Re: [PATCH v2 05/16] PCI: Add pci_reachable_set()

[Jason Gunthorpe <jgg@nvidia.com>]

On Thu, Jul 17, 2025 at 06:04:04PM -0400, Donald Dutile wrote:
> > Implement pci_reachable_set() to efficiently compute a set of devices on
> > the same bus that are "reachable" from a starting device. The meaning of
> > reachability is defined by the caller through a callback function.
> > 
> This comment made me review get_pci_alias_group(), which states in its description:
> * Look for aliases to or from the given device for existing groups. DMA
>  * aliases are only supported on the same bus, therefore the search
>  * space is quite small
> 
> So why does it do the for loop:
>   for_each_pci_dev(tmp) {
> 
> vs getting the pdev->bus->devices -- list of devices on that bus, and only
> scan that smaller list, vs all pci devices on the system?

Because it can't access the required lock pci_bus_sem to use that
list.

The lock is only available within the PCI core itself which is why I
moved a few functions over there so they can use the lock.

> Could we move this to just before patch 11 where it is used?

Yes

> or could this be used to improve get_pci_alias_group() and get_pci_function_alias_group() ?

IMHO it is not really worth the churn

Jason