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Date: Fri, 2 Nov 2012 20:18:24 +0000
From: Alan Cox <alan@lxorguk.ukuu.org.uk>
To: Tejun Heo <tj@kernel.org>
Cc: Paolo Bonzini <pbonzini@redhat.com>, Ric Wheeler <rwheeler@redhat.com>,
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        Jens Axboe <axboe@kernel.dk>, linux-kernel@vger.kernel.org,
        "James E.J. Bottomley" <James.Bottomley@HansenPartnership.com>
Subject: 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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>  * Devices are given standard filter matching the device class.  Any
>    !CAP_SYS_RAWIO user can only issue commands allowed by the filter.
> 
>  * CAP_SYS_RAWIO can issue an ioctl to disable the filter all
>    accessors of the fd and transfer it.
> 
> That should be enough, no?

No 

a - there are lots of cases you want to allow only a subset of commands.

b - if you are using a BPF filter which is the obvious way to do it then
the flexibility comes for free without any extra complexity as the kernel
provides a generic implementation, and even a JIT for complex cases.

Alan