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

Andrew Morton
2009-06-25T00:33:52Z

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