Patchwork ext4: correctly calculate number of blocks for fiemap

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Submitter Surbhi Palande
Date April 1, 2010, 8:30 a.m.
Message ID <1270110626-5018-1-git-send-email-surbhi.palande@canonical.com>
Download mbox | patch
Permalink /patch/49197/
State Superseded
Delegated to: Andy Whitcroft
Headers show

Comments

Surbhi Palande - April 1, 2010, 8:30 a.m.
The following cherry-picked patch fixes the calculation of extents in fiemap.
The commit id in the upstream code is: aca92ff6f57c000d1b4523e383c8bd6b8269b8b1
This patch fixes bug 474597 on LP. Do consider merging this in Lucid.

From dfaa33f0502a8bf9dff0e596783a40ce330c7a9b Mon Sep 17 00:00:00 2001
From: Leonard Michlmayr <leonard.michlmayr@gmail.com>
Date: Thu, 4 Mar 2010 17:07:28 -0500
Subject: [PATCH] ext4: correctly calculate number of blocks for fiemap

http://launchpad.net/bugs/474597

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@gmail.com>
Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>
(cherry picked from commit aca92ff6f57c000d1b4523e383c8bd6b8269b8b1)

Signed-off-by: Surbhi Palande <surbhi.palande@canonical.com>
---
 fs/ext4/extents.c |    9 +++++++--
 1 files changed, 7 insertions(+), 2 deletions(-)
Stefan Bader - April 1, 2010, 8:55 a.m.
Surbhi Palande wrote:
> The following cherry-picked patch fixes the calculation of extents in fiemap.
> The commit id in the upstream code is: aca92ff6f57c000d1b4523e383c8bd6b8269b8b1
> This patch fixes bug 474597 on LP. Do consider merging this in Lucid.

Surbhi,

it would be better to give a quick summary about what the symptom of it is and
how the fix affects it here. Saves us going to LP and read through it. ;-)

> From dfaa33f0502a8bf9dff0e596783a40ce330c7a9b Mon Sep 17 00:00:00 2001
> From: Leonard Michlmayr <leonard.michlmayr@gmail.com>
> Date: Thu, 4 Mar 2010 17:07:28 -0500
> Subject: [PATCH] ext4: correctly calculate number of blocks for fiemap
> 
> http://launchpad.net/bugs/474597
BugLink: ...
> 
> 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@gmail.com>
> Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>
> (cherry picked from commit aca92ff6f57c000d1b4523e383c8bd6b8269b8b1)
(... upstream)
> Signed-off-by: Surbhi Palande <surbhi.palande@canonical.com>
> ---
>  fs/ext4/extents.c |    9 +++++++--
>  1 files changed, 7 insertions(+), 2 deletions(-)
> 
> diff --git a/fs/ext4/extents.c b/fs/ext4/extents.c
> index 8b8bae4..f199d20 100644
> --- a/fs/ext4/extents.c
> +++ b/fs/ext4/extents.c
> @@ -3711,7 +3711,6 @@ 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 */
> @@ -3725,8 +3724,14 @@ 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 len_blks;
> +		__u64 last_blk;
> +
>  		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;
> +		if (last_blk >= EXT_MAX_BLOCK)
> +			last_blk = EXT_MAX_BLOCK-1;
> +		len_blks = ((ext4_lblk_t) last_blk) - start_blk + 1;
>  
>  		/*
>  		 * Walk the extent tree gathering extent information.
Andy Whitcroft - April 22, 2010, 5:54 p.m.
On Thu, Apr 01, 2010 at 11:30:26AM +0300, Surbhi Palande wrote:
> The following cherry-picked patch fixes the calculation of extents in fiemap.
> The commit id in the upstream code is: aca92ff6f57c000d1b4523e383c8bd6b8269b8b1
> This patch fixes bug 474597 on LP. Do consider merging this in Lucid.
> 
> From dfaa33f0502a8bf9dff0e596783a40ce330c7a9b Mon Sep 17 00:00:00 2001
> From: Leonard Michlmayr <leonard.michlmayr@gmail.com>
> Date: Thu, 4 Mar 2010 17:07:28 -0500
> Subject: [PATCH] ext4: correctly calculate number of blocks for fiemap
> 
> http://launchpad.net/bugs/474597
> 
> 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@gmail.com>
> Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>
> (cherry picked from commit aca92ff6f57c000d1b4523e383c8bd6b8269b8b1)
> 
> Signed-off-by: Surbhi Palande <surbhi.palande@canonical.com>
> ---
>  fs/ext4/extents.c |    9 +++++++--
>  1 files changed, 7 insertions(+), 2 deletions(-)
> 
> diff --git a/fs/ext4/extents.c b/fs/ext4/extents.c
> index 8b8bae4..f199d20 100644
> --- a/fs/ext4/extents.c
> +++ b/fs/ext4/extents.c
> @@ -3711,7 +3711,6 @@ 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 */
> @@ -3725,8 +3724,14 @@ 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 len_blks;
> +		__u64 last_blk;
> +
>  		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;
> +		if (last_blk >= EXT_MAX_BLOCK)
> +			last_blk = EXT_MAX_BLOCK-1;
> +		len_blks = ((ext4_lblk_t) last_blk) - start_blk + 1;
>  
>  		/*
>  		 * Walk the extent tree gathering extent information.

Ok that seems ok.

Acked-by: Andy Whitcroft <apw@canonical.com>

-apw

Patch

diff --git a/fs/ext4/extents.c b/fs/ext4/extents.c
index 8b8bae4..f199d20 100644
--- a/fs/ext4/extents.c
+++ b/fs/ext4/extents.c
@@ -3711,7 +3711,6 @@  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 */
@@ -3725,8 +3724,14 @@  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 len_blks;
+		__u64 last_blk;
+
 		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;
+		if (last_blk >= EXT_MAX_BLOCK)
+			last_blk = EXT_MAX_BLOCK-1;
+		len_blks = ((ext4_lblk_t) last_blk) - start_blk + 1;
 
 		/*
 		 * Walk the extent tree gathering extent information.