> A while ago I initiated a thread about mounting a NTFS partition as FAT
> partition. The problem is that FAT partitions do not have a real
> fingerprint, so the FAT driver mounts almost anything.
>
> The current 2.5 driver only tests if some values in the bootsector are
> non-zero. IMHO, this is not strict enough. For example, the number of FATs
> is always 1 or 2 (anyone ever seen more ?). Besides, when there are two
> FATs, all entries in those FATs should be equal. If they are not, we deal
> with a non-FAT or broken FAT partition, and we should not mount.
>
> It's not a real fingerprint, but what are the chances all sectors of what
> we think is the FAT are equal on non-FAT filesystems ? Yes, when you just
> did a
>
> dd if=/dev/zero of=/dev/partition; mkfs.somefs /dev/partition
>
> there is a chance, but that's an empty filesystem. Data corruption isn't
> that bad on an empty disk. We know that a FAT is at the beginning of a
> partition and I assume that any other filesystem will fill up those first
> sectors very soon.
>
> Questions:
>
> 1) How do you think about the checking of the FAT tables ? It definitely
> will slow down the mount.
Reading FATs is very fast, and they are probably going to be needed,
anyway. I guess its okay.
> 2) If I implement it, where shoud it go ? At the moment, I hacked
> fat_read_super, for there the FAT fs is validated, but I got the
> feeling this is not the place to be.
> 3) Anyone seen more than two FATs on a filesystem ? Can I assume there is
> a limit ?
No. I think you can only have two.
Pavel
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