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Re: [Xen-devel] [PATCH 1 of 2] libxl: Allow multiple USB devices on HVM domain creation

On 29/11/12 11:16, Ian Campbell wrote:
On Wed, 2012-11-28 at 12:16 +0000, George Dunlap wrote:
# HG changeset patch
# User George Dunlap <george.dunlap@xxxxxxxxxxxxx>
# Date 1354101445 0
# Node ID 538d9ffbd71b41e8cf6d7da0ded9e0a0b07f3c0d
# Parent  ae6fb202b233af815466055d9f1a635802a50855
libxl: Allow multiple USB devices on HVM domain creation

This patch allows an HVM domain to be created with multiple USB

Since the previous interface only allowed the passing of a single
device, this requires us to add a new element to the hvm struct of
libxl_domain_build_info -- usbdevice_list.  For API compatibility, the
old element, usbdevice, remains.

If b_info->hvm.usbdevice is non-NULL, then it will be used exclusively;
otherwise, libxl will check for b_info->hvm.usbdevice_list instead.
Is this the right way round? If the caller knows about usbdevice_list
enough to have set it to something then surely that's the one it wanted?

Well, I had considered returning an error if both were set. :-) I suppose actually that's probably the way that is likely to flag up bugs in the toolstack the best -- only doing one or the other will cause weird buggy behavior that will be hard to track down. Does that sound good to you?

Each device listed will cause an extra "-usbdevice [foo]" to be appended
to the qemu command line.

In order to allow users of libxl to write software compatible with older
versions of libxl, also define LIBXL_HAVE_BUILDINFO_USBDEVICE_LIST.  If
this is present, the caller should use b_info->hvm.usbdevice_list; otherwise
they should use b_info->hvm.usbdevice.
Actually it's a both stricter and looser than that, if
LIBXL_HAVE_BUILDINFO_USBDEVICE_LIST is defined then the caller can
choose to use usbdevice_list but can also use usbdevice if they wish
(but not both). If it is not present then they must not use
usbdevice_list at all.

Hmm, I think I wrote this first and then changed it and forgot to update it. :-) I also forgot that in this kind of "API spec" document, "should" and "must" are technical terms with very specific definitions. I'll revise it when I re-spin.

I wonder if this LIBXL_HAVE should also be contained in a #ifdef
LIBXL_API_VERSION >= 0x040300?

What would be the purpose of that?


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