Re: [RFC PATCH v10 12/50] bpf tools: Collect eBPF programs from their own sections

[Arnaldo Carvalho de Melo]

Em Wed, Jul 01, 2015 at 02:14:00AM +0000, Wang Nan escreveu:
> This patch collects all programs in an object file into an array of
> 'struct bpf_program' for further processing. That structure is for
> representing each eBPF program. 'bpf_prog' should be a better name, but
> it has been used by linux/filter.h. Although it is a kernel space name,
> I still prefer to call it 'bpf_program' to prevent possible confusion.
> 
> Signed-off-by: Wang Nan <wangnan0@xxxxxxxxxx>
> Acked-by: Alexei Starovoitov <ast@xxxxxxxxxxxx>
> ---
>  tools/lib/bpf/libbpf.c | 107 +++++++++++++++++++++++++++++++++++++++++++++++++
>  1 file changed, 107 insertions(+)
> 
> diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
> index 9b016c0..9c01b55f 100644
> --- a/tools/lib/bpf/libbpf.c
> +++ b/tools/lib/bpf/libbpf.c
> @@ -78,12 +78,27 @@ void libbpf_set_print(libbpf_print_fn_t warn,
>  # define LIBBPF_ELF_C_READ_MMAP ELF_C_READ
>  #endif
>  
> +/*
> + * bpf_prog should be a better name but it has been used in
> + * linux/filter.h.
> + */
> +struct bpf_program {
> +	/* Index in elf obj file, for relocation use. */
> +	int idx;
> +	char *section_name;
> +	struct bpf_insn *insns;
> +	size_t insns_cnt;
> +};
> +
>  struct bpf_object {
>  	char license[64];
>  	u32 kern_version;
>  	void *maps_buf;
>  	size_t maps_buf_sz;
>  
> +	struct bpf_program *programs;
> +	size_t nr_programs;
> +
>  	/*
>  	 * Information when doing elf related work. Only valid if fd
>  	 * is valid.
> @@ -100,6 +115,74 @@ struct bpf_object {
>  };
>  #define obj_elf_valid(o)	((o)->efile.elf)
>  
> +static void bpf_program__clear(struct bpf_program *prog)
> +{
> +	if (!prog)
> +		return;
> +
> +	zfree(&prog->section_name);
> +	zfree(&prog->insns);
> +	prog->insns_cnt = 0;
> +	prog->idx = -1;
> +}
> +
> +static struct bpf_program *
> +bpf_program__new(struct bpf_object *obj, void *data, size_t size,
> +		 char *name, int idx)
> +{
> +	struct bpf_program *prog, *progs;
> +	int nr_progs;
> +
> +	if (size < sizeof(struct bpf_insn)) {
> +		pr_warning("corrupted section '%s'\n", name);
> +		return NULL;
> +	}
> +
> +	progs = obj->programs;
> +	nr_progs = obj->nr_programs;
> +
> +	progs = realloc(progs, sizeof(*prog) * (nr_progs + 1));
> +	if (!progs) {
> +		/*
> +		 * In this case the original obj->programs
> +		 * is still valid, so don't need special treat for
> +		 * bpf_close_object().
> +		 */
> +		pr_warning("failed to alloc a new program '%s'\n",
> +			   name);
> +		return NULL;
> +	}
> +
> +	obj->programs = progs;
> +
> +	prog = &progs[nr_progs];
> +	bzero(prog, sizeof(*prog));
> +
> +	obj->nr_programs = nr_progs + 1;

So here you basically commited your allocator, i.e. obj->nr_programs
now includes one extra program, but...

> +	prog->section_name = strdup(name);
> +	if (!prog->section_name) {
> +		pr_warning("failed to alloc name for prog %s\n",
> +			   name);
> +		goto out;

Here, that BTW could be better named "goto out_clear", you bail out
by calling...

> +	}
> +
> +	prog->insns = malloc(size);
> +	if (!prog->insns) {
> +		pr_warning("failed to alloc insns for %s\n", name);
> +		goto out;
> +	}
> +	prog->insns_cnt = size / sizeof(struct bpf_insn);
> +	memcpy(prog->insns, data,
> +	       prog->insns_cnt * sizeof(struct bpf_insn));
> +	prog->idx = idx;
> +
> +	return prog;
> +out:

... bpf_program__clear(), that will not reduce the number of entries in
obj->nr_programs, how will you garbage collect the unused entries?

Why not decouple bpf_program__new() from bpf_object?

I.e. you call it it will allocate space for a new bpf_program, if all
goes well, you then insert it into that bpf_object instance, no?

Even with this problem, I am applying it to my local tree to continue
looking at the other patches and to test the end result.

- Arnaldo

> +	bpf_program__clear(prog);
> +	return NULL;
> +}
> +
>  static struct bpf_object *bpf_object__new(const char *path,
>  					  void *obj_buf,
>  					  size_t obj_buf_sz)
> @@ -342,6 +425,21 @@ static int bpf_object__elf_collect(struct bpf_object *obj)
>  				err = -EEXIST;
>  			} else
>  				obj->efile.symbols = data;
> +		} else if ((sh.sh_type == SHT_PROGBITS) &&
> +			   (sh.sh_flags & SHF_EXECINSTR) &&
> +			   (data->d_size > 0)) {
> +			struct bpf_program *prog;
> +
> +			prog = bpf_program__new(obj, data->d_buf,
> +						data->d_size, name,
> +						idx);
> +			if (!prog) {
> +				pr_warning("failed to alloc program %s (%s)",
> +					   name, obj->path);
> +				err = -ENOMEM;
> +			} else
> +				pr_debug("found program %s\n",
> +					 prog->section_name);
>  		}
>  		if (err)
>  			goto out;
> @@ -415,11 +513,20 @@ struct bpf_object *bpf_object__open_buffer(void *obj_buf,
>  
>  void bpf_object__close(struct bpf_object *obj)
>  {
> +	size_t i;
> +
>  	if (!obj)
>  		return;
>  
>  	bpf_object__elf_finish(obj);
>  
>  	zfree(&obj->maps_buf);
> +
> +	if (obj->programs && obj->nr_programs) {
> +		for (i = 0; i < obj->nr_programs; i++)
> +			bpf_program__clear(&obj->programs[i]);
> +	}
> +	zfree(&obj->programs);
> +
>  	free(obj);
>  }
> -- 
> 1.8.3.4
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