On 11/04/2014 03:54 AM, Alexei Starovoitov wrote:
add new map type BPF_MAP_TYPE_ARRAY and its implementation
- optimized for fastest possible lookup()
. in the future verifier/JIT may recognize lookup() with constant key
and optimize it into constant pointer. Can optimize non-constant
key into direct pointer arithmetic as well, since pointers and
value_size are constant for the life of the eBPF program.
In other words array_map_lookup_elem() may be 'inlined' by verifier/JIT
while preserving concurrent access to this map from user space
- two main use cases for array type:
. 'global' eBPF variables: array of 1 element with key=0 and value is a
collection of 'global' variables which programs can use to keep the state
between events
. aggregation of tracing events into fixed set of buckets
- all array elements pre-allocated and zero initialized at init time
- key as an index in array and can only be 4 byte
- map_delete_elem() returns EINVAL, since elements cannot be deleted
- map_update_elem() replaces elements in an non-atomic way
(for atomic updates hashtable type should be used instead)
Signed-off-by: Alexei Starovoitov <a...@plumgrid.com>
...
+/* Called from syscall or from eBPF program */
+static int array_map_update_elem(struct bpf_map *map, void *key, void *value,
+ u64 map_flags)
+{
+ struct bpf_array *array = container_of(map, struct bpf_array, map);
+ u32 index = *(u32 *)key;
+
+ if (map_flags > BPF_MAP_UPDATE_ONLY)
+ /* unknown flags */
+ return -EINVAL;
+
+ if (map_flags == BPF_MAP_CREATE_ONLY)
+ return -EINVAL;
+
+ if (index >= array->map.max_entries)
+ /* all elements were pre-allocated, cannot insert a new one */
+ return -E2BIG;
+
+ memcpy(array->value + array->elem_size * index, value,
array->elem_size);
What would protect this from concurrent updates?
+ return 0;
+}
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