Re: [PATCH] fix ext3 mounts at 16T

On Aug 11, 2006  15:29 -0700, Mingming Cao wrote:
> On Fri, 2006-08-11 at 17:13 -0500, Eric Sandeen wrote:
> > I figure before we get too fired up about 48 bits and ext4 let's fix 32 bits on ext3 :)
> > 
> > I need to do some actual IO testing now, but this gets things mounting for a 16T ext3 filesystem.
> > (patched up e2fsprogs is needed too, I'll send that off the kernel list)
> > 
> > This patch fixes these issues in the kernel:
> > 
> > o sbi->s_groups_count overflows in ext3_fill_super()
> > 
> > 	sbi->s_groups_count = (le32_to_cpu(es->s_blocks_count) -
> > 			       le32_to_cpu(es->s_first_data_block) +
> > 			       EXT3_BLOCKS_PER_GROUP(sb) - 1) /
> > 			      EXT3_BLOCKS_PER_GROUP(sb);
> > 
> > at 16T, s_blocks_count is already maxed out; adding EXT3_BLOCKS_PER_GROUP(sb) overflows it and 
> > groups_count comes out to 0.  Not really what we want, and causes a failed mount.
> > 
> > Feel free to check my math (actually, please do!), but changing it this way should work & 
> > avoid the overflow:
> > 
> > (A + B - 1)/B changed to: ((A - 1)/B) + 1
> > 
> > o ext3_check_descriptors() overflows range checks

This is generally not safe because of underflow, but it also isn't possible
to have a 0-block filesystem so it should be OK.

Cheers, Andreas
--
Andreas Dilger
Principal Software Engineer
Cluster File Systems, Inc.


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