pnfs-obj: autologin: Add support for protocol autologin

The pnfs-objects protocol mandates that we autologin into devices not
present in the system, according to information specified in the
get_device_info returned from the server.

The Protocol specifies two login hints.
1. An IP address:port combination
2. A string URI which is constructed as a URL with a protocol prefix
   followed by :// and a string as address. For each  protocol prefix
   the string-address format might be different.

We only support the second option. The first option is just redundant
to the second one.
NOTE: The Kernel part of autologin does not parse the URI string. It
just channels it to a user-mode script. So any new login protocols should
only update the user-mode script which is a part of the nfs-utils package,
but the Kernel need not change.

We implement the autologin by using the call_usermodehelper() API.
(Thanks to Steve Dickson <steved@redhat.com> for pointing it out)
So there is no running daemon needed, and/or special setup.

We Add the osd_login_prog Kernel module parameters which defaults to:
	/sbin/osd_login

Kernel try's to upcall the program specified in osd_login_prog. If the file is
not found or the execution fails Kernel will disable any farther upcalls, by
zeroing out  osd_login_prog, Until Admin re-enables it by setting the
osd_login_prog parameter to a proper program.

Also add text about the osd_login program command line API to:
	Documentation/filesystems/nfs/pnfs.txt
and documentation of the new  osd_login_prog  module parameter to:
	Documentation/kernel-parameters.txt

TODO: Add timeout option in the case osd_login program gets
              stuck

Signed-off-by: Sachin Bhamare <sbhamare@panasas.com>
Signed-off-by: Boaz Harrosh <bharrosh@panasas.com>
Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>

1 files changed, 6 insertions, 0 deletions

diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt
index 7bae0fd3b63c..0d79a88f4de9 100644
--- a/Documentation/kernel-parameters.txt
+++ b/Documentation/kernel-parameters.txt
@@ -1687,6 +1687,12 @@ bytes respectively. Such letter suffixes can also be entirely omitted.
                         information.
 
 
+        objlayoutdriver.osd_login_prog=
+                        [NFS] [OBJLAYOUT] sets the pathname to the program which
+                        is used to automatically discover and login into new
+                        osd-targets. Please see:
+                        Documentation/filesystems/pnfs.txt for more explanations
+
         nmi_debug=      [KNL,AVR32,SH] Specify one or more actions to take
                         when a NMI is triggered.
                         Format: [state][,regs][,debounce][,die]