[RFC PATCH v2, part 2 01/18] PCI: introduce hotplug-safe PCI bus iterators

[Jiang Liu <liuj97@gmail.com>]

Introduce hotplug-safe PCI bus iterators as below, which hold a
reference on the returned PCI bus object.
bool pci_bus_exists(int domain, int busnr);
struct pci_bus *pci_get_bus(int domain, int busnr);
struct pci_bus *pci_get_next_bus(struct pci_bus *from);
struct pci_bus *pci_get_next_root_bus(struct pci_bus *from);
#define for_each_pci_bus(b) for (b = NULL; (b = pci_get_next_bus(b)); )
#define for_each_pci_root_bus(b)  \
		for (b = NULL; (b = pci_get_next_root_bus(b)); )

The long-term goal is to remove hotplug-unsafe pci_find_bus(),
pci_find_next_bus() and the global pci_root_buses list.

These new interfaces may be a littler slower than existing interfaces,
but it should be acceptable because they are not used on hot paths.

Signed-off-by: Jiang Liu <jiang.liu@huawei.com>
Cc: linux-pci@vger.kernel.org
Cc: linux-kernel@vger.kernel.org
---
 drivers/pci/pci.h    |   1 +
 drivers/pci/probe.c  |   2 +-
 drivers/pci/search.c | 159 +++++++++++++++++++++++++++++++++++++++++----------
 include/linux/pci.h  |  23 +++++++-
 4 files changed, 153 insertions(+), 32 deletions(-)

diff --git a/drivers/pci/pci.h b/drivers/pci/pci.h
index 68678ed..8fe15f6 100644
--- a/drivers/pci/pci.h
+++ b/drivers/pci/pci.h
@@ -126,6 +126,7 @@ static inline void pci_remove_legacy_files(struct pci_bus *bus) { return; }
 
 /* Lock for read/write access to pci device and bus lists */
 extern struct rw_semaphore pci_bus_sem;
+extern struct class pcibus_class;
 
 extern raw_spinlock_t pci_lock;
 
diff --git a/drivers/pci/probe.c b/drivers/pci/probe.c
index e59433a..6b77333 100644
--- a/drivers/pci/probe.c
+++ b/drivers/pci/probe.c
@@ -93,7 +93,7 @@ static void release_pcibus_dev(struct device *dev)
 	kfree(pci_bus);
 }
 
-static struct class pcibus_class = {
+struct class pcibus_class = {
 	.name		= "pci_bus",
 	.dev_release	= &release_pcibus_dev,
 	.dev_attrs	= pcibus_dev_attrs,
diff --git a/drivers/pci/search.c b/drivers/pci/search.c
index d0627fa..16ccaf8 100644
--- a/drivers/pci/search.c
+++ b/drivers/pci/search.c
@@ -52,20 +52,27 @@ pci_find_upstream_pcie_bridge(struct pci_dev *pdev)
 	return tmp;
 }
 
-static struct pci_bus *pci_do_find_bus(struct pci_bus *bus, unsigned char busnr)
+struct pci_bus_match_arg {
+	int domain;
+	int bus;
+};
+
+static int pci_match_bus(struct device *dev, const void *data)
 {
-	struct pci_bus* child;
-	struct list_head *tmp;
+	struct pci_bus *bus = to_pci_bus(dev);
+	const struct pci_bus_match_arg *arg = data;
 
-	if(bus->number == busnr)
-		return bus;
+	return (pci_domain_nr(bus) == arg->domain && bus->number == arg->bus);
+}
 
-	list_for_each(tmp, &bus->children) {
-		child = pci_do_find_bus(pci_bus_b(tmp), busnr);
-		if(child)
-			return child;
-	}
-	return NULL;
+static int pci_match_next_bus(struct device *dev, const void *data)
+{
+	return 1;
+}
+
+static int pci_match_next_root_bus(struct device *dev, const void *data)
+{
+	return pci_is_root_bus(to_pci_bus(dev));
 }
 
 /**
@@ -76,20 +83,19 @@ static struct pci_bus *pci_do_find_bus(struct pci_bus *bus, unsigned char busnr)
  * Given a PCI bus number and domain number, the desired PCI bus is located
  * in the global list of PCI buses.  If the bus is found, a pointer to its
  * data structure is returned.  If no bus is found, %NULL is returned.
+ *
+ * Note: it's not hotplug safe, the returned bus may be destroyed at any time.
+ * Please use pci_get_bus() instead which holds a reference on the returned
+ * PCI bus.
  */
-struct pci_bus * pci_find_bus(int domain, int busnr)
+struct pci_bus *pci_find_bus(int domain, int busnr)
 {
-	struct pci_bus *bus = NULL;
-	struct pci_bus *tmp_bus;
+	struct pci_bus *bus;
 
-	while ((bus = pci_find_next_bus(bus)) != NULL)  {
-		if (pci_domain_nr(bus) != domain)
-			continue;
-		tmp_bus = pci_do_find_bus(bus, busnr);
-		if (tmp_bus)
-			return tmp_bus;
-	}
-	return NULL;
+	bus = pci_get_bus(domain, busnr);
+	pci_bus_put(bus);
+
+	return bus;
 }
 
 /**
@@ -100,21 +106,114 @@ struct pci_bus * pci_find_bus(int domain, int busnr)
  * initiated by passing %NULL as the @from argument.  Otherwise if
  * @from is not %NULL, searches continue from next device on the
  * global list.
+ *
+ * Note: it's not hotplug safe, the returned bus may be destroyed at any time.
+ * Please use pci_get_next_root_bus() instead which holds a reference
+ * on the returned PCI root bus.
  */
 struct pci_bus * 
 pci_find_next_bus(const struct pci_bus *from)
 {
-	struct list_head *n;
-	struct pci_bus *b = NULL;
+	struct device *dev = from ? (struct device *)&from->dev : NULL;
+
+	dev = class_find_device(&pcibus_class, dev, NULL,
+				&pci_match_next_root_bus);
+	if (dev) {
+		put_device(dev);
+		return to_pci_bus(dev);
+	}
+
+	return NULL;
+}
+
+bool pci_bus_exists(int domain, int busnr)
+{
+	struct device *dev;
+	struct pci_bus_match_arg arg = { domain, busnr };
 
 	WARN_ON(in_interrupt());
-	down_read(&pci_bus_sem);
-	n = from ? from->node.next : pci_root_buses.next;
-	if (n != &pci_root_buses)
-		b = pci_bus_b(n);
-	up_read(&pci_bus_sem);
-	return b;
+	dev = class_find_device(&pcibus_class, NULL, &arg, &pci_match_bus);
+	if (dev)
+		put_device(dev);
+
+	return dev != NULL;
+}
+EXPORT_SYMBOL(pci_bus_exists);
+
+/**
+ * pci_get_bus - locate PCI bus from a given domain and bus number
+ * @domain: number of PCI domain to search
+ * @busnr: number of desired PCI bus
+ *
+ * Given a PCI bus number and domain number, the desired PCI bus is located.
+ * If the bus is found, a pointer to its data structure is returned.
+ * If no bus is found, %NULL is returned.
+ * Caller needs to release the returned bus by calling pci_bus_put().
+ */
+struct pci_bus *pci_get_bus(int domain, int busnr)
+{
+	struct device *dev;
+	struct pci_bus_match_arg arg = { domain, busnr };
+
+	WARN_ON(in_interrupt());
+	dev = class_find_device(&pcibus_class, NULL, &arg, &pci_match_bus);
+	if (dev)
+		return to_pci_bus(dev);
+
+	return NULL;
+}
+EXPORT_SYMBOL(pci_get_bus);
+
+/**
+ * pci_get_next_bus - begin or continue searching for a PCI bus
+ * @from: Previous PCI bus found, or %NULL for new search.
+ *
+ * Iterates through the list of known PCI busses. If a PCI bus is found,
+ * the reference count to the bus is incremented and a pointer to it is
+ * returned. Otherwise, %NULL is returned. A new search is initiated by
+ * passing %NULL as the @from argument. Otherwise if @from is not %NULL,
+ * searches continue from next bus on the global list. The reference count
+ * for @from is always decremented if it is not %NULL.
+ */
+struct pci_bus *pci_get_next_bus(struct pci_bus *from)
+{
+	struct device *dev = from ? &from->dev : NULL;
+
+	WARN_ON(in_interrupt());
+	dev = class_find_device(&pcibus_class, dev, NULL, &pci_match_next_bus);
+	pci_bus_put(from);
+	if (dev)
+		return to_pci_bus(dev);
+
+	return NULL;
+}
+EXPORT_SYMBOL(pci_get_next_bus);
+
+/**
+ * pci_find_next_root_bus - begin or continue searching for a PCI root bus
+ * @from: Previous PCI bus found, or %NULL for new search.
+ *
+ * Iterates through the list of known PCI root busses. If a PCI bus is found,
+ * the reference count to the root bus is incremented and a pointer to it is
+ * returned. Otherwise, %NULL is returned. A new search is initiated by
+ * passing %NULL as the @from argument. Otherwise if @from is not %NULL,
+ * searches continue from next root bus on the global list. The reference
+ * count for @from is always decremented if it is not %NULL.
+ */
+struct pci_bus *pci_get_next_root_bus(struct pci_bus *from)
+{
+	struct device *dev = from ? &from->dev : NULL;
+
+	WARN_ON(in_interrupt());
+	dev = class_find_device(&pcibus_class, dev, NULL,
+				&pci_match_next_root_bus);
+	pci_bus_put(from);
+	if (dev)
+		return to_pci_bus(dev);
+
+	return NULL;
 }
+EXPORT_SYMBOL(pci_get_next_root_bus);
 
 /**
  * pci_get_slot - locate PCI device for a given PCI slot
diff --git a/include/linux/pci.h b/include/linux/pci.h
index cc4ce27..c88d4e6 100644
--- a/include/linux/pci.h
+++ b/include/linux/pci.h
@@ -454,6 +454,9 @@ struct pci_bus {
 
 #define pci_bus_b(n)	list_entry(n, struct pci_bus, node)
 #define to_pci_bus(n)	container_of(n, struct pci_bus, dev)
+#define for_each_pci_bus(b)	for (b = NULL; (b = pci_get_next_bus(b)); )
+#define for_each_pci_root_bus(b) \
+			for (b = NULL; (b = pci_get_next_root_bus(b)); )
 
 /*
  * Returns true if the pci bus is root (behind host-pci bridge),
@@ -718,7 +721,6 @@ void pcibios_resource_to_bus(struct pci_dev *dev, struct pci_bus_region *region,
 void pcibios_bus_to_resource(struct pci_dev *dev, struct resource *res,
 			     struct pci_bus_region *region);
 void pcibios_scan_specific_bus(int busn);
-struct pci_bus *pci_find_bus(int domain, int busnr);
 void pci_bus_add_devices(const struct pci_bus *bus);
 struct pci_bus * __deprecated pci_scan_bus_parented(struct device *parent,
 			int bus, struct pci_ops *ops, void *sysdata);
@@ -778,8 +780,15 @@ int pci_find_ext_capability(struct pci_dev *dev, int cap);
 int pci_find_next_ext_capability(struct pci_dev *dev, int pos, int cap);
 int pci_find_ht_capability(struct pci_dev *dev, int ht_cap);
 int pci_find_next_ht_capability(struct pci_dev *dev, int pos, int ht_cap);
+
+struct pci_bus *pci_find_bus(int domain, int busnr);
 struct pci_bus *pci_find_next_bus(const struct pci_bus *from);
 
+bool pci_bus_exists(int domain, int busnr);
+struct pci_bus *pci_get_bus(int domain, int busnr);
+struct pci_bus *pci_get_next_bus(struct pci_bus *from);
+struct pci_bus *pci_get_next_root_bus(struct pci_bus *from);
+
 struct pci_dev *pci_get_device(unsigned int vendor, unsigned int device,
 				struct pci_dev *from);
 struct pci_dev *pci_get_subsys(unsigned int vendor, unsigned int device,
@@ -1429,6 +1438,18 @@ static inline void pci_unblock_cfg_access(struct pci_dev *dev)
 static inline struct pci_bus *pci_find_next_bus(const struct pci_bus *from)
 { return NULL; }
 
+static inline bool pci_bus_exists(int domain, int busnr)
+{ return false; }
+
+static inline struct pci_bus *pci_get_bus(int domain, int busnr)
+{ return NULL; }
+
+static inline struct pci_bus *pci_get_next_bus(struct pci_bus *from)
+{ return NULL; }
+
+static inline struct pci_bus *pci_get_next_root_bus(struct pci_bus *from)
+{ return NULL; }
+
 static inline struct pci_dev *pci_get_slot(struct pci_bus *bus,
 						unsigned int devfn)
 { return NULL; }
-- 
1.8.1.2