Re: [PATCH v2 2/3] iotests: Improve mirror-sparse on ext4

[Markus Armbruster <armbru@redhat.com>]

Eric Blake <eblake@redhat.com> writes:

> On Wed, May 28, 2025 at 10:45:35AM -0500, Eric Blake wrote:
>> On Fri, May 23, 2025 at 11:27:22AM -0500, Eric Blake wrote:
>> > Fiona reported that an ext4 filesystem on top of LVM can sometimes
>> > report over-allocation to du (based on the hueristics the filesystem
>> > is making while observing the contents being mirrored); even though
>> > the contents and actual size matched, about 50% of the time the size
>> > reported by disk_usage was too large by 4k, failing the test.  In
>> > auditing other iotests, this is a common problem we've had to deal
>> > with.
>> > 
>> > Reported-by: Fiona Ebner <f.ebner@proxmox.com>
>> > Fixes: c0ddcb2c ("tests: Add iotest mirror-sparse for recent patches")
>> > Signed-off-by: Eric Blake <eblake@redhat.com>
>> > Reviewed-by: Fiona Ebner <f.ebner@proxmox.com>
>> > Tested-by: Fiona Ebner <f.ebner@proxmox.com>
>> > 
>> > ---
>> > v2: Drop sync for ZFS
>> > ---
>> >  tests/qemu-iotests/tests/mirror-sparse | 4 +++-
>> >  1 file changed, 3 insertions(+), 1 deletion(-)
>> 
>> Squashing this in since Markus is reporting failures even with this
>> patch applied, and I'm lacking enough context to see what else might
>> be interfering:
>> 
>> diff --git i/tests/qemu-iotests/tests/mirror-sparse w/tests/qemu-iotests/tests/mirror-sparse
>> index 39e3196c811..a30e52de41d 100755
>> --- i/tests/qemu-iotests/tests/mirror-sparse
>> +++ w/tests/qemu-iotests/tests/mirror-sparse
>> @@ -105,7 +105,7 @@ if test $result -lt $((3*1024*1024)); then
>>  elif test $result -gt $((19*1024*1024)); then
>>      actual=full
>>  else
>> -    actual=unknown
>> +    actual="unexpected size ($result)"
>
> I reproduced Markus' situation on XFS (since XFS is easier than ZFS to
> install on Fedora) - it turns out that XFS rounds disk usage in terms
> of allocation groups which default to a size of 1M; so I need to treat
> exactly 3M as sparse, not unknown.  I'm also squashing in:
>
> diff --git i/tests/qemu-iotests/tests/mirror-sparse w/tests/qemu-iotests/tests/mirror-sparse
> index a30e52de41d..cfcaa600ab4 100755
> --- i/tests/qemu-iotests/tests/mirror-sparse
> +++ w/tests/qemu-iotests/tests/mirror-sparse
> @@ -100,7 +100,7 @@ $QEMU_IMG compare -U -f $IMGFMT -F raw $TEST_IMG.base $TEST_IMG
>  # Some filesystems can fudge allocations for various reasons; rather
>  # than expecting precise 2M and 20M images, it is better to allow for slop.
>  result=$(disk_usage $TEST_IMG)
> -if test $result -lt $((3*1024*1024)); then
> +if test $result -lt $((4*1024*1024)); then
>      actual=sparse
>  elif test $result -gt $((19*1024*1024)); then
>      actual=full

This one-liner appears to fix it for me.  Thanks!