Re: incorrect handling of holes in ext2 files

[Jason Thomas]

This fix looks fine to me. Anyone see a problem? If not I'll upload it!

On Thu, Aug 05, 2004 at 02:41:57PM -0700, Michael Hohnbaum wrote:
> Grub is not correctly handling holes in files in ext2 filesystems.
> The current code in stage2/fsys_ext2fs.c does not check upon
> return from ext2fs_block_map() if a zero was returned.  Rather,
> it happily reads in block zero from the filesystem.  Most of
> the time this works alright as block 0 tends to be sparsely
> populated.  However, it does not contain all zeroes and the 
> extra bits can lead to problems.  
> 
> This problem goes away with reiserfs.  I've not tried other filesystems.
> 
> I've ran into this problem on multiple machines with various versions
> of Linux including:
>   P3 based machines with RedHat 8, SuSE SLES 9, Fedora Core 1
>   P4 based machine with Debian
>   Athlon64 machine with Fedora Core 2
> 
> Grub versions have included 0.92 and 0.95.
> 
> The following patch against 0.95 solves this problem.  Any chance this,
> or something similar can be applied for the next release?
> 
> --- grub-0.95.orig/stage2/fsys_ext2fs.c 2003-12-30 04:34:03.000000000
> -0800
> +++ grub-0.95/stage2/fsys_ext2fs.c      2004-08-05 13:37:07.000000000
> -0700
> @@ -432,12 +432,16 @@
>        if (size > len)
>         size = len;
> 
> -      disk_read_func = disk_read_hook;
> +      if ( map == 0 ) {
> +       memset ((char *) buf, 0, size);
> +      } else {
> +       disk_read_func = disk_read_hook;
> 
> -      devread (map * (EXT2_BLOCK_SIZE (SUPERBLOCK) / DEV_BSIZE),
> +       devread (map * (EXT2_BLOCK_SIZE (SUPERBLOCK) / DEV_BSIZE),
>                offset, size, buf);
> 
> -      disk_read_func = NULL;
> +       disk_read_func = NULL;
> +      }
> 
>        buf += size;
>        len -= size;
> 
> 
> -- 
> 
> Michael Hohnbaum                      503-578-5486
> address@hidden                   T/L 775-5486
> 
> 
> 
> 
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-- 
Jason Thomas
Linux System Administrator
Planet Netcom P/L

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