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Subject[PATCH net-next 3/4] bpf: bpf_htab: Add syscall to iterate percpu value of a key
Date
Add map_lookup_percpu_elem() syscall to lookup value
of a particular CPU.

The user is expected to loop through all CPU values by:
for (cpu = 0; cpu < sysconf(_SC_NPROCESSORS_CONF); cpu++) {
if (!bpf_map_lookup_percpu_elem(map, &key, &value, cpu))
total_value += value;
}

* If the cpu is offline, errno == ENXIO
* If the key is deleted before the iteration is done,
errno == ENOENT.

Signed-off-by: Martin KaFai Lau <kafai@fb.com>
---
include/uapi/linux/bpf.h | 2 ++
kernel/bpf/syscall.c | 93 ++++++++++++++++++++++++++++++++++++++++++++++++
2 files changed, 95 insertions(+)

diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
index e4f8060..96ce561 100644
--- a/include/uapi/linux/bpf.h
+++ b/include/uapi/linux/bpf.h
@@ -73,6 +73,7 @@ enum bpf_cmd {
BPF_PROG_LOAD,
BPF_OBJ_PIN,
BPF_OBJ_GET,
+ BPF_MAP_LOOKUP_PERCPU_ELEM,
};

enum bpf_map_type {
@@ -115,6 +116,7 @@ union bpf_attr {
__aligned_u64 next_key;
};
__u64 flags;
+ __u32 cpu;
};

struct { /* anonymous struct used by BPF_PROG_LOAD command */
diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c
index 6373970..ba1172b 100644
--- a/kernel/bpf/syscall.c
+++ b/kernel/bpf/syscall.c
@@ -289,6 +289,96 @@ err_put:
return err;
}

+/* last field in 'union bpf_attr' used by this command */
+#define BPF_MAP_LOOKUP_PERCPU_ELEM_LAST_FIELD cpu
+
+struct percpu_map_value_info {
+ struct bpf_map *map;
+ void *key;
+ void *value;
+ bool found;
+};
+
+static void percpu_map_lookup_value(void *i)
+{
+ struct percpu_map_value_info *info = (struct percpu_map_value_info *)i;
+ struct bpf_map *map = info->map;
+ void *ptr;
+
+ rcu_read_lock();
+ ptr = map->ops->map_lookup_elem(map, info->key);
+ if (ptr) {
+ memcpy(info->value, ptr, map->value_size);
+ info->found = true;
+ } else {
+ info->found = false;
+ }
+ rcu_read_unlock();
+}
+
+static int map_lookup_percpu_elem(union bpf_attr *attr)
+{
+ void __user *ukey = u64_to_ptr(attr->key);
+ void __user *uvalue = u64_to_ptr(attr->value);
+ u32 __user ucpu = attr->cpu;
+ int ufd = attr->map_fd;
+ struct percpu_map_value_info value_info;
+ struct bpf_map *map;
+ void *key, *value;
+ struct fd f;
+ int err;
+
+ if (CHECK_ATTR(BPF_MAP_LOOKUP_PERCPU_ELEM) ||
+ ucpu >= num_possible_cpus())
+ return -EINVAL;
+
+ f = fdget(ufd);
+ map = __bpf_map_get(f);
+ if (IS_ERR(map))
+ return PTR_ERR(map);
+
+ err = -ENOMEM;
+ key = kmalloc(map->key_size, GFP_USER);
+ if (!key)
+ goto err_put;
+
+ err = -EFAULT;
+ if (copy_from_user(key, ukey, map->key_size) != 0)
+ goto free_key;
+
+ err = -ENOMEM;
+ value = kmalloc(map->value_size, GFP_USER | __GFP_NOWARN);
+ if (!value)
+ goto free_key;
+
+ value_info.map = map;
+ value_info.key = key;
+ value_info.value = value;
+
+ err = smp_call_function_single(ucpu, percpu_map_lookup_value,
+ &value_info, 1);
+ if (err)
+ goto free_value;
+
+ err = -ENOENT;
+ if (!value_info.found)
+ goto free_value;
+
+ err = -EFAULT;
+ if (copy_to_user(uvalue, value, map->value_size) != 0)
+ goto free_value;
+
+ err = 0;
+
+free_value:
+ kfree(value);
+free_key:
+ kfree(key);
+err_put:
+ fdput(f);
+ return err;
+}
+
#define BPF_MAP_UPDATE_ELEM_LAST_FIELD flags

static int map_update_elem(union bpf_attr *attr)
@@ -792,6 +882,9 @@ SYSCALL_DEFINE3(bpf, int, cmd, union bpf_attr __user *, uattr, unsigned int, siz
case BPF_OBJ_GET:
err = bpf_obj_get(&attr);
break;
+ case BPF_MAP_LOOKUP_PERCPU_ELEM:
+ err = map_lookup_percpu_elem(&attr);
+ break;
default:
err = -EINVAL;
break;
--
2.5.1
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