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

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Date:	Sat, 24 Apr 2010 11:01:35 -0700
From:	ebiederm@...ssion.com (Eric W. Biederman)
To:	ron minnich <rminnich@...il.com>
Cc:	"Serge E. Hallyn" <serue@...ibm.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

ron minnich <rminnich@...il.com> writes:

> 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.

A fs provides user space policy control of naming.  I.e. where the two files go.
That can also be a very big deal.  Especially when files are writable.

You have no idea how much I am frustrated by sysfs right now, because
it does not provide userspace policy control and instead mandates a
sometimes inappropriate naming convention.

Eric


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