[PATCH 05/15] bpf: Export a map-clearing function

[Tom Zanussi]

Add a new map_clear() function to bpf_map_ops along with a
tracing_map_clear() export for external users.

Map implementations that it makes sense for should implement it,
otherwise it's not required.  The bpf hashtab implementation does
implement a clear operation, but since it doesn't make sense for bpf
arraymaps, the arraymap implementation doesn't.

Signed-off-by: Tom Zanussi <tom.zanussi@xxxxxxxxxxxxxxx>
---
 include/linux/bpf.h  |  2 ++
 kernel/bpf/hashtab.c |  8 ++++++++
 kernel/bpf/syscall.c | 17 +++++++++++++++++
 3 files changed, 27 insertions(+)

diff --git a/include/linux/bpf.h b/include/linux/bpf.h
index 900405bf..f7f95d7 100644
--- a/include/linux/bpf.h
+++ b/include/linux/bpf.h
@@ -18,6 +18,7 @@ struct bpf_map_ops {
 	/* funcs callable from userspace (via syscall) */
 	struct bpf_map *(*map_alloc)(union bpf_attr *attr);
 	void (*map_free)(struct bpf_map *);
+	void (*map_clear)(struct bpf_map *);
 	int (*map_get_next_key)(struct bpf_map *map, void *key, void *next_key);
 
 	/* funcs callable from userspace and from eBPF programs */
@@ -144,6 +145,7 @@ extern struct bpf_func_proto bpf_map_delete_elem_proto;
 
 struct bpf_map *tracing_map_create(union bpf_attr *attr);
 void tracing_map_destroy(struct bpf_map *map);
+void tracing_map_clear(struct bpf_map *map);
 int tracing_map_update_elem(struct bpf_map *map, void *key, void *value,
 			    union bpf_attr *attr);
 int tracing_map_lookup_elem(struct bpf_map *map, void *key, void *uvalue);
diff --git a/kernel/bpf/hashtab.c b/kernel/bpf/hashtab.c
index b3ba436..addf3a8 100644
--- a/kernel/bpf/hashtab.c
+++ b/kernel/bpf/hashtab.c
@@ -325,6 +325,13 @@ static void delete_all_elements(struct bpf_htab *htab)
 	}
 }
 
+static void htab_map_clear(struct bpf_map *map)
+{
+	struct bpf_htab *htab = container_of(map, struct bpf_htab, map);
+
+	delete_all_elements(htab);
+}
+
 /* Called when map->refcnt goes to zero, either from workqueue or from syscall */
 static void htab_map_free(struct bpf_map *map)
 {
@@ -348,6 +355,7 @@ static void htab_map_free(struct bpf_map *map)
 static struct bpf_map_ops htab_ops = {
 	.map_alloc = htab_map_alloc,
 	.map_free = htab_map_free,
+	.map_clear = htab_map_clear,
 	.map_get_next_key = htab_map_get_next_key,
 	.map_lookup_elem = htab_map_lookup_elem,
 	.map_update_elem = htab_map_update_elem,
diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c
index cac8df6..0f28904 100644
--- a/kernel/bpf/syscall.c
+++ b/kernel/bpf/syscall.c
@@ -362,6 +362,23 @@ int tracing_map_delete_elem(struct bpf_map *map, void *key)
 }
 EXPORT_SYMBOL_GPL(tracing_map_delete_elem);
 
+/**
+ * tracing_map_clear - Clear a bpf_map
+ * @map: The bpf_map to clear
+ *
+ * Clear the bpf_map.
+ *
+ * Return: nothing, map clearing always succeeds
+ */
+void tracing_map_clear(struct bpf_map *map)
+{
+	rcu_read_lock();
+	if (map->ops->map_clear)
+		map->ops->map_clear(map);
+	rcu_read_unlock();
+}
+EXPORT_SYMBOL_GPL(tracing_map_clear);
+
 #define BPF_MAP_DELETE_ELEM_LAST_FIELD key
 
 static int map_delete_elem(union bpf_attr *attr)
-- 
1.9.3

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