This option can be used for passing file descriptors on the
command line. It mirrors the existing add-fd QMP command which
allows an fd to be passed to QEMU via SCM_RIGHTS and added to an
fd set.
This can be combined with commands such as -drive to link file
descriptors in an fd set to a drive:
This example adds dups of fds 3 and 4, and the accompanying opaque
strings to the fd set with ID=2. qemu_open() already knows how
to handle a filename of this format. qemu_open() searches the
corresponding fd set for an fd and when it finds a match, QEMU
goes on to use a dup of that fd just like it would have used an
fd that it opened itself.
Signed-off-by: Corey Bryant <coreyb@linux.vnet.ibm.com> Reviewed-by: Eric Blake <eblake@redhat.com> Signed-off-by: Kevin Wolf <kwolf@redhat.com>