linux-kernel - Re: [RFC][PATCH] kmemdup_from

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Date:	Fri, 06 Mar 2009 17:01:48 +0800
From:	Li Zefan <lizf@...fujitsu.com>
To:	Andrew Morton <akpm@...ux-foundation.org>
CC:	Alexey Dobriyan <adobriyan@...il.com>,
	LKML <linux-kernel@...r.kernel.org>,
	"linux-mm@...ck.org" <linux-mm@...ck.org>
Subject: Re: [RFC][PATCH] kmemdup_from_user(): introduce

Andrew Morton wrote:
> On Fri, 06 Mar 2009 16:27:53 +0800 Li Zefan <lizf@...fujitsu.com> wrote:
> 
>>> Let's not add wrapper for every two lines that happen to be used
>>> together.
>>>
>> Why not if we have good reasons? And I don't think we can call this
>> "happen to" if there are 250+ of them?
> 
> The change is a good one.  If a reviewer (me) sees it then you know the
> code's all right and the review effort becomes less - all you need to check
> is that the call site is using IS_ERR/PTR_ERR and isn't testing for
> NULL.  Less code, less chance for bugs.
> 
> Plus it makes kernel text smaller.
> 
> Yes, the name is a bit cumbersome.
> 

How about memdup_user()? like kstrndup() vs strndup_user().

Here is the statistics when using 5 kmemdup_from_user() in btrfs:

$ diffstat
 ioctl.c |   49 ++++++++++++-------------------------------------
 super.c |   13 ++++---------
 2 files changed, 16 insertions(+), 46 deletions(-)

the kernel size on i386:

   text    data     bss     dec     hex filename
 288339    1924     508  290771   46fd3 fs/btrfs/btrfs.o.orig
   text    data     bss     dec     hex filename
 288255    1924     508  290687   46f7f fs/btrfs/btrfs.o

so saves 84 bytes.

the kernel size on IA64:

   text    data     bss     dec     hex filename
 898752    3736     109  902597   dc5c5 fs/btrfs/btrfs.o.orig
   text    data     bss     dec     hex filename
 898176    3712     109  901997   dc36d fs/btrfs/btrfs.o

so saves 576 bytes.
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