On Wed, Jan 11, 2012 at 17:58, Stephen Hemminger [off-list ref] wrote:

On Wed, 11 Jan 2012 11:07:47 +0400
Michael Tokarev [off-list ref] wrote:

quoted

On 11.01.2012 08:54, Stephen Hemminger wrote:

quoted

By adding the a module alias, programs (or users) won't have to explicitly
call modprobe. Vhost-net will always be available if built into the kernel.
It does require assigning a permanent minor number for depmod to work.
Choose one next to TUN since this driver is related to it.

Why do you think a statically-allocated device number will do any good
at all?

It's totally fine to use them for single-instance devices. You are
right, enumerated devices must _never_ use any facility like that.
That would just be broken.

quoted

Static /dev is gone almost completely, at least on the systems
where whole virt stuff makes any sense, so you don't have pre-created
vhost-net device anymore, and hence this allocation makes no sense.
Just IMHO anyway.

It makes a lot of sense in this case. The kernel module files
advertise the dev_t, it's not stored anywhere else. UDev finds these
static numbers and does inplicit mkdev() for them.

The statically allocated device number is required for the udev/module
autoloading to work. Probably the udev infrastructure needs a consistent
number to hang off of.

It does that properly.

Just check:
  $ cat /lib/modules/$(uname -r)/modules.devname
  # Device nodes to trigger on-demand module loading.
  fuse fuse c10:229
  btrfs btrfs-control c10:234
  ppp_generic ppp c108:0
  tun net/tun c10:200
  uinput uinput c10:223
  ...

Kay