On Mon, Mar 15, 2021 at 10:05 PM Matthew Wilcox <willy@xxxxxxxxxxxxx> wrote: > > On Mon, Mar 15, 2021 at 08:18:24PM +0000, Matthew Wilcox wrote: > > On Mon, Mar 15, 2021 at 09:02:38PM +0100, Matteo Croce wrote: > > > From: Matteo Croce <mcroce@xxxxxxxxxxxxx> > > > > > > Add a sequence number to the disk devices. This number is put in the > > > uevent so userspace can correlate events when a driver reuses a device, > > > like the loop one. > > > > Should this be documented as monotonically increasing? I think this > > is actually a media identifier. Consider (if you will) a floppy disc. > > Back when such things were common, it was possible with personal computers > > of the era to have multiple floppy discs "in play" and be prompted to > > insert them as needed. So shouldn't it be possible to support something > > similar here -- you're really removing the media from the loop device. > > With a monotonically increasing number, you're always destroying the > > media when you remove it, but in principle, it should be possible to > > reinsert the same media and have the same media identifier number. > > So ... a lot of devices have UUIDs or similar. eg: > > $ cat /sys/block/nvme0n1/uuid > e8238fa6-bf53-0001-001b-448b49cec94f > > https://linux.die.net/man/8/scsi_id (for scsi) > Hi, I don't have uuid anywhere: matteo@saturno:~$ ll /dev/sd? brw-rw---- 1 root disk 8, 0 feb 16 13:24 /dev/sda brw-rw---- 1 root disk 8, 16 feb 16 13:24 /dev/sdb brw-rw---- 1 root disk 8, 32 feb 16 13:24 /dev/sdc brw-rw---- 1 root disk 8, 48 feb 16 13:24 /dev/sdd brw-rw---- 1 root disk 8, 64 mar 4 06:26 /dev/sde brw-rw---- 1 root disk 8, 80 feb 16 13:24 /dev/sdf matteo@saturno:~$ ll /sys/block/*/uuid ls: cannot access '/sys/block/*/uuid': No such file or directory mcroce@t490s:~$ ll /dev/nvme0n1 brw-rw----. 1 root disk 259, 0 25 mar 14.22 /dev/nvme0n1 mcroce@t490s:~$ ll /sys/block/*/uuid ls: cannot access '/sys/block/*/uuid': No such file or directory I find it only on a mdraid array: $ cat /sys/devices/virtual/block/md127/md/uuid 26117338-4f54-f14e-b5d4-93feb7fe825d I'm using a vanilla 5.11 kernel. Regards, -- per aspera ad upstream
