linux-kernel - Re: setting up CDB filters in udev (was Re: [PATCH v2 0/3] block: add queue-private command filter, editable via sysfs)

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Date:	Fri, 02 Nov 2012 18:49:43 +0100
From:	Paolo Bonzini <pbonzini@...hat.com>
To:	Tejun Heo <tj@...nel.org>
CC:	Ric Wheeler <rwheeler@...hat.com>,
	Petr Matousek <pmatouse@...hat.com>,
	Kay Sievers <kay@...hat.com>, Jens Axboe <axboe@...nel.dk>,
	linux-kernel@...r.kernel.org,
	"James E.J. Bottomley" <James.Bottomley@...senPartnership.com>
Subject: Re: setting up CDB filters in udev (was Re: [PATCH v2 0/3] block:
 add queue-private command filter, editable via sysfs)

Il 02/11/2012 17:51, Tejun Heo ha scritto:
>>> > > What disturbs me is that it's a completely new interface to userland
>>> > > and at the same a very limited one at that.  So, yeah, it's
>>> > > bothersome.  I personally would prefer SCM_RIGHTS behavior change +
>>> > > hard coded filters per device class.
>> > 
>> > I think hard-coded filters are bad (I prefer to move policy to
>> > userspace), and SCM_RIGHTS without a ioctl is out of question, really.
> No rule is really absolute.  To me, it seems the suggested in-kernel
> per-device command code filter is both too big for the given problem

Is it?  150 lines of code?  The per-class filters would share the first
two patches with this series, add a long list of commands to filter, and
the ioctl would be on top of that.

Long lists are better kept in configuration files than in kernel
sources; not to mention the higher cost of getting the API wrong for a
ioctl vs. sysfs.

> while being too limited for much beyond that.

What are the use cases beyond these?  AFAIK these were the first two in
ten years or so...

> So, if we can get away
> with adding an ioctl, I personally think that would be a better
> approach.

I would really prefer to get a green light from Jens/James for per-class
filters in the kernel (which are worth a few hundred lines of data)
before implementing that.

Paolo
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