linux-kernel - Re: [PATCH 5/5] tracing: add binary buffer files for use with splice

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Message-ID: <49AE05CD.9000402@zytor.com>
Date:	Tue, 03 Mar 2009 20:38:37 -0800
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Steven Rostedt <rostedt@...dmis.org>
CC:	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org, Ingo Molnar <mingo@...e.hu>,
	Peter Zijlstra <peterz@...radead.org>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Theodore Tso <tytso@....edu>,
	Arjan van de Ven <arjan@...radead.org>,
	Pekka Paalanen <pq@....fi>,
	Arnaldo Carvalho de Melo <acme@...hat.com>,
	Mathieu Desnoyers <compudj@...stal.dyndns.org>,
	Martin Bligh <mbligh@...gle.com>,
	"Frank Ch. Eigler" <fche@...hat.com>,
	Tom Zanussi <tzanussi@...il.com>,
	Masami Hiramatsu <mhiramat@...hat.com>,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	Jason Baron <jbaron@...hat.com>,
	Christoph Hellwig <hch@...radead.org>,
	Jiaying Zhang <jiayingz@...gle.com>,
	Eduard - Gabriel Munteanu <eduard.munteanu@...ux360.ro>,
	mrubin@...gle.com, md@...gle.com,
	Steven Rostedt <srostedt@...hat.com>
Subject: Re: [PATCH 5/5] tracing: add binary buffer files for use with splice

Steven Rostedt wrote:
>> Conventionally a read() system call will return the number of bytes
>> copied, and will only return -EFOO if the number of bytes copied was
>> zero.
>>
>> Lots of parts of the kernel break this, but it's usually device drivers
>> and scruffy pseudo files, in which case a partial file read doesn't
>> make much sense.  This doesn't make the broken behaviour right, but at
>> least we have a bit of a weaselly excuse in that case.
> 
> I just went by the read man page:
> 
>        EFAULT buf is outside your accessible address space.

Yes, and that is the correct value if no bytes were copied.

	-hpa

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