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Date: Wed, 14 Feb 2018 13:29:37 -0800
From: Matthew Wilcox <willy@...radead.org>
To: Joe Perches <joe@...ches.com>
Cc: Andrew Morton <akpm@...ux-foundation.org>,
Matthew Wilcox <mawilcox@...rosoft.com>, linux-mm@...ck.org,
Kees Cook <keescook@...omium.org>, linux-kernel@...r.kernel.org,
kernel-hardening@...ts.openwall.com
Subject: Re: [PATCH v2 2/8] mm: Add kvmalloc_ab_c and kvzalloc_struct
On Wed, Feb 14, 2018 at 01:24:09PM -0800, Joe Perches wrote:
> On Wed, 2018-02-14 at 13:12 -0800, Matthew Wilcox wrote:
> > On Wed, Feb 14, 2018 at 12:45:52PM -0800, Joe Perches wrote:
> > > Perhaps kv[zm]alloc_buf_and_array is better naming.
> >
> > I think that's actively misleading. The programmer isn't allocating a
> > buf, they're allocating a struct. kvzalloc_hdr_arr was the earlier name,
> > and that made some sense; they're allocating an array with a header.
> > But nobody thinks about it like that; they're allocating a structure
> > with a variably sized array at the end of it.
> >
> > If C macros had decent introspection, I'd like it to be:
> >
> > sev = kvzalloc_struct(elems, GFP_KERNEL);
> >
> > and have the macro examine the structure pointed to by 'sev', check
> > the last element was an array, calculate the size of the array element,
> > and call kvzalloc_ab_c. But we don't live in that world, so I have to
> > get the programmer to tell me the structure and the name of the last
> > element in it.
>
> Look at your patch 4
>
> - dev_dax = kzalloc(sizeof(*dev_dax) + sizeof(*res) * count, GFP_KERNEL);
> + dev_dax = kvzalloc_struct(dev_dax, res, count, GFP_KERNEL);
>
> Here what is being allocated is exactly a struct
> and an array.
No, it's a struct *containing* an array. Look at patches 5 & 8 where I
have to convert the structs to contain the array which was silently
being allocated immediately after them.
> And this doesn't compile either.
Does for me. What error are you seeing?
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