fs: add field to superblock to support cleancache
fs: add field to superblock to support cleancache

This second patch of eight in this cleancache series adds a field to
the generic superblock to squirrel away a pool identifier that is
dynamically provided by cleancache-enabled filesystems at mount time
to uniquely identify files and pages belonging to this mounted filesystem.

Details and a FAQ can be found in Documentation/vm/cleancache.txt

[v8: trivial merge conflict update]
Signed-off-by: Dan Magenheimer <017adcb67eaa7bc3974e87882304023d2fcc0db7@oracle.com>
Reviewed-by: Jeremy Fitzhardinge <b3f594e10a9edcf5413cf1190121d45078c62290@goop.org>
Reviewed-by: Konrad Rzeszutek Wilk <da3a51b335cef0eb0e2c329c5ef6bcd6acef687a@oracle.com>
Cc: Andrew Morton <5c1e68b099950c134891f0b6e179498a8ebe9cf9@linux-foundation.org>
Cc: Al Viro <de609eb4d5d70b1d38ec6642adbfc33a2781f63c@ZenIV.linux.org.uk>
Cc: Matthew Wilcox <f80d0ca101e967b50b730ddf8e8aca0de85e8df6@wil.cx>
Cc: Nick Piggin <24829078df5003d9dd1dd871ca2aeb0b1cf95ef4@kernel.dk>
Cc: Mel Gorman <2f629c4d93e35c3d371f0463b040c6ef04a5c1e5@csn.ul.ie>
Cc: Rik Van Riel <a21938f5d463ddf41aa718934c205ca2cce8ebbc@redhat.com>
Cc: Jan Beulich <051346888327db48cce19d2cfd0e1c700bb7cf16@novell.com>
Cc: Chris Mason <a169954b4cb1a46cee25f659d3bddfebe02b5fba@oracle.com>
Cc: Andreas Dilger <fd4823dd86d134508df78a168e24c446ce7699f3@sun.com>
Cc: Ted Ts'o <4ed386e0495d3e109932df055831d9ec2f824927@mit.edu>
Cc: Mark Fasheh <8f0bc92cac940f3e83deb53ced7a1f201bce5732@suse.com>
Cc: Joel Becker <823d0e2e55da83c1616b20ae9a15f9456fa076e5@oracle.com>
Cc: Nitin Gupta <cc4fec8a34766005dd45d48be045c08d736c11ed@vflare.org>

KristFoundation/Programs,TeamVee-Kanas/android_kernel_samsung_kanas,KristFoundation/Programs,TeamVee-Kanas/android_kernel_samsung_kanas,KristFoundation/Programs,TeamVee-Kanas/android_kernel_samsung_kanas,KristFoundation/Programs,TeamVee-Kanas/android_kernel_samsung_kanas,KristFoundation/Programs,KristFoundation/Programs,TeamVee-Kanas/android_kernel_samsung_kanas