From mboxrd@z Thu Jan  1 00:00:00 1970
From: Arnd Bergmann <arnd@arndb.de>
Subject: Re: [PATCH v6] mmc: Add mmc CMD+ACMD passthrough ioctl
Date: Thu, 21 Apr 2011 14:39:14 +0200
Message-ID: <201104211439.14510.arnd@arndb.de>
References: <alpine.DEB.2.00.1104131713570.15392@peruna> <201104211315.51984.arnd@arndb.de> <BANLkTikTBK+0_KLjcB_sk4kF+a_vdaOckQ@mail.gmail.com>
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To: =?iso-8859-2?q?Micha=B3_Miros=B3aw?= <mirqus@gmail.com>
Cc: John Calixto <john.calixto@modsystems.com>, linux-mmc@vger.kernel.org, Andrei Warkentin <andreiw@motorola.com>, Chris Ball <cjb@laptop.org>

On Thursday 21 April 2011, Micha=B3 Miros=B3aw wrote:
> W dniu 21 kwietnia 2011 13:15 u=BFytkownik Arnd Bergmann <arnd@arndb.=
de> napisa=B3:

> static int mmc_blk_compat_ioctl(struct block_device *bdev, fmode_t mo=
de,
>     unsigned int cmd, unsigned long arg)
> {
>   struct mmc_ioc_cmd blk;
>=20
>   if (cmd !=3D MMC_IOC_CMD)
>     return -EINVAL;
>=20
>   copy_from_user(compat_ptr(arg), &blk) ...
>   blk.data_ptr =3D compat_ptr(blk.__data_ptr_storage32);
>=20
>   return mmc_blk_ioctl_cmd(bdev, &blk);
> }

Yes, this works, but it requires having a compat_ioctl() handler functi=
on that
knows about the data structure, which we generally try to avoid.
The same method would even work if you only had a pointer member in the
structure and did not even attempt to make the structure compatible.

	Arnd