ext4: support simple conversion of extent-mapped inodes to use i_blocks

In order to make it simpler to test the code which support
i_blocks/indirect-mapped inodes, support the conversion of inodes
which are less than 12 blocks and which are contained in no more than
a single extent.

The primary intended use of this code is to converting freshly created
zero-length files and empty directories.

Note that the version of chattr in e2fsprogs 1.42.7 and earlier has a
check that prevents the clearing of the extent flag.  A simple patch
which allows "chattr -e <file>" to work will be checked into the
e2fsprogs git repository.
Signed-off-by: N"Theodore Ts'o" <tytso@mit.edu>

fs/ext4/ext4.h

@@ -403,7 +403,7 @@ struct flex_groups {
 #define EXT4_RESERVED_FL		0x80000000 /* reserved for ext4 lib */
 
 #define EXT4_FL_USER_VISIBLE		0x004BDFFF /* User visible flags */
-#define EXT4_FL_USER_MODIFIABLE		0x004B80FF /* User modifiable flags */
+#define EXT4_FL_USER_MODIFIABLE		0x004380FF /* User modifiable flags */
 
 /* Flags that should be inherited by new inodes from their parent. */
 #define EXT4_FL_INHERITED (EXT4_SECRM_FL | EXT4_UNRM_FL | EXT4_COMPR_FL |\
@@ -2608,6 +2608,7 @@ extern int ext4_find_delalloc_range(struct inode *inode,
 extern int ext4_find_delalloc_cluster(struct inode *inode, ext4_lblk_t lblk);
 extern int ext4_fiemap(struct inode *inode, struct fiemap_extent_info *fieinfo,
 			__u64 start, __u64 len);
+extern int ext4_ind_migrate(struct inode *inode);
 
 
 /* move_extent.c */

fs/ext4/extents.c

@@ -4610,3 +4610,62 @@ int ext4_fiemap(struct inode *inode, struct fiemap_extent_info *fieinfo,
 
 	return error;
 }
+
+/*
+ * Migrate a simple extent-based inode to use the i_blocks[] array
+ */
+int ext4_ind_migrate(struct inode *inode)
+{
+	struct ext4_extent_header	*eh;
+	struct ext4_super_block		*es = EXT4_SB(inode->i_sb)->s_es;
+	struct ext4_inode_info		*ei = EXT4_I(inode);
+	struct ext4_extent		*ex;
+	unsigned int			i, len;
+	ext4_fsblk_t			blk;
+	handle_t			*handle;
+	int				ret;
+
+	if (!EXT4_HAS_INCOMPAT_FEATURE(inode->i_sb,
+				       EXT4_FEATURE_INCOMPAT_EXTENTS) ||
+	    (!ext4_test_inode_flag(inode, EXT4_INODE_EXTENTS)))
+		return -EINVAL;
+
+	down_write(&EXT4_I(inode)->i_data_sem);
+	ret = ext4_ext_check_inode(inode);
+	if (ret)
+		goto errout;
+
+	eh = ext_inode_hdr(inode);
+	ex  = EXT_FIRST_EXTENT(eh);
+	if (ext4_blocks_count(es) > EXT4_MAX_BLOCK_FILE_PHYS ||
+	    eh->eh_depth != 0 || eh->eh_entries > 1) {
+		ret = -EOPNOTSUPP;
+		goto errout;
+	}
+	if (eh->eh_entries == 0)
+		blk = len = 0;
+	else {
+		len = le16_to_cpu(ex->ee_len);
+		blk = ext4_ext_pblock(ex);
+		if (len > EXT4_NDIR_BLOCKS) {
+			ret = -EOPNOTSUPP;
+			goto errout;
+		}
+	}
+
+	handle = ext4_journal_start(inode, EXT4_HT_MIGRATE, 1);
+	if (IS_ERR(handle)) {
+		ret = PTR_ERR(handle);
+		goto errout;
+	}
+
+	ext4_clear_inode_flag(inode, EXT4_INODE_EXTENTS);
+	memset(ei->i_data, 0, sizeof(ei->i_data));
+	for (i=0; i < len; i++)
+		ei->i_data[i] = cpu_to_le32(blk++);
+	ext4_mark_inode_dirty(handle, inode);
+	ext4_journal_stop(handle);
+errout:
+	up_write(&EXT4_I(inode)->i_data_sem);
+	return ret;
+}

fs/ext4/ioctl.c

@@ -83,17 +83,8 @@ long ext4_ioctl(struct file *filp, unsigned int cmd, unsigned long arg)
 			if (!capable(CAP_SYS_RESOURCE))
 				goto flags_out;
 		}
-		if (oldflags & EXT4_EXTENTS_FL) {
-			/* We don't support clearning extent flags */
-			if (!(flags & EXT4_EXTENTS_FL)) {
-				err = -EOPNOTSUPP;
-				goto flags_out;
-			}
-		} else if (flags & EXT4_EXTENTS_FL) {
-			/* migrate the file */
+		if ((flags ^ oldflags) & EXT4_EXTENTS_FL)
 			migrate = 1;
-			flags &= ~EXT4_EXTENTS_FL;
-		}
 
 		if (flags & EXT4_EOFBLOCKS_FL) {
 			/* we don't support adding EOFBLOCKS flag */
@@ -137,8 +128,13 @@ long ext4_ioctl(struct file *filp, unsigned int cmd, unsigned long arg)
 			err = ext4_change_inode_journal_flag(inode, jflag);
 		if (err)
 			goto flags_out;
-		if (migrate)
-			err = ext4_ext_migrate(inode);
+		if (migrate) {
+			if (flags & EXT4_EXTENTS_FL)
+				err = ext4_ext_migrate(inode);
+			else
+				err = ext4_ind_migrate(inode);
+		}
+
 flags_out:
 		mutex_unlock(&inode->i_mutex);
 		mnt_drop_write_file(filp);