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From: Paul Mackerras <paulus@samba.org>
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Date: Tue, 22 May 2001 12:28:00 +1000 (EST)
To: Alexander Viro <viro@math.psu.edu>
Cc: linux-kernel@vger.kernel.org
Subject: Re: [RFD w/info-PATCH] device arguments from lookup, partion code
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Alexander Viro writes:

> drivers/net/ppp_generic.c:
> ppp_set_compress(struct ppp *ppp, unsigned long arg)
> {
[snip]
>         if (copy_from_user(&data, (void *) arg, sizeof(data))
>             || (data.length <= CCP_MAX_OPTION_LENGTH
>                 && copy_from_user(ccp_option, data.ptr, data.length)))
>                 goto out;
> 
> And that's far from being uncommon. They _do_ follow pointers. Some - more
> than once.

:) That particular example is one that would probably be much cleaner
as a write on a control fd.  What is there currently is just a
relatively ugly way of getting a variable-sized lump of data from
usermode into the kernel.

Paul.