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Date: Sun, 1 Sep 2002 00:30:23 +0200
To: Luca Barbieri <ldb@ldb.ods.org>
Cc: Linus Torvalds <torvalds@transmeta.com>,
       Linux FSdevel <linux-fsdevel@vger.kernel.org>,
       Linux Kernel <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH] Initial support for struct vfs_cred   [0/1]
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From: Trond Myklebust <trond.myklebust@fys.uio.no>
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>>>>> " " == Luca Barbieri <ldb@ldb.ods.org> writes:

     > Then the rest of the code doesn't need to know at all that
     > credentials are shared and is simpler and faster.  We have
     > however a larger penalty on credential change but, as you say,
     > that's extremely rare (well, perhaps not necessarily extremely,
     > but still rare).

What if I, in a fit of madness/perversion, decide to use CLONE_CRED
between 2 kernel threads (i.e. no 'kernel entry')?


Leaving CLONE_CRED aside, please do not forget that most of the
motivation for vfs_cred is the need to *cache* credentials.
This is something which we already do today in several filesystems:
Coda, Intermezzo, NFS, to name but the most obvious.
The result of the lack of a VFS-sanctioned credential is that we have
to use 'struct file' as a vehicle for passing credentials in, for
instance, the address_space_operations, and that each filesystem ends
up having to keep its own private copies of those credentials in
file->private_data.

Cheers,
  Trond
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