Re: [PATCH 7/8] pci: Add pci_for_each_device_all()

[Michael S. Tsirkin]

On Fri, Oct 22, 2021 at 10:33:15AM +0800, Peter Xu wrote:
> Hi, Michael,
> 
> On Thu, Oct 21, 2021 at 06:54:59AM -0400, Michael S. Tsirkin wrote:
> > > +typedef struct {
> > > +    pci_bus_dev_fn fn;
> > > +    void *opaque;
> > > +} pci_bus_dev_args;
> > 
> > code style violation. CamelCase for structs pls.
> 
> OK.
> 
> > > +/* Call 'fn' for each pci device on the system */
> > > +void pci_for_each_device_all(pci_bus_dev_fn fn, void *opaque);
> > 
> > Instead of hacking pci making initialization o(N^2),
> 
> Why it's O(N^2)?  One vIOMMU walks O(N), and we only have one vIOMMU, or am I
> wrong?

What I meant is this is O(N) and if called M times will be O(N * M)
yes your patches only call once so O(N), still we can do better.

> > can't we add a variant of object_resolve_path_type ?
> 
> Could you elaborate?  Here what we want to do is to make sure there're no
> specific PCI devices registered, and potentially it can be more than one type
> of device in the future.
> 
> Thanks,

All you seem to care about is checking there's no VFIO
(why - should really be documented in a code comment much more clearly).
Looks like object_resolve_path_type does that with O(1) complexity.
If we need a variant that checks for multiple types we can add that.

> -- 
> Peter Xu