Re: [Qemu-devel] virtio-scsi limits

["Richard W.M. Jones" <rjones@redhat.com>]

On Tue, Apr 18, 2017 at 06:17:03PM +0100, Richard W.M. Jones wrote:
> On Tue, Apr 18, 2017 at 05:30:52PM +0200, Paolo Bonzini wrote:
> > > When I changed libguestfs to use LUNs instead of targets (target=0
> > > unit=i), I got a peculiar bug.  It looks like there is some kind of
> > > race when enumerating the device, where /sys is populated before the
> > > device is actually available.
> > 
> > That's not _too_ surprising because devtmpfs processes creation/deletion
> > requests asynchronously.
> 
> I had a bit of a look into this, and I don't think this can be right.
> At this point we're running inside the initramfs environment, where
> /dev is a rootfs (a special case of either ramfs or tmpfs).
> 
> Would it still be the case that a single process that does mknod
> followed by mount could not see the effect of the mknod?
> 
> The mount error (EINVAL) should indicate an invalid superblock rather
> than a missing inode (if you believe the documentation, so that may be
> wrong).
> 
> The sequence of events (happening in a single init process) is as
> described below:

I see now: this turns out to be a problem in the unpredictable
enumeration order when we use LUNs instead of targets, and nothing to
do with virtio-scsi.

Rich.

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