On Thu, Aug 20, 2020 at 3:50 PM Yonghong Song <yhs@xxxxxx> wrote:
>
> This patch implemented bpf_link callback functions
> show_fdinfo and fill_link_info to support link_query
> interface.
>
> The general interface for show_fdinfo and fill_link_info
> will print/fill the target_name. Each targets can
> register show_fdinfo and fill_link_info callbacks
> to print/fill more target specific information.
>
> For example, the below is a fdinfo result for a bpf
> task iterator.
> $ cat /proc/1749/fdinfo/7
> pos: 0
> flags: 02000000
> mnt_id: 14
> link_type: iter
> link_id: 11
> prog_tag: 990e1f8152f7e54f
> prog_id: 59
> target_name: task
>
> Signed-off-by: Yonghong Song <yhs@xxxxxx>
> ---
> include/linux/bpf.h | 6 ++++
> include/uapi/linux/bpf.h | 7 ++++
> kernel/bpf/bpf_iter.c | 58 ++++++++++++++++++++++++++++++++++
> tools/include/uapi/linux/bpf.h | 7 ++++
> 4 files changed, 78 insertions(+)
>
[...]
> +
> +static int bpf_iter_link_fill_link_info(const struct bpf_link *link,
> + struct bpf_link_info *info)
> +{
> + struct bpf_iter_link *iter_link =
> + container_of(link, struct bpf_iter_link, link);
> + char __user *ubuf = u64_to_user_ptr(info->iter.target_name);
> + bpf_iter_fill_link_info_t fill_link_info;
> + u32 ulen = info->iter.target_name_len;
> + const char *target_name;
> + u32 target_len;
> +
> + if (ulen && !ubuf)
> + return -EINVAL;
> +
> + target_name = iter_link->tinfo->reg_info->target;
> + target_len = strlen(target_name);
> + info->iter.target_name_len = target_len + 1;
> + if (!ubuf)
> + return 0;
this might return prematurely before fill_link_info() below gets a
chance to fill in some extra info?
> +
> + if (ulen >= target_len + 1) {
> + if (copy_to_user(ubuf, target_name, target_len + 1))
> + return -EFAULT;
> + } else {
> + char zero = '\0';
> +
> + if (copy_to_user(ubuf, target_name, ulen - 1))
> + return -EFAULT;
> + if (put_user(zero, ubuf + ulen - 1))
> + return -EFAULT;
> + return -ENOSPC;
> + }
> +
> + fill_link_info = iter_link->tinfo->reg_info->fill_link_info;
> + if (fill_link_info)
> + return fill_link_info(&iter_link->aux, info);
> +
> + return 0;
> +}
> +
[...]
