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

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Date:	Fri, 06 Mar 2009 16:27:53 +0800
From:	Li Zefan <lizf@...fujitsu.com>
To:	Alexey Dobriyan <adobriyan@...il.com>
CC:	Andrew Morton <akpm@...ux-foundation.org>,
	LKML <linux-kernel@...r.kernel.org>,
	"linux-mm@...ck.org" <linux-mm@...ck.org>
Subject: Re: [RFC][PATCH] kmemdup_from_user(): introduce

Alexey Dobriyan wrote:
> On Fri, Mar 06, 2009 at 03:04:12PM +0800, Li Zefan wrote:
>> I notice there are many places doing copy_from_user() which follows
>> kmalloc():
>>
>>         dst = kmalloc(len, GFP_KERNEL);
>>         if (!dst)
>>                 return -ENOMEM;
>>         if (copy_from_user(dst, src, len)) {
>> 		kfree(dst);
>> 		return -EFAULT
>> 	}
>>
>> kmemdup_from_user() is a wrapper of the above code. With this new
>> function, we don't have to write 'len' twice, which can lead to
>> typos/mistakes. It also produces smaller code.
> 
> Name totally sucks, it mixes kernel idiom of allocation with purely
> userspace function.
> 

I'm not good at English, and I don't know why "kernel memory duplicated
from user space" is so bad...

or memdup_user() ?

>> A qucik grep shows 250+ places where kmemdup_from_user() *may* be
>> used. I'll prepare a patchset to do this conversion.
> 
> 250?
> 

I just found out how many copy_from_user() following km/zalloc(), so
not all of them are replace-able.

> 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?

> BTW, can we drop strstarts() and kzfree() on the same reasoning?
> 

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