Re: [PATCH 12/12] docs: document using passt backend with <interface type='vhostuser'>
On Sat, Feb 15, 2025 at 12:20:17AM -0500, Laine Stump wrote:
+vhost-user connection with passt backend
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+:since:`Since 11.1.0 (QEMU and KVM only)` passt can be used as the
+other end of the vhost-user connection. This is a compelling
+alternative, because passt provides all of its network connectivity
+without requiring any elevated privileges or capabilities, and
+vhost-user uses shared memory to make this unprivileged connection
+very high performance as well. You can set a type='vhostuser'
+interface to use passt as the backend by adding ``<backend
+type='passt'/>``. When passt is the backend, only a single driver
+queue is supported,
This should be added to the validation step. Otherwise:
error: internal error: QEMU unexpectedly closed the monitor (vm='test'):
qemu-system-x86_64: -netdev
{"type":"vhost-user","chardev":"charnet0","queues":5,"id":"hostnet0"}:
Failed to read msg header. Read -1 instead of 12. Original request 1.
qemu-system-x86_64: -netdev
{"type":"vhost-user","chardev":"charnet0","queues":5,"id":"hostnet0"}:
vhost_backend_init failed: Protocol error
qemu-system-x86_64: -netdev
{"type":"vhost-user","chardev":"charnet0","queues":5,"id":"hostnet0"}:
failed to init vhost_net for queue 0
qemu-system-x86_64: -netdev
{"type":"vhost-user","chardev":"charnet0","queues":5,"id":"hostnet0"}:
Failed to connect to '/run/libvirt/qemu/passt/1-test-net0.socket':
Connection refused
qemu-system-x86_64: -netdev
{"type":"vhost-user","chardev":"charnet0","queues":5,"id":"hostnet0"}:
Device 'vhost-user' could not be initialized
and the ``<source>`` path/type/mode are all
+implied to be "matching the passt process" so **must not** be
+specified.
These seem to simply be ignored if specified, which I guess is better
than accepting values that we know aren't going to work. Explicitly
rejecting them might be better.
Incidentally, dumpxml doesn't report the actual values, which I kinda
expected to happen. Not sure how other vhost-user device behave in
this sense.
--
Andrea Bolognani / Red Hat / Virtualization