netdev - Re: [Suggestion] net/atm : for sprintf, need check the total write length whether larger than a page.

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Message-ID: <20121205095503.6d1c083d@thirdoffive.cmf.nrl.navy.mil>
Date:	Wed, 5 Dec 2012 09:55:03 -0500
From:	chas williams - CONTRACTOR <chas@....nrl.navy.mil>
To:	Chen Gang <gang.chen@...anux.com>
Cc:	David Miller <davem@...emloft.net>, netdev <netdev@...r.kernel.org>
Subject: Re: [Suggestion] net/atm : for sprintf, need check the total write
 length whether larger than a page.

On Wed, 05 Dec 2012 13:59:26 +0800
Chen Gang <gang.chen@...anux.com> wrote:

> 于 2012年12月05日 13:40, Chen Gang 写道:
> > 于 2012年12月05日 12:56, Chen Gang 写道:
> >>>>>>>> -		pos += sprintf(pos, "\n");
> >>>>>>>> +		count += scnprintf(buf + count, PAGE_SIZE - count, "\n");
> >>>> ..
> >>>>>>  need we judge whether count >= PAGE_SIZE ?
> >>>>
> >>>> count will eventually make PAGE_SIZE - count reach 0 at which point,
> >>>> scnprintf() won't be able to write into the buffer.
> >>   I also think so.
> >>
> >>   I think, maybe it will be better to break the loop when we already
> >> know that "count >= PAGE_SIZE" (it can save waste looping, although it
> >> seems unlikly happen, for example, using unlikly(...) ).

it doesn't seem like optimizing for this corner case is a huge
concern.  the list cannot be infinitely long.

> >>
> >> By the way:
> >>   will it be better that always let "\n" at the end ?
> >>   (if count == PAGE_SIZE in a loop, we can not let "\n" at the end).
> > 
> >    oh, sorry ! count will never >= PAGE_SIZE.
> > 
> >    I think let "PAGE_SIZE - 2" instead of "PAGE_SIZE" in the loop, so we
> > can make the room for the end of "\n".
> > 
> > 
> > 
>    sorry, "PAGE_SIZE - 1" is enough, not need "PAGE_SIZE - 2".

did you mean '\0' instead of '\n'?  scnprintf() considers the trailing
'\0' when formatting.
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