linux-kernel - Re: [PATCH 3/3] p9auth: add p9auth driver

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Date:	Sat, 24 Apr 2010 09:25:08 -0700
From:	ron minnich <rminnich@...il.com>
To:	"Serge E. Hallyn" <serue@...ibm.com>
Cc:	"Eric W. Biederman" <ebiederm@...ssion.com>,
	Greg KH <greg@...ah.com>, lkml <linux-kernel@...r.kernel.org>,
	David Howells <dhowells@...hat.com>,
	Ashwin Ganti <ashwin.ganti@...il.com>, rsc@...ch.com,
	ericvh@...il.com, linux-security-module@...r.kernel.org,
	jt.beard@...il.com, Andrew Morton <akpm@...ux-foundation.org>,
	Andrew Morgan <morgan@...nel.org>, oleg@...ibm.com,
	Eric Paris <eparis@...hat.com>, linux-api@...r.kernel.org,
	Randy Dunlap <rdunlap@...otime.net>
Subject: Re: [PATCH 3/3] p9auth: add p9auth driver

On Fri, Apr 23, 2010 at 8:36 PM, Serge E. Hallyn <serue@...ibm.com> wrote:

> An fs actually seems overkill for two write-only files for
> process-related information.  Would these actually be candidates
> for new /proc files?
>
>        /proc/grantcred - replaces /dev/caphash, for privileged
>                tasks to tell the kernel about new setuid
>                capabilities
>        /proc/self/usecred - replaces /dev/capuse for unprivileged
>                tasks to make use of a setuid capability

An fs is fine.

To relate this to Plan 9, where it all began, might be useful. There's
no equivalent in Plan 9 to Linux/Unix devices of the major/minor
number etc. variety. In-kernel drivers and out-of-kernel servers both
end up providing the services (i.e. file name spaces) that we see in a
Linux file system. So the Plan 9 driver for the capability device
really does match closely in function and interface to a Linux
kernel-based file system.

Hence, making devcap a file system is entirely appropriate, because it
best fits the way it works in Plan 9: a kernel driver that provides
two files.

It's pretty easy to write a Linux VFS anyway, so it makes sense from
that point of view.

Eric, that was a great suggestion.

ron
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