Xen devel - Sep 2005 - /dev/misc/evtchn , /dev/xen/evtchn and the event channel driver : a little question

Hello,
   This is something I do not understand : I have a version of
xen-unstable from
a few days ago. (I am using the default "make world"  and make
install, which means 2.6.* versions; and I run it on x386).

 I had looked at the code of evtchn.c (/drivers/xen/evtchn in the sparse tree).

I see there:

err = misc_register(&evtchn_miscdev);
	if (err != 0)
	   {
	   printk(KERN_ALERT "Could not register /dev/misc/evtchn\n");
	  return err;
         }

and also:
static struct miscdevice evtchn_miscdev = {
	.minor        = EVTCHN_MINOR,
	.name         = "evtchn",
	.fops         = &evtchn_fops,
#if LINUX_VERSION_CODE >= KERNEL_VERSION(2,6,0)
	.devfs_name   = "misc/evtchn",
#endif
};

I had booted Xen (domain 0).

But I do not have /dev/misc/evtchn !
(as ls /dev/misc/evtchn shows).
On the other hand I *DO* have /dev/xen/evtchn and it seems to me that
other modules in tools use /dev/xen/evtchn and not /dev/misc/evtchn.

What is the truth behind this mystery ?

TIA,
MR

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Mark Ryden wrote:
>Hello,
>
>I had booted Xen (domain 0).
>
>But I do not have /dev/misc/evtchn !
>(as ls /dev/misc/evtchn shows).
>On the other hand I *DO* have /dev/xen/evtchn and it seems to me that
>other modules in tools use /dev/xen/evtchn and not /dev/misc/evtchn.
>
>What is the truth behind this mystery ?
>  
>
This is all left-over crude from devfs/udev and trying to support 2.4 
and 2.6.  I imagine that you''re actually seeing a /dev/evtchn from udev
and Xend is manually creating /dev/xen/evtchn at startup.

There''s a general cleanup needed here that''s on my TODO list. 
Just been
overly distracted lately.

Regards,

Anthony Liguori
>TIA,
>MR
>
>_______________________________________________
>Xen-devel mailing list
>Xen-devel@lists.xensource.com
>http://lists.xensource.com/xen-devel
>
>  
>

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On 29 Sep 2005, at 14:53, Mark Ryden wrote:
> But I do not have /dev/misc/evtchn !
> (as ls /dev/misc/evtchn shows).
> On the other hand I *DO* have /dev/xen/evtchn and it seems to me that
> other modules in tools use /dev/xen/evtchn and not /dev/misc/evtchn.
>
> What is the truth behind this mystery ?
It''ll appear under /dev/misc/evtchn only if you have devfs enabled 
(which is unlikely as it is removed from 2.6.13). Instead 
/dev/xe/evtchn has to be manually created by userspace.

The correct answer is probably to use udev to set up /dev/xen/evtchn.

  -- Keir


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