linux-kernel - Re: [PATCH RESUBMIT 0/2] fs/seq_file: Add seq_open

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Message-ID: <CAGXu5jLxxWD-_c6YzPRGcJwUa8CUw5DdR9OsP2NjfLG1t0zapQ@mail.gmail.com>
Date:	Thu, 25 Sep 2014 10:40:29 -0700
From:	Kees Cook <keescook@...omium.org>
To:	Rob Jones <rob.jones@...ethink.co.uk>
Cc:	Randy Dunlap <rdunlap@...radead.org>,
	Al Viro <viro@...iv.linux.org.uk>,
	"linux-doc@...r.kernel.org" <linux-doc@...r.kernel.org>,
	"linux-fsdevel@...r.kernel.org" <linux-fsdevel@...r.kernel.org>,
	LKML <linux-kernel@...r.kernel.org>,
	linux-kernel@...ethink.co.uk,
	Andrew Morton <akpm@...ux-foundation.org>,
	Tetsuo Handa <penguin-kernel@...ove.sakura.ne.jp>
Subject: Re: [PATCH RESUBMIT 0/2] fs/seq_file: Add seq_open_init()

On Thu, Sep 25, 2014 at 10:36 AM, Rob Jones <rob.jones@...ethink.co.uk> wrote:
>
>
> On 25/09/14 17:09, Kees Cook wrote:
>>
>> On Thu, Sep 25, 2014 at 1:57 AM, Rob Jones <rob.jones@...ethink.co.uk>
>> wrote:
>>>
>>>
>>>
>>> On 24/09/14 19:06, Kees Cook wrote:
>>>>
>>>>
>>>> On Wed, Sep 24, 2014 at 4:15 AM, Rob Jones <rob.jones@...ethink.co.uk>
>>>> wrote:
>>>>>
>>>>>
>>>>> Series resubmitted due to a typo in an email address.
>>>>>
>>>>> This patch series implements and documents a new interface function for
>>>>> seq_file.
>>>>>
>>>>> The existing set of open functions: seq_open(), seq_open_private() and
>>>>> __seq_open_private() satisfy the majority of use cases however there is
>>>>> one more use case that is also very common that this new function
>>>>> addresses.
>>>>>
>>>>> This case is where the iterator needs information that is available
>>>>> only
>>>>> at
>>>>> the time the seq_file is opened but does not need any space allocated,
>>>>> e.g.
>>>>> access to the inode structure. This type of open occurs, by my best
>>>>> estimate,
>>>>> in well over 40 places.
>>>>>
>>>>> Using the new function saves at least two lines of boilerplate code per
>>>>> instance as well as making the code easier to follow. The additional
>>>>> code
>>>>> in seq_file.c to implement the function is minimal as the first place
>>>>> that
>>>>> code can be removed is within seq_file.c itself.
>>>>>
>>>>> Once this patch is accepted, the instances of boilerplate code can be
>>>>> addressed.
>>>>
>>>>
>>>>
>>>> Would it be possible to write a coccinelle patch for the replacements?
>>>
>>>
>>>
>>> I'm afraid I don't know what that means.
>>
>>
>> It's a very flexible tool that should be able to find all the places
>> where this pattern is being used, and you can replace it with the new
>> function call:
>>
>> http://lwn.net/Articles/315686/
>
>
> I suspect that the learning curve would exceed the utility but I'll have
> a look at it. Unless there's a coccinelle expert available to do it, in
> which case I could point them in the right direction.
>
> My gut reaction would be that by the time I had analysed enough cases
> to come up with a viable set of SmPL scripts I would have done most of
> the work required, especially if I had to learn a new syntax and tool
> to do it.
>
> But first impressions aren't always right.

No worries; I was just curious if it would be easy. Sounds like
"probably not", which is fine. :)

-Kees

-- 
Kees Cook
Chrome OS Security
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