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Date: Wed, 9 Jun 2010 13:06:59 +0300
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Subject: Re: [PATCH 00/12] treewide: Remove unnecessary kmalloc casts
From: Pekka Enberg <penberg@cs.helsinki.fi>
To: Milton Miller <miltonm@bga.com>
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Hi Milton,

On Wed, Jun 9, 2010 at 10:20 AM, Milton Miller <miltonm@bga.com> wrote:
> However, in this case you are removing casts that, while not necessary
> for C, are indeed there for a reason.
>
> Specifically, they are of the form
> =A0 type *p;
> =A0 <code>
> =A0 p =3D (type *)kmalloc(sizeof(type), ...);
>
> For example, from the powerpc patch:
>> goto out;
>> }
>> - tmp_part =3D (struct nvram_partition *)
>> - kmalloc(sizeof(struct nvram_partition), GFP_KERNEL);
>> + tmp_part =3D kmalloc(sizeof(struct nvram_partition), GFP_KERNEL);
>> err =3D -ENOMEM;
>
> The reason they casts are present is to guard against someone changing
> the type of p at the top of the function and not changing the type at
> the kmalloc.

If you're worried about that...

[snip]

> There may have been discussion of doing the above vs
> =A0 p =3D kmalloc(sizeof(*p), ...);

...it's better to use this form. There's actually a mention of this in
"Chapter 14: Allocating memory" of Documentation/CodingStyle. The
guard is not really a guard as someone can still change the "sizeof"
part to something else and the cast from "void *" will silently ignore
it.

                        Pekka