36735a6a2b
Instead of doing that upon each ipcns creation, we do that the first time mq_open(2) or mqueue mount is done in an ipcns. What's more, doing that allows to get rid of mount_ns() use - we can go with considerably cheaper mount_nodev(), avoiding the loop over all mqueue superblock instances; ipcns->mq_mnt is used to locate preexisting instance in O(1) time instead of O(instances) mount_ns() would've cost us. Based upon the version by Giuseppe Scrivano <gscrivan@redhat.com>; I've added handling of userland mqueue mounts (original had been broken in that area) and added a switch to mount_nodev(). Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>