[libvirt] [PATCH v2 0/2] add debugcon-isa chardev guest interface

[Ján Tomko]

On Tue, Feb 12, 2019 at 05:21:56PM +0100, Andrea Bolognani wrote:
>On Tue, 2019-02-12 at 16:07 +0100, Ján Tomko wrote:
>> On Tue, Feb 12, 2019 at 02:44:05PM +0000, Nikolay Shirokovskiy wrote:
>> > On 12.02.2019 17:37, Ján Tomko wrote:
>> > > On Thu, Feb 07, 2019 at 02:31:47PM +0300, Nikolay Shirokovskiy wrote:
>> > > > Diff from v1 [1]:
>> > > > =================
>> > > > - expose the device as serial device instead of channel in config
>> > > >
>> > > > I use isa-debugcon name becase libvirt passes these names to qemu as-is
>> > > > so I don't want to make exception for this device.
>> > >
>> > > There should be no pressure to maintain the 1:1 mapping.
>> > > For QEMU, the devices need to be represented in single namespace, so
>> > > they have to include the bus. In libvirt, we already have the serial
>> > > type and the <address> element. It does not have to be duplicated in the
>> > > model name as well.
>
>Note that the <address> element is not automatically added for
>ISA devices, so that specific duplication is not present.
>

The other duplication in serial type is more worrying.
Also, the device will be given an iobase by QEMU, we should represent
that in the XML and fill in that default.

>> > Yeah. But we already have models like isa-serial, usb-serial etc. And thus
>> > we don't need map libvirt models to qemu models i.e. internally
>> > we use virDomainChrSerialTargetModelTypeToString to generates names for
>> > qemu. It would be odd if I start to use map just for debugcon now.
>>
>> My point is that the internal implementation is not relevant here
>> (we do map XML attributes to QEMU devices elsewhere, see
>> qemuDeviceVideo), it's the XML that matters.
>>
>> The 'usb-serial', 'pci-serial', 'isa-serial' models are all a generic
>> repetition of the target type, all of those are IMO better than
>> <model name='serial'/> or <model name='generic'/>
>>
>> However
>> <target type='isa-serial'>
>>   <model name='debugcon'/>
>> </target>
>> looks better to me than
>> <target type='isa-serial'>
>>   <model name='isa-debugcon'/>
>> </target>
>
>We are consistently using the QEMU device name as the model
>attribute for <serial> devices,

Consistently mapping QEMU device names to libvirt attributes is
explicitly a non-goal of libvirt. The reason for the XML should
be: "it represents the device well", not "we won't need to add another
enum". See "virtio-scsi"

>so I don't really see a compelling
>reason to start adding inconsistencies now...
>

  Do you remember when you lost your passion for this work?
    -- Lisa Simpson

Jano

>-- 
>Andrea Bolognani / Red Hat / Virtualization
>
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