Re: [PATCH 02/39] bpf tools: Collect eBPF programs from their own sections

[Arnaldo Carvalho de Melo]

Em Thu, Jul 09, 2015 at 12:35:05PM +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.
> 
> bpf_program__new() creates a new 'struct bpf_program' object. It first
> init a variable in stack using __bpf_program__new(), then if success,
> enlarges obj->programs array and copy the new object in.
> 
> Signed-off-by: Wang Nan <wangnan0@xxxxxxxxxx>
> Acked-by: Alexei Starovoitov <ast@xxxxxxxxxxxx>
> Cc: Brendan Gregg <brendan.d.gregg@xxxxxxxxx>
> Cc: Daniel Borkmann <daniel@xxxxxxxxxxxxx>
> Cc: David Ahern <dsahern@xxxxxxxxx>
> Cc: He Kuang <hekuang@xxxxxxxxxx>
> Cc: Jiri Olsa <jolsa@xxxxxxxxxx>
> Cc: Kaixu Xia <xiakaixu@xxxxxxxxxx>
> Cc: Masami Hiramatsu <masami.hiramatsu.pt@xxxxxxxxxxx>
> Cc: Namhyung Kim <namhyung@xxxxxxxxxx>
> Cc: Paul Mackerras <paulus@xxxxxxxxx>
> Cc: Peter Zijlstra <a.p.zijlstra@xxxxxxxxx>
> Cc: Zefan Li <lizefan@xxxxxxxxxx>
> Cc: pi3orama@xxxxxxx
> Link: http://lkml.kernel.org/r/1435716878-189507-13-git-send-email-wangnan0@xxxxxxxxxx
> Signed-off-by: Arnaldo Carvalho de Melo <acme@xxxxxxxxxx>
> ---
>  tools/lib/bpf/libbpf.c | 117 +++++++++++++++++++++++++++++++++++++++++++++++++
>  1 file changed, 117 insertions(+)
> 
> diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
> index 9b016c0..3b717de 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 +115,84 @@ 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;
> +}

So in perf land we use 'bpf_program__exit()' as the counterpart of
bpf_program__init(), i.e. one just initializes fields, allocating
memory for 'struct bpf_program' members, but does not allocates the
struct bpf_program itself, because sometimes we embed it inside other
structs, or we have it in arrays, as you do.

So, to keep that convention, please rename bpf_program__clear() to
bpf_program__exit() and the next function, __bpf_program__new() to
bpf_program__init(), with 'struct bpf_program *prog' as the first
parameter.

To speed things up, from now on, when I see such stuff, I will do the
changes, put them in a branch with a commiter note, and wait for your
Ack (or not, if you disagree with something).

One more comment below.

> +
> +static int
> +__bpf_program__new(void *data, size_t size, char *name, int idx,
> +		   struct bpf_program *prog)
> +{
> +	if (size < sizeof(struct bpf_insn)) {
> +		pr_warning("corrupted section '%s'\n", name);
> +		return -EINVAL;
> +	}
> +
> +	bzero(prog, sizeof(*prog));
> +
> +	prog->section_name = strdup(name);
> +	if (!prog->section_name) {
> +		pr_warning("failed to alloc name for prog %s\n",
> +			   name);
> +		goto errout;
> +	}
> +
> +	prog->insns = malloc(size);
> +	if (!prog->insns) {
> +		pr_warning("failed to alloc insns for %s\n", name);
> +		goto errout;
> +	}
> +	prog->insns_cnt = size / sizeof(struct bpf_insn);
> +	memcpy(prog->insns, data,
> +	       prog->insns_cnt * sizeof(struct bpf_insn));
> +	prog->idx = idx;
> +
> +	return 0;
> +errout:
> +	bpf_program__clear(prog);
> +	return -ENOMEM;
> +}
> +
> +static struct bpf_program *
> +bpf_program__new(struct bpf_object *obj, void *data, size_t size,
> +		 char *name, int idx)

This, as well, is not a 'bpf_program' method, it is a 'struct
bpf_object' one, that will manipulate 'struct bpf_object' internal
state, changing its struct members to get space for an extra bpf_program
that was initialized on the stack, if the initialization of such
bpf_program went well, or bail out otherwise.

So I suggest you rename this to:

int bpf_object__add_program(struct bpf_object *obj, void *data, size_t size, char *name, int idx)

And probably move that debug that uses prog->section_name to just after
the realloc, here in this function.

I will look at the other patches after lunch, thanks for providing the
git tree, I will try and use it before looking at the patches
individually, to get a feel of the whole thing.

Ah, I also noticed that you provided way more comments in other patches,
that really helps, keep it up!

Thanks,

- Arnaldo

> +{
> +	struct bpf_program prog, *progs;
> +	int nr_progs, err;
> +
> +	err = __bpf_program__new(data, size, name, idx, &prog);
> +	if (err)
> +		return NULL;
> +
> +	progs = obj->programs;
> +	nr_progs = obj->nr_programs;
> +
> +	progs = realloc(progs, sizeof(progs[0]) * (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);
> +		bpf_program__clear(&prog);
> +		return NULL;
> +	}
> +
> +	obj->programs = progs;
> +	obj->nr_programs = nr_progs + 1;
> +	progs[nr_progs] = prog;
> +	return &progs[nr_progs];
> +}
> +
>  static struct bpf_object *bpf_object__new(const char *path,
>  					  void *obj_buf,
>  					  size_t obj_buf_sz)
> @@ -342,6 +435,21 @@ 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 +523,20 @@ 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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