linux-kernel - Re: [PATCH 8/9] aio: implement io

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Date:   Wed, 21 Mar 2018 10:29:26 +0100
From:   Christoph Hellwig <hch@....de>
To:     Greg KH <gregkh@...uxfoundation.org>
Cc:     Christoph Hellwig <hch@....de>, viro@...iv.linux.org.uk,
        Avi Kivity <avi@...lladb.com>, linux-aio@...ck.org,
        linux-fsdevel@...r.kernel.org, linux-api@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 8/9] aio: implement io_pgetevents

On Wed, Mar 21, 2018 at 10:24:43AM +0100, Greg KH wrote:
> On Wed, Mar 21, 2018 at 08:32:31AM +0100, Christoph Hellwig wrote:
> > This is the io_getevents equivalent of ppoll/pselect and allows to
> > properly mix signals and aio completions (especially with IOCB_CMD_POLL)
> > and atomically executes the following sequence:
> > 
> > 	sigset_t origmask;
> > 
> > 	pthread_sigmask(SIG_SETMASK, &sigmask, &origmask);
> > 	ret = io_getevents(ctx, min_nr, nr, events, timeout);
> > 	pthread_sigmask(SIG_SETMASK, &origmask, NULL);
> > 
> > Note that unlike many other signal related calls we do not pass a sigmask
> > size, as that would get us to 7 arguments, which aren't easily supported
> > by the syscall infrastructure.  It seems a lot less painful to just add a
> > new syscall variant in the unlikely case we're going to increase the
> > sigset size.
> 
> Do we have a manpage for this new syscall and maybe a test program for
> it so we can exercise it as part of the kselftests?

The man page and test cases where submitted to libaio:

http://git.infradead.org/users/hch/libaio.git/shortlog/refs/heads/aio-poll

In the meantime the man page apparently moved to man-pages, I'll do that
work once we make some forward progress.

> And do we really need a compat thunk for a new syscall?  Ugh, I guess
> it's needed due to the long mess, right?  No way to just define it the
> same way for both arch sizes?

Not without making it a pain to use.  It should be a drop-in enhancement
to the existing aio abis, which all work on these types.