[Bug 221973] cam iosched: BIO_ZONE commands probably shouldn't use the read queue

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https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=221973

            Bug ID: 221973
           Summary: cam iosched: BIO_ZONE commands probably shouldn't use
                    the read queue
           Product: Base System
           Version: CURRENT
          Hardware: Any
                OS: Any
            Status: New
          Keywords: patch
          Severity: Affects Some People
          Priority: ---
         Component: kern
          Assignee: freebsd-bugs at FreeBSD.org
          Reporter: fk at fabiankeil.de
             Flags: mfc-stable11?

Created attachment 185970
  --> https://bugs.freebsd.org/bugzilla/attachment.cgi?id=185970&action=edit
cam iosched: Use the write queue for BIO_ZONE commands

The attached patch lets iosched put BIO_ZONE commands on the write queue
so they can't get executed ahead of writes that were sent after them.

I'm not completely sure but believe that this is less likely to cause problems
than putting them one the read queue.

As I currently don't use SMR drives the patch hasn't been properly tested.

It prevents the kernel message:
kernel: Found bio_cmd = 0x9
which cam_iosched_next_bio() emits when finding commands
other than BIO_READ in the read queue, though.

The fact that BIO_ZONE commands are sometimes sent to non-SMR
drives may indicate another problem but I haven't looked into this
yet.

Obtained from: ElectroBSD

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