-------- Original Message --------
Subject: Re: [PATCH v2] btrfs: Return right extent when fiemap gives
unaligned offset and len.
From: Satoru Takeuchi <takeuchi_sat...@jp.fujitsu.com>
To: Qu Wenruo <quwen...@cn.fujitsu.com>, <linux-btrfs@vger.kernel.org>
Date: 2014年07月25日 15:52
Hi Qu,
(2014/07/25 10:49), Qu Wenruo wrote:
When page aligned start and len passed to extent_fiemap(), the result is
good, but when start and len is not aligned, e.g. start = 1 and len =
4095 is passed to extent_fiemap(), it returns no extent.
The problem is that start and len is all rounded up which causes the
problem. This patch will round down start and round up (start + len) to
return right extent.
Reported-by: Chandan Rajendra <chan...@linux.vnet.ibm.com>
Signed-off-by: Qu Wenruo <quwen...@cn.fujitsu.com>
---
changelog:
v2: reword the description(ALIGN rounds up, not rounds down).
---
fs/btrfs/extent_io.c | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)
diff --git a/fs/btrfs/extent_io.c b/fs/btrfs/extent_io.c
index a389820..1c70cff 100644
--- a/fs/btrfs/extent_io.c
+++ b/fs/btrfs/extent_io.c
@@ -4213,8 +4213,8 @@ int extent_fiemap(struct inode *inode, struct
fiemap_extent_info *fieinfo,
return -ENOMEM;
path->leave_spinning = 1;
- start = ALIGN(start, BTRFS_I(inode)->root->sectorsize);
- len = ALIGN(len, BTRFS_I(inode)->root->sectorsize);
+ start = round_down(start, BTRFS_I(inode)->root->sectorsize);
+ len = round_up(max, BTRFS_I(inode)->root->sectorsize) - start;
I have one question.
Why isn't it "len = round_up(len, BTRFS_I(inode)->root->sectorsize);" ?
Old behavior make len sectorsize aligned. However, if start is not
aligned to sectorsize, new bahavior make len not sectorsize aligned.
Does it an expected behavior?
In fact, in my code, len is also aligned.
The calculation is somewhat easy, round_down original 'start' and
round_up original end(in the code, max is original
unaligned end position),
then calculate 'len' by minus aligned end with aligned 'start'.
Since the *new* 'start' is already aligned and the new end is aligned,
the len will also be aligned.
Thanks,
Qu
CMIIW. I'm not good at extent code.
Thanks,
Satoru
/*
* lookup the last file extent. We're not using i_size here
--
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