Document desired functionality for ceph-as-root.baserock/robtaylor/cephboot

This is based of nfsroot, but simplifying and generalising as there are no
backwards compatibility concerns.

We also use DYNAMIC_DEBUG rather than have a custom boot debugging method.

4 files changed, 113 insertions, 0 deletions

diff --git a/Documentation/filesystems/ceph.txt b/Documentation/filesystems/ceph/ceph.txt
index b08c6ba553f0..b08c6ba553f0 100644
--- a/Documentation/filesystems/ceph.txt
+++ b/Documentation/filesystems/ceph/ceph.txt
diff --git a/Documentation/filesystems/ceph/cephroot.txt b/Documentation/filesystems/ceph/cephroot.txt
new file mode 100644
index 000000000000..a0c8df0e4935
--- /dev/null
+++ b/Documentation/filesystems/ceph/cephroot.txt
@@ -0,0 +1,111 @@
+Mounting the root filesystem via Ceph (cephroot)
+===============================================
+
+Written 2013 by Rob Taylor <rob.taylor@codethink.co.uk>
+
+derived from nfsroot.txt:
+
+Written 1996 by Gero Kuhlmann <gero@gkminix.han.de>
+Updated 1997 by Martin Mares <mj@atrey.karlin.mff.cuni.cz>
+Updated 2006 by Nico Schottelius <nico-kernel-nfsroot@schottelius.org>
+Updated 2006 by Horms <horms@verge.net.au>
+
+
+
+In order to use a diskless system, such as an X-terminal or printer server
+for example, it is necessary for the root filesystem to be present on a
+non-disk device. This may be an initramfs (see Documentation/filesystems/
+ramfs-rootfs-initramfs.txt), a ramdisk (see Documentation/initrd.txt), a
+filesystem mounted via NFS or a filesystem mounted via Ceph. The following 
+text describes on how to use NFS for the root filesystem.
+
+For the rest of this text 'client' means the diskless system, and 'server'
+means the NFS server.
+
+
+
+
+1.) Enabling cephroot capabilities
+    -----------------------------
+
+In order to use cephroot, CEPH_FS needs to be selected as
+built-in during configuration. Once this has been selected, the cephroot
+option will become available, which should also be selected.
+
+In the networking options, kernel level autoconfiguration can be selected,
+along with the types of autoconfiguration to support. Selecting all of
+DHCP, BOOTP and RARP is safe.
+
+
+
+
+2.) Kernel command line
+    -------------------
+
+When the kernel has been loaded by a boot loader (see below) it needs to be
+told what root fs device to use. And in the case of nfsroot, where to find
+both the server and the name of the directory on the server to mount as root.
+This can be established using the following kernel command line parameters:
+
+
+root=/dev/ceph
+
+  This is necessary to enable the pseudo-Ceph-device. Note that it's not a
+  real device but just a synonym to tell the kernel to use Ceph instead of
+  a real device.
+
+
+cephroot=<monaddr1>[,<monaddr2>,...]:/[<subdir>]
+
+  If cephroot is not specified, it is expected that that a valid mount will be
+found via DHCP option 17, Root Path [1]
+
+  <monaddrX>    Monitor address. Each takes the form host[:port]. If the port
+		is not specified, the Ceph default of 6789 is assumed.
+
+  <subdir>	A subdirectory subdir may be specified if a subset of the file
+		system is to be mounted
+
+cephrootopts=<ceph-opts>
+
+  <ceph-opts>	Standard Ceph options. All options are separated by commas.
+		See Documentation/filesystems/ceph/ceph.txt for options and
+		their defaults.
+
+cephrootappendip=1
+		If cephrootappendip is set, then the subdir path has
+		'/A.B.C.D' appended to it, where A.B.C.D is the primary client IP.
+
+ip=<client-ip>:<server-ip>:<gw-ip>:<netmask>:<hostname>:<device>:<autoconf>:
+   <dns0-ip>:<dns1-ip>
+
+  If the ip parameter is used with cephboot, then <server-ip> is disregarded. 
+
+
+ddebug_query="module ceph"
+
+  This parameter enables debugging messages to appear in the kernel
+  log at boot time so that administrators can verify that the correct
+  Ceph mount options, server address, and root path are passed to the
+  Ceph client.
+
+4.) References
+    ----------
+
+[1] http://tools.ietf.org/html/rfc2132
+
+5.) Credits
+    -------
+
+  cephroot was derived from nfsroot by Rob Taylor <rob.taylor@codethink.co.uk>
+
+  The nfsroot code in the kernel and the RARP support have been written
+  by Gero Kuhlmann <gero@gkminix.han.de>.
+
+  The rest of the IP layer autoconfiguration code has been written
+  by Martin Mares <mj@atrey.karlin.mff.cuni.cz>.
+
+  In order to write the initial version of nfsroot I would like to thank
+  Jens-Uwe Mager <jum@anubis.han.de> for his help.
+
+
diff --git a/include/linux/root_dev.h b/include/linux/root_dev.h
index ed241aad7c17..af6b1825b462 100644
--- a/include/linux/root_dev.h
+++ b/include/linux/root_dev.h
@@ -16,6 +16,7 @@ enum {
 	Root_SDA2 = MKDEV(SCSI_DISK0_MAJOR, 2),
 	Root_HDC1 = MKDEV(IDE1_MAJOR, 1),
 	Root_SR0 = MKDEV(SCSI_CDROM_MAJOR, 0),
+	Root_CEPH = MKDEV(UNNAMED_MAJOR, 254),
 };
 
 extern dev_t ROOT_DEV;
diff --git a/init/do_mounts.c b/init/do_mounts.c
index a2b49f2c1bd8..6cd19b1f33ff 100644
--- a/init/do_mounts.c
+++ b/init/do_mounts.c
@@ -195,6 +195,7 @@ done:
  *	   is a zero-filled hex representation of the 1-based partition number.
  *	7) PARTUUID=<UUID>/PARTNROFF=<int> to select a partition in relation to
  *	   a partition with a known unique id.
+ *      8) /dev/ceph represents Root_CEPH
  *
  *	If name doesn't have fall into the categories above, we return (0,0).
  *	block_class is used to check if something is a disk name. If the disk