Re: minor device number request for /dev/kvm (kernel-based virtual machine)

Re: minor device number request for /dev/kvm (kernel-based virtual machine)

[Avi Kivity]

Mathiasen, Torben wrote:
>>  10 char        Non-serial mice, misc features
>>     nnn = /dev/kvm  kernel-based virtual machine (hardware
>> virtualization extensions)
>>
>>     
>
> Major 10, minor 256 has been assigned to /dev/kvm. Let me know if this is nok okay.
>
>   

It doesn't work.  The culprit appears to be

drivers/char/misc.c:

    register_chrdev(MISC_MAJOR,"misc",&misc_fops)


which in turn means:


fs/char_dev.c:
> int register_chrdev(unsigned int major, const char *name,
>             const struct file_operations *fops)
> {
>     struct char_device_struct *cd;
>     struct cdev *cdev;
>     char *s;
>     int err = -ENOMEM;
>
>     cd = __register_chrdev_region(major, 0, 256, name);

So misc minor numbers under 256 are not supported.

What's the way out?  Increase the region size?  I don't know if that's safe.

-- 
error compiling committee.c: too many arguments to function

Re: minor device number request for /dev/kvm (kernel-based virtual machine)

[Jan Engelhardt]

On Mar 1 2007 13:58, Avi Kivity wrote:
>
> fs/char_dev.c:
>> int register_chrdev(unsigned int major, const char *name,
>>            const struct file_operations *fops)
>> {
>> struct char_device_struct *cd;
>> struct cdev *cdev;
>> char *s;
>> int err = -ENOMEM;
>> 
>> cd = __register_chrdev_region(major, 0, 256, name);
>
> So misc minor numbers under 256 are not supported.
>
> What's the way out?  Increase the region size?  I don't know if that's safe.

If it does not increase memory usage, then possibly:

  __register_chrdev_region(major, 0, (~0U) & MINORMASK, name);
                                  or (1<<MINORMASK)-1 if that's more clear


Jan
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Re: minor device number request for /dev/kvm (kernel-based virtual machine)

[Avi Kivity]

Jan Engelhardt wrote:
> On Mar 1 2007 13:58, Avi Kivity wrote:
>   
>> fs/char_dev.c:
>>     
>>> int register_chrdev(unsigned int major, const char *name,
>>>            const struct file_operations *fops)
>>> {
>>> struct char_device_struct *cd;
>>> struct cdev *cdev;
>>> char *s;
>>> int err = -ENOMEM;
>>>
>>> cd = __register_chrdev_region(major, 0, 256, name);
>>>       
>> So misc minor numbers under 256 are not supported.
>>
>> What's the way out?  Increase the region size?  I don't know if that's safe.
>>     
>
> If it does not increase memory usage, then possibly:
>
>   __register_chrdev_region(major, 0, (~0U) & MINORMASK, name);
>                                   or (1<<MINORMASK)-1 if that's more clear
>
>   

I'm more worried about something in the chardev bowels not supporting 
 >8bit minors well.


-- 
error compiling committee.c: too many arguments to function

RE: minor device number request for /dev/kvm (kernel-based virtual machine)

[Mathiasen, Torben]

> > If it does not increase memory usage, then possibly:
> >
> >   __register_chrdev_region(major, 0, (~0U) & MINORMASK, name);
> >                                   or (1<<MINORMASK)-1 if that's more
> clear
> >
> >
> 
> I'm more worried about something in the chardev bowels not supporting
>  >8bit minors well.
> 

I was under the impression that large minors was supported for misc.
Skimming the code that does not seem to be the case. Can someone
comment?

Torben