If a virtio-vsock device was installed or present in the guest kernel then -o qemu mode would add the parameter -device vhost-vsock-pci to the qemu command line. This fails with: qemu-system-x86_64: -device vhost-vsock-pci: guest-cid property must be greater than 2 Thanks: Stefano Garzarella Fixes: commit 4f6b143c1cb32a29cbd3ff04635ba220e5db82ed --- output/output_qemu.ml | 26 ++++++++++++++++++++++++-- 1 file changed, 24 insertions(+), 2 deletions(-) diff --git a/output/output_qemu.ml b/output/output_qemu.ml index 4e0a3de6f0..da7278b88b 100644 --- a/output/output_qemu.ml +++ b/output/output_qemu.ml @@ -292,8 +292,30 @@ module QEMU = struct arg "-device" "virtio-balloon"; if guestcaps.gcaps_isa_pvpanic then arg_list "-device" ["pvpanic"; "ioport=0x505"]; - if guestcaps.gcaps_virtio_socket then - arg "-device" "vhost-vsock-pci"; + if guestcaps.gcaps_virtio_socket then ( + (* qemu requires a free guest CID to be chosen. If you use libvirt + * then it does this by iterating over the CIDs doing + * ioctl(fd, VHOST_VSOCK_SET_GUEST_CID, &val) on each one until + * it finds a free CID. See: + * https://bugzilla.redhat.com/show_bug.cgi?id=1291851#c6 + * + * As that is essentially impossible to do from the shell script, + * instead assign a semi-random one here. Using the PID of + * virt-v2v means that we're most likely to assign an unused + * CID, especially with modern Linux which has a very large + * PID space. Note that CID must be [3..UINT32_MAX-1] and + * max PID in Linux is 2^22. + *) + let pid = getpid () in + let pid = max 3 pid in + (* In OCaml 4.13 we could use this, if we were worried about a + future system having very large PIDs: + let pid = Int64.( min (max 3L (of_int (getpid ()))) + (of_int32 Int32.max_int) ) in + *) + let guest_cid = sprintf "guest-cid=%d" pid in + arg_list "-device" ["vhost-vsock-pci"; guest_cid ] + ); (* Add a serial console to Linux guests. *) if inspect.i_type = "linux" then -- 2.35.1