From: Joel Knight <knight.joel@gmail.com>
Subject: Re: Probe xnf(4) and xbf(4) on Xen 4.17
To: tech <tech@openbsd.org>
Date: Wed, 20 Nov 2024 07:11:11 -0700

On Tue, Nov 19, 2024 at 10:18 PM Jonathan Gray <jsg@jsg.id.au> wrote:
>
> On Wed, Nov 13, 2024 at 05:14:00PM -0700, Joel Knight wrote:
> > Hi. As reported here[1], something changed between Xen 4.13 and 4.17
> > which causes xnf and xbf to no longer probe on boot. The culprit
> > appears to be XenStore advertising a "9pfs" device, which OpenBSD
> > doesn't support, so xen_probe_devices() aborts early. The 9pfs device
> > is first in the list of devices returned by XS.
> >
>
> Why is a device not attaching fatal?
>
> Could the below diff work instead?  I can't find a list of xen devices,
> but that would avoid the same problem the next time another is added.
>
> Index: sys/dev/pv/xen.c
> ===================================================================
> RCS file: /cvs/src/sys/dev/pv/xen.c,v
> diff -u -p -U8 -r1.98 xen.c
> --- sys/dev/pv/xen.c    24 May 2024 10:05:55 -0000      1.98
> +++ sys/dev/pv/xen.c    20 Nov 2024 05:10:47 -0000
> @@ -1421,17 +1421,17 @@ xen_probe_devices(struct xen_softc *sc)
>                 for (j = 0; j < iov2_cnt; j++) {
>                         error = xen_attach_device(sc, xdl,
>                             (const char *)iovp1[i].iov_base,
>                             (const char *)iovp2[j].iov_base);
>                         if (error) {
>                                 printf("%s: failed to attach \"%s/%s\"\n",
>                                     sc->sc_dev.dv_xname, path,
>                                     (const char *)iovp2[j].iov_base);
> -                               goto out;
> +                               continue;
>                         }
>                 }
>                 /* Setup a watch for every device subtree */
>                 if (xs_watch(sc, "device", (char *)iovp1[i].iov_base,
>                     &xdl->dl_task, xen_hotplug, xdl))
>                         printf("%s: failed to setup hotplug watch for \"%s\"\n",
>                             sc->sc_dev.dv_xname, (char *)iovp1[i].iov_base);
>                 SLIST_INSERT_HEAD(&sc->sc_devlists, xdl, dl_entry);
>
>

Fair. This works as well. Might as well remove the special case for
the 'suspend' device while we're at it.

On this version of Xen, there are just the 3 devices:

% hostctl device
9pfs
vbd
vif

dmesg with attached diff:

bios0: vendor Xen version "4.17" date 10/02/2024
bios0: Xen HVM domU
pvbus0 at mainbus0: Xen 4.17
xen0 at pvbus0: features 0x112705, 64 grant table frames, event channel 3
xen0: failed to attach "device/9pfs/"
xbf0 at xen0 backend 0 channel 8: cdrom
xbf1 at xen0 backend 0 channel 8: disk
sd0 at scsibus1 targ 0 lun 0: <Xen, phy xvda 768, 0000>
xbf2 at xen0 backend 0 channel 9: disk
sd1 at scsibus2 targ 0 lun 0: <Xen, phy xvdb 832, 0000>
xnf0 at xen0 backend 0 channel 10: address 4e:4b:b7:f4:f4:94
xspd0 at pci0 dev 3 function 0 "XenSource Platform Device" rev 0x02
xen0: failed to attach "device/9pfs/"


Index: sys/dev/pv/xen.c
===================================================================
RCS file: /cvs/src/sys/dev/pv/xen.c,v
diff -p -u -r1.98 xen.c
--- sys/dev/pv/xen.c    24 May 2024 10:05:55 -0000      1.98
+++ sys/dev/pv/xen.c    20 Nov 2024 14:05:52 -0000
@@ -1403,8 +1403,6 @@ xen_probe_devices(struct xen_softc *sc)
                return (error);

        for (i = 0; i < iov1_cnt; i++) {
-               if (strcmp("suspend", (char *)iovp1[i].iov_base) == 0)
-                       continue;
                snprintf(path, sizeof(path), "device/%s",
                    (char *)iovp1[i].iov_base);
                if ((error = xs_cmd(&xst, XS_LIST, path, &iovp2,
@@ -1426,7 +1424,7 @@ xen_probe_devices(struct xen_softc *sc)
                                printf("%s: failed to attach \"%s/%s\"\n",
                                    sc->sc_dev.dv_xname, path,
                                    (const char *)iovp2[j].iov_base);
-                               goto out;
+                               continue;
                        }
                }
                /* Setup a watch for every device subtree */