vfs: Add IOP_XATTR inode operations flag

The IOP_XATTR inode operations flag in inode->i_opflags indicates that
the inode has xattr support.  The flag is automatically set by
new_inode() on filesystems with xattr support (where sb->s_xattr is
defined), and cleared otherwise.  Filesystems can explicitly clear it
for inodes that should not have xattr support.
Signed-off-by: Andreas Gruenbacher <agruenba@redhat.com>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

fs/inode.c

@@ -140,6 +140,8 @@ int inode_init_always(struct super_block *sb, struct inode *inode)
 	inode->i_fop = &no_open_fops;
 	inode->__i_nlink = 1;
 	inode->i_opflags = 0;
+	if (sb->s_xattr)
+		inode->i_opflags |= IOP_XATTR;
 	i_uid_write(inode, 0);
 	i_gid_write(inode, 0);
 	atomic_set(&inode->i_writecount, 0);

fs/xattr.c

@@ -53,10 +53,13 @@ strcmp_prefix(const char *a, const char *a_prefix)
  * Find the xattr_handler with the matching prefix.
  */
 static const struct xattr_handler *
-xattr_resolve_name(const struct xattr_handler **handlers, const char **name)
+xattr_resolve_name(struct inode *inode, const char **name)
 {
+	const struct xattr_handler **handlers = inode->i_sb->s_xattr;
 	const struct xattr_handler *handler;
 
+	if (!(inode->i_opflags & IOP_XATTR))
+		return ERR_PTR(-EOPNOTSUPP);
 	for_each_xattr_handler(handlers, handler) {
 		const char *n;
 
@@ -298,6 +301,7 @@ vfs_getxattr(struct dentry *dentry, const char *name, void *value, size_t size)
 		error = -EOPNOTSUPP;
 
 	return error;
+
 }
 EXPORT_SYMBOL_GPL(vfs_getxattr);
 
@@ -700,7 +704,7 @@ generic_getxattr(struct dentry *dentry, struct inode *inode,
 {
 	const struct xattr_handler *handler;
 
-	handler = xattr_resolve_name(dentry->d_sb->s_xattr, &name);
+	handler = xattr_resolve_name(inode, &name);
 	if (IS_ERR(handler))
 		return PTR_ERR(handler);
 	return handler->get(handler, dentry, inode,
@@ -755,7 +759,7 @@ generic_setxattr(struct dentry *dentry, struct inode *inode, const char *name,
 
 	if (size == 0)
 		value = "";  /* empty EA, do not remove */
-	handler = xattr_resolve_name(dentry->d_sb->s_xattr, &name);
+	handler = xattr_resolve_name(inode, &name);
 	if (IS_ERR(handler))
 		return PTR_ERR(handler);
 	return handler->set(handler, dentry, inode, name, value, size, flags);
@@ -770,7 +774,7 @@ generic_removexattr(struct dentry *dentry, const char *name)
 {
 	const struct xattr_handler *handler;
 
-	handler = xattr_resolve_name(dentry->d_sb->s_xattr, &name);
+	handler = xattr_resolve_name(d_inode(dentry), &name);
 	if (IS_ERR(handler))
 		return PTR_ERR(handler);
 	return handler->set(handler, dentry, d_inode(dentry), name, NULL,

include/linux/fs.h

@@ -591,6 +591,7 @@ is_uncached_acl(struct posix_acl *acl)
 #define IOP_FASTPERM	0x0001
 #define IOP_LOOKUP	0x0002
 #define IOP_NOFOLLOW	0x0004
+#define IOP_XATTR	0x0008
 
 /*
  * Keep mostly read-only and often accessed (especially for