2:19 p.m.
While playing with the idea of forcing explicit USB controller models, I
ended up with the qemuargv2xml test failing; it ended up that this was
because changes I had made to qemuDomainDefPostParse() were affecting
the XML produced by qemuParseCommandline(). The reason - after
constructing a virDomainDef object by parsing a qemu commandline,
qemuParseCommandline() calls two functions that are supposed to be
called after parsing domain XML - virDomainDefPostParse() (which calls
qemuDomainDefPostParse()).
In my opinion, qemuParseCommandLine() shouldn't be calling
virDomainDefPostParse() (or virDomainefAddImplicitControllers(), which
it calls in the wrong order relative to virDomainDefPostParse() BTW).
The reasons are:
1) this is causing the argv-to-xml conversion to include things in the
XML that were not on the original commandline, in particular "default"
devices like PCI and USB controllers (added in qemuDomainDefPostParse()
based on machinetype) as well as disk, smartcard, virtio-serial, and
hostdev-scsi controllers in virDomainDefAddImplicitControllers() (why
the duality there, anyway?)
2) If the output of argv-to-xml is used for a virDomainDefine, those
post-parse functions will be called then, and the implicit/auto devices
will be added at that time anyway, so in practice nothing is gained by
adding them during argv-to-xml.
Does anyone else have an opinion about this?
4:12 a.m.
On 18.11.2015 21:19, Laine Stump wrote:
While playing with the idea of forcing explicit USB controller
models, I
ended up with the qemuargv2xml test failing; it ended up that this was
because changes I had made to qemuDomainDefPostParse() were affecting
the XML produced by qemuParseCommandline(). The reason - after
constructing a virDomainDef object by parsing a qemu commandline,
qemuParseCommandline() calls two functions that are supposed to be
called after parsing domain XML - virDomainDefPostParse() (which calls
qemuDomainDefPostParse()).
I'm afraid you are touching area of the code that is not maintained.
Brace yourself :)
In my opinion, qemuParseCommandLine() shouldn't be calling
virDomainDefPostParse() (or virDomainefAddImplicitControllers(), which
it calls in the wrong order relative to virDomainDefPostParse() BTW).
The reasons are:
1) this is causing the argv-to-xml conversion to include things in the
XML that were not on the original commandline, in particular "default"
devices like PCI and USB controllers (added in qemuDomainDefPostParse()
based on machinetype) as well as disk, smartcard, virtio-serial, and
hostdev-scsi controllers in virDomainDefAddImplicitControllers() (why
the duality there, anyway?)
Hold on, so they are not even visible in the guest? I mean, if I run
qemu by hand, don't I always get virtio-serial? If not, then we should
not add them during cmd line parse.
2) If the output of argv-to-xml is used for a virDomainDefine, those
post-parse functions will be called then, and the implicit/auto devices
will be added at that time anyway, so in practice nothing is gained by
adding them during argv-to-xml.
Correct.
Does anyone else have an opinion about this?
I believe there's not much gain in calling post parse callbacks during
cmd line parsing.
Michal
6:50 a.m.
On Thu, Nov 19, 2015 at 11:12:29 +0100, Michal Privoznik wrote:
On 18.11.2015 21:19, Laine Stump wrote:
[...]
>
> Does anyone else have an opinion about this?
>
I believe there's not much gain in calling post parse callbacks during
cmd line parsing.
Well, then you have to extract all the code that is setting the
hypervisor-specific defaults that can be omitted on the commandline but
need to be present in the definition (e.g. default network card model)
into the command line parser, otherwise certain parts of the code will
crash (e.g. network card model formatter).
Peter
9:15 a.m.
On 11/19/2015 07:50 AM, Peter Krempa wrote:
On Thu, Nov 19, 2015 at 11:12:29 +0100, Michal Privoznik wrote:
> On 18.11.2015 21:19, Laine Stump wrote:
[...]
>> Does anyone else have an opinion about this?
>>
> I believe there's not much gain in calling post parse callbacks during
> cmd line parsing.
Well, then you have to extract all the code that is setting the
hypervisor-specific defaults that can be omitted on the commandline but
need to be present in the definition (e.g. default network card model)
into the command line parser, otherwise certain parts of the code will
crash (e.g. network card model formatter).
Ugh. Right - once you've got the XML out it will get all the defaults
when it is fed back in to the parser with a virDomainDefine. But the
very first time it is formatted, right at the end of the argv-to-xml,
that could cause a problem.
I would say though that, rather than fixing up the object created from
parsing a qemu commandline by calling functions that are supposed to be
called to post-process the results of parsing XML to get it ready for
turning into a qemu commandline, we should instead make the formatter
more robust, so that it is able to format whatever it is fed without a
crash (I know that's a tall order!).
What a can of worms...
9:29 a.m.
On Thu, Nov 19, 2015 at 10:15:25 -0500, Laine Stump wrote:
On 11/19/2015 07:50 AM, Peter Krempa wrote:
> On Thu, Nov 19, 2015 at 11:12:29 +0100, Michal Privoznik wrote:
>> On 18.11.2015 21:19, Laine Stump wrote:
> [...]
>
>>> Does anyone else have an opinion about this?
>>>
>> I believe there's not much gain in calling post parse callbacks during
>> cmd line parsing.
> Well, then you have to extract all the code that is setting the
> hypervisor-specific defaults that can be omitted on the commandline but
> need to be present in the definition (e.g. default network card model)
> into the command line parser, otherwise certain parts of the code will
> crash (e.g. network card model formatter).
Ugh. Right - once you've got the XML out it will get all the defaults
when it is fed back in to the parser with a virDomainDefine. But the
very first time it is formatted, right at the end of the argv-to-xml,
that could cause a problem.
That is the same case as when you try to attach to a existing process.
It's very unlikely to actually work, but there is a possibility to reuse
the object created from argv parsing directly. In that case we probably
do need to have the definiton working.
Peter
11:08 a.m.
On 11/19/2015 10:29 AM, Peter Krempa wrote:
On Thu, Nov 19, 2015 at 10:15:25 -0500, Laine Stump wrote:
> On 11/19/2015 07:50 AM, Peter Krempa wrote:
>> On Thu, Nov 19, 2015 at 11:12:29 +0100, Michal Privoznik wrote:
>>> On 18.11.2015 21:19, Laine Stump wrote:
>> [...]
>>
>>>> Does anyone else have an opinion about this?
>>>>
>>> I believe there's not much gain in calling post parse callbacks during
>>> cmd line parsing.
>> Well, then you have to extract all the code that is setting the
>> hypervisor-specific defaults that can be omitted on the commandline but
>> need to be present in the definition (e.g. default network card model)
>> into the command line parser, otherwise certain parts of the code will
>> crash (e.g. network card model formatter).
> Ugh. Right - once you've got the XML out it will get all the defaults
> when it is fed back in to the parser with a virDomainDefine. But the
> very first time it is formatted, right at the end of the argv-to-xml,
> that could cause a problem.
That is the same case as when you try to attach to a existing process.
It's very unlikely to actually work, but there is a possibility to reuse
the object created from argv parsing directly. In that case we probably
do need to have the definiton working.
That could be handled by either adding the post-parse stuff into
qemuDomainAttach(), or alternately by doing a format-parse cycle on the
object (again, in qemuDomainAttach()) rather than using it directly
(which I actually think could give better results, as long as
qemuParseCommandLine() itself is doing the right stuff).
Note that in the case where the original commandline doesn't include the
PCI addresses of devices, we're very likely to end up with incorrect
address info in the XML, so hopefully nobody relies on that...
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5 comments
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participants (3)
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Laine Stump -
Michal Privoznik -
Peter Krempa