[PATCH v2 2/2] Documentation: Document the cephroot functionality

[mark . doffman]

From: Rob Taylor <rob.taylor@xxxxxxxxxxxxxxx>

Document using the cephfs as a root device, its purpose,
functionality and use.

Signed-off-by: Mark Doffman <mark.doffman@xxxxxxxxxxxxxxx>
Signed-off-by: Rob Taylor <rob.taylor@xxxxxxxxxxxxxxx>
Reviewed-by: Ian Molton <ian.molton@xxxxxxxxxxxxxxx>
---
 Documentation/filesystems/{ => ceph}/ceph.txt |  0
 Documentation/filesystems/ceph/cephroot.txt   | 86 +++++++++++++++++++++++++++
 2 files changed, 86 insertions(+)
 rename Documentation/filesystems/{ => ceph}/ceph.txt (100%)
 create mode 100644 Documentation/filesystems/ceph/cephroot.txt

diff --git a/Documentation/filesystems/ceph.txt b/Documentation/filesystems/ceph/ceph.txt
similarity index 100%
rename from Documentation/filesystems/ceph.txt
rename to Documentation/filesystems/ceph/ceph.txt
diff --git a/Documentation/filesystems/ceph/cephroot.txt b/Documentation/filesystems/ceph/cephroot.txt
new file mode 100644
index 0000000..deda4f0
--- /dev/null
+++ b/Documentation/filesystems/ceph/cephroot.txt
@@ -0,0 +1,86 @@
+Mounting the root filesystem via Ceph (cephroot)
+===============================================
+
+Written 2013 by Rob Taylor <rob.taylor@xxxxxxxxxxxxxxx>
+
+derived from nfsroot.txt:
+
+Written 1996 by Gero Kuhlmann <gero@xxxxxxxxxxxxxx>
+Updated 1997 by Martin Mares <mj@xxxxxxxxxxxxxxxxxxxxxxxx>
+Updated 2006 by Nico Schottelius <nico-kernel-nfsroot@xxxxxxxxxxxxxxx>
+Updated 2006 by Horms <horms@xxxxxxxxxxxx>
+
+
+
+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 Ceph for the root filesystem.
+
+For the rest of this text 'client' means the diskless system, and 'server'
+means the Ceph 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 cephroot, 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.
+
+If cephroot is not specified, it is expected that that a valid mount will be
+found via DHCP option 17, Root Path [1]
+
+cephroot=<monaddrs>:/[<subdir>],<ceph-opts>
+
+  <monaddrs>    Monitor addresses separated by commas. 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
+
+  <ceph-opts>	Standard Ceph options. All options are separated by commas.
+		See Documentation/filesystems/ceph/ceph.txt for options and
+		their defaults.
+
+4.) References
+    ----------
+
+[1] http://tools.ietf.org/html/rfc2132
+
+5.) Credits
+    -------
+
+  cephroot was derived from nfsroot by Rob Taylor <rob.taylor@xxxxxxxxxxxxxxx>
+  and Mark Doffman <mark.doffman@xxxxxxxxxxxxxxx>
+
+  The nfsroot code in the kernel and the RARP support have been written
+  by Gero Kuhlmann <gero@xxxxxxxxxxxxxx>.
+
+  The rest of the IP layer autoconfiguration code has been written
+  by Martin Mares <mj@xxxxxxxxxxxxxxxxxxxxxxxx>.
+
+  In order to write the initial version of nfsroot I would like to thank
+  Jens-Uwe Mager <jum@xxxxxxxxxxxxx> for his help.
-- 
1.8.4

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