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SubjectRe: [PATCH bpf-next 2/3] bpf: add bpffs pretty print for cgroup local storage maps
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On 12/7/18 4:53 PM, Roman Gushchin wrote:
> Implement bpffs pretty printing for cgroup local storage maps
> (both shared and per-cpu).
> Output example (captured for tools/testing/selftests/bpf/netcnt_prog.c):
>
> Shared:
> $ cat /sys/fs/bpf/map_2
> # WARNING!! The output is for debug purpose only
> # WARNING!! The output format will change
> {4294968594,1}: {9999,1039896}
>
> Per-cpu:
> $ cat /sys/fs/bpf/map_1
> # WARNING!! The output is for debug purpose only
> # WARNING!! The output format will change
> {4294968594,1}: {
> cpu0: {0,0,0,0,0}
> cpu1: {0,0,0,0,0}
> cpu2: {1,104,0,0,0}
> cpu3: {0,0,0,0,0}
> }
>
> Signed-off-by: Roman Gushchin <guro@fb.com>
> Cc: Alexei Starovoitov <ast@kernel.org>
> Cc: Daniel Borkmann <daniel@iogearbox.net>
> ---
> include/linux/btf.h | 10 +++++
> kernel/bpf/local_storage.c | 90 +++++++++++++++++++++++++++++++++++++-
> 2 files changed, 99 insertions(+), 1 deletion(-)
>
> diff --git a/include/linux/btf.h b/include/linux/btf.h
> index 8c2199b5d250..ac67bc4cbfd9 100644
> --- a/include/linux/btf.h
> +++ b/include/linux/btf.h
> @@ -5,6 +5,7 @@
> #define _LINUX_BTF_H 1
>
> #include <linux/types.h>
> +#include <uapi/linux/btf.h>
>
> struct btf;
> struct btf_type;
> @@ -63,4 +64,13 @@ static inline const char *btf_name_by_offset(const struct btf *btf,
> }
> #endif
>
> +static inline const struct btf_type *btf_orig_type(const struct btf *btf,
> + const struct btf_type *t)
> +{
> + while (t && BTF_INFO_KIND(t->info) == BTF_KIND_TYPEDEF)
> + t = btf_type_by_id(btf, t->type);
technically, type modifier "const" and "volatile" can apply to member
type as well. But these modifiers really don't make sense here.
Could you add a comment here to mention that they will be treated
as an error since such a programming is not really recommended?

> +
> + return t;
> +}
> +
> #endif
> diff --git a/kernel/bpf/local_storage.c b/kernel/bpf/local_storage.c
> index b65017dead44..7b51fe1aba3c 100644
> --- a/kernel/bpf/local_storage.c
> +++ b/kernel/bpf/local_storage.c
> @@ -1,11 +1,13 @@
> //SPDX-License-Identifier: GPL-2.0
> #include <linux/bpf-cgroup.h>
> #include <linux/bpf.h>
> +#include <linux/btf.h>
> #include <linux/bug.h>
> #include <linux/filter.h>
> #include <linux/mm.h>
> #include <linux/rbtree.h>
> #include <linux/slab.h>
> +#include <uapi/linux/btf.h>
>
> DEFINE_PER_CPU(struct bpf_cgroup_storage*, bpf_cgroup_storage[MAX_BPF_CGROUP_STORAGE_TYPE]);
>
> @@ -308,6 +310,91 @@ static int cgroup_storage_delete_elem(struct bpf_map *map, void *key)
> return -EINVAL;
> }
>
> +static int cgroup_storage_check_btf(const struct bpf_map *map,
> + const struct btf *btf,
> + const struct btf_type *key_type,
> + const struct btf_type *value_type)
> +{
> + const struct btf_type *st, *t;
> + struct btf_member *m;
> +
> + /* Key is expected to be of struct bpf_cgroup_storage_key type,
> + * which is:
> + * struct bpf_cgroup_storage_key {
> + * __u64 cgroup_inode_id;
> + * __u32 attach_type;
> + * };
> + */
> +
> + /*
> + * Key_type must be a structure (or a typedef of a structure) with
> + * two members.
> + */
> + st = btf_orig_type(btf, key_type);
> + if (BTF_INFO_KIND(st->info) != BTF_KIND_STRUCT ||
> + BTF_INFO_VLEN(st->info) != 2)
> + return -EINVAL;
> +
> + /*
> + * The first field must be a 64 bit integer at 0 offset.
> + */
> + m = (struct btf_member *)(st + 1);
> + t = btf_orig_type(btf, btf_type_by_id(btf, m->type));
> + if (!t || BTF_INFO_KIND(t->info) != BTF_KIND_INT || m->offset ||
> + t->size !=
> + FIELD_SIZEOF(struct bpf_cgroup_storage_key, cgroup_inode_id))
> + return -EINVAL;

We should not use t->size here. The "t->size" is the type size, and the
real number of bits held by the member is BTF_INT_BITS(...) with the
argument of the u32 int value after "t".

> +
> + /*
> + * The second field must be a 32 bit integer at 0 offset.
> + */
> + m = m + 1;
> + t = btf_orig_type(btf, btf_type_by_id(btf, m->type));
> + if (!t || BTF_INFO_KIND(t->info) != BTF_KIND_INT ||
> + m->offset != offsetof(struct bpf_cgroup_storage_key, attach_type) *
> + BITS_PER_BYTE || t->size !=
> + FIELD_SIZEOF(struct bpf_cgroup_storage_key, attach_type))
> + return -EINVAL;

The same is here. t->size should not be used.
BTF_INT_BITS(...) should be used.

> +
> + return 0;
> +}
> +
> +static void cgroup_storage_seq_show_elem(struct bpf_map *map, void *_key,
> + struct seq_file *m)
> +{
> + enum bpf_cgroup_storage_type stype = cgroup_storage_type(map);
> + struct bpf_cgroup_storage_key *key = _key;
> + struct bpf_cgroup_storage *storage;
> + int cpu;
> +
> + rcu_read_lock();
> + storage = cgroup_storage_lookup(map_to_storage(map), key, false);
> + if (!storage) {
> + rcu_read_unlock();
> + return;
> + }
> +
> + btf_type_seq_show(map->btf, map->btf_key_type_id, key, m);
> + stype = cgroup_storage_type(map);
> + if (stype == BPF_CGROUP_STORAGE_SHARED) {
> + seq_puts(m, ": ");
> + btf_type_seq_show(map->btf, map->btf_value_type_id,
> + &READ_ONCE(storage->buf)->data[0], m);
> + seq_puts(m, "\n");
> + } else {
> + seq_puts(m, ": {\n");
> + for_each_possible_cpu(cpu) {
> + seq_printf(m, "\tcpu%d: ", cpu);
> + btf_type_seq_show(map->btf, map->btf_value_type_id,
> + per_cpu_ptr(storage->percpu_buf, cpu),
> + m);
> + seq_puts(m, "\n");
> + }
> + seq_puts(m, "}\n");
> + }
> + rcu_read_unlock();
> +}
> +
> const struct bpf_map_ops cgroup_storage_map_ops = {
> .map_alloc = cgroup_storage_map_alloc,
> .map_free = cgroup_storage_map_free,
> @@ -315,7 +402,8 @@ const struct bpf_map_ops cgroup_storage_map_ops = {
> .map_lookup_elem = cgroup_storage_lookup_elem,
> .map_update_elem = cgroup_storage_update_elem,
> .map_delete_elem = cgroup_storage_delete_elem,
> - .map_check_btf = map_check_no_btf,
> + .map_check_btf = cgroup_storage_check_btf,
> + .map_seq_show_elem = cgroup_storage_seq_show_elem,
> };
>
> int bpf_cgroup_storage_assign(struct bpf_prog *prog, struct bpf_map *_map)
>
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