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

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Message-ID: <x49h9zzspgv.fsf@segfault.boston.devel.redhat.com>
Date:	Mon, 22 Sep 2014 10:24:16 -0400
From:	Jeff Moyer <jmoyer@...hat.com>
To:	Jonathan Corbet <corbet@....net>
Cc:	Milosz Tanski <milosz@...in.com>,
	LKML <linux-kernel@...r.kernel.org>,
	Christoph Hellwig <hch@...radead.org>,
	"linux-fsdevel\@vger.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>, "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)

Jonathan Corbet <corbet@....net> writes:

> 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?

Hi, Jon,

Back when I tried to introduct O_NONBLOCK for regular files, the squid
proxy actually broke.  Software that dealt with burning optical media
also broke.  See my mail message here for more details:
  https://lkml.org/lkml/2014/9/15/942

Cheers,
Jeff
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