max_to_defrag represents the number of pages to defrag rather than the last page of the file range to be defragged. Consider a file having 10 4k blocks (i.e. blocks in the range [0 - 9]). If the defrag ioctl was invoked for the block range [3 - 6], then max_to_defrag should actually have the value 4. Instead in the current code we end up setting it to 6. Now, this does not (yet) cause an issue since the first part of the while loop condition in btrfs_defrag_file() (i.e. "i <= last_index") causes the control to flow out of the while loop before any buggy behavior is actually caused. So the patch just makes sure that max_to_defrag ends up having the right value rather than fixing a bug. I did run the xfstests suite to make sure that the code does not regress. Changelog: v1->v2: Provide a much descriptive commit message. Signed-off-by: Chandan Rajendra <chandan@xxxxxxxxxxxxxxxxxx> --- fs/btrfs/ioctl.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/fs/btrfs/ioctl.c b/fs/btrfs/ioctl.c index ca5d968..2a45026 100644 --- a/fs/btrfs/ioctl.c +++ b/fs/btrfs/ioctl.c @@ -1318,7 +1318,7 @@ int btrfs_defrag_file(struct inode *inode, struct file *file, i = range->start >> PAGE_CACHE_SHIFT; } if (!max_to_defrag) - max_to_defrag = last_index + 1; + max_to_defrag = last_index - i + 1; /* * make writeback starts from i, so the defrag range can be -- 2.1.0 -- To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
