Date: Sat, 7 Jun 2003 14:32:19 +0200
From: Ingo Oeser <ingo.oeser@informatik.tu-chemnitz.de>
To: Linus Torvalds <torvalds@transmeta.com>
Cc: linux-kernel@vger.kernel.org
Subject: Re: __user annotations
Message-ID: <20030607143219.U626@nightmaster.csn.tu-chemnitz.de>
References: <7369DBDA-983E-11D7-8338-000A95A0560C@us.ibm.com> <Pine.LNX.4.44.0306061016250.20324-100000@home.transmeta.com>
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In-Reply-To: <Pine.LNX.4.44.0306061016250.20324-100000@home.transmeta.com>; from torvalds@transmeta.com on Fri, Jun 06, 2003 at 10:28:22AM -0700
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Hi Linus,

On Fri, Jun 06, 2003 at 10:28:22AM -0700, Linus Torvalds wrote:
> HOWEVER, usually it's very obvious to fix the whole chain, unless some
> type is sometimes used for kernel addresses and sometimes for user 
> addresses (which networking does with iovec's, for example).
 
Then it's not very useful for me. I usally define the ABI between
user space and kernel space trough IOCTL like that:

/* These structures are usally bigger and nested deeper */
struct in_foo_ioctl_name {
   int bla;
}

struct out_foo_ioctl_name {
   char blubb;
}

union foo_ioctl_name {
   struct in_foo_ioctl_name in;
   struct out_foo_ioctl_name out;
}

#define SUBSYS_IOCTL 0xee

#define SUBSYS_FOO _IOWR(SUBSYS_IOCTL, 0x1, union foo_ioctl_name)

Now I do in principle

   union foo_ioctl_name k, *u = (union foo_ioctl_name *)arg;

   if (copy_from_user(&k.in, &u, sizeof(k.in)) return -EFAULT;
   if (handle_foo(&k)) return -EINVAL;
   if (copy_to_user(&u, &k.out, sizeof(k.out)) return -EFAULT;
   
which I consider very clean (our project provides both: The
only ABI provider and the only ABI user) and works from 2.0
trough 2.5 so far.

This will NOT work anymore with __user annotations, right?

That's a big pity. How do I workaround this? I would like to
help resolving this issues, if you are interested.

Regards

Ingo Oeser
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