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

["Christoph Badura via gnats" <gnats-admin%NetBSD.org@localhost>]

The following reply was made to PR kern/59165; it has been noted by GNATS.

From: Christoph Badura <bad%bsd.de@localhost>
To: gnats-bugs%netbsd.org@localhost
Cc: Ryota Ozaki <ozaki-r%netbsd.org@localhost>
Subject: Re: kern/59165: vio9p(4): expose tag through sysctl or device
 properties
Date: Tue, 18 Mar 2025 00:27:00 +0100

 On Mon, Mar 17, 2025 at 05:33:44PM +0900, Ryota Ozaki wrote:
 > On Tue, Mar 11, 2025 at 8:53â?¯PM Christoph Badura <bad%bsd.de@localhost> wrote:
 > > If you attach multiple virtio-9p file systems to the VM, does your patch
 > > create hw.vio9p0.tag, hw.vio9p1.tag etc.?
 > Thank you for pointing this out. It assumed there was just one vio9p.
 
 I've been using at least two since last summer. :-)
 
 > I've put a fixed version:
 > https://www.netbsd.org/~ozaki-r/vio9p-tag-sysctl.v2.patch
 
 I guess the change from the previsous version is the use of
 device_xname(self) in:
 +	    device_xname(self), SYSCTL_DESCR("VirtIO 9p status"),
 
 That all looks fine to me.
 
 There is one more thing to think about: discoverability.
 How do we find out which hw.vio9pN sysctl nodes exist?
 
 Of course, we can do "sysctl hw | grep \^hw.vio9p" and process that.
 But that seems not right to me.
 We should have something like hw.disknames for vio9p.
 Maybe hw.vio9p.instances with a list of the instance names as strings?
 
 That shouldn't prevent you from committing your change
 
 Actually, I wish used a better MIB design in sysctl.
 Like:
   hw.vio9p.instances = vio9p0 vio9p1
   hw.vio9p.vio9p0.tag = tag1
   hw.vio9p.vio9p1.tag = tag2
 
 And likewise:
   hw.vm.wm0.*
   hw.vm.wm1.*
 etc.
 
 And a way for sysctl to just enumerate the immediate children of a node
 Like:
   $ sysctl --enumerate-children hw.wm
   hw.wm.wm0
   hw.wm.wm1
   $
 
 But we don't have that.  We could make a start with the hw.vio9p sub-MIB,
 though.
 
 But perhaps this should be discussed on tech-kern.
 
 --chris