Re: [Qemu-devel] [PATCH v2 0/2] qcow2: Repair OFLAG_COPIED when fixing leaks

[Max Reitz]

On 2018-05-09 22:00, Max Reitz wrote:
> Suppose you have an image with consistent OFLAG_COPIED and refcounts.
> Now further suppose that image has leaked clusters (single reference,
> but refcount 2).  When checking such an image with qemu-img check, it
> will notify you of the leakage, and that's it.
> 
> Now when trying to repair that image, you naturally use -r leaks because
> that should be sufficient and you want to give qemu-img check just as
> many "permissions" as it needs so it doesn't destroy your image by
> accident.  But while the qcow2 driver will fix the refcounts, alas! it
> will now complain about OFLAG_COPIED because that should be set now.
> However, it will not set that without -r all.  So, congratulations, now
> you have an image that qemu-img check tells you is really corrupted.
> 
> This series makes -r leaks fix OFLAG_COPIED as well, but only if
> repairing the refcounts was completely successful.
> 
> There is a Red Hat Bugzilla entry here:
> https://bugzilla.redhat.com/show_bug.cgi?id=1527085
> 
> ...but I'm afraid the bug description is set to confidential, although I
> don't know why.  Sorry. :-/
> For everyone who cannot read it, let's say the test case in this series
> may very well be a good indication of what you don't see.
> 
> 
> v2:
> - Reworded the comment in patch 2 on why the test does not support
>   refcount_bits=1 -- it's not just because of the snapshotting, but
>   mostly because we test OFLAG_COPIED and refcount_bits=1 won't get us
>   far there [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
> 
> 001/2:[----] [--] 'qcow2: Repair OFLAG_COPIED when fixing leaks'
> 002/2:[0003] [FC] 'iotests: Repairing error during snapshot deletion'
> 
> 
> Max Reitz (2):
>   qcow2: Repair OFLAG_COPIED when fixing leaks
>   iotests: Repairing error during snapshot deletion
> 
>  block/qcow2-refcount.c     | 25 ++++++++-----
>  tests/qemu-iotests/217     | 90 
> ++++++++++++++++++++++++++++++++++++++++++++++
>  tests/qemu-iotests/217.out | 42 ++++++++++++++++++++++
>  tests/qemu-iotests/group   |  1 +
>  4 files changed, 150 insertions(+), 8 deletions(-)
>  create mode 100755 tests/qemu-iotests/217
>  create mode 100644 tests/qemu-iotests/217.out

Applied to my block branch.

Max

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