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

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Message-ID: <50BED40D.9080100@asianux.com>
Date:	Wed, 05 Dec 2012 12:56:45 +0800
From:	Chen Gang <gang.chen@...anux.com>
To:	"Chas Williams (CONTRACTOR)" <chas@....nrl.navy.mil>
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.

于 2012年12月05日 11:57, Chas Williams (CONTRACTOR) 写道:
> In message <50BEA2CB.9000800@...anux.com>,Chen Gang writes:
>>> -	for (i = 0; i < (ESI_LEN - 1); i++)
>>> -		pos += sprintf(pos, "%02x:", adev->esi[i]);
>>> -	pos += sprintf(pos, "%02x\n", adev->esi[i]);
>>>  
>>> -	return pos - buf;
>>> +	return scnprintf(buf, PAGE_SIZE, "%pM\n", adev->esi);
>>>  }
>>>  
>>
>>  "%p" seems print a pointer, not contents of pointer (is it correct ?)
>>  will it change the original display format to outside ?
> 
> %pM means format this pointer as a mac address.  it didnt exist when the
> atm stack was originally written but can be used now to save a bit of
> messy code.
> 

  it is my fault. thank you

  :-)

>>> -		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(...) ).

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).

  I think what I said above are minor, if you think, for this patch, do
not need consider them, it is ok (at least for me, it is true).

  :-)

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> 

-- 
Chen Gang

Asianux Corporation
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