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From: Nick Piggin <nickpiggin@yahoo.com.au>
To: Paul Mackerras <paulus@samba.org>
Subject: Re: [perfmon] Re: [perfmon2] perfmon2 merge news
Date: Wed, 14 Nov 2007 10:49:48 +1100
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Cc: David Miller <davem@davemloft.net>, hch@infradead.org,
       akpm@linux-foundation.org, gregkh@suse.de, mucci@cs.utk.edu,
       eranian@hpl.hp.com, wcohen@redhat.com, robert.richter@amd.com,
       linux-kernel@vger.kernel.org, andi@firstfloor.org
References: <20071114103805.GA16652@infradead.org> <20071114.031216.11725447.davem@davemloft.net> <18234.57272.590960.860941@cargo.ozlabs.ibm.com>
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On Wednesday 14 November 2007 22:44, Paul Mackerras wrote:
> David Miller writes:
> > This is my impression too, all of the things being done with
> > a slew of system calls would be better served by real special
> > files and appropriate fops.
>
> Special files and fops really only work well if you can coerce the
> interface into one where data flows predominantly one way.  I don't
> think they work so well for something that is more like an RPC across
> the user/kernel barrier.  For that a system call is better.
>
> For instance, if you have something that kind-of looks like
>
> 	read_pmds(int n, int *pmd_numbers, u64 *pmd_values);
>
> where the caller supplies an array of PMD numbers and the function
> returns their values (and you want that reading to be done atomically
> in some sense), how would you do that using special files and fops?

Could you implement it with readv()?
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