kern/59165: vio9p(4): expose tag through sysctl or device properties

[campbell+netbsd%mumble.net@localhost]

>Number:         59165
>Category:       kern
>Synopsis:       vio9p(4): expose tag through sysctl or device properties
>Confidential:   no
>Severity:       serious
>Priority:       medium
>Responsible:    kern-bug-people
>State:          open
>Class:          change-request
>Submitter-Id:   net
>Arrival-Date:   Sun Mar 09 22:50:00 +0000 2025
>Originator:     Taylor R Campbell
>Release:        current, 10, 9, ...
>Organization:
The Net9P Mountation
>Environment:
>Description:
In virtio-9p, the host passes a tag identifying each possible 9p mount point to the guest.  The mount tag is an arbitrary(?) string configured in the host (e.g., qemu -device virtio-9p-pci,mount_tag=FOO,...).

Currently, NetBSD only prints it to dmesg:

[     1.049667] vio9p0: tagged as FOO

It would be nice if this were exposed to userland via sysctl, device properties, or something, so that, e.g., a devpubd(8) hook could automatically create a symlink for it.
>How-To-Repeat:
try to juggle a collection of /dev/vio9pN mount points in the guest and host VM configuration
>Fix:
Yes, please!