linux-kernel - Re: [PATCH] Fix proc_file

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Date:	Fri, 07 Aug 2009 23:59:12 -0700
From:	ebiederm@...ssion.com (Eric W. Biederman)
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	Stefani Seibold <stefani@...bold.net>,
	linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org
Subject: Re: [PATCH] Fix proc_file_write missing ppos update

Andrew Morton <akpm@...ux-foundation.org> writes:

> On Fri, 07 Aug 2009 23:43:07 +0200
> Stefani Seibold <stefani@...bold.net> wrote:
>

>> So what is your suggestion? Should we drop this patch or should we
>> analyze the users and fix it?
>
> Well.
>
> We could review all implementations of ->write_proc.  There only seem
> to be twenty or so.
>
> If any of them will have their behaviour altered by this patch then
> let's look at those on a case-by-case basis and decide whether making
> this change will have an acceptable risk.
>
> If we _do_ find one for which we simply cannot make this behavioural
> change then..  ugh.  We could perhaps add a new `bool
> proc_dir_entry.implement_old_broken_behaviour' and set that flag for
> the offending driver(s) and test it within proc_write_file().
>
> Or we could do
>
> 	if (pde->write_proc_new) {
> 		rv = pde->write_proc_new(file, buffer, count, pde->data);
> 		*ppos += rv;
> 	} else {
> 		rv = pde->write_proc(file, buffer, count, pde->data);
> 	}
>
> which is really the same thing and isn't obviously better ;)
>
>> My opinion is to fix it, because it is wrong and it limits the usage of
>> the proc_write operation. Many embedded developers like me count on proc
>> support, because it is much simpler to use than the seqfile thing.

The simple and portable answer is to implement your own file_operations.

It is unlikely that implementing a new totally unstructured proc file is
a good idea.

I'm not quite up to speed on write_proc but I believe we have been spraying
read_proc and write_proc because of problems with the interface.

Eric
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