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SubjectRe: [PATCH 2/5] bpf: convert queue and stack map to map_copy_value
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On Tue, Mar 10, 2020 at 06:47 PM CET, Lorenz Bauer wrote:
> Migrate BPF_MAP_TYPE_QUEUE and BPF_MAP_TYPE_STACK to map_copy_value,
> by introducing small wrappers that discard the (unused) key argument.
>
> Signed-off-by: Lorenz Bauer <lmb@cloudflare.com>
> ---
> kernel/bpf/queue_stack_maps.c | 18 ++++++++++++++++++
> kernel/bpf/syscall.c | 5 +----
> 2 files changed, 19 insertions(+), 4 deletions(-)
>
> diff --git a/kernel/bpf/queue_stack_maps.c b/kernel/bpf/queue_stack_maps.c
> index f697647ceb54..5c89b7583cd2 100644
> --- a/kernel/bpf/queue_stack_maps.c
> +++ b/kernel/bpf/queue_stack_maps.c
> @@ -262,11 +262,28 @@ static int queue_stack_map_get_next_key(struct bpf_map *map, void *key,
> return -EINVAL;
> }
>
> +/* Called from syscall */
> +static int queue_map_copy_value(struct bpf_map *map, void *key, void *value)
> +{
> + (void)key;

Alternatively, there's is the __always_unused compiler attribute from
include/linux/compiler_attributes.h that seems to be in wide use.

> +
> + return queue_map_peek_elem(map, value);
> +}
> +
> +/* Called from syscall */
> +static int stack_map_copy_value(struct bpf_map *map, void *key, void *value)
> +{
> + (void)key;
> +
> + return stack_map_peek_elem(map, value);
> +}
> +
> const struct bpf_map_ops queue_map_ops = {
> .map_alloc_check = queue_stack_map_alloc_check,
> .map_alloc = queue_stack_map_alloc,
> .map_free = queue_stack_map_free,
> .map_lookup_elem = queue_stack_map_lookup_elem,
> + .map_copy_value = queue_map_copy_value,
> .map_update_elem = queue_stack_map_update_elem,
> .map_delete_elem = queue_stack_map_delete_elem,
> .map_push_elem = queue_stack_map_push_elem,
> @@ -280,6 +297,7 @@ const struct bpf_map_ops stack_map_ops = {
> .map_alloc = queue_stack_map_alloc,
> .map_free = queue_stack_map_free,
> .map_lookup_elem = queue_stack_map_lookup_elem,
> + .map_copy_value = stack_map_copy_value,
> .map_update_elem = queue_stack_map_update_elem,
> .map_delete_elem = queue_stack_map_delete_elem,
> .map_push_elem = queue_stack_map_push_elem,
> diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c
> index 6503824e81e9..20c6cdace275 100644
> --- a/kernel/bpf/syscall.c
> +++ b/kernel/bpf/syscall.c
> @@ -218,10 +218,7 @@ static int bpf_map_copy_value(struct bpf_map *map, void *key, void *value,
> return bpf_map_offload_lookup_elem(map, key, value);
>
> bpf_disable_instrumentation();
> - if (map->map_type == BPF_MAP_TYPE_QUEUE ||
> - map->map_type == BPF_MAP_TYPE_STACK) {
> - err = map->ops->map_peek_elem(map, value);
> - } else if (map->ops->map_copy_value) {
> + if (map->ops->map_copy_value) {
> err = map->ops->map_copy_value(map, key, value);
> } else {
> rcu_read_lock();

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