NAS-134891 / 25.10 / linux: zvols: correctly detect flush requests (#17131)

[ixhamza]

since 4.10, bio->bi_opf needs to be checked to determine all kinds of flush requests. this was the case prior to the commit referenced below, but the order of ifdefs was not the usual one (newest up top), which might have caused this to slip through.

this fixes a regression when using zvols as Qemu block devices, but might have broken other use cases as well. the symptoms are that all sync writes from within a VM configured to use such a virtual block devices are ignored and treated as async writes by the host ZFS layer.

this can be verified using fio in sync mode inside the VM, for example with

fio
--filename=/dev/sda --ioengine=libaio --loops=1 --size=10G
--time_based --runtime=60 --group_reporting --stonewall --name=cc1
--description="CC1" --rw=write --bs=4k --direct=1 --iodepth=1
--numjobs=1 --sync=1

which shows an IOPS number way above what the physical device underneath supports, with "zpool iostat -r 1" on the hypervisor side showing no sync IO occuring during the benchmark.

with the regression fixed, both fio inside the VM and the IO stats on the host show the expected numbers.

Fixes: 846b598
"config: remove HAVE_REQ_OP_* and HAVE_REQ_*"

Reviewed-by: Alexander Motin [email protected]
Reviewed-by: Tony Hutter [email protected]

Motivation and Context

Description

• CI Testing
• Scale Build: http://jenkins.eng.ixsystems.net:8080/job/master/job/custom/1007/.

How Has This Been Tested?

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Performance enhancement (non-breaking change which improves efficiency)
• Code cleanup (non-breaking change which makes code smaller or more readable)
• Breaking change (fix or feature that would cause existing functionality to change)
• Library ABI change (libzfs, libzfs_core, libnvpair, libuutil and libzfsbootenv)
• Documentation (a change to man pages or other documentation)

Checklist:

• My code follows the OpenZFS code style requirements.
• I have updated the documentation accordingly.
• I have read the contributing document.
• I have added tests to cover my changes.
• I have run the ZFS Test Suite with this change applied.
• All commit messages are properly formatted and contain Signed-off-by.

[bugclerk]

Jira URL: https://ixsystems.atlassian.net/browse/NAS-134891

[bugclerk]

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