linux-kernel - Re: [PATCH v2 05/17] compat_ioctl: move more drivers to generic_compat_ioctl

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Message-ID: <20180912130131.2c6581d5@coco.lan>
Date:   Wed, 12 Sep 2018 13:01:31 -0300
From:   Mauro Carvalho Chehab <mchehab+samsung@...nel.org>
To:     Arnd Bergmann <arnd@...db.de>
Cc:     viro@...iv.linux.org.uk, linux-fsdevel@...r.kernel.org,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "David S. Miller" <davem@...emloft.net>,
        devel@...verdev.osuosl.org, linux-kernel@...r.kernel.org,
        qat-linux@...el.com, linux-crypto@...r.kernel.org,
        linux-media@...r.kernel.org, dri-devel@...ts.freedesktop.org,
        linaro-mm-sig@...ts.linaro.org, amd-gfx@...ts.freedesktop.org,
        linux-input@...r.kernel.org, linux-iio@...r.kernel.org,
        linux-rdma@...r.kernel.org, linux-nvdimm@...ts.01.org,
        linux-nvme@...ts.infradead.org, linux-pci@...r.kernel.org,
        platform-driver-x86@...r.kernel.org,
        linux-remoteproc@...r.kernel.org, sparclinux@...r.kernel.org,
        linux-scsi@...r.kernel.org, linux-usb@...r.kernel.org,
        linux-fbdev@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org,
        linux-btrfs@...r.kernel.org, ceph-devel@...r.kernel.org,
        linux-wireless@...r.kernel.org, netdev@...r.kernel.org
Subject: Re: [PATCH v2 05/17] compat_ioctl: move more drivers to
 generic_compat_ioctl_ptrarg

Em Wed, 12 Sep 2018 17:08:52 +0200
Arnd Bergmann <arnd@...db.de> escreveu:

> The .ioctl and .compat_ioctl file operations have the same prototype so
> they can both point to the same function, which works great almost all
> the time when all the commands are compatible.
> 
> One exception is the s390 architecture, where a compat pointer is only
> 31 bit wide, and converting it into a 64-bit pointer requires calling
> compat_ptr(). Most drivers here will ever run in s390, but since we now
> have a generic helper for it, it's easy enough to use it consistently.
> 
> I double-checked all these drivers to ensure that all ioctl arguments
> are used as pointers or are ignored, but are not interpreted as integer
> values.
> 
> Signed-off-by: Arnd Bergmann <arnd@...db.de>
> ---

>  drivers/media/rc/lirc_dev.c                 | 4 +---

> diff --git a/drivers/media/rc/lirc_dev.c b/drivers/media/rc/lirc_dev.c
> index f862f1b7f996..077209f414ed 100644
> --- a/drivers/media/rc/lirc_dev.c
> +++ b/drivers/media/rc/lirc_dev.c
> @@ -730,9 +730,7 @@ static const struct file_operations lirc_fops = {
>  	.owner		= THIS_MODULE,
>  	.write		= ir_lirc_transmit_ir,
>  	.unlocked_ioctl	= ir_lirc_ioctl,
> -#ifdef CONFIG_COMPAT
> -	.compat_ioctl	= ir_lirc_ioctl,
> -#endif
> +	.compat_ioctl	= generic_compat_ioctl_ptrarg,
>  	.read		= ir_lirc_read,
>  	.poll		= ir_lirc_poll,
>  	.open		= ir_lirc_open,

Adding an infrared remote controller to a s390 mainframe sounds fun :-)

I suspect that one could implement it on a s390 platform 
using gpio-ir-recv and/or gpio-ir-tx drivers. Perhaps one possible
practical usage would be to let the mainframe to send remote
controller codes to adjust the air conditioning system ;-)

From lirc driver's PoV, there's nothing that really prevents one to
do that and use lirc API, and the driver is generic enough to work
on any hardware platform.

I didn't check the implementation of generic_compat_ioctl_ptrarg(),
but assuming it is ok,

Acked-by: Mauro Carvalho Chehab <mchehab+samsung@...nel.org>

Thanks,
Mauro