[add linux-scsi mailing list] On 10/3/19 1:32 PM, Bradley LaBoon wrote: > Hello, LKML! > > Beginning with kernel 5.3 the order in which SCSI devices are probed and > named has become non-deterministic. This is a result of a patch that was > submitted to add asynchronous device probing (specifically, commit > f049cf1a7b6737c75884247c3f6383ef104d255a). Previously, devices would > always be probed in the order in which they exist on the bus, resulting > in the first device being named 'sda', the second device 'sdb', and so on. > > This is important in the case of mass VM deployments where many VMs are > created from a single base image. Partition UUIDs cannot be used in the > fstab of such an image because the UUIDs will be different for each VM > and are not known in advance. Normally you can't rely on device names > being consistent between boots, but with QEMU you can set the bus order > of each block device and thus we currently use that to control the > device order in the guest. With the introduction of the aforementioned > patch this is no longer possible and the device ordering is different on > every boot, resulting in the guest booting into an emergency shell > unless the devices randomly happen to be loaded in the expected order. > > I have created a patch which reverts back to the previous behavior, but > I wanted to open this topic to discussion before posting it. I'm not > totally familiar with the low-level details of SCSI device probing, so I > don't know if the non-deterministic device order was the intended > behavior of the patch or just a side-effect. If that is the intended > behavior then is there perhaps some other way to ensure a consistent > device ordering for a guest VM? > > I am not subscribed to the list, so please CC me on any replies. > > Thank you! > Bradley LaBoon > -- ~Randy
