coredump_filter: permit changing of the default filter

Introduce a new kernel parameter `coredump_filter'.  Setting a value to
this parameter causes the default bitmask of coredump_filter to be
changed.

It is useful for users to change coredump_filter settings for the whole
system at boot time.  Without this parameter, users have to change
coredump_filter settings for each /proc/<pid>/ in an initializing script.

Signed-off-by: Hidehiro Kawai <hidehiro.kawai.ez@hitachi.com>
Cc: Roland McGrath <roland@redhat.com>
Cc: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt
index 3ccf1bc..0b3f671 100644
--- a/Documentation/kernel-parameters.txt
+++ b/Documentation/kernel-parameters.txt
@@ -551,6 +551,11 @@
 			not work reliably with all consoles, but is known
 			to work with serial and VGA consoles.
 
+	coredump_filter=
+			[KNL] Change the default value for
+			/proc/<pid>/coredump_filter.
+			See also Documentation/filesystems/proc.txt.
+
 	cpcihp_generic=	[HW,PCI] Generic port I/O CompactPCI driver
 			Format:
 			<first_slot>,<last_slot>,<port>,<enum_bit>[,<debug>]