fs: get_acl() must be allowed to return EOPNOTSUPP

posix_acl_xattr_get requires get_acl() to return EOPNOTSUPP if the
filesystem cannot support acls. This is needed for NFS, which can't
know whether or not the server supports acls until it tries to get/set
one.
This patch converts posix_acl_chmod and posix_acl_create to deal with
EOPNOTSUPP return values from get_acl().
Reported-by: Russell King <linux@arm.linux.org.uk>
Link: http://lkml.kernel.org/r/20140130140834.GW15937@n2100.arm.linux.org.uk
Cc: Al Viro viro@zeniv.linux.org.uk>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Tested-by: Takashi Iwai <tiwai@suse.de>
Signed-off-by: Trond Myklebust <trond.myklebust@primarydata.com>

fs/posix_acl.c

@@ -521,8 +521,11 @@ posix_acl_chmod(struct inode *inode, umode_t mode)
 		return -EOPNOTSUPP;
 
 	acl = get_acl(inode, ACL_TYPE_ACCESS);
-	if (IS_ERR_OR_NULL(acl))
+	if (IS_ERR_OR_NULL(acl)) {
+		if (acl == ERR_PTR(-EOPNOTSUPP))
+			return 0;
 		return PTR_ERR(acl);
+	}
 
 	ret = __posix_acl_chmod(&acl, GFP_KERNEL, mode);
 	if (ret)
@@ -544,14 +547,15 @@ posix_acl_create(struct inode *dir, umode_t *mode,
 		goto no_acl;
 
 	p = get_acl(dir, ACL_TYPE_DEFAULT);
-	if (IS_ERR(p))
+	if (IS_ERR(p)) {
+		if (p == ERR_PTR(-EOPNOTSUPP))
+			goto apply_umask;
 		return PTR_ERR(p);
-
-	if (!p) {
-		*mode &= ~current_umask();
-		goto no_acl;
 	}
 
+	if (!p)
+		goto apply_umask;
+
 	*acl = posix_acl_clone(p, GFP_NOFS);
 	if (!*acl)
 		return -ENOMEM;
@@ -575,6 +579,8 @@ posix_acl_create(struct inode *dir, umode_t *mode,
 	}
 	return 0;
 
+apply_umask:
+	*mode &= ~current_umask();
 no_acl:
 	*default_acl = NULL;
 	*acl = NULL;