[ovirt-users] Re: [OT] Major and minor numbers assigned to /dev/vdx virtio devices

On Mon, Jul 13, 2020 at 09:53:31PM +0300, Nir Soffer wrote: > On Wed, Jul 1, 2020 at 5:55 PM Gianluca Cecchi > <gianluca.cecchi(a)gmail.com&gt; wrote: > > > > Hello, > > isn't there an official major/minor numbering scheme for virtio disks? > > Sometimes I see 251 major or 252 or so... what is the udev assignment logic? > > Reading here: > > https://www.kernel.org/doc/Documentation/admin-guide/devices.txt > > > > 240-254 block LOCAL/EXPERIMENTAL USE > > Allocated for local/experimental use. For devices not > > assigned official numbers, these ranges should be > > used in order to avoid conflicting with future assignments. > > > > it seems they are in the range of experimental ones, while for example Xen /dev/xvdx devices have their own static assignment (202 major) No, the Linux virtio_blk driver does not use a static device major number. Regarding udev, on my Fedora system /usr/lib/udev/rules.d/60-persistent-storage.rules has rules like this: KERNEL=="vd*[!0-9]", ATTRS{serial}=="?*", ENV{ID_SERIAL}="$attr{serial}", SYMLINK+="disk/by-id/virtio-$env{ID_SERIAL}" The rules match on the "vd*" name. If you are writing udev rules you could use the same approach. Is there a specific problem faced when there is no static device major number? Stefan