netdev - Re: [PATCH bpf-next 1/2] bpf: introduce BPF_F_SHARE

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Message-ID: <20200929190054.4a2chcuxuvicndtu@ast-mbp.dhcp.thefacebook.com>
Date:   Tue, 29 Sep 2020 12:00:54 -0700
From:   Alexei Starovoitov <alexei.starovoitov@...il.com>
To:     Daniel Borkmann <daniel@...earbox.net>
Cc:     Song Liu <songliubraving@...com>, netdev@...r.kernel.org,
        bpf@...r.kernel.org, kernel-team@...com, ast@...nel.org,
        john.fastabend@...il.com, kpsingh@...omium.org
Subject: Re: [PATCH bpf-next 1/2] bpf: introduce BPF_F_SHARE_PE for perf
 event array

On Tue, Sep 29, 2020 at 04:02:10PM +0200, Daniel Borkmann wrote:
> > +
> > +/* Share perf_event among processes */
> > +	BPF_F_SHARE_PE		= (1U << 11),
> 
> nit but given UAPI: maybe name into something more self-descriptive
> like BPF_F_SHAREABLE_EVENT ?

I'm not happy with either name.
It's not about sharing and not really about perf event.
I think the current behavior of perf_event_array is unusual and surprising.
Sadly we cannot fix it without breaking user space, so flag is needed.
How about BPF_F_STICKY_OBJECTS or BPF_F_PRESERVE_OBJECTS
or the same with s/OBJECTS/FILES/ ?

> > +static void perf_event_fd_array_map_free(struct bpf_map *map)
> > +{
> > +	struct bpf_event_entry *ee;
> > +	struct bpf_array *array;
> > +	int i;
> > +
> > +	if ((map->map_flags & BPF_F_SHARE_PE) == 0) {
> > +		fd_array_map_free(map);
> > +		return;
> > +	}
> > +
> > +	array = container_of(map, struct bpf_array, map);
> > +	for (i = 0; i < array->map.max_entries; i++) {
> > +		ee = READ_ONCE(array->ptrs[i]);
> > +		if (ee)
> > +			fd_array_map_delete_elem(map, &i);
> > +	}
> > +	bpf_map_area_free(array);
> 
> Why not simplify into:
> 
> 	if (map->map_flags & BPF_F_SHAREABLE_EVENT)
> 		bpf_fd_array_map_clear(map);
> 	fd_array_map_free(map);

+1

> > +}
> > +
> >   static void *prog_fd_array_get_ptr(struct bpf_map *map,
> >   				   struct file *map_file, int fd)
> >   {
> > @@ -1134,6 +1158,9 @@ static void perf_event_fd_array_release(struct bpf_map *map,
> >   	struct bpf_event_entry *ee;
> >   	int i;

add empty line pls.

> > +	if (map->map_flags & BPF_F_SHARE_PE)
> > +		return;
> > +