On Wed, Mar 15, 2023 at 7:37 PM Kui-Feng Lee <kuifeng@xxxxxxxx> wrote:
>
> By improving the BPF_LINK_UPDATE command of bpf(), it should allow you
> to conveniently switch between different struct_ops on a single
> bpf_link. This would enable smoother transitions from one struct_ops
> to another.
>
> The struct_ops maps passing along with BPF_LINK_UPDATE should have the
> BPF_F_LINK flag.
>
> Signed-off-by: Kui-Feng Lee <kuifeng@xxxxxxxx>
> ---
> include/linux/bpf.h | 2 ++
> include/uapi/linux/bpf.h | 8 +++++--
> kernel/bpf/bpf_struct_ops.c | 38 ++++++++++++++++++++++++++++++++++
> kernel/bpf/syscall.c | 20 ++++++++++++++++++
> net/bpf/bpf_dummy_struct_ops.c | 6 ++++++
> net/ipv4/bpf_tcp_ca.c | 6 ++++++
> tools/include/uapi/linux/bpf.h | 8 +++++--
> 7 files changed, 84 insertions(+), 4 deletions(-)
>
> diff --git a/include/linux/bpf.h b/include/linux/bpf.h
> index 455b14bf8f28..56e6ab7559ef 100644
> --- a/include/linux/bpf.h
> +++ b/include/linux/bpf.h
> @@ -1474,6 +1474,7 @@ struct bpf_link_ops {
> void (*show_fdinfo)(const struct bpf_link *link, struct seq_file *seq);
> int (*fill_link_info)(const struct bpf_link *link,
> struct bpf_link_info *info);
> + int (*update_map)(struct bpf_link *link, struct bpf_map *new_map);
> };
>
> struct bpf_tramp_link {
> @@ -1516,6 +1517,7 @@ struct bpf_struct_ops {
> void *kdata, const void *udata);
> int (*reg)(void *kdata);
> void (*unreg)(void *kdata);
> + int (*update)(void *kdata, void *old_kdata);
> int (*validate)(void *kdata);
> const struct btf_type *type;
> const struct btf_type *value_type;
> diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
> index 42f40ee083bf..24e1dec4ad97 100644
> --- a/include/uapi/linux/bpf.h
> +++ b/include/uapi/linux/bpf.h
> @@ -1555,8 +1555,12 @@ union bpf_attr {
>
> struct { /* struct used by BPF_LINK_UPDATE command */
> __u32 link_fd; /* link fd */
> - /* new program fd to update link with */
> - __u32 new_prog_fd;
> + union {
> + /* new program fd to update link with */
> + __u32 new_prog_fd;
> + /* new struct_ops map fd to update link with */
> + __u32 new_map_fd;
> + };
> __u32 flags; /* extra flags */
> /* expected link's program fd; is specified only if
> * BPF_F_REPLACE flag is set in flags */
> diff --git a/kernel/bpf/bpf_struct_ops.c b/kernel/bpf/bpf_struct_ops.c
> index 8ce6c7581ca3..5a9e10b92423 100644
> --- a/kernel/bpf/bpf_struct_ops.c
> +++ b/kernel/bpf/bpf_struct_ops.c
> @@ -807,10 +807,48 @@ static int bpf_struct_ops_map_link_fill_link_info(const struct bpf_link *link,
> return 0;
> }
>
> +static int bpf_struct_ops_map_link_update(struct bpf_link *link, struct bpf_map *new_map)
> +{
> + struct bpf_struct_ops_map *st_map, *old_st_map;
> + struct bpf_struct_ops_link *st_link;
> + struct bpf_map *old_map;
> + int err = 0;
> +
> + st_link = container_of(link, struct bpf_struct_ops_link, link);
> + st_map = container_of(new_map, struct bpf_struct_ops_map, map);
> +
> + if (!bpf_struct_ops_valid_to_reg(new_map))
> + return -EINVAL;
> +
> + mutex_lock(&update_mutex);
> +
> + old_map = rcu_dereference_protected(st_link->map, lockdep_is_held(&update_mutex));
> + old_st_map = container_of(old_map, struct bpf_struct_ops_map, map);
> + /* The new and old struct_ops must be the same type. */
> + if (st_map->st_ops != old_st_map->st_ops) {
> + err = -EINVAL;
> + goto err_out;
> + }
> +
> + err = st_map->st_ops->update(st_map->kvalue.data, old_st_map->kvalue.data);
> + if (err)
> + goto err_out;
> +
> + bpf_map_inc(new_map);
> + rcu_assign_pointer(st_link->map, new_map);
> + bpf_map_put(old_map);
> +
> +err_out:
> + mutex_unlock(&update_mutex);
> +
> + return err;
> +}
> +
> static const struct bpf_link_ops bpf_struct_ops_map_lops = {
> .dealloc = bpf_struct_ops_map_link_dealloc,
> .show_fdinfo = bpf_struct_ops_map_link_show_fdinfo,
> .fill_link_info = bpf_struct_ops_map_link_fill_link_info,
> + .update_map = bpf_struct_ops_map_link_update,
> };
>
> int bpf_struct_ops_link_create(union bpf_attr *attr)
> diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c
> index 5a45e3bf34e2..6fa10d108278 100644
> --- a/kernel/bpf/syscall.c
> +++ b/kernel/bpf/syscall.c
> @@ -4676,6 +4676,21 @@ static int link_create(union bpf_attr *attr, bpfptr_t uattr)
> return ret;
> }
>
> +static int link_update_map(struct bpf_link *link, union bpf_attr *attr)
> +{
> + struct bpf_map *new_map;
> + int ret = 0;
> +
> + new_map = bpf_map_get(attr->link_update.new_map_fd);
> + if (IS_ERR(new_map))
> + return -EINVAL;
I was expecting a check for the BPF_F_LINK flag here. Isn't it
necessary to verify that here?
> +
> + ret = link->ops->update_map(link, new_map);
> +
> + bpf_map_put(new_map);
> + return ret;
> +}
> +
> #define BPF_LINK_UPDATE_LAST_FIELD link_update.old_prog_fd
>
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