From mboxrd@z Thu Jan  1 00:00:00 1970
From: Ian Campbell <Ian.Campbell@citrix.com>
Subject: Re: [PATCH RFC] libxl: set disk defaults in
 remove/destroy functions
Date: Mon, 2 Feb 2015 13:27:13 +0000
Message-ID: <1422883633.19293.19.camel@citrix.com>
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To: Jim Fehlig <jfehlig@suse.com>
Cc: Wei Liu <wei.liu2@citrix.com>, Ian Jackson <Ian.Jackson@eu.citrix.com>, "xen-devel@lists.xen.org" <xen-devel@lists.xen.org>
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On Mon, 2015-01-26 at 16:14 -0700, Jim Fehlig wrote:

Cc-ing the other toolstack maintainers, both of whom have more
familiarity with this part of libxl than I.

> The attached patch is a hack I cooked up to fix one of the libvirt-TCK
> Xen failures.  The test (200-disk-hotplug.t) attempts to hot add and
> remove a disk from a running domain.  The add works fine, but remove
> fails with
> 
> libxl: debug: libxl.c:3858:libxl_device_disk_remove: ao 0x7f9b9c0015a0:
> create: how=(nil) callback=(nil) poller=
> 0x7f9ba0004590
> libxl: error: libxl.c:2399:libxl__device_from_disk: unrecognized disk
> backend type: 0
> 
> The test does not define a backend type, in which case the libvirt libxl
> driver allows libxl to choose an appropriate backend via
> libxl__device_disk_set_backend().  The backend type is never set on a
> remove operation, hence it fails with the above error.
> 
> I spent some time trying to figure out the best place to set backend
> type on remove, but in the end could only come up with this hack.  It
> wouldn't feel so gross if I could have simply added
> 'libxl__device_##type##_setdefault(gc, type);' to the existing
> DEFINE_DEVICE_REMOVE macro, but alas libxl__device_nic_setdefault() has
> a different prototype than the other devices.
> 
> Better suggestions welcomed!  One I considered was fixing this in
> libvirt.  But the Xen community suggested allowing libxl to choose a
> suitable backend when not specified, so I think this recommendation
> should be symmetrical in the add and remove operations.
> 
> Regards,
> Jim
> 
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