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SubjectRe: [PATCH] Initial support for struct vfs_cred [0/1]
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>>>>> " " == Luca Barbieri <ldb@ldb.ods.org> writes:

> And, in the common case of open, why do you need to copy the
> structure to check permissions? I think that open should just
> check the current values. open might want to copy credentials

Because, as has been explained to you, we have things like Coda,
Intermezzo, NFS, for which this is insufficient.

> in case you want to do the inode lookup asynchronously but then
> it doesn't make sense to optimize for this since you already
> have the huge disk read penalty. BTW, the 2.5.32 open does the
> check in vfs_permission without copying anything. Anyway it's
> just a 3 long copy plus an atomic inc vs. 1 long copy and
> atomic inc. And if you don't need the groups array, it's just
> a 2 longs copy that on some architectures with very slow atomic
> operations (e.g. sparc) is much better.

But we we do need to check the groups array in the VFS. And as Linus
pointed out, there is a good case for passing info from the
user_struct too (crypto), etc...

Cheers,
Trond
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