From 070034bdf98544b23a7fcf500618fd31dec06ab2 Mon Sep 17 00:00:00 2001 From: chandan Date: Tue, 9 Jun 2015 10:35:11 +0530 Subject: [PATCH] Btrfs: btrfs_defrag_file: Fix calculation of max_to_defrag. 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 Signed-off-by: Chris Mason --- 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 25c422b11bdb..9041f154cc32 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 -- 2.30.2