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Date: Wed, 03 Mar 2010 16:47:28 +0900
From: Akira Fujita <a-fujita@...jp.nec.com>
To: "Theodore Ts'o" <tytso@....edu>,
Leonard Michlmayr <leonard.michlmayr@...il.com>
CC: Ext4 Developers List <linux-ext4@...r.kernel.org>
Subject: Re: [PATCH 11/28] ext4: correctly calculate number of blocks for
fiemap
Hi,
> From: Leonard Michlmayr<leonard.michlmayr@...il.com>
>
> ext4_fiemap() rounds the length of the requested range down to
> blocksize, which is is not the true number of blocks that cover the
> requested region. This problem is especially impressive if the user
> requests only the first byte of a file: not a single extent will be
> reported.
<snip>
> start_blk = start>> inode->i_sb->s_blocksize_bits;
> - len_blks = len>> inode->i_sb->s_blocksize_bits;
> + last_blk = (start + len - 1)>> inode->i_sb->s_blocksize_bits;
> + len_blks = last_blk - start_blk + 1;
In 1KB block size, the overflow occurs at above line.
Since last_blk is set 0xffffffff when len is equal to s_maxbytes.
Therefore ext4_fiemap() can not get correct extent information
with 0 length. How about adding this change?
Signed-off-by: Akira Fujita <a-fujita@...jp.nec.com>
---
extents.c | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)
--- linux-2.6.33-rc8-a/fs/ext4/extents.c 2010-03-03 14:53:49.000000000 +0900
+++ linux-2.6.33-rc8-b/fs/ext4/extents.c 2010-03-03 15:31:57.000000000 +0900
@@ -3912,7 +3912,8 @@ int ext4_fiemap(struct inode *inode, str
start_blk = start >> inode->i_sb->s_blocksize_bits;
last_blk = (start + len - 1) >> inode->i_sb->s_blocksize_bits;
- len_blks = last_blk - start_blk + 1;
+ len_blks = (loff_t)last_blk - start_blk + 1 < EXT_MAX_BLOCK ?
+ last_blk - start_blk + 1 : EXT_MAX_BLOCK;
/*
* Walk the extent tree gathering extent information.
(2010/03/03 3:18), Theodore Ts'o wrote:
> From: Leonard Michlmayr<leonard.michlmayr@...il.com>
>
> ext4_fiemap() rounds the length of the requested range down to
> blocksize, which is is not the true number of blocks that cover the
> requested region. This problem is especially impressive if the user
> requests only the first byte of a file: not a single extent will be
> reported.
>
> We fix this by calculating the last block of the region and then
> subtract to find the number of blocks in the extents.
>
> Signed-off-by: Leonard Michlmayr<leonard.michlmayr@...il.com>
> Signed-off-by: "Theodore Ts'o"<tytso@....edu>
> ---
> fs/ext4/extents.c | 6 ++++--
> 1 files changed, 4 insertions(+), 2 deletions(-)
>
> diff --git a/fs/ext4/extents.c b/fs/ext4/extents.c
> index bd80891..bc9860f 100644
> --- a/fs/ext4/extents.c
> +++ b/fs/ext4/extents.c
> @@ -3768,7 +3768,6 @@ int ext4_fiemap(struct inode *inode, struct fiemap_extent_info *fieinfo,
> __u64 start, __u64 len)
> {
> ext4_lblk_t start_blk;
> - ext4_lblk_t len_blks;
> int error = 0;
>
> /* fallback to generic here if not in extents fmt */
> @@ -3782,8 +3781,11 @@ int ext4_fiemap(struct inode *inode, struct fiemap_extent_info *fieinfo,
> if (fieinfo->fi_flags& FIEMAP_FLAG_XATTR) {
> error = ext4_xattr_fiemap(inode, fieinfo);
> } else {
> + ext4_lblk_t last_blk, len_blks;
> +
> start_blk = start>> inode->i_sb->s_blocksize_bits;
> - len_blks = len>> inode->i_sb->s_blocksize_bits;
> + last_blk = (start + len - 1)>> inode->i_sb->s_blocksize_bits;
> + len_blks = last_blk - start_blk + 1;
>
> /*
> * Walk the extent tree gathering extent information.
--
Akira Fujita <a-fujita@...jp.nec.com>
The First Fundamental Software Development Group,
Software Development Division,
NEC Software Tohoku, Ltd.
--Separator@...ujita@...jp.nec.com:
--
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