linux-kernel - Re: [PATCH -v2] memdup

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Date:	Sat, 07 Mar 2009 08:54:14 -0800
From:	Roland Dreier <rdreier@...co.com>
To:	Arjan van de Ven <arjan@...radead.org>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Li Zefan <lizf@...fujitsu.com>, adobriyan@...il.com,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [PATCH -v2] memdup_user(): introduce

 > I would like to question the use of the gfp argument here;
 > copy_from_user sleeps, so you can't use GFP_ATOMIC anyway.
 > You can't use GFP_NOFS etc, because the pagefault path will happily do
 > things that are equivalent, if not identical, to GFP_KERNEL.

That's a convincing argument, and furthermore, strndup_user() does not
take a gfp parameter, so interface consistency also argues that the
function prototype should just be

void *memdup_user(const void __user *src, size_t len);

(By the way, the len parameter of strndup_user() is declared as long,
which seems strange, since it matches neither the userspace strndup()
nor the kernel kstrndup(), which both use size_t.  So using size_t for
memdup_user() and possibly fixing strndup_user() to use size_t as well
seems like the sanest thing)

 - R.


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