Re: [PATCH v4] PCI: introduce two interfaces to walk PCI buses
From: Bjorn Helgaas <bhelgaas@google.com>
Date: 2012-09-26 20:15:17
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On Fri, Sep 21, 2012 at 10:07 AM, Jiang Liu [off-list ref] wrote:
The pci_find_next_bus() is not hotplug safe, so introduce PCI hotplug
safe interfaces to walk PCI buses. To avoid some deadlock scenarios,
two interfaces are introduced.
The first one is pci_for_each_bus(), which walks all PCI buses holding
read lock on the pci_bus_sem.
The second one is pci_for_each_started_bus(), which walks all started
PCI buses without holding any global locks. Started PCI buses are those
which have been added to the device tree by calling device_add().
---
Hi Bjorn,
How about this PCI bus iterator design? It's a little ugly that
we need to two interfaces to work around some deadlock scenarios.
And I plan to split the task into two parts:
1) a hotplug safe PCI bus iteraror to replace pci_find_next_bus
2) handle hotplug notifications to update bus related states.
My patchset at http://www.spinics.net/lists/linux-pci/msg17515.html has
patially solved issue 2 above for x86/ACPI, and will add more supports
for other platforms.
Thanks!
Gerry
I like this interface:
int pci_for_each_bus(int (* cb)(struct pci_bus *, void *), void *data)
quite a bit because it has the potential for removing all the list
knowledge from the callers, but there are two things I don't like:
1) The interface would allow the PCI core to call the callback for
future hot-added buses, but your implementation doesn't have that yet.
2) I'd rather have something like "pci_for_each_dev()" so this is
device-based instead of bus-based. The struct pci_bus is of limited
usefulness outside the core, except as a container for a set of
devices. So the users of pci_for_each_bus() would often iterate
through that set of devices, and given the complications of SR-IOV
virtual buses, I don't think it's really clear how to do that
iteration correctly.
quoted hunk ↗ jump to hunk
--- drivers/pci/bus.c | 42 ++++++++++++++++++++++++++++++++++++++++++ include/linux/pci.h | 1 + 2 files changed, 43 insertions(+)diff --git a/drivers/pci/bus.c b/drivers/pci/bus.c index e16a8f0f..21b0ade 100644 --- a/drivers/pci/bus.c +++ b/drivers/pci/bus.c@@ -327,6 +327,48 @@ void pci_walk_bus(struct pci_bus *top, int (*cb)(struct pci_dev *, void *), } EXPORT_SYMBOL_GPL(pci_walk_bus); +static int pci_bus_iter(struct pci_bus *bus, + int (* cb)(struct pci_bus *, void *), void *data) +{ + int rc; + + rc = cb(bus, data); + if (rc == 0) + list_for_each_entry(bus, &bus->children, node) { + rc = pci_bus_iter(bus, cb, data); + if (rc) + break; + } + + return rc; +} + +/** pci_for_each_bus - walk all PCI buses and call the provided callback. + * @cb callback to be called for each bus found + * @data arbitrary pointer to be passed to callback. + * + * Walk all PCI buses and call the provided callback with pci_bus_sem held. + * + * We check the return of @cb each time. If it returns anything + * other than 0, we break out. + */ +int pci_for_each_bus(int (* cb)(struct pci_bus *, void *), void *data) +{ + int rc = 0; + struct pci_bus *bus; + + down_read(&pci_bus_sem); + list_for_each_entry(bus, &pci_root_buses, node) { + rc = pci_bus_iter(bus, cb, data); + if (rc) + break; + } + up_read(&pci_bus_sem); + + return rc; +} +EXPORT_SYMBOL(pci_for_each_bus); + 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 3c5017d..1423a24 100644 --- a/include/linux/pci.h +++ b/include/linux/pci.h@@ -1060,6 +1060,7 @@ 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); +int pci_for_each_bus(int (* cb)(struct pci_bus *, void *), void *data); int pci_cfg_space_size_ext(struct pci_dev *dev); int pci_cfg_space_size(struct pci_dev *dev); unsigned char pci_bus_max_busnr(struct pci_bus *bus); --1.7.9.5