linux-kernel - Re: [PATCH 34/36] tty: add 'active' sysfs attribute to tty0 and console device

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Date:	Fri, 7 Jan 2011 14:20:58 +0100
From:	Kay Sievers <kay.sievers@...y.org>
To:	Jiri Slaby <jslaby@...e.cz>
Cc:	Greg Kroah-Hartman <gregkh@...e.de>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 34/36] tty: add 'active' sysfs attribute to tty0 and
 console device

On Fri, Jan 7, 2011 at 10:09, Jiri Slaby <jslaby@...e.cz> wrote:
> On 01/06/2011 11:23 PM, Greg Kroah-Hartman wrote:
>> --- a/drivers/tty/tty_io.c
>> +++ b/drivers/tty/tty_io.c
>> @@ -3232,9 +3232,45 @@ static int __init tty_class_init(void)
>>  postcore_initcall(tty_class_init);
>>
>>  /* 3/2004 jmc: why do these devices exist? */
>> -
>>  static struct cdev tty_cdev, console_cdev;
>>
>> +static ssize_t show_cons_active(struct device *dev,
>> +                             struct device_attribute *attr, char *buf)
>> +{
>> +     struct console *cs[16];
>> +     int i = 0;
>> +     struct console *c;
>> +     ssize_t count = 0;
>> +
>> +     acquire_console_sem();
>> +     for (c = console_drivers; c; c = c->next) {
>
> This should be:
> for_each_console(c)
> like somebody already suggested.

That's exported now? It was local to printk.c at least that time.

Anyway, the only sensible change here is to convert that home-grown
->next thing to a proper kernel linked list, and use the common
iterators instead of doing it on our own, or export new custom ones.

>> +             if (!c->device)
>> +                     continue;
>
> Why are consoles without devices ignored here?

It's a common pattern all over the place. What is a "console without a
device" that would be interesting here?

> Other than that there are 2 build warnings, see below.
>
>> -     device_create(tty_class, NULL, MKDEV(TTY_MAJOR, 0), NULL, "tty0");
>> +     tty0dev = device_create(tty_class, NULL, MKDEV(TTY_MAJOR, 0), NULL, "tty0");
>> +     if (IS_ERR(tty0dev))
>> +             tty0dev = NULL;
>> +     else
>> +             device_create_file(tty0dev, &dev_attr_active);
>
> drivers/tty/vt/vt.c: In function ‘vty_init’:
> drivers/tty/vt/vt.c:2997:21: warning: ignoring return value of
> ‘device_create_file’, declared with attribute warn_unused_result

The code doesn't even check device_create(). :)

Anyway we actually don't want to check the return value of
file_create(), it's a non-fatal error, if it ever happens.

What's the preferred way to do that:
  int ignore = device_create_file()
?

Kay
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