On Sun, May 3, 2020 at 11:26 PM Yonghong Song <yhs@xxxxxx> wrote:
>
> Given a bpf program, the step to create an anonymous bpf iterator is:
> - create a bpf_iter_link, which combines bpf program and the target.
> In the future, there could be more information recorded in the link.
> A link_fd will be returned to the user space.
> - create an anonymous bpf iterator with the given link_fd.
>
> The bpf_iter_link can be pinned to bpffs mount file system to
> create a file based bpf iterator as well.
>
> The benefit to use of bpf_iter_link:
> - using bpf link simplifies design and implementation as bpf link
> is used for other tracing bpf programs.
> - for file based bpf iterator, bpf_iter_link provides a standard
> way to replace underlying bpf programs.
> - for both anonymous and free based iterators, bpf link query
> capability can be leveraged.
>
> The patch added support of tracing/iter programs for BPF_LINK_CREATE.
> A new link type BPF_LINK_TYPE_ITER is added to facilitate link
> querying. Currently, only prog_id is needed, so there is no
> additional in-kernel show_fdinfo() and fill_link_info() hook
> is needed for BPF_LINK_TYPE_ITER link.
>
> Signed-off-by: Yonghong Song <yhs@xxxxxx>
> ---
LGTM. See small nit about __GFP_NOWARN.
Acked-by: Andrii Nakryiko <andriin@xxxxxx>
> include/linux/bpf.h | 1 +
> include/linux/bpf_types.h | 1 +
> include/uapi/linux/bpf.h | 1 +
> kernel/bpf/bpf_iter.c | 62 ++++++++++++++++++++++++++++++++++
> kernel/bpf/syscall.c | 14 ++++++++
> tools/include/uapi/linux/bpf.h | 1 +
> 6 files changed, 80 insertions(+)
>
[...]
> +int bpf_iter_link_attach(const union bpf_attr *attr, struct bpf_prog *prog)
> +{
> + struct bpf_link_primer link_primer;
> + struct bpf_iter_target_info *tinfo;
> + struct bpf_iter_link *link;
> + bool existed = false;
> + u32 prog_btf_id;
> + int err;
> +
> + if (attr->link_create.target_fd || attr->link_create.flags)
> + return -EINVAL;
> +
> + prog_btf_id = prog->aux->attach_btf_id;
> + mutex_lock(&targets_mutex);
> + list_for_each_entry(tinfo, &targets, list) {
> + if (tinfo->btf_id == prog_btf_id) {
> + existed = true;
> + break;
> + }
> + }
> + mutex_unlock(&targets_mutex);
> + if (!existed)
> + return -ENOENT;
> +
> + link = kzalloc(sizeof(*link), GFP_USER | __GFP_NOWARN);
nit: all existing link implementation don't specify __GFP_NOWARN,
wonder if bpf_iter_link should be special?
> + if (!link)
> + return -ENOMEM;
> +
> + bpf_link_init(&link->link, BPF_LINK_TYPE_ITER, &bpf_iter_link_lops, prog);
> + link->tinfo = tinfo;
> +
> + err = bpf_link_prime(&link->link, &link_primer);
> + if (err) {
> + kfree(link);
> + return err;
> + }
> +
> + return bpf_link_settle(&link_primer);
> +}
[...]
