linux-kernel - Re: [PATCH] Fix generic_block_fiemap for files bigger than 4GB

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Date:	Wed, 28 Oct 2009 23:00:22 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Mike Hommey <mh@...ndium.org>
Cc:	Alexander Viro <viro@...iv.linux.org.uk>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	linux-kernel@...r.kernel.org,
	Steven Whitehouse <swhiteho@...hat.com>,
	"Theodore Ts'o" <tytso@....edu>, Eric Sandeen <sandeen@....com>,
	Josef Bacik <jbacik@...hat.com>, Mark Fasheh <mfasheh@...e.com>
Subject: Re: [PATCH] Fix generic_block_fiemap for files bigger than 4GB

On Mon, 26 Oct 2009 18:24:28 +0100 Mike Hommey <mh@...ndium.org> wrote:

> Because of an integer overflow on start_blk, various kind of wrong results
> would be returned by the generic_block_fiemap handler, such as no extents
> when there is a 4GB+ hole at the beginning of the file, or wrong fe_logical
> when an extent starts after the first 4GB.
> 
> Signed-off-by: Mike Hommey <mh@...ndium.org>
> ---
>  fs/ioctl.c |    2 +-
>  1 files changed, 1 insertions(+), 1 deletions(-)
> 
> diff --git a/fs/ioctl.c b/fs/ioctl.c
> index 7b17a14..6c75110 100644
> --- a/fs/ioctl.c
> +++ b/fs/ioctl.c
> @@ -254,7 +254,7 @@ int __generic_block_fiemap(struct inode *inode,
>  			   u64 len, get_block_t *get_block)
>  {
>  	struct buffer_head tmp;
> -	unsigned int start_blk;
> +	unsigned long long start_blk;
>  	long long length = 0, map_len = 0;
>  	u64 logical = 0, phys = 0, size = 0;
>  	u32 flags = FIEMAP_EXTENT_MERGED;

Well.  Should it be unsigned long long, or u64 or sector_t?  Or even loff_t.

The code's a bit confused about types in there.  And it's made much
more confusing by the moronic and wholly unnecessary use of macros for
blk_to_logical() and logical_to_blk().

It's also unhelpful that the `u64 start' argument forgot to get itself
documented in the kerneldoc comment.  Sigh.

Ah, generic_block_fiemap() has it:

 * @start: The initial block to map

I guess u64 was logical there as it comes in from userspace.  But at
some boundary we should start talking kernel types so I suspect the
correct thing to do here is to use sector_t?

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