down] : patch is downstream-only
The flags [FC] indicate (F)unctional and (C)ontextual differences, respectively

001/3:[----] [--] 'qemu-img: Allow rebase with no input base'
002/3:[----] [--] 'qemu-img: Use zero writes after source backing EOF'
003/3:[0059] [FC] 'iotests: Add test for rebase without input base'


v2:
- Patch 1: Added example to the commit message, and made a note that
           this is about rebase without -u [Eric]

git backport-diff against v1:

Key:
[----] : patches are identical
[####] : number of functional differences between upstream/downstream patch
[down] : patch is downstream-only
The flags [FC] indicate (F)unctional and (C)ontextual differences, respectively

001/3:[----] [--] 'qemu-img: Allow rebase with no input base'
002/3:[----] [--] 'qemu-img: Use zero writes after source backing EOF'
003/3:[----] [--] 'iotests: Add test for rebase without input base'


Max Reitz (3):
  qemu-img: Allow rebase with no input base
  qemu-img: Use zero writes after source backing EOF
  iotests: Add test for rebase without input base

 qemu-img.c                 |  72 ++++++++++++---------
 tests/qemu-iotests/252     | 124 +++++++++++++++++++++++++++++++++++++
 tests/qemu-iotests/252.out |  39 ++++++++++++
 tests/qemu-iotests/group   |   1 +
 4 files changed, 207 insertions(+), 29 deletions(-)
 create mode 100755 tests/qemu-iotests/252
 create mode 100644 tests/qemu-iotests/252.out

-- 
2.21.0


Re: [Qemu-devel] [PATCH v3 0/3] qemu-img: Allow rebase with no input base
Posted by Kevin Wolf 4 years, 10 months ago
Am 09.05.2019 um 19:52 hat Max Reitz geschrieben:
> This series allows using qemu-img rebase (without -u) on images that do
> not have a backing file.  Right now, this fails with the rather cryptic
> error message:
> 
> $ qemu-img rebase -b base.qcow2 foo.qcow2
> qemu-img: Could not open old backing file '': The 'file' block driver requires a file name
> 
> Yeah, well, OK.
> 
> With how rebase currently works, this would lead to the overlay being
> filled with zeroes, however.  This is where patch 2 comes in and instead
> makes rebase use blk_pwrite_zeroes() whenever it handles an area past
> the input’s backing file’s EOF.
> 
> (Note that additionally we could try to punch holes in the overlay
> whenever it matches the new backing file, but that’s something I’ll put
> off for later.  (We don’t even have a reliable method for punching holes
> into an overlay yet, although I would like to have such because it could
> make active commit more efficient.))
> 
> 
> And patch 3 adds the usual test.
> 
> 
> v3:
> - Patch 3: Move test to own file so it doesn’t run for qed or qcow2 v2
>   (because it can’t, it requires zero clusters)

Thanks, updated in the block branch.

Kevin