Re: [PATCH] Bluetooth: allocate static minor for vhci

[Greg KH <gregkh@linuxfoundation.org>]

On Mon, Feb 17, 2014 at 04:01:25PM -0300, Lucas De Marchi wrote:
> [ CC'ing Kay and Greg ]
> 
> On Mon, Feb 17, 2014 at 08:34:32AM -0800, Marcel Holtmann wrote:
> > Hi Lucas,
> > 
> > > Commit bfacbb9 (Bluetooth: Use devname:vhci module alias for virtual HCI
> > > driver) added the module alias to hci_vhci module so it's possible to
> > > create the /dev/vhci node. However creating an alias without
> > > specifying the minor doesn't allow us to create the node ahead,
> > > triggerring module auto-load when it's first accessed.
> > > 
> > > Starting with depmod from kmod 16 we started to warn if there's a
> > > devname alias without specifying the major and minor.
> > > 
> > > Let's do the same done for uhid, kvm, fuse and others, specifying a
> > > fixed minor. In systems with systemd as the init the following will
> > > happen: on early boot systemd will call "kmod static-nodes" to read
> > > /lib/modules/$(uname -r)/modules.devname and then create the nodes. When
> > > first accessed these "dead" nodes will trigger the module loading.
> > > 
> > > Signed-off-by: Lucas De Marchi <lucas.demarchi@intel.com>
> > > ---
> > > drivers/bluetooth/hci_vhci.c | 3 ++-
> > > include/linux/miscdevice.h   | 1 +
> > > 2 files changed, 3 insertions(+), 1 deletion(-)
> > > 
> > > diff --git a/drivers/bluetooth/hci_vhci.c b/drivers/bluetooth/hci_vhci.c
> > > index 1ef6990..add1c6a 100644
> > > --- a/drivers/bluetooth/hci_vhci.c
> > > +++ b/drivers/bluetooth/hci_vhci.c
> > > @@ -359,7 +359,7 @@ static const struct file_operations vhci_fops = {
> > > static struct miscdevice vhci_miscdev= {
> > > 	.name	= "vhci",
> > > 	.fops	= &vhci_fops,
> > > -	.minor	= MISC_DYNAMIC_MINOR,
> > > +	.minor	= VHCI_MINOR,
> > > };
> > > 
> > > static int __init vhci_init(void)
> > > @@ -385,3 +385,4 @@ MODULE_DESCRIPTION("Bluetooth virtual HCI driver ver " VERSION);
> > > MODULE_VERSION(VERSION);
> > > MODULE_LICENSE("GPL");
> > > MODULE_ALIAS("devname:vhci");
> > > +MODULE_ALIAS_MISCDEV(VHCI_MINOR);
> > > diff --git a/include/linux/miscdevice.h b/include/linux/miscdevice.h
> > > index 3737f72..846a317 100644
> > > --- a/include/linux/miscdevice.h
> > > +++ b/include/linux/miscdevice.h
> > > @@ -48,6 +48,7 @@
> > > #define LOOP_CTRL_MINOR		237
> > > #define VHOST_NET_MINOR		238
> > > #define UHID_MINOR		239
> > > +#define VHCI_MINOR		240
> > > #define MISC_DYNAMIC_MINOR	255
> > 
> > you have read Documentation/devices.txt where it states that 240-254 is reserved for local use.
> 
> I haven't seen that. So, are we out of minors or.. can I use e.g.
> 142, 129 or the ones below 128?

As Kay said, larger than 255 should be fine, but you should test this,
and also provide a patch for the devices.txt file to ensure you reserve
the minor number properly.  Looks like someone forgot to do that for the
UHID minor number :(

thanks,

greg k-h