Re: [PATCH bpf-next v3 1/3] libbpf: add helpers for preparing netlink attributes

[Yonghong Song <yhs@fb.com>]

On 4/20/21 12:37 PM, Kumar Kartikeya Dwivedi wrote:
> This change introduces a few helpers to wrap open coded attribute
> preparation in netlink.c.
> 
> Every nested attribute's closure must happen using the helper
> nlattr_end_nested, which sets its length properly. NLA_F_NESTED is
> enforeced using nlattr_begin_nested helper. Other simple attributes

typo: enforced

> can be added directly.
> 
> The maxsz parameter corresponds to the size of the request structure
> which is being filled in, so for instance with req being:
> 
> struct {
> 	struct nlmsghdr nh;
> 	struct tcmsg t;
> 	char buf[4096];
> } req;
> 
> Then, maxsz should be sizeof(req).
> 
> This change also converts the open coded attribute preparation with the
> helpers. Note that the only failure the internal call to nlattr_add
> could result in the nested helper would be -EMSGSIZE, hence that is what
> we return to our caller.
> 
> Reviewed-by: Toke Høiland-Jørgensen <toke@redhat.com>
> Signed-off-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>
> ---
>   tools/lib/bpf/netlink.c | 37 ++++++++++++++-----------------
>   tools/lib/bpf/nlattr.h  | 48 +++++++++++++++++++++++++++++++++++++++++
>   2 files changed, 64 insertions(+), 21 deletions(-)
> 
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