[PATCH RFC net v2 3/3] vsock: Fix IOCTL_VM_SOCKETS_GET_LOCAL_CID to check also `transport_local`

[Michal Luczaj]

Support returning VMADDR_CID_LOCAL in case no other vsock transport is
available.

Fixes: 0e12190578d0 ("vsock: add local transport support in the vsock core")
Suggested-by: Stefano Garzarella <sgarz...@redhat.com>
Signed-off-by: Michal Luczaj <m...@rbox.co>
---
man vsock(7) mentions IOCTL_VM_SOCKETS_GET_LOCAL_CID vs. VMADDR_CID_LOCAL:

   Ioctls
       ...
       IOCTL_VM_SOCKETS_GET_LOCAL_CID
              ...
              Consider using VMADDR_CID_ANY when binding instead of
              getting the local CID with IOCTL_VM_SOCKETS_GET_LOCAL_CID.

   Local communication
       ....
       The local CID obtained with IOCTL_VM_SOCKETS_GET_LOCAL_CID can be
       used for the same purpose, but it is preferable to use
       VMADDR_CID_LOCAL.

I was wondering it that would need some rewriting, since we're adding
VMADDR_CID_LOCAL as a possible ioctl's return value.
---
 net/vmw_vsock/af_vsock.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/net/vmw_vsock/af_vsock.c b/net/vmw_vsock/af_vsock.c
index 
a1b1073a2c89f865fcdb58b38d8e7feffcf1544f..4bdb4016bd14d790f3d217d5063be64a1553b194
 100644
--- a/net/vmw_vsock/af_vsock.c
+++ b/net/vmw_vsock/af_vsock.c
@@ -2577,6 +2577,8 @@ static long vsock_dev_do_ioctl(struct file *filp,
                cid = vsock_transport_local_cid(&transport_g2h);
                if (cid == VMADDR_CID_ANY)
                        cid = vsock_transport_local_cid(&transport_h2g);
+               if (cid == VMADDR_CID_ANY && transport_local)
+                       cid = VMADDR_CID_LOCAL;
 
                if (put_user(cid, p) != 0)
                        retval = -EFAULT;

-- 
2.49.0