ext4: minor defrag code improvements

Modify the error returns for two file types that can't be defragged to
more clearly communicate those restrictions to a caller.  When the
defrag code is applied to swap files, return -ETXTBSY, and when applied
to quota files, return -EOPNOTSUPP.  Move an extent tree search whose
results are only occasionally required to the site always requiring them
for improved efficiency.  Address a few typos.
Signed-off-by: Eric Whitney <enwlinux@gmail.com>
Link: https://lore.kernel.org/r/20220722163910.268564-1-enwlinux@gmail.comSigned-off-by: Theodore Ts'o <tytso@mit.edu>

fs/ext4/move_extent.c

@@ -472,19 +472,17 @@ mext_check_arguments(struct inode *orig_inode,
 	if (IS_IMMUTABLE(donor_inode) || IS_APPEND(donor_inode))
 		return -EPERM;
 
-	/* Ext4 move extent does not support swapfile */
+	/* Ext4 move extent does not support swap files */
 	if (IS_SWAPFILE(orig_inode) || IS_SWAPFILE(donor_inode)) {
-		ext4_debug("ext4 move extent: The argument files should "
-			"not be swapfile [ino:orig %lu, donor %lu]\n",
+		ext4_debug("ext4 move extent: The argument files should not be swap files [ino:orig %lu, donor %lu]\n",
 			orig_inode->i_ino, donor_inode->i_ino);
-		return -EBUSY;
+		return -ETXTBSY;
 	}
 
 	if (ext4_is_quota_file(orig_inode) && ext4_is_quota_file(donor_inode)) {
-		ext4_debug("ext4 move extent: The argument files should "
-			"not be quota files [ino:orig %lu, donor %lu]\n",
+		ext4_debug("ext4 move extent: The argument files should not be quota files [ino:orig %lu, donor %lu]\n",
 			orig_inode->i_ino, donor_inode->i_ino);
-		return -EBUSY;
+		return -EOPNOTSUPP;
 	}
 
 	/* Ext4 move extent supports only extent based file */
@@ -631,11 +629,11 @@ ext4_move_extents(struct file *o_filp, struct file *d_filp, __u64 orig_blk,
 		if (ret)
 			goto out;
 		ex = path[path->p_depth].p_ext;
-		next_blk = ext4_ext_next_allocated_block(path);
 		cur_blk = le32_to_cpu(ex->ee_block);
 		cur_len = ext4_ext_get_actual_len(ex);
 		/* Check hole before the start pos */
 		if (cur_blk + cur_len - 1 < o_start) {
+			next_blk = ext4_ext_next_allocated_block(path);
 			if (next_blk == EXT_MAX_BLOCKS) {
 				ret = -ENODATA;
 				goto out;
@@ -663,7 +661,7 @@ ext4_move_extents(struct file *o_filp, struct file *d_filp, __u64 orig_blk,
 		donor_page_index = d_start >> (PAGE_SHIFT -
 					       donor_inode->i_blkbits);
 		offset_in_page = o_start % blocks_per_page;
-		if (cur_len > blocks_per_page- offset_in_page)
+		if (cur_len > blocks_per_page - offset_in_page)
 			cur_len = blocks_per_page - offset_in_page;
 		/*
 		 * Up semaphore to avoid following problems: