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SubjectRe: [PATCH 2/5] bpf: convert queue and stack map to map_copy_value
Jakub Sitnicki wrote:
> 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.
>

+1 use the attribute its much nicer imo.

> > +
> > + 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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