linux-kernel - Re: [PATCH] drivers: Conversions from kmalloc+memset to k(z|c)alloc.

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Date:	Fri, 21 Jul 2006 10:21:14 +0000
From:	"Daniel K." <daniel@...ded.net>
To:	Rolf Eike Beer <eike-kernel@...tec.de>
CC:	Panagiotis Issaris <takis@...umba.uhasselt.be>,
	linux-kernel@...r.kernel.org, len.brown@...el.com,
	chas@....nrl.navy.mil, miquel@...uba.ar, kkeil@...e.de,
	benh@...nel.crashing.org, video4linux-list@...hat.com,
	rmk+mmc@....linux.org.uk, Neela.Kolli@...enio.com,
	jgarzik@...ox.com, vandrove@...cvut.cz, adaplas@....net,
	thomas@...ischhofer.net, weissg@...nna.at, philb@....org,
	linux-pcmcia@...ts.infradead.org, jkmaline@...hut.fi,
	paulus@...ba.org
Subject: Re: [PATCH] drivers: Conversions from kmalloc+memset to k(z|c)alloc.

Rolf Eike Beer wrote:
> Am Donnerstag, 20. Juli 2006 21:05 schrieb Panagiotis Issaris:
>> @@ -443,12 +442,11 @@ int con_clear_unimap(struct vc_data *vc,
>>  	p = (struct uni_pagedir *)*vc->vc_uni_pagedir_loc;
>>  	if (p && p->readonly) return -EIO;
>>  	if (!p || --p->refcount) {
>> -		q = (struct uni_pagedir *)kmalloc(sizeof(*p), GFP_KERNEL);
>> +		q = kzalloc(sizeof(*p), GFP_KERNEL);
>>  		if (!q) {
>>  			if (p) p->refcount++;
>>  			return -ENOMEM;
>>  		}
>> -		memset(q, 0, sizeof(*q));
>>  		q->refcount=1;
>>  		*vc->vc_uni_pagedir_loc = (unsigned long)q;
>>  	} else {
> 
> This one still changes the way the code works. Before your patch *p will be 
> always zeroed out. Now if p is there before it will keep it's contents.

No, it doesn't, the data at *p is/was not zeroed inside the if { .. } block.
Read carefully, the multiple statements on one line obfuscations might
have thrown you off. 

However, it is slightly confusing that the value assigned to `q' is
kzalloced using sizeof(*p). It is an improvement though, as the old version
kmalloced using sizeof(*p), and memset using sizeof(*q).
That was really strange.

Daniel K.
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