pstore_dump() can be called with many different "reason" codes. Save
the name of the code in the persistent store record.

Also - only worthwhile calling pstore_mkfile for KMSG_DUMP_OOPS - that
is the only one where the kernel will continue running.
Reviewed-by: NSeiji Aguchi <seiji.aguchi@hds.com>
Signed-off-by: NTony Luck <tony.luck@intel.com>

/sys/fs is a somewhat strange way to tweak what could more
obviously be tuned with a mount option.
Suggested-by: NChristoph Hellwig <hch@infradead.org>
Signed-off-by: NTony Luck <tony.luck@intel.com>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

Some platforms have a small amount of non-volatile storage that
can be used to store information useful to diagnose the cause of
a system crash.  This is the generic part of a file system interface
that presents information from the crash as a series of files in
/dev/pstore.  Once the information has been seen, the underlying
storage is freed by deleting the files.
Signed-off-by: NTony Luck <tony.luck@intel.com>