[PATCH 0/1] vhost: tolerate fd in REM_MEM_REG for interop

[pravin.bathija at dell.com]

From: Pravin M Bathija <pravin.bathija at dell.com>

The VHOST_USER_REM_MEM_REG handler rejects messages carrying a file
descriptor, but the vhost-user specification allows back-ends to
accept one for compatibility with incorrect front-end implementations.

libblkio (v1.5.0) sends an fd with REM_MEM_REG because it shares a
message helper with ADD_MEM_REG.  This causes DPDK to drop the
connection with:

  expect 0 FDs for request VHOST_USER_REM_MEM_REG, received 1

QEMU's libvhost-user reference back-end already tolerates this.

The fix accepts the message and closes any unexpected fd without
using it, conforming to the specification's compatibility clause.

Tested with:
 - QEMU VM bring-up with add/remove memory regions via monitor
 - QEMU post-copy live migration between source and destination
 - SPDK vhost-blk with libblkio fio engine (write + md5 verify)
 - libblkio alloc-mem-region and map-mem-region unit tests
   (ADD/REM/ADD cycles against SPDK vhost-blk)

Pravin M Bathija (1):
  vhost: tolerate file descriptor in REM_MEM_REG msg

 lib/vhost/vhost_user.c | 9 ++++++++-
 1 file changed, 8 insertions(+), 1 deletion(-)

-- 
2.43.0