f2fs crypto: add encryption policy and password salt support

This patch adds encryption policy and password salt support through ioctl
implementation.

It adds three ioctls:
 F2FS_IOC_SET_ENCRYPTION_POLICY,
 F2FS_IOC_GET_ENCRYPTION_POLICY,
 F2FS_IOC_GET_ENCRYPTION_PWSALT, which use xattr operations.

Note that, these definition and codes are taken from ext4 crypto support.
For f2fs, xattr operations and on-disk flags for superblock and inode were
changed.

Signed-off-by: Michael Halcrow <mhalcrow@google.com>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
Signed-off-by: Ildar Muslukhov <muslukhovi@gmail.com>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>
diff --git a/fs/f2fs/xattr.c b/fs/f2fs/xattr.c
index 9757f65..07449b98 100644
--- a/fs/f2fs/xattr.c
+++ b/fs/f2fs/xattr.c
@@ -584,6 +584,9 @@
 		inode->i_ctime = CURRENT_TIME;
 		clear_inode_flag(fi, FI_ACL_MODE);
 	}
+	if (index == F2FS_XATTR_INDEX_ENCRYPTION &&
+			!strcmp(name, F2FS_XATTR_NAME_ENCRYPTION_CONTEXT))
+		f2fs_set_encrypted_inode(inode);
 
 	if (ipage)
 		update_inode(inode, ipage);