linux-kernel - Re: [PATCH] HID: uhid: allocate static minor

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Date:	Mon, 9 Sep 2013 18:51:55 +0200
From:	Tom Gundersen <teg@...m.no>
To:	David Herrmann <dh.herrmann@...il.com>
Cc:	"linux-input@...r.kernel.org" <linux-input@...r.kernel.org>,
	Kay Sievers <kay.sievers@...y.org>,
	Marcel Holtmann <marcel@...tmann.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] HID: uhid: allocate static minor

On Mon, Sep 9, 2013 at 6:33 PM, David Herrmann <dh.herrmann@...il.com> wrote:
> udev has this nice feature of creating "dead" /dev/<node> device-nodes if
> it finds a devnode:<node> modalias. Once the node is accessed, the kernel
> automatically loads the module that provides the node. However, this
> requires udev to know the major:minor code to use for the node. This
> feature was introduced by:
>
>   commit 578454ff7eab61d13a26b568f99a89a2c9edc881
>   Author: Kay Sievers <kay.sievers@...y.org>
>   Date:   Thu May 20 18:07:20 2010 +0200
>
>       driver core: add devname module aliases to allow module on-demand auto-loading
>
> However, uhid uses dynamic minor numbers so this doesn't actually work. We
> need to load uhid to know which minor it's going to use.
>
> Hence, allocate a static minor (just like uinput does) and we're good
> to go.
>
> Reported-by: Tom Gundersen <teg@...m.no>

Thanks, this works (I only tested the creation of the device node, not
the actual module loading).

> Signed-off-by: David Herrmann <dh.herrmann@...il.com>
> ---
>  drivers/hid/uhid.c         | 3 ++-
>  include/linux/miscdevice.h | 1 +
>  2 files changed, 3 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/hid/uhid.c b/drivers/hid/uhid.c
> index 5bf2fb7..93b00d7 100644
> --- a/drivers/hid/uhid.c
> +++ b/drivers/hid/uhid.c
> @@ -615,7 +615,7 @@ static const struct file_operations uhid_fops = {
>
>  static struct miscdevice uhid_misc = {
>         .fops           = &uhid_fops,
> -       .minor          = MISC_DYNAMIC_MINOR,
> +       .minor          = UHID_MINOR,
>         .name           = UHID_NAME,
>  };
>
> @@ -634,4 +634,5 @@ module_exit(uhid_exit);
>  MODULE_LICENSE("GPL");
>  MODULE_AUTHOR("David Herrmann <dh.herrmann@...il.com>");
>  MODULE_DESCRIPTION("User-space I/O driver support for HID subsystem");
> +MODULE_ALIAS_MISCDEV(UHID_MINOR);
>  MODULE_ALIAS("devname:" UHID_NAME);
> diff --git a/include/linux/miscdevice.h b/include/linux/miscdevice.h
> index 09c2300..cb35835 100644
> --- a/include/linux/miscdevice.h
> +++ b/include/linux/miscdevice.h
> @@ -45,6 +45,7 @@
>  #define MAPPER_CTRL_MINOR      236
>  #define LOOP_CTRL_MINOR                237
>  #define VHOST_NET_MINOR                238
> +#define UHID_MINOR             239
>  #define MISC_DYNAMIC_MINOR     255
>
>  struct device;
> --
> 1.8.4
>
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