EX-4182 sec: support of PCC-RO for encrypted files

EX-4182 sec: support of PCC-RO for encrypted files

In order to support PCC-RO for encrypted files, we decide to store
in PCC the ciphertext version of the Lustre files. We proceed to
decryption of PCC files only in the page cache, so cleartext is just
in memory. When a Lustre file is detached from PCC, or when the
encryption key is removed, we trash those PCC page cache pages.

As PCC files contain ciphertext, their sizes are aligned on
LUSTRE_ENCRYPTION_UNIT_SIZE instead of being lustre inode's clear
text size. In order to keep track of Lustre files' actual sizes,
we use a dedicated xattr on the PCC files. Its value is set at pcc
attach time, which is fine for PCC-RO.

Also add sanity-pcc test_21j to exercise this.

Signed-off-by: Sebastien Buisson <sbuisson@ddn.com>
Change-Id: Id7d96adb4eb4770c813a042acf7ed6c42224b9bf
Reviewed-on: https://review.whamcloud.com/45910
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>