Re: [Qemu-devel] [PATCH v6 03/10] qcow2: Assert that cluster operations are aligned

[Max Reitz <mreitz@redhat.com>]

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On 08.03.2017 03:54, Eric Blake wrote:
> qcow2_discard_clusters() is set up to silently ignore sub-cluster
> head or tail on unaligned requests.  However, it is easy to audit
> the various callers: qcow2_snapshot_create() has always passed
> aligned data since the call was introduced in 1ebf561;
> qcow2_co_pdiscard() has passed aligned clusters since commit
> ecdbead taught the block layer the preferred discard alignment (the
> block layer can still pass sub-cluster values, but those are
> handled directly in qcow2_co_pdiscard()); and qcow2_make_empty()
> was fixed to pass aligned clusters in commit a3e1505.  Replace
> rounding with assertions to hold us to the tighter contract,
> eliminating the now-impossible case of an early exit for a
> sub-cluster request.
> 
> qcow2_zero_clusters() has always been called with cluster-aligned
> arguments from its lone caller qcow2_co_pwrite_zeroes() (like
> qcow2_co_pdiscard(), the caller takes care of sub-cluster requests
> from the block layer; and qcow2_zero_clusters() would have
> misbehaved on unaligned requests), but it deserves the same
> assertion for symmetry.
> 
> Signed-off-by: Eric Blake <eblake@redhat.com>
> 
> ---
> v6: avoid assertion on non-cluster-aligned image, use s->cluster_sectors
> to avoid a shift, drop R-b
> v5: no change
> v4: new patch
> ---
>  block/qcow2-cluster.c | 15 ++++++++-------
>  1 file changed, 8 insertions(+), 7 deletions(-)

Reviewed-by: Max Reitz <mreitz@redhat.com>


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