On Wed, May 28, 2014 at 03:29:09PM -0700, Alexander Duyck wrote:
> This function provides a simple means for applying a given function to all
> devices on bus and all of it's children, including virtual busses. To do
> this the function begins by processing all devices on the bus, then it will
> proceed through bus->children and process each of the child busses.
Yeah, I think this makes sense. I forgot that the pci_bus has a list of
all child buses, and the virtual buses *are* on that list. It's just that
there's no bridge pci_dev where dev->subordinate is the virtual bus, so if
we iterate over the bus->devices list as pci_walk_bus() does, we won't find
a bridge leading to the virtual bus.
But it seems like we could use pci_walk_vbus() as you implemented it here
for both purposes, i.e., we could just change pci_walk_bus() to work this
way. Would that break anything? It'd be nicer to just have one "walk bus"
interface, especially since these differ in a pretty subtle way.
I don't really want to elevate the "virtual bus" idea, i.e., the idea that
we have a bus that is not the secondary bus of a bridge, to a first-class
PCI citizen. It seems like a wart that I'd like to get rid of if we had a
way to do it.
I'm curious about what Windows does for this situation. I have a dim
memory that it creates some kind of virtual bridge device leading to a bus
like this. But I have no reference, and maybe I just made that up.
Bjorn
> Signed-off-by: Alexander Duyck <alexander.h.duyck@xxxxxxxxx>
> ---
> drivers/pci/bus.c | 44 ++++++++++++++++++++++++++++++++++++++++++++
> include/linux/pci.h | 2 ++
> 2 files changed, 46 insertions(+), 0 deletions(-)
>
> diff --git a/drivers/pci/bus.c b/drivers/pci/bus.c
> index fb8aed3..769bbcb 100644
> --- a/drivers/pci/bus.c
> +++ b/drivers/pci/bus.c
> @@ -336,6 +336,50 @@ void pci_walk_bus(struct pci_bus *top, int (*cb)(struct pci_dev *, void *),
> }
> EXPORT_SYMBOL_GPL(pci_walk_bus);
>
> +/** pci_walk_vbus - walk devices on/under bus, calling callback.
> + * @top bus whose devices should be walked
> + * @cb callback to be called for each device found
> + * @userdata arbitrary pointer to be passed to callback.
> + *
> + * Walk the given bus, including any child buses under this bus.
> + * Call the provided callback on each device found.
> + *
> + * We check the return of @cb each time. If it returns anything
> + * other than 0, we break out.
> + *
> + */
> +void pci_walk_vbus(struct pci_bus *top, int (*cb)(struct pci_dev *, void *),
> + void *userdata)
> +{
> + struct list_head *bus_next;
> + struct pci_bus *bus;
> + struct pci_dev *dev;
> +
> + down_read(&pci_bus_sem);
> + bus_next = &top->node;
> + for (;;) {
> + /* prep bus for next iteration */
> + bus = list_entry(bus_next, struct pci_bus, node);
> +
> + /* process each device on this bus */
> + list_for_each_entry(dev, &bus->devices, bus_list) {
> + if (cb(dev, userdata))
> + goto release_semaphore;
> + }
> +
> + /* end of this bus, go to child, next bus, or finish */
> + for (bus_next = bus->children.next;
> + bus_next == &bus->children;
> + bus_next = bus->node.next, bus = bus->parent) {
> + if (bus == top)
> + goto release_semaphore;
> + }
> + }
> +release_semaphore:
> + up_read(&pci_bus_sem);
> +}
> +EXPORT_SYMBOL_GPL(pci_walk_vbus);
> +
> struct pci_bus *pci_bus_get(struct pci_bus *bus)
> {
> if (bus)
> diff --git a/include/linux/pci.h b/include/linux/pci.h
> index aab57b4..1fb18a8 100644
> --- a/include/linux/pci.h
> +++ b/include/linux/pci.h
> @@ -1118,6 +1118,8 @@ int pci_scan_bridge(struct pci_bus *bus, struct pci_dev *dev, int max,
>
> void pci_walk_bus(struct pci_bus *top, int (*cb)(struct pci_dev *, void *),
> void *userdata);
> +void pci_walk_vbus(struct pci_bus *top, int (*cb)(struct pci_dev *, void *),
> + void *userdata);
> int pci_cfg_space_size(struct pci_dev *dev);
> unsigned char pci_bus_max_busnr(struct pci_bus *bus);
> void pci_setup_bridge(struct pci_bus *bus);
>
--
To unsubscribe from this list: send the line "unsubscribe linux-pci" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
