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

Panagiotis Issaris
2006-07-21T10:31:09Z

Hi,

On vr, 2006-07-21 at 08:50 +0200, Rolf Eike Beer wrote:
>[...]
> Space after comma.
>[...]
> sizeof(*ltp)?
>
> [more of this snipped]

>
> > @@ -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.
Hmm. I do not really see the functional change here: If the memory
allocation failed, then in both cases, q will be zero and the function
will return. If the memory allocation succeeds, then in both cases a
memset will occur. Is it more subtle than that?

Before change:
if (!p || --p->refcount) {
q = kmalloc(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;
}

After change:
if (!p || --p->refcount) {
q = kzalloc(sizeof(*p), GFP_KERNEL);
if (!q) {
if (p)
p->refcount++;
return -ENOMEM;
}
q->refcount=1;
*vc->vc_uni_pagedir_loc = (unsigned long)q;
}

If !p then in both cases, q will be assigned some memory,
and if that succeeds, the block of memory will be cleared,
if it fails, it will not be cleared and the function will
exit.

If p then if --p->refcount<>0, a new block will be allocated
and if the allocation succeeds, it will be cleared in both cases.
If --p->refcount==0, nothing will be allocated nor cleared, in both
cases.

With friendly regards,
Takis