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Re: [libvirt] [PATCH 2/3] qemu: improve device flag parsing



[replying to myself]

On 01/18/2011 08:16 AM, Eric Blake wrote:
> On 01/17/2011 10:39 PM, Wen Congyang wrote:
>>> +    cmd = virCommandNewArgList(qemu,
>>> +                               "-device", "pci-assign,?",
>>> +                               NULL);
>>
>> The qemu that I used does not support '-device pci-assign,?'...
>> So, I can not start the guest with this patch.
>>
>> The qemu is cloned from here:
>> http://git.qemu.org/git/qemu.git
> 
> What do the following commands produce (assuming that both qemu and
> qemu-kvm on your PATH are the binaries that you are testing with)?
> 
> qemu -version
> qemu-kvm -version
> qemu -device '?'
> echo $?
> qemu -device 'pci-assign,?'
> echo $?
> qemu -device '?' -device 'pci-assign,?'
> echo $?
> qemu-kvm -device '?'
> echo $?
> qemu-kvm -device 'pci-assign,?'
> echo $?
> qemu-kvm -device '?' -device 'pci-assign,?'
> echo $?

I may have reproduced your problem.  With a Fedora 13 VM (no nested kvm
support), I see:

$ qemu -version
QEMU PC emulator version 0.12.5 (qemu-kvm-0.12.5), Copyright (c)
2003-2008 Fabrice Bellard

$ qemu-kvm -device pci-assign,?
open /dev/kvm: No such file or directory
Could not initialize KVM, will disable KVM support
property "pci-assign.?" not found
can't set property "?" to "on" for "pci-assign"
$ echo $?
1

$ qemu -device pci-assign,?
The pci-assign device has not been found
$ echo $?
1

$ qemu -device ?
name "pci-bridge", bus PCI
...
name "isabus-bridge", bus System, no-user
$ echo ?
1

$ qemu -device pci-bridge,?
property "pci-bridge.?" not found
can't set property "?" to "on" for "pci-bridge"
$ echo ?
1

Looks like -device was added in qemu 0.12.x, but device-specific
property parsing via -device name,? wasn't added until 0.13.x.
Furthermore, -device ? works in both versions to list available devices,
but in 0.12.x it always makes qemu fail with non-zero status (which we
can probably safely ignore).  Thankfully, this is reflected in -help output:

0.12.5:
-device driver[,options]  add device
-name ...

0.13.0:
-device driver[,prop[=value][,...]]
                add device (based on driver)
                prop=value,... sets driver properties
                use -device ? to print all possible drivers
                use -device driver,? to print all possible properties
File ...

In fact, rather than keying off of QEMUD_CMD_FLAG_DEVICE (which is
whether -device is present at all) to call qemuCapsExtractDeviceStr, it
may be as simple as keying off of "-device driver,?" in the -help
output.  Patch coming up shortly...

-- 
Eric Blake   eblake redhat com    +1-801-349-2682
Libvirt virtualization library http://libvirt.org

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