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

[Arnaldo Carvalho de Melo <acme@kernel.org>]

Em Fri, Jul 10, 2015 at 11:07:53AM +0800, Wangnan (F) escreveu:
> On 2015/7/9 23:58, Arnaldo Carvalho de Melo wrote:
> >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@huawei.com>
> >>Acked-by: Alexei Starovoitov <ast@plumgrid.com>
> >>Cc: Brendan Gregg <brendan.d.gregg@gmail.com>
> >>Cc: Daniel Borkmann <daniel@iogearbox.net>
> >>Cc: David Ahern <dsahern@gmail.com>
> >>Cc: He Kuang <hekuang@huawei.com>
> >>Cc: Jiri Olsa <jolsa@kernel.org>
> >>Cc: Kaixu Xia <xiakaixu@huawei.com>
> >>Cc: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>
> >>Cc: Namhyung Kim <namhyung@kernel.org>
> >>Cc: Paul Mackerras <paulus@samba.org>
> >>Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
> >>Cc: Zefan Li <lizefan@huawei.com>
> >>Cc: pi3orama@163.com
> >>Link: http://lkml.kernel.org/r/1435716878-189507-13-git-send-email-wangnan0@huawei.com
> >>Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
> >>---
> >>  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.
> 
> I didn't find your code, so I updated my git tree. Please see:
> 
>  https://github.com/WangNan0/linux/commit/e5ffa4f070ee36cce5130d08622dc305ad9cdb31

Ok, so used bpf_object__add_program, but you still return a bpf_program
pointer, that you do not use for anything, i.e. the failure of
bpf_object__add_program is reported only via a NULL return and you then
assume this was because ENOMEM was the reason, when there are multiple
errors that can cause bpf_object__add_program to fail.

Noted that with a comment on that patch, checked that no later patches
use that return, etc.

- Arnaldo