linux-kernel - Re: [PATCH 00/17] [RFC] AFS: Implement OpenAFS pioctls(version)s

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Message-ID: <11650.1245198358@redhat.com>
Date:	Wed, 17 Jun 2009 01:25:58 +0100
From:	David Howells <dhowells@...hat.com>
To:	Alan Cox <alan@...rguk.ukuu.org.uk>
Cc:	dhowells@...hat.com, torvalds@...l.org, akpm@...ux-foundation.org,
	linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-afs@...ts.infradead.org
Subject: Re: [PATCH 00/17] [RFC] AFS: Implement OpenAFS pioctls(version)s

Alan Cox <alan@...rguk.ukuu.org.uk> wrote:

> But if we add an ABI we end up stuck with it and this one is really
> really rather ugly.

Somewhat less ugly than ioctl, for instance, but you're not entirely wrong.
There is no good way of doing this.

> Can you not put pioctl() into a C library linked with the openafs utilities
> that generates more sensible interface calls?  I mean you have to produce
> the pioctl() syscall wrapper anyway so why not make "pioctl" a user space
> compat library?

pioctl() is almost implementable with a combination of (l)setxattr,
(l)getxattr, set_key, keyctl_read, and if all else fails, open + ioctl or
open(O_NOFOLLOW) + ioctl, but not quite completely.  There are things you can't
open, even with O_NOFOLLOW.  And doing state-retaining setxattr/getxattr pairs
is even more nasty than pioctl (IIRC, that's something Christoph suggested a
while back).

Besides, I want a set of utilities that I can use in conjunction with both kAFS
and OpenAFS without having to recompile.

David
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