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Re: [Xen-devel] [Qemu-devel] [v5][PATCH 2/5] xen, gfx passthrough: create pseudo intel isa bridge

On 2014/7/1 3:34, Stefano Stabellini wrote:

On Fri, 27 Jun 2014, Chen, Tiejun wrote:

On 2014/6/25 17:58, Chen, Tiejun wrote:

On 2014/6/25 17:44, Michael S. Tsirkin wrote:

On Wed, Jun 25, 2014 at 05:28:48PM +0800, Chen, Tiejun wrote:

On 2014/6/25 17:21, Michael S. Tsirkin wrote:

On Wed, Jun 25, 2014 at 05:14:30PM +0800, Chen, Tiejun wrote:

On 2014/6/25 17:04, Michael S. Tsirkin wrote:

On Wed, Jun 25, 2014 at 04:48:02PM +0800, Chen, Tiejun wrote:

On 2014/6/25 16:43, Michael S. Tsirkin wrote:

On Wed, Jun 25, 2014 at 04:39:07PM +0800, Chen, Tiejun wrote:

In fact it's exactly what passthrough does.
I wonder if more bits from ./hw/i386/kvm/pci-assign.c
can be reused. How do you poke at the host device? sysfs?


Yes, sysfs.

Thanks
Tiejun


Then you should be able to re-use large chunks of
./hw/i386/kvm/pci-assign.c: basically everything
that deals with emulation.


Do you mean those hooks to get info from the real device? Xen
have its own
wrapper, xen_host_pci_get_block(), so we always go there in xen
scenario.

Thanks
Tiejun


Yes and that's not good.  We have two pieces of code doing mostly
identical things slightly differently.
hw/i386/kvm/pci-assign.c is a bit younger so it's cleaner,
but these really need to be unified.


Sorry, take a look at this again,

xen_host_pci_get_block(XenHostPCIDevice *d, int pos, uint8_t *buf,
int len)
     |
     + xen_host_pci_config_read(d, pos, buf, len)
         |
         + pread(d->config_fd, buf, len, pos)

I thinks this should be same as kvm.

Thanks
Tiejun


get_block is trivial.

I really mean the whole PT infrastructure for
- discovering host devices through sysfs
- virtualizing devices

rom, bars, msi ...
the list goes on.

logic is mostly the same.


Looks you mean we can unify the entire PT infrastructure between kvm
and xen
inside qemu. But I'm afraid its not easy to do in a short time, so
maybe we
can queue this as next phase.

Thanks
Tiejun


I'm afraid once we merge your code, you'll lose interest :)


Currently we have to push this feature into upstream as our first
priority, so unless something is really needed to address. Of course I
hope this point what we're talking is not such a thing :)

But I can promise here I'd like to do this optimization with your guide
next :)

At least, don't add duplicate code for ROM.


Let me try this.


Its not easy as expected.

kvm always work with this structure, AssignedDevice, and especially this is
just activated in kvm_enabled(). And then set all properties to this
structure.

In xen case, the similar structure, XenHostPCIDevice, is not easy transferred
into the structure, AssignedDevice. So this mean we have to split
assigned_dev_load_option_rom() as line by line for xen and kvm, respectively.

I really agree we definitely need to unify PT infrastructure between kvm and
xen after this try since I can't understand why we originally introduce same
way to do same thing :(

Do you have better idea? If not, I prefer we open this completely as next
action to follow-up. But this time I'm afraid I can't get in this.


The Xen PT code came first. At the time Anthony Liguori and I argued for
sharing the PT code with KVM going forward but Avi wanted to retain the
KVM PT code as is in order not to introduce any regressions on KVM.

Ah.. the good old times :-)

Thanks for your information. So now what's next I should do now? Thanks Tiejun

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