lkml.org 
[lkml]   [2019]   [Oct]   [3]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
SubjectRe: SCSI device probing non-deterministic in 5.3
From
Date
[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

\
 
 \ /
  Last update: 2019-10-03 23:20    [W:0.067 / U:0.120 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site