Re: [Xen-devel] PCI passthrough with stubdomain

[Marek Marczykowski-Górecki <marmarek@xxxxxxxxxxxxxxxxxxxxxx>]

On Fri, Sep 23, 2016 at 04:51:33PM +0200, Samuel Thibault wrote:
> Marek Marczykowski-Górecki, on Fri 23 Sep 2016 16:25:41 +0200, wrote:
> > Toolstack during (stub)domain startup setup two things, mostly
> > asynchronously:
> > 1. pciback/pcifront (through standard xenstore entries)
> > 2. instruct qemu to attach device (by writing "pci-ins" to
> > device-model/xxx/command)
> 
> Ah, since pcifront_watches runs in a separate thread, it may not have
> called init_pcifront before qemu calls libpci, i.e. pcifront_scan.

Yes, exactly.

> I'd say that's where the fix should be: make pcifront_scan wait for
> init_pcifront to be done.  It's however not so simple: we want to make
> pcifront_scan do nothing if no pciback is to be launched. My memory is
> rusty: is there something we are sure will show up in the xenstore when
> a pciback is to be launched?  If so, pcifront_scan could do this: wait
> for pcifront_watches to have checked for the potential presence of
> pciback. If pciback is not to be started, just do nothing; if pciback is
> to be started, wait for init_pcifront to have been called by
> pcifront_watches. Then it will find the devices.

Ok. So, two questions:
1. How to do this? ;) I.e. what synchronization primitives are available
in mini-os? Just pthread_mutex_lock/unlock?

2. Wouldn't the same problem be with other stubdomain implementations?
Like Linux + qemu-xen or rumprun + qemu-xen? At least in Linux case
pcifront driver will also needs some time for initialization...

-- 
Best Regards,
Marek Marczykowski-Górecki
Invisible Things Lab
A: Because it messes up the order in which people normally read text.
Q: Why is top-posting such a bad thing?

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