Libguestfs - Sep 2013 - Re: [PATCH] virt-v2v: Remove iface:ide parameter (RHBZ#895898)

The iface:ide parameter (used in the libguestfs add_drive call) does not work
with a libvirt backend. The error usually seen is:

 'iface' parameter is not supported by the libvirt attach-method at
 /usr/share/perl5/vendor_perl/Sys/VirtConvert/GuestfsHandle.pm line 96.

This issue was previously mentioned in this thread: 
https://www.redhat.com/archives/libguestfs/2013-February/msg00057.html, and a 
workaround of 'export LIBGUESTFS_ATTACH_METHOD=appliance' was suggested.
However, as mentioned in the bug, this parameter is likely no longer required. 
Unless there is a use-case where this setting is required, it seems like a 
good idea to remove it completely (which should work in
either libvirt or direct mode), rather than recommend the workaround.

---
 lib/Sys/VirtConvert/GuestfsHandle.pm | 5 +----
 1 file changed, 1 insertion(+), 4 deletions(-)

diff --git a/lib/Sys/VirtConvert/GuestfsHandle.pm 
b/lib/Sys/VirtConvert/GuestfsHandle.pm
index 549ba11..71f11da 100644
--- a/lib/Sys/VirtConvert/GuestfsHandle.pm
+++ b/lib/Sys/VirtConvert/GuestfsHandle.pm
@@ -73,21 +73,18 @@ sub new
     # Open a guest handle
     my $g;
     my $open = sub {
-        my $interface = "ide";
-
         $g = Sys::Guestfs->new();
         foreach my $disk (@{$disks}) {
             my ($name, $path, $format) = @$disk;

             $g->add_drive_opts($path,
                                format => $format,
-                               iface => $interface,
                                name => $name);
         }

         # Add the transfer iso if there is one
         $g->add_drive_opts($transfer,
-                           format => 'raw', iface => $interface,
readonly =>
1)
+                           format => 'raw', readonly => 1)
             if defined($transfer);

         # Enable networking in the guest
-- 
1.8.1.4

On Tuesday, September 03, 2013 06:09:26 PM Mike Latimer
wrote:
> However, as mentioned in the bug, this parameter is likely no longer
> required. Unless there is a use-case where this setting is required, it
> seems like a good idea to remove it completely (which should work in
> either libvirt or direct mode), rather than recommend the workaround.
As much as I hate to reply to myself... I just did some additional testing and 
realized that if 'iface:ide' is removed, the disks could be inaccessible
in
environments that don't have virtio_scsi (in the guestfs environment). In 
other words, with just ata_piix, the 'iface:ide' might be required.

Do we know if there are any environments which are commonly missing the virtio 
stack? (If the answer is not much, I'd still rather drop iface:ide, and work
with both backend types (through virtio_scsi).

-Mike

On Tue, Sep 03, 2013 at 11:30:07PM -0600, Mike Latimer
wrote:
> On Tuesday, September 03, 2013 06:09:26 PM Mike Latimer wrote:
> > However, as mentioned in the bug, this parameter is likely no longer
> > required. Unless there is a use-case where this setting is required,
it
> > seems like a good idea to remove it completely (which should work in
> > either libvirt or direct mode), rather than recommend the workaround.
> 
> As much as I hate to reply to myself... I just did some additional testing
and
> realized that if 'iface:ide' is removed, the disks could be
inaccessible in
> environments that don't have virtio_scsi (in the guestfs environment).
In
> other words, with just ata_piix, the 'iface:ide' might be required.
I'll give you a bit of background to this (mis-)feature.  The
"iface"
optional argument was added so that you could use qemu's IDE interface
instead of whatever the default is (virtio-scsi, falling back to
virtio-blk).

This has no effect (only limitations) for ordinary libguestfs users,
but for virt-v2v it allows us to run the 'mkinitrd' command in the
guest and have it work for very old and buggy mkinitrd / guests that
got confused by virtio.  I think it was for RHEL 4 ...

What it does do is cause endless problems, mainly because people want
to use virt-v2v with more disks than IDE allows (just 2, once you take
into account the transfer disk and the libguestfs appliance).

So I wouldn't worry about removing iface => "ide".
> Do we know if there are any environments which are commonly missing
> the virtio stack?
Even ARM has it these days.  libguestfs doesn't work without it.

Rich.

-- 
Richard Jones, Virtualization Group, Red Hat http://people.redhat.com/~rjones
virt-top is 'top' for virtual machines.  Tiny program with many
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http://people.redhat.com/~rjones/virt-top