[fs/9P] Add posixacl mount option

The mount option access=client is overloaded as it assumes acl too.
Adding posixacl option to enable POSIX ACLs makes it explicit and clear.
Also it is convenient in the future to add other types of acls like richacls.

Ideally, the access mode 'client' should be just like V9FS_ACCESS_USER
except it underscores the location of access check.
Traditional 9P protocol lets the server perform access checks but with
this mode, all the access checks will be performed on the client itself.
Server just follows the client's directive.

Signed-off-by: Venkateswararao Jujjuri <jvrao@linux.vnet.ibm.com>
Signed-off-by: Eric Van Hensbergen <ericvh@gmail.com>
diff --git a/fs/9p/v9fs.c b/fs/9p/v9fs.c
index d34f293..f5a3200 100644
--- a/fs/9p/v9fs.c
+++ b/fs/9p/v9fs.c
@@ -55,7 +55,7 @@
 	/* Cache options */
 	Opt_cache_loose, Opt_fscache,
 	/* Access options */
-	Opt_access,
+	Opt_access, Opt_posixacl,
 	/* Error token */
 	Opt_err
 };
@@ -73,6 +73,7 @@
 	{Opt_fscache, "fscache"},
 	{Opt_cachetag, "cachetag=%s"},
 	{Opt_access, "access=%s"},
+	{Opt_posixacl, "posixacl"},
 	{Opt_err, NULL}
 };
 
@@ -194,13 +195,7 @@
 			else if (strcmp(s, "any") == 0)
 				v9ses->flags |= V9FS_ACCESS_ANY;
 			else if (strcmp(s, "client") == 0) {
-#ifdef CONFIG_9P_FS_POSIX_ACL
 				v9ses->flags |= V9FS_ACCESS_CLIENT;
-#else
-				P9_DPRINTK(P9_DEBUG_ERROR,
-					"Not defined CONFIG_9P_FS_POSIX_ACL. "
-					"Ignoring access=client option\n");
-#endif
 			} else {
 				v9ses->flags |= V9FS_ACCESS_SINGLE;
 				v9ses->uid = simple_strtoul(s, &e, 10);
@@ -210,6 +205,16 @@
 			kfree(s);
 			break;
 
+		case Opt_posixacl:
+#ifdef CONFIG_9P_FS_POSIX_ACL
+			v9ses->flags |= V9FS_POSIX_ACL;
+#else
+			P9_DPRINTK(P9_DEBUG_ERROR,
+					"Not defined CONFIG_9P_FS_POSIX_ACL. "
+					"Ignoring posixacl option\n");
+#endif
+			break;
+
 		default:
 			continue;
 		}
@@ -304,6 +309,14 @@
 		v9ses->flags |= V9FS_ACCESS_ANY;
 		v9ses->uid = ~0;
 	}
+	if (!v9fs_proto_dotl(v9ses) ||
+		!((v9ses->flags & V9FS_ACCESS_MASK) == V9FS_ACCESS_CLIENT)) {
+		/*
+		 * We support ACL checks on clinet only if the protocol is
+		 * 9P2000.L and access is V9FS_ACCESS_CLIENT.
+		 */
+		v9ses->flags &= ~V9FS_ACL_MASK;
+	}
 
 	fid = p9_client_attach(v9ses->clnt, NULL, v9ses->uname, ~0,
 							v9ses->aname);