netdev - Re: libbpf backward compatibility (was: [PATCH bpf-next v5 09/10] bpf: btf: Add BTF support to libbpf)

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Message-ID: <20180509152057.2aeae80f@cakuba.netronome.com>
Date:   Wed, 9 May 2018 15:20:57 -0700
From:   Jakub Kicinski <jakub.kicinski@...ronome.com>
To:     Martin KaFai Lau <kafai@...com>, Alexei Starovoitov <ast@...com>,
        Daniel Borkmann <daniel@...earbox.net>,
        Andrey Ignatov <rdna@...com>
Cc:     <netdev@...r.kernel.org>, <kernel-team@...com>,
        David Beckett <david.beckett@...ronome.com>
Subject: Re: libbpf backward compatibility (was: [PATCH bpf-next v5 09/10]
 bpf: btf: Add BTF support to libbpf)

On Wed, 9 May 2018 15:17:12 -0700, Jakub Kicinski wrote:
> On Wed, 18 Apr 2018 15:56:05 -0700, Martin KaFai Lau wrote:
> > diff --git a/tools/lib/bpf/bpf.h b/tools/lib/bpf/bpf.h
> > index 39f6a0d64a3b..01bda076310f 100644
> > --- a/tools/lib/bpf/bpf.h
> > +++ b/tools/lib/bpf/bpf.h
> > @@ -26,6 +26,20 @@
> >  #include <linux/bpf.h>
> >  #include <stddef.h>
> >  
> > +struct bpf_create_map_attr {
> > +	const char *name;
> > +	enum bpf_map_type map_type;
> > +	__u32 map_flags;
> > +	__u32 key_size;
> > +	__u32 value_size;
> > +	__u32 max_entries;
> > +	__u32 numa_node;
> > +	__u32 btf_fd;
> > +	__u32 btf_key_id;
> > +	__u32 btf_value_id;
> > +};
> > +
> > +int bpf_create_map_xattr(const struct bpf_create_map_attr *create_attr);
> >  int bpf_create_map_node(enum bpf_map_type map_type, const char *name,
> >  			int key_size, int value_size, int max_entries,
> >  			__u32 map_flags, int node);
> > @@ -87,4 +101,6 @@ int bpf_obj_get_info_by_fd(int prog_fd, void *info, __u32 *info_len);
> >  int bpf_prog_query(int target_fd, enum bpf_attach_type type, __u32 query_flags,
> >  		   __u32 *attach_flags, __u32 *prog_ids, __u32 *prog_cnt);
> >  int bpf_raw_tracepoint_open(const char *name, int prog_fd);
> > +int bpf_load_btf(void *btf, __u32 btf_size, char *log_buf, __u32 log_buf_size,
> > +		 bool do_log);
> >  #endif  
> 
> Does libbpf have to provide backward compatibility?  Are the function
> prototypes not supposed to change?
> 
> Recently a number of *_xattr functions were added, these are nice for
> limiting the number of parameters passed to functions, but they don't
> buy us anything in terms of extensibility unless we can grow the
> structures.  Should structure size be passed in as one of parameters?

Or is the backward compatibility not at the binary level so we can grow
the structures at will?