linux-kernel - Re: [RFC v2 0/5] Non-blockling buffered fs read (page cache only)

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Message-ID: <20140922101221.4bf46809@lwn.net>
Date:	Mon, 22 Sep 2014 10:12:21 -0400
From:	Jonathan Corbet <corbet@....net>
To:	Milosz Tanski <milosz@...in.com>
Cc:	LKML <linux-kernel@...r.kernel.org>,
	Christoph Hellwig <hch@...radead.org>,
	"linux-fsdevel@...r.kernel.org" <linux-fsdevel@...r.kernel.org>,
	linux-aio@...ck.org, Mel Gorman <mgorman@...e.de>,
	Volker Lendecke <Volker.Lendecke@...net.de>,
	Tejun Heo <tj@...nel.org>, Jeff Moyer <jmoyer@...hat.com>,
	"Theodore Ts'o" <tytso@....edu>, Al Viro <viro@...iv.linux.org.uk>
Subject: Re: [RFC v2 0/5] Non-blockling buffered fs read (page cache only)

On Fri, 19 Sep 2014 13:33:14 -0400
Milosz Tanski <milosz@...in.com> wrote:

> >  - Non-blocking I/O has long been supported with a well-understood set
> >    of operations - O_NONBLOCK and fcntl().  Why do we need a different
> >    mechanism here - one that's only understood in the context of
> >    buffered file I/O?  I assume you didn't want to implement support
> >    for poll() and all that, but is that a good enough reason to add a
> >    new Linux-specific non-blocking I/O technique?  
> 
> I realized that I didn't answer this question well in my other long
> email. O_NONBLOCK doesn't work on files under any commonly used OS,
> and people have gotten use to this behavior so I doubt we could change
> that without breaking a lot of folks applications.

So I'm not contesting this, but I am genuinely curious: do you think
there are applications out there requesting non-blocking behavior on
regular files that will then break if they actually get non-blocking
behavior?  I don't suppose you have an example?

Thanks,

jon
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