Re: kernel patch support large fat partitions

From: Vijay Kumar (
Date: Thu Jan 03 2002 - 19:34:21 EST

At 05:24 PM 1/3/2002 -0700, Andreas Dilger wrote:
>On Jan 03, 2002 15:42 -0800, Vijay Kumar wrote:
> > This limitation is imposed by the data structures used by the linux fat
> > implementation to read/write directory entries. A 'long' data type is used
> > to access directory entries on the disk, of which only 28 bits are used to
> > identify the sector that contains the directory entry and the rest 4 bits
> > are used to specify offset of the directory entry inside the sector. Using
> > 28 bits to identify a sector means we cannot access sectors beyond 128GB
> > (2^28*512), thus limiting us from creating partitions larger than 128GB on
> > large disk drives.
>Some minor notes on your patch:
>1) It appears you are running an editor with 4-space tabs, and as a result
> it has broken the indentation of some of your changes. This is easily
> seen when looking at the patch.

Well, I could fix it with little effort.

>2) It is almost certainly wrong to use "loff_t" for an inode number. Maybe
> you could use "u64" instead? I also think that using "long long"
> explicitly is frowned upon.

I guess its using u64 verses using loff_t. I have chosen the later because
its actually an offset. For fat implementations inode number is nothing but
offset of the directory entry on the disk. So I thought it makes more sense
to use loff_t.

> > I have made changes to fat, vfat and msdos file system implementations in
> > the kernel to use larger data types, thus allowing us to create larger
> > partitions. As per the GPL I would like to make the patch available to
> > everyone and also in case somebody has run into the same problem(who cares
> > about fat in the linux world). The patch has been fairly well tested only
> > on our systems(p3, 700MHz with FC). I truly appreciate if you & anybody in
> > the kernel mailing list have any feedback about the changes.
>Does this change the on-disk format for FAT at all, or is it merely a
>kernel filesystem code issue? I think only the latter, but best to check.

Doesn't change on disk format, only fixes implementation.

- Vijay

>Cheers, Andreas
>Andreas Dilger

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