doc: document new CephFS mount device syntax

Signed-off-by: Venky Shankar <vshankar@redhat.com>
Reviewed-by: Jeff Layton <jlayton@kernel.org>
Signed-off-by: Ilya Dryomov <idryomov@gmail.com>

Author: vshankar

Documentation/filesystems/ceph.rst

@@ -82,24 +82,43 @@ Mount Syntax
 
 The basic mount syntax is::
 
- # mount -t ceph monip[:port][,monip2[:port]...]:/[subdir] mnt
+ # mount -t ceph user@fsid.fs_name=/[subdir] mnt -o mon_addr=monip1[:port][/monip2[:port]]
 
 You only need to specify a single monitor, as the client will get the
 full list when it connects.  (However, if the monitor you specify
 happens to be down, the mount won't succeed.)  The port can be left
 off if the monitor is using the default.  So if the monitor is at
 1.2.3.4::
 
- # mount -t ceph 1.2.3.4:/ /mnt/ceph
+ # mount -t ceph cephuser@07fe3187-00d9-42a3-814b-72a4d5e7d5be.cephfs=/ /mnt/ceph -o mon_addr=1.2.3.4
 
 is sufficient.  If /sbin/mount.ceph is installed, a hostname can be
-used instead of an IP address.
+used instead of an IP address and the cluster FSID can be left out
+(as the mount helper will fill it in by reading the ceph configuration
+file)::
 
+  # mount -t ceph cephuser@cephfs=/ /mnt/ceph -o mon_addr=mon-addr
 
+Multiple monitor addresses can be passed by separating each address with a slash (`/`)::
+
+  # mount -t ceph cephuser@cephfs=/ /mnt/ceph -o mon_addr=192.168.1.100/192.168.1.101
+
+When using the mount helper, monitor address can be read from ceph
+configuration file if available. Note that, the cluster FSID (passed as part
+of the device string) is validated by checking it with the FSID reported by
+the monitor.
 
 Mount Options
 =============
 
+  mon_addr=ip_address[:port][/ip_address[:port]]
+	Monitor address to the cluster. This is used to bootstrap the
+        connection to the cluster. Once connection is established, the
+        monitor addresses in the monitor map are followed.
+
+  fsid=cluster-id
+	FSID of the cluster (from `ceph fsid` command).
+
   ip=A.B.C.D[:N]
 	Specify the IP and/or port the client should bind to locally.
 	There is normally not much reason to do this.  If the IP is not