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[Pádraig Brady <P@xxxxxxxxxxxxxx>]

On 06/12/2012 04:07 PM, Fredric Morenius wrote:
> From: Scott Moser [mailto:ssmoser2@xxxxxxxxx] On Behalf Of Scott Moser
> Sent: den 11 juni 2012 23:16
> 
>> ...Without digging around on older versions of OS's and their included kernel/udev/kpartx.... i'd have to say that from your message above, and my testing that running 'kpartx' is no longer necessary.  That can reasonably be expected to be created by >the kernel or some other plumbing bits automatically...
> 
> I just now tested to remove the kpartx invocation from /nova/virt/disk/mount.py, like this:
> 
> diff --git a/nova/virt/disk/mount.py b/nova/virt/disk/mount.py
> index 11959b2..4d9527b 100644
> --- a/nova/virt/disk/mount.py
> +++ b/nova/virt/disk/mount.py
> @@ -61,25 +61,9 @@ class Mount(object):
>          if self.partition == -1:
>              self.error = _('partition search unsupported with %s') % self.mode
>          elif self.partition:
> -            map_path = '/dev/mapper/%sp%s' % (os.path.basename(self.device),
> -                                              self.partition)
> -            assert(not os.path.exists(map_path))
> -
> -            # Note kpartx can output warnings to stderr and succeed
> -            # Also it can output failures to stderr and "succeed"
> -            # So we just go on the existence of the mapped device
> -            _out, err = utils.trycmd('kpartx', '-a', self.device,
> -                                     run_as_root=True, discard_warnings=True)
> -
> -            # Note kpartx does nothing when presented with a raw image,
> -            # so given we only use it when we expect a partitioned image, fail
> -            if not os.path.exists(map_path):
> -                if not err:
> -                    err = _('partition %s not found') % self.partition
> -                self.error = _('Failed to map partitions: %s') % err
> -            else:
> -                self.mapped_device = map_path
> -                self.mapped = True
> +            #qemu-nbd already has mapped the partition for mounting
> +            self.mapped_device = '%sp%s' % (self.device, self.partition)
> +            self.mapped = True

Looks good. That should also support raw through the /dev/loop%s devices.

It might be safer to fallback to kpartx if not exists ...
  '%sp%s' % (self.device, self.partition)
That would support kernels before 3.2
I'd also add a comment in the code, that nbd must be mounted with param
max_part=16 or whatever.

cheers,
Pádraig.