Re: [PATCH] qrap: Pass PCI device numbers to qemu in base 10, not in base 16

[Stefano Brivio <sbrivio@redhat.com>]

On Wed, 22 Feb 2023 02:40:32 -0800
Andrea Bolognani <abologna@redhat.com> wrote:

> On Tue, Feb 21, 2023 at 08:24:25PM +0100, Stefano Brivio wrote:
> >  		if (!has_json) {
> >  			snprintf(dev_str, ARG_MAX,
> > -			         "%s,%s%x%s,netdev=hostnet0,x-txburst=4096",
> > +			         "%s,%s%i%s,netdev=hostnet0,x-txburst=4096",
> >  			         dev->name, dev->template, i, dev->template_post);
> >  		} else {
> >  			snprintf(dev_str, ARG_MAX,
> > -			         "{\"driver\":\"%s\",%s%x\"%s,\"netdev\":\"hostnet0\",\"x-txburst\":4096}",
> > +			         "{\"driver\":\"%s\",%s%i\"%s,\"netdev\":\"hostnet0\",\"x-txburst\":4096}",
> >  			         dev->name, dev->template_json, i, dev->template_json_post);
> >  		}  
> 
> I don't think this is going to work.
> 
> The problem is that, while PCI buses are indeed named with increasing
> numbers in integer format (pci.9, pci.10 and so on), PCI slots are
> addressed using hexadecimal format (0x9, 0xa and so on). libvirt uses
> this naming convention because it matches QEMU's.
> 
> So if you have an i440fx machine with many devices, they will all[1]
> be put on pci.0, the corresponding arguments will look like
> 
>   -device virtio-net-pci,bus=pci.0,addr=0xa
> 
> and the original version of the code will work correctly.
> 
> If the machine is q35, however, devices will not be put on pcie.0
> directly but rather attached to pcie-root-ports, each one of which
> creates a separate PCI bus. So the arguments will look like
> 
>   -device virtio-net-pci,bus=pci.10,addr=0x0
> 
> where it is the new version of the code that would do the right
> thing.

Oh, oops, I didn't know that.

> What I think needs to happen, is that each pci_dev should contain a
> base value (16 for i440fx and 10 for q35), which is used both in the
> strtol() call used to parse the command line produced by libvirt and
> to decide whether %x or %i should be used with snprintf() to generate
> qrap's own arguments.

Right, I think it makes sense. Will you prepare a patch in this sense
or should I try?

-- 
Stefano