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Date:   Mon, 03 Aug 2020 17:37:51 -0700
From:   John Fastabend <john.fastabend@...il.com>
To:     Yonghong Song <yhs@...com>, bpf@...r.kernel.org,
        netdev@...r.kernel.org
Cc:     Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>, kernel-team@...com
Subject: RE: [PATCH bpf-next v3 1/2] bpf: change uapi for bpf iterator map
 elements

Yonghong Song wrote:
> Commit a5cbe05a6673 ("bpf: Implement bpf iterator for
> map elements") added bpf iterator support for
> map elements. The map element bpf iterator requires
> info to identify a particular map. In the above
> commit, the attr->link_create.target_fd is used
> to carry map_fd and an enum bpf_iter_link_info
> is added to uapi to specify the target_fd actually
> representing a map_fd:
>     enum bpf_iter_link_info {
> 	BPF_ITER_LINK_UNSPEC = 0,
> 	BPF_ITER_LINK_MAP_FD = 1,
> 
> 	MAX_BPF_ITER_LINK_INFO,
>     };
> 
> This is an extensible approach as we can grow
> enumerator for pid, cgroup_id, etc. and we can
> unionize target_fd for pid, cgroup_id, etc.
> But in the future, there are chances that
> more complex customization may happen, e.g.,
> for tasks, it could be filtered based on
> both cgroup_id and user_id.
> 
> This patch changed the uapi to have fields
> 	__aligned_u64	iter_info;
> 	__u32		iter_info_len;
> for additional iter_info for link_create.
> The iter_info is defined as
> 	union bpf_iter_link_info {
> 		struct {
> 			__u32   map_fd;
> 		} map;
> 	};
> 
> So future extension for additional customization
> will be easier. The bpf_iter_link_info will be
> passed to target callback to validate and generic
> bpf_iter framework does not need to deal it any
> more.
> 
> Note that map_fd = 0 will be considered invalid
> and -EBADF will be returned to user space.
> 
> Signed-off-by: Yonghong Song <yhs@...com>
> ---

LGTM. I had to do some git log research on latest bpf iter work though to
parse the commit message, but I needed to do that anyways.

Acked-by: John Fastabend <john.fastabend@...il.com>

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