events: include zio type in IO error reports

[robn]

[Sponsors: Klara, Inc., Wasabi Technology, Inc.]

Motivation and Context

I am making more and varied IO shapes that fail aggressively. This patch is helping me!

Description

Adds io_type to error reports.

Usually the IO type can be inferred from the other fields (in particular, priority and flags) sometimes it's not easy to see. This is just another little debug helper.

    May 27 2025 00:54:54.024110493 ereport.fs.zfs.data
            class = "ereport.fs.zfs.data"
            ena = 0x1f5ecfae600801
            ...
            zio_delta = 0x0
            zio_type = 0x2 [WRITE]
            zio_priority = 0x3 [ASYNC_WRITE]
            zio_objset = 0x0

I added descriptions of zio_type and zio_priority to zpool-events.8 as well (the latter because I thought I missed it in an earlier commit, only to find it had nothing to do with me, oh well).

How Has This Been Tested?

Used in anger on Linux for a while. Compile checked on FreeBSD just now. events test tag passed, though nothing in ZTS actually considers the event output in any depth, so that's not surprising.

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)
• Quality assurance (non-breaking change which makes the code more robust against bugs)
• 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.

[amotin]

@robn Conflict has appeared here.

[behlendorf]

Looks good after resolving the conflict.

[robn]

Weird, the conflict was in the ABI dump, so I pushed without that change to get a new one generated, and it succeeded? Not sure I expected that, but I will trust the system and shrug and move on.