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

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Date:	Fri, 6 Mar 2009 12:03:13 +0300
From:	Alexey Dobriyan <adobriyan@...il.com>
To:	Li Zefan <lizf@...fujitsu.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

On Fri, Mar 06, 2009 at 04:27:53PM +0800, Li Zefan wrote:
> 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?

Please, read through them. This "250+" number suddenly will become
like 20, because wrapper is not good enough.
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