linux-kernel - Re: [perfmon] Re: [perfmon2] perfmon2 merge news

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Message-Id: <20071114.040758.101673950.davem@davemloft.net>
Date:	Wed, 14 Nov 2007 04:07:58 -0800 (PST)
From:	David Miller <davem@...emloft.net>
To:	paulus@...ba.org
Cc:	hch@...radead.org, akpm@...ux-foundation.org, gregkh@...e.de,
	mucci@...utk.edu, eranian@....hp.com, wcohen@...hat.com,
	robert.richter@....com, linux-kernel@...r.kernel.org,
	andi@...stfloor.org
Subject: Re: [perfmon] Re: [perfmon2] perfmon2 merge news

From: Paul Mackerras <paulus@...ba.org>
Date: Wed, 14 Nov 2007 23:03:24 +1100

> You're suggesting that the behaviour of a read() should depend on what
> was in the buffer before the read?  Gack!  Surely you have better
> taste than that?

Absolutely that's what I mean, it's atomic and gives you exactly what
you need.

I see nothing wrong or gross with these semantics.  Nothing in the
"book of UNIX" specifies that for a device or special file the passed
in buffer cannot contain input control data.

> > Another alternative is to use generic netlink.
> 
> Then you end up with two system calls to get the data rather than one
> (one to send the request and another to read the reply).  For
> something that needs to be quick that is a suboptimal interface.

Not necessarily, consider the possibility of using recvmsg() control
message data.  With that it could be done in one go.

This also suggests that it could be implemented as it's own protocol
family.
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