CIFS: Add strictcache mount option

Use for switching on strict cache mode. In this mode the
client reads from the cache all the time it has Oplock Level II,
otherwise - read from the server. As for write - the client stores
a data in the cache in Exclusive Oplock case, otherwise - write
directly to the server.

Signed-off-by: Pavel Shilovsky <piastryyy@gmail.com>
Reviewed-by: Jeff Layton <jlayton@redhat.com>
Signed-off-by: Steve French <sfrench@us.ibm.com>

fs/cifs/connect.c

@@ -87,6 +87,7 @@ struct smb_vol {
 	bool no_xattr:1;   /* set if xattr (EA) support should be disabled*/
 	bool server_ino:1; /* use inode numbers from server ie UniqueId */
 	bool direct_io:1;
+	bool strict_io:1; /* strict cache behavior */
 	bool remap:1;      /* set to remap seven reserved chars in filenames */
 	bool posix_paths:1; /* unset to not ask for posix pathnames. */
 	bool no_linux_ext:1;
@@ -1344,6 +1345,8 @@ cifs_parse_mount_options(char *options, const char *devname,
 			vol->direct_io = 1;
 		} else if (strnicmp(data, "forcedirectio", 13) == 0) {
 			vol->direct_io = 1;
+		} else if (strnicmp(data, "strictcache", 11) == 0) {
+			vol->strict_io = 1;
 		} else if (strnicmp(data, "noac", 4) == 0) {
 			printk(KERN_WARNING "CIFS: Mount option noac not "
 				"supported. Instead set "
@@ -2584,6 +2587,8 @@ static void setup_cifs_sb(struct smb_vol *pvolume_info,
 	if (pvolume_info->multiuser)
 		cifs_sb->mnt_cifs_flags |= (CIFS_MOUNT_MULTIUSER |
 					    CIFS_MOUNT_NO_PERM);
+	if (pvolume_info->strict_io)
+		cifs_sb->mnt_cifs_flags |= CIFS_MOUNT_STRICT_IO;
 	if (pvolume_info->direct_io) {
 		cFYI(1, "mounting share using direct i/o");
 		cifs_sb->mnt_cifs_flags |= CIFS_MOUNT_DIRECT_IO;