netdev - Re: [RFC PATCH bpf-next 05/16] bpf: create file or anonymous dumpers

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Message-ID: <20200410030017.errh35srmbmd7uk5@ast-mbp.dhcp.thefacebook.com>
Date:   Thu, 9 Apr 2020 20:00:17 -0700
From:   Alexei Starovoitov <alexei.starovoitov@...il.com>
To:     Yonghong Song <yhs@...com>
Cc:     Andrii Nakryiko <andriin@...com>, bpf@...r.kernel.org,
        Martin KaFai Lau <kafai@...com>, netdev@...r.kernel.org,
        Alexei Starovoitov <ast@...com>,
        Daniel Borkmann <daniel@...earbox.net>, kernel-team@...com
Subject: Re: [RFC PATCH bpf-next 05/16] bpf: create file or anonymous dumpers

On Wed, Apr 08, 2020 at 04:25:26PM -0700, Yonghong Song wrote:
> diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
> index 0f1cbed446c1..b51d56fc77f9 100644
> --- a/include/uapi/linux/bpf.h
> +++ b/include/uapi/linux/bpf.h
> @@ -354,6 +354,7 @@ enum {
>  /* Flags for accessing BPF object from syscall side. */
>  	BPF_F_RDONLY		= (1U << 3),
>  	BPF_F_WRONLY		= (1U << 4),
> +	BPF_F_DUMP		= (1U << 5),
...
>  static int bpf_obj_pin(const union bpf_attr *attr)
>  {
> -	if (CHECK_ATTR(BPF_OBJ) || attr->file_flags != 0)
> +	if (CHECK_ATTR(BPF_OBJ) || attr->file_flags & ~BPF_F_DUMP)
>  		return -EINVAL;
>  
> +	if (attr->file_flags == BPF_F_DUMP)
> +		return bpf_dump_create(attr->bpf_fd,
> +				       u64_to_user_ptr(attr->dumper_name));
> +
>  	return bpf_obj_pin_user(attr->bpf_fd, u64_to_user_ptr(attr->pathname));
>  }

I think kernel can be a bit smarter here. There is no need for user space
to pass BPF_F_DUMP flag to kernel just to differentiate the pinning.
Can prog attach type be used instead?