pstore: Add pmsg - user-space accessible pstore object

A secured user-space accessible pstore object. Writes
to /dev/pmsg0 are appended to the buffer, on reboot
the persistent contents are available in
/sys/fs/pstore/pmsg-ramoops-[ID].

One possible use is syslogd, or other daemon, can
write messages, then on reboot provides a means to
triage user-space activities leading up to a panic
as a companion to the pstore dmesg or console logs.

Signed-off-by: Mark Salyzyn <salyzyn@android.com>
Acked-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Tony Luck <tony.luck@intel.com>
diff --git a/fs/pstore/Kconfig b/fs/pstore/Kconfig
index 983d951..916b8e2 100644
--- a/fs/pstore/Kconfig
+++ b/fs/pstore/Kconfig
@@ -21,6 +21,16 @@
 	  When the option is enabled, pstore will log all kernel
 	  messages, even if no oops or panic happened.
 
+config PSTORE_PMSG
+	bool "Log user space messages"
+	depends on PSTORE
+	help
+	  When the option is enabled, pstore will export a character
+	  interface /dev/pmsg0 to log user space messages. On reboot
+	  data can be retrieved from /sys/fs/pstore/pmsg-ramoops-[ID].
+
+	  If unsure, say N.
+
 config PSTORE_FTRACE
 	bool "Persistent function tracer"
 	depends on PSTORE