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SubjectRe: dcache problems with vfat


On Wed, 6 Jan 1999, Gordon Chaffee wrote:
>
> You run into inconsistency problems with vfat aliases. You could
> be accessing a path two ways:

UMSDOS handles this by being careful about never allowing aliases, and
thus avoiding the problem completely.

One way of avoiding aliases is roughly:
- when you do a lookup, you check (after the lookup is basically
complete) whether the same parent has another dentry pointing to the
same file.
- if there is another dentry, you:
- unhash that other dentry if it has no other users, essentially
replacing it with the new one you just looked up.
- if the older dentry already had users, you instead drop the new
one and return the old dentry instead (which is the same file,
just aliased).

The above has two problems:
- the current VFS dentry code won't allow you to return any dentry but
the one it allocated for you. That shouldn't be horribly hard to
change.
- it's inefficient for the case where somebody actually uses both
names interchangably - one of them simply will not be cached at all.

I don't think either problem should be all that big, but..

Linus


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