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

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Date:	Tue, 24 Sep 2013 18:28:30 +0200
From:	David Herrmann <dh.herrmann@...il.com>
To:	Tom Gundersen <teg@...m.no>
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>,
	Jiri Kosina <jkosina@...e.cz>
Subject: Re: [PATCH] HID: uhid: allocate static minor

Hey Jiri

I forgot to put you on CC on the initial patch. Any comments on this?

Cheers
David

On Mon, Sep 9, 2013 at 6:51 PM, Tom Gundersen <teg@...m.no> wrote:
> 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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