Re: [net-next PATCH 2/9] bpf: sockmap, remove STRPARSER map_flags and add multi-map support

Alexei Starovoitov
2017-08-28T17:31:18Z

On Mon, Aug 28, 2017 at 07:10:25AM -0700, John Fastabend wrote:
> The addition of map_flags BPF_SOCKMAP_STRPARSER flags was to handle a
> specific use case where we want to have BPF parse program disabled on
> an entry in a sockmap.
>
> However, Alexei found the API a bit cumbersome and I agreed. Lets
> remove the STRPARSER flag and support the use case by allowing socks
> to be in multiple maps. This allows users to create two maps one with
> programs attached and one without. When socks are added to maps they
> now inherit any programs attached to the map. This is a nice
> generalization and IMO improves the API.
>
> The API rules are less ambiguous and do not need a flag:
>
> - When a sock is added to a sockmap we have two cases,
>
> i. The sock map does not have any attached programs so
> we can add sock to map without inheriting bpf programs.
> The sock may exist in 0 or more other maps.
>
> ii. The sock map has an attached BPF program. To avoid duplicate
> bpf programs we only add the sock entry if it does not have
> an existing strparser/verdict attached, returning -EBUSY if
> a program is already attached. Otherwise attach the program
> and inherit strparser/verdict programs from the sock map.
>
> This allows for socks to be in a multiple maps for redirects and
> inherit a BPF program from a single map.
>
> Also this patch simplifies the logic around BPF_{EXIST|NOEXIST|ANY}
> flags. In the original patch I tried to be extra clever and only
> update map entries when necessary. Now I've decided the complexity
> is not worth it. If users constantly update an entry with the same
> sock for no reason (i.e. update an entry without actually changing
> any parameters on map or sock) we still do an alloc/release. Using
> this and allowing multiple entries of a sock to exist in a map the
> logic becomes much simpler.
>
> Note: Now that multiple maps are supported the "maps" pointer called
> when a socket is closed becomes a list of maps to remove the sock from.
> To keep the map up to date when a sock is added to the sockmap we must
> add the map/elem in the list. Likewise when it is removed we must
> remove it from the list. This results in searching the per psock list
> on delete operation. On TCP_CLOSE events we walk the list and remove
> the psock from all map/entry locations. I don't see any perf
> implications in this because at most I have a psock in two maps. If
> a psock were to be in many maps its possibly this might be noticeable
> on delete but I can't think of a reason to dup a psock in many maps.
> The sk_callback_lock is used to protect read/writes to the list. This
> was convenient because in all locations we were taking the lock
> anyways just after working on the list. Also the lock is per sock so
> in normal cases we shouldn't see any contention.
>
> Suggested-by: Alexei Starovoitov <ast@kernel.org>
> Fixes: 174a79ff9515 ("bpf: sockmap with sk redirect support")
> Signed-off-by: John Fastabend <john.fastabend@gmail.com>

nice. I think implementation got cleaner too.
thanks for addresing the comments quickly!
Acked-by: Alexei Starovoitov <ast@kernel.org>

> ---
> include/uapi/linux/bpf.h | 3 -
> kernel/bpf/sockmap.c | 269 ++++++++++++++++++++++++++++------------------
> 2 files changed, 165 insertions(+), 107 deletions(-)
>
> diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
> index 97227be..08c206a 100644
> --- a/include/uapi/linux/bpf.h
> +++ b/include/uapi/linux/bpf.h
> @@ -143,9 +143,6 @@ enum bpf_attach_type {
>
> #define MAX_BPF_ATTACH_TYPE __MAX_BPF_ATTACH_TYPE
>
> -/* If BPF_SOCKMAP_STRPARSER is used sockmap will use strparser on receive */
> -#define BPF_SOCKMAP_STRPARSER (1U << 0)
> -

Please update tools/include/uapi/linux/bpf.h as well.
Right now it's kinda messed up and still has:
enum bpf_sockmap_flags {
BPF_SOCKMAP_UNSPEC,
BPF_SOCKMAP_STRPARSER,
__MAX_BPF_SOCKMAP_FLAG
};
that's separate patch of course. Not a blocker for this set.