linux-kernel - Re: [PATCH] Support single byte reads from integers published in procfs by kernel/sysctl.c

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Date:	Mon, 23 Jan 2012 08:43:57 -0800
From:	ebiederm@...ssion.com (Eric W. Biederman)
To:	Earl Chew <echew@...acom.com>
Cc:	Ingo Molnar <mingo@...e.hu>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Eric Paris <eparis@...hat.com>,
	"Serge E. Hallyn" <serge.hallyn@...onical.com>,
	"linux-kernel\@vger.kernel.org" <linux-kernel@...r.kernel.org>,
	<adobriyan@...il.com>
Subject: Re: [PATCH] Support single byte reads from integers published in procfs by kernel/sysctl.c

ebiederm@...ssion.com (Eric W. Biederman) writes:

>>
>> [ I also note that the patch allows multiple short reads (not necessarily
>>   just a single byte at a time) from these entries in procfs. ]
>>
>> I think there is a reasonable userspace expectation that entities
>> that present themselves as text files to produce results that are
>> consistent with the userspace model of a text file.
>>
>> For a more concrete example, consider the following BusyBox ash(1) code:
>>
>> read X < /proc/sys/kernel/threads-max
>> Y=$(cat /proc/sys/kernel/threads-max)
>>
>> read A < /proc/sys/kernel/core_pattern
>> B=$(cat /proc/sys/kernel/core_pattern)
>
>
>> The fact that these yield different results is surprising given that
>> the user sees these as text files.

To be precise /proc/sys/kernel/threads-max does not present itself as
an ordinary text file.  It reports that it's file length is 0 bytes
long.   That is different from an ordinary text file.

Eric
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