linux-kernel - Re: perfmon3 interface overview

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Message-ID: <20081005054433.GB469@yookeroo.seuss>
Date:	Sun, 5 Oct 2008 16:44:33 +1100
From:	David Gibson <david@...son.dropbear.id.au>
To:	eranian@...il.com
Cc:	linux-kernel@...r.kernel.org,
	perfmon2-devel <perfmon2-devel@...ts.sourceforge.net>
Subject: Re: perfmon3 interface overview

On Sat, Oct 04, 2008 at 09:20:00AM +0200, stephane eranian wrote:
> David,
> 
> On Sat, Oct 4, 2008 at 8:05 AM, David Gibson
> <david@...son.dropbear.id.au> wrote:
> >>
> >> If we wanted to go even further, we could combine start/stop, attach/detach
> >> into  a single syscall:
> >
> > Well, you could.  But the attach/detach take a parameter which
> > start/stop don't, making it a less obvious merge to make.
> >
> Unless you make the 3rd argument optional and hide this in a
> user library. This is how this is handled for pfm_create_session()
> for instance. The library would define this as follows:
> 
>    int pfm_control_session(int fd, int flags, ...);
> 
> Based upon flags, it would use va_arg() to get to the 3rd argument and
> pass it to the syscall which implements the version below. A dummy value
> would be passed with the flags is not equal to PFM_CTFL_ATTACH.

Yeah, that's what I'm saying.  You could do it, but it feels like
you're forcing it, at least to me.  As you say it starts to look a bit
like ioctl() again.

-- 
David Gibson			| I'll have my music baroque, and my code
david AT gibson.dropbear.id.au	| minimalist, thank you.  NOT _the_ _other_
				| _way_ _around_!
http://www.ozlabs.org/~dgibson
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