On Fri, Jul 24, 2020 at 1:39 PM Alexei Starovoitov
<alexei.starovoitov@xxxxxxxxx> wrote:
>
> From: Alexei Starovoitov <ast@xxxxxxxxxx>
>
> Refactor the code a bit to extract bpf_link_get_by_id() helper.
The commit log doesn't match the code: bpf_link_get_by_id() vs.
bpf_link_by_id().
> It's similar to existing bpf_prog_by_id().
>
> Signed-off-by: Alexei Starovoitov <ast@xxxxxxxxxx>
> Acked-by: Andrii Nakryiko <andriin@xxxxxx>
Other than that,
Acked-by: Song Liu <songliubraving@xxxxxx>
> ---
> include/linux/bpf.h | 1 +
> kernel/bpf/syscall.c | 46 +++++++++++++++++++++++++++-----------------
> 2 files changed, 29 insertions(+), 18 deletions(-)
>
> diff --git a/include/linux/bpf.h b/include/linux/bpf.h
> index 8357be349133..d5c4e2cc24a0 100644
> --- a/include/linux/bpf.h
> +++ b/include/linux/bpf.h
> @@ -1355,6 +1355,7 @@ int btf_check_type_match(struct bpf_verifier_env *env, struct bpf_prog *prog,
> struct btf *btf, const struct btf_type *t);
>
> struct bpf_prog *bpf_prog_by_id(u32 id);
> +struct bpf_link *bpf_link_by_id(u32 id);
>
> const struct bpf_func_proto *bpf_base_func_proto(enum bpf_func_id func_id);
> #else /* !CONFIG_BPF_SYSCALL */
> diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c
> index ee290b1f2d9e..42eb0d622980 100644
> --- a/kernel/bpf/syscall.c
> +++ b/kernel/bpf/syscall.c
> @@ -3984,40 +3984,50 @@ static int link_update(union bpf_attr *attr)
> return ret;
> }
>
> -static int bpf_link_inc_not_zero(struct bpf_link *link)
> +static struct bpf_link *bpf_link_inc_not_zero(struct bpf_link *link)
> {
> - return atomic64_fetch_add_unless(&link->refcnt, 1, 0) ? 0 : -ENOENT;
> + return atomic64_fetch_add_unless(&link->refcnt, 1, 0) ? link : ERR_PTR(-ENOENT);
> }
>
> -#define BPF_LINK_GET_FD_BY_ID_LAST_FIELD link_id
> -
> -static int bpf_link_get_fd_by_id(const union bpf_attr *attr)
> +struct bpf_link *bpf_link_by_id(u32 id)
> {
> struct bpf_link *link;
> - u32 id = attr->link_id;
> - int fd, err;
>
> - if (CHECK_ATTR(BPF_LINK_GET_FD_BY_ID))
> - return -EINVAL;
> -
> - if (!capable(CAP_SYS_ADMIN))
> - return -EPERM;
> + if (!id)
> + return ERR_PTR(-ENOENT);
>
> spin_lock_bh(&link_idr_lock);
> - link = idr_find(&link_idr, id);
> /* before link is "settled", ID is 0, pretend it doesn't exist yet */
> + link = idr_find(&link_idr, id);
> if (link) {
> if (link->id)
> - err = bpf_link_inc_not_zero(link);
> + link = bpf_link_inc_not_zero(link);
> else
> - err = -EAGAIN;
> + link = ERR_PTR(-EAGAIN);
> } else {
> - err = -ENOENT;
> + link = ERR_PTR(-ENOENT);
> }
> spin_unlock_bh(&link_idr_lock);
> + return link;
> +}
>
> - if (err)
> - return err;
> +#define BPF_LINK_GET_FD_BY_ID_LAST_FIELD link_id
> +
> +static int bpf_link_get_fd_by_id(const union bpf_attr *attr)
> +{
> + struct bpf_link *link;
> + u32 id = attr->link_id;
> + int fd;
> +
> + if (CHECK_ATTR(BPF_LINK_GET_FD_BY_ID))
> + return -EINVAL;
> +
> + if (!capable(CAP_SYS_ADMIN))
> + return -EPERM;
> +
> + link = bpf_link_by_id(id);
> + if (IS_ERR(link))
> + return PTR_ERR(link);
>
> fd = bpf_link_new_fd(link);
> if (fd < 0)
> --
> 2.23.0
>
