Re: [PATCH] Initial support for struct vfs_cred [0/1]

[Trond Myklebust <trond.myklebust@fys.uio.no>]

>>>>> " " == 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