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

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Date:	Sun, 29 Jan 2012 17:13:18 -0800
From:	Earl Chew <echew@...acom.com>
To:	"Eric W. Biederman" <ebiederm@...ssion.com>
CC:	Andrew Morton <akpm@...ux-foundation.org>,
	Ingo Molnar <mingo@...e.hu>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Eric Paris <eparis@...hat.com>,
	"Serge E. Hallyn" <serge.hallyn@...onical.com>,
	"linux-kernel@...r.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

> I suspect what we want for writes is to read the existing value into an
> internal buffer, and then allow partial writes to the internal buffer.

Oh I see. Hmm ... I get the feeling that doubles the scope of the exercise ;-)

I'll give it some more thought.

> I don't know if writable seq_files exist.

No, they don't -- at least not out-of-the-box. From fs/seq_file.c :

>         /*
>          * seq_files support lseek() and pread().  They do not implement
>          * write() at all, but we clear FMODE_PWRITE here for historical
>          * reasons.
>          *
>          * If a client of seq_files a) implements file.write() and b) wishes to
>          * support pwrite() then that client will need to implement its own
>          * file.open() which calls seq_open() and then sets FMODE_PWRITE.
>          */
>         file->f_mode &= ~FMODE_PWRITE;

Earl

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