Btrfs: Add readonly inode flag

This patch adds readonly inode flag support.  A file with this flag
can't be modified, but can be deleted.
Signed-off-by: Chris Mason <chris.mason@oracle.com>

fs/btrfs/ctree.h

@@ -451,9 +451,9 @@ struct btrfs_root {
 /*
  * Inode flags
  */
-#define BTRFS_INODE_NODATASUM 		0x1
-#define BTRFS_INODE_NODATACOW 		0x2
-
+#define BTRFS_INODE_NODATASUM		(1 << 0)
+#define BTRFS_INODE_NODATACOW		(1 << 1)
+#define BTRFS_INODE_READONLY		(1 << 2)
 #define btrfs_clear_flag(inode, flag)	(BTRFS_I(inode)->flags &= \
 					 ~BTRFS_INODE_##flag)
 #define btrfs_set_flag(inode, flag)	(BTRFS_I(inode)->flags |= \

fs/btrfs/inode.c

@@ -2850,6 +2850,13 @@ static int btrfs_symlink(struct inode *dir, struct dentry *dentry,
 	btrfs_throttle(root);
 	return err;
 }
+static int btrfs_permission(struct inode *inode, int mask,
+			    struct nameidata *nd)
+{
+	if (btrfs_test_flag(inode, READONLY) && (mask & MAY_WRITE))
+		return -EACCES;
+	return generic_permission(inode, mask, NULL);
+}
 
 static struct inode_operations btrfs_dir_inode_operations = {
 	.lookup		= btrfs_lookup,
@@ -2866,12 +2873,12 @@ static struct inode_operations btrfs_dir_inode_operations = {
 	.getxattr	= generic_getxattr,
 	.listxattr	= btrfs_listxattr,
 	.removexattr	= generic_removexattr,
+	.permission	= btrfs_permission,
 };
-
 static struct inode_operations btrfs_dir_ro_inode_operations = {
 	.lookup		= btrfs_lookup,
+	.permission	= btrfs_permission,
 };
-
 static struct file_operations btrfs_dir_file_operations = {
 	.llseek		= generic_file_llseek,
 	.read		= generic_read_dir,
@@ -2916,15 +2923,16 @@ static struct inode_operations btrfs_file_inode_operations = {
 	.getxattr	= generic_getxattr,
 	.listxattr      = btrfs_listxattr,
 	.removexattr	= generic_removexattr,
+	.permission	= btrfs_permission,
 };
-
 static struct inode_operations btrfs_special_inode_operations = {
 	.getattr	= btrfs_getattr,
 	.setattr	= btrfs_setattr,
+	.permission	= btrfs_permission,
 };
-
 static struct inode_operations btrfs_symlink_inode_operations = {
 	.readlink	= generic_readlink,
 	.follow_link	= page_follow_link_light,
 	.put_link	= page_put_link,
+	.permission	= btrfs_permission,
 };