linux-kernel - Re: [patch] eventfd - revised interface and cleanups (2nd rev)

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Message-Id: <20090624173316.a129672d.akpm@linux-foundation.org>
Date:	Wed, 24 Jun 2009 17:33:16 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Davide Libenzi <davidel@...ilserver.org>
Cc:	linux-kernel@...r.kernel.org, avi@...hat.com, kvm@...r.kernel.org,
	ghaskins@...ell.com, rusty@...tcorp.com.au, bcrl@...ck.org
Subject: Re: [patch] eventfd - revised interface and cleanups (2nd rev)

On Wed, 24 Jun 2009 16:52:06 -0700 (PDT)
Davide Libenzi <davidel@...ilserver.org> wrote:

> > umm, yes please, I believe the patches should be split.  And I'm still
> > not seeing the justification for forcing CONFIG_EVENTFD onto all
> > CONFIG_AIO users!
> 
> Eventfd notifications became part of the AIO API (it's not even delivered 
> through a new syscall, from the AIO side - same existing aiocb struct and 
> io_submit syscall) once we merged it,

That was a regression for existing embedded AIO users ;)

> so IMHO (AIO && !EVENTFD) would be 
> similar to split AIO in AIO_READ and AIO_WRITE and have (AIO && !AIO_WRITE).
> Considering that the kernel config, once you unleash the CONFIG_EMBEDDED 
> pandora box, allows you to select (AIO && !EVENTFD) w/out even a warning 
> about possible userspace breakages, this makes it rather a confusing 
> configuration if you ask me.

Sure.  But we do assume that one someone sets CONFIG_EMBEDDED, they
know what they're doing.  We prefer to give them maximum flexibility
and foot-shooting ability.  As long as the maintenance cost of doing so
in each case is reasonable, of course.

> It's not a biggie from the kernel side, just a few ugly errors wrappers 
> around functions. For me AIO (or whatever userspace visible kernel 
> subsystem) should select all the components that are part of the userspace 
> API, but my argument ends here.

Sure, it's not a biggie either way.  Doubtful if many tiny systems are
using AIO anyway.  Heck, lots of them are running 2.4.18...

But from the general this-is-the-way-we-do-things POV, it's preferred
that the two features be separable under CONFIG_EMBEDDED if poss.


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