[libvirt] [PATCH] qemu: Forcibly mknod() even if it exists

[Daniel P. Berrangé]

On Wed, Nov 20, 2019 at 10:37:14AM +0000, Daniel P. Berrangé wrote:
> On Wed, Nov 20, 2019 at 11:34:24AM +0100, Michal Privoznik wrote:
> > On 11/20/19 11:05 AM, Daniel P. Berrangé wrote:
> > > On Wed, Nov 20, 2019 at 10:51:47AM +0100, Michal Privoznik wrote:
> > > > Another weird bug appeared concerning qemu namespaces. Basically
> > > > the problem is as follows:
> > > > 
> > > > 1) Issue an API that causes libvirt to create a node in domain's
> > > >     namespace, say /dev/sda with 8:0 as major:minor (the API can
> > > >     be attach-disk for instance). Or simply create the node from
> > > >     a console by hand.
> > > > 
> > > > 2) Detach the disk from qemu.
> > > > 
> > > > 3) Do something that makes /dev/sda change it's minor number.
> > > 
> > > Wait, what ?
> > > 
> > > major/minor numbers for SCSI disks are a defined standard
> > > IIUC
> > > 
> > > $ grep SCSI ./admin-guide/devices.txt | grep block
> > >     8 block	SCSI disk devices (0-15)
> > >    11 block	SCSI CD-ROM devices
> > >    65 block	SCSI disk devices (16-31)
> > >    66 block	SCSI disk devices (32-47)
> > >    67 block	SCSI disk devices (48-63)
> > >    68 block	SCSI disk devices (64-79)
> > >    69 block	SCSI disk devices (80-95)
> > >    70 block	SCSI disk devices (96-111)
> > >    71 block	SCSI disk devices (112-127)
> > >   128 block       SCSI disk devices (128-143)
> > >   129 block       SCSI disk devices (144-159)
> > >   130 block       SCSI disk devices (160-175)
> > >   131 block       SCSI disk devices (176-191)
> > >   132 block       SCSI disk devices (192-207)
> > >   133 block       SCSI disk devices (208-223)
> > >   134 block       SCSI disk devices (224-239)
> > >   135 block       SCSI disk devices (240-255)
> > > 
> > > 
> > > IOW, /dev/sda should always be 8,0
> > > 
> > > There is, however, the possibiity of dynamically assign
> > > major/minor numbers so its possible we'll see a block
> > > device with a changable number, but AFAIK, such a block
> > > device should never be call /dev/sda !??!
> > > 
> > > IOW, the commit is fine, but is this commit message
> > > really accurate ?
> > 
> > Ah, the bug talks about /dev/nvmeN that has changed MIN number. I haven't
> > found corresponding docs on NVMe though. Is s/sda/nvmeN/ on the commit
> > message enough?
> 
> Yeah, that makes more sense as nvme devices are allocated from the
> dynamic range.

Opps, I should have added

Reviewed-by: Daniel P. Berrangé <berrange at redhat.com>


Regards,
Daniel
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