[Devel] [PATCH hci-8.1] drivers/md/dm-qcow2: truncate unused tail of image on suspend

[no-reply at sashiko.virtuozzo.com]

> On postsuspend we truncate the image file only down to
> file_preallocated_area_start, i.e. we drop preallocations only.
> Clusters at the end of the file freed by discard (refcount dropped
> to zero) are never given back, so the file size never shrinks.
> 
> Add qcow2_calc_used_end(), which scans refcount blocks backward from
> the end of the file and returns the end of the last cluster with
> non-zero refcount. Refcount ranges with no allocated refblock are
> skipped at once. Metadata pages are taken from md cache or read
> synchronously. This is called on suspended device after md
> writeback, so R1 and R2 can't change under us.
> 
> Truncate the file to min(file_preallocated_area_start, used end).
> Skip the scan if md writeback failed, as refcounts on disk are stale
> then, and fall back to the old behaviour on scan error.
> 
> https://virtuozzo.atlassian.net/browse/VSTOR-148171
> Feature: dm-qcow2: block device over QCOW2 files driver
> 
> Signed-off-by: Alexander Ivanov <alexander.ivanov at virtuozzo.com>

Sashiko has reviewed this patch and found no issues. It looks great!

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Sashiko AI review · https://sashiko.vzint.dev/#/patchset/20261006144428.341824-1-alexander.ivanov@virtuozzo.com?part=1