Re: [PATCH 13/31] bpf tools: Load a program with different instances using preprocessor

From: Arnaldo Carvalho de Melo
Date: Thu Oct 29 2015 - 18:44:19 EST

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Em Wed, Oct 14, 2015 at 12:41:24PM +0000, Wang Nan escreveu:
> In this patch, caller of libbpf is able to control the loaded programs
> by installing a preprocessor callback for a BPF program. With
> preprocessor, different instances can be created from one BPF program.

Why would one want to do that? I'm new to eBPF, as many other here, I
guess, so giving some more context as to what will this achieve will
help me in processing these patches.

> This patch will be used by perf to generate different prologue for
> different 'struct probe_trace_event' instances matched by one
> 'struct perf_probe_event'.
>
> bpf_program__set_prep() is added to support this feature. Caller
> should pass libbpf the number of instances should be created and a
that
> preprocessor function which will be called when doing real loading.
the
> The callback should return instructions arrays for each instances.
instruction arrays for each instance.
>
> fd field in bpf_programs is replaced by instance, which has an nr field

The fd field in the bpf_programs struct is replaced by instance
(instance of what?)

> and fds array. bpf_program__nth_fd() is introduced for read fd of
> instances. Old interface bpf_program__fd() is reimplemented by
> returning the first fd.
>
> Signed-off-by: Wang Nan <wangnan0@xxxxxxxxxx>
> Signed-off-by: He Kuang <hekuang@xxxxxxxxxx>
> Cc: 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
> Cc: Arnaldo Carvalho de Melo <acme@xxxxxxxxxx>
> Link: http://lkml.kernel.org/n/ebpf-6yw9eg0ej3l4jnqhinngkw86@xxxxxxxxxxxxxx
> ---
> tools/lib/bpf/libbpf.c | 143 +++++++++++++++++++++++++++++++++++++++++++++----
> tools/lib/bpf/libbpf.h | 22 ++++++++
> 2 files changed, 156 insertions(+), 9 deletions(-)
>
> diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
> index 4252fc2..6a07b26 100644
> --- a/tools/lib/bpf/libbpf.c
> +++ b/tools/lib/bpf/libbpf.c
> @@ -98,7 +98,11 @@ struct bpf_program {
> } *reloc_desc;
> int nr_reloc;
>
> - int fd;
> + struct {
> + int nr;
> + int *fds;
> + } instance;
> + bpf_program_prep_t preprocessor;
>
> struct bpf_object *obj;
> void *priv;
> @@ -152,10 +156,24 @@ struct bpf_object {
>
> static void bpf_program__unload(struct bpf_program *prog)
> {
> + int i;
> +
> if (!prog)
> return;
>
> - zclose(prog->fd);
> + /*
> + * If the object is opened but the program is never loaded,
> + * it is possible that prog->instance.nr == -1.
> + */
> + if (prog->instance.nr > 0) {
> + for (i = 0; i < prog->instance.nr; i++)
> + zclose(prog->instance.fds[i]);
> + } else if (prog->instance.nr != -1)
> + pr_warning("Internal error: instance.nr is %d\n",
> + prog->instance.nr);
> +
> + prog->instance.nr = -1;
> + zfree(&prog->instance.fds);
> }
>
> static void bpf_program__exit(struct bpf_program *prog)
> @@ -206,7 +224,8 @@ bpf_program__init(void *data, size_t size, char *name, int idx,
> memcpy(prog->insns, data,
> prog->insns_cnt * sizeof(struct bpf_insn));
> prog->idx = idx;
> - prog->fd = -1;
> + prog->instance.fds = NULL;
> + prog->instance.nr = -1;
>
> return 0;
> errout:
> @@ -795,13 +814,71 @@ static int
> bpf_program__load(struct bpf_program *prog,
> char *license, u32 kern_version)
> {
> - int err, fd;
> + int err = 0, fd, i;
> +
> + if (prog->instance.nr < 0 || !prog->instance.fds) {
> + if (prog->preprocessor) {
> + pr_warning("Internal error: can't load program '%s'\n",
> + prog->section_name);
> + return -EINVAL;
> + }
> +
> + prog->instance.fds = malloc(sizeof(int));
> + if (!prog->instance.fds) {
> + pr_warning("No enough memory for fds\n");
> + return -ENOMEM;
> + }
> + prog->instance.nr = 1;
> + prog->instance.fds[0] = -1;
> + }
> +
> + if (!prog->preprocessor) {
> + if (prog->instance.nr != 1)
> + pr_warning("Program '%s' inconsistent: nr(%d) not 1\n",
> + prog->section_name, prog->instance.nr);
>
> - err = load_program(prog->insns, prog->insns_cnt,
> - license, kern_version, &fd);
> - if (!err)
> - prog->fd = fd;
> + err = load_program(prog->insns, prog->insns_cnt,
> + license, kern_version, &fd);
> + if (!err)
> + prog->instance.fds[0] = fd;
> + goto out;
> + }
> +
> + for (i = 0; i < prog->instance.nr; i++) {
> + struct bpf_prog_prep_result result;
> + bpf_program_prep_t preprocessor = prog->preprocessor;
> +
> + bzero(&result, sizeof(result));
> + err = preprocessor(prog, i, prog->insns,
> + prog->insns_cnt, &result);
> + if (err) {
> + pr_warning("Preprocessing %dth instance of program '%s' failed\n",
> + i, prog->section_name);
> + goto out;
> + }
> +
> + if (!result.new_insn_ptr || !result.new_insn_cnt) {
> + pr_debug("Skip loading %dth instance of program '%s'\n",
> + i, prog->section_name);
> + prog->instance.fds[i] = -1;
> + continue;
> + }
> +
> + err = load_program(result.new_insn_ptr,
> + result.new_insn_cnt,
> + license, kern_version, &fd);
> +
> + if (err) {
> + pr_warning("Loading %dth instance of program '%s' failed\n",
> + i, prog->section_name);
> + goto out;
> + }
>
> + if (result.pfd)
> + *result.pfd = fd;
> + prog->instance.fds[i] = fd;
> + }
> +out:
> if (err)
> pr_warning("failed to load program '%s'\n",
> prog->section_name);
> @@ -1052,5 +1129,53 @@ const char *bpf_program__title(struct bpf_program *prog, bool dup)
>
> int bpf_program__fd(struct bpf_program *prog)
> {
> - return prog->fd;
> + return bpf_program__nth_fd(prog, 0);
> +}
> +
> +int bpf_program__set_prep(struct bpf_program *prog, int nr_instance,
> + bpf_program_prep_t prep)
> +{
> + int *instance_fds;
> +
> + if (nr_instance <= 0 || !prep)
> + return -EINVAL;
> +
> + if (prog->instance.nr > 0 || prog->instance.fds) {
> + pr_warning("Can't set pre-processor after loading\n");
> + return -EINVAL;
> + }
> +
> + instance_fds = malloc(sizeof(int) * nr_instance);
> + if (!instance_fds) {
> + pr_warning("alloc memory failed for instance of fds\n");
> + return -ENOMEM;
> + }
> +
> + /* fill all fd with -1 */
> + memset(instance_fds, 0xff, sizeof(int) * nr_instance);
> +
> + prog->instance.nr = nr_instance;
> + prog->instance.fds = instance_fds;
> + prog->preprocessor = prep;
> + return 0;
> +}
> +
> +int bpf_program__nth_fd(struct bpf_program *prog, int n)
> +{
> + int fd;
> +
> + if (n >= prog->instance.nr || n < 0) {
> + pr_warning("Can't get the %dth fd from program %s: only %d instances\n",
> + n, prog->section_name, prog->instance.nr);
> + return -EINVAL;
> + }
> +
> + fd = prog->instance.fds[n];
> + if (fd < 0) {
> + pr_warning("%dth instance of program '%s' is invalid\n",
> + n, prog->section_name);
> + return -ENOENT;
> + }
> +
> + return fd;
> }
> diff --git a/tools/lib/bpf/libbpf.h b/tools/lib/bpf/libbpf.h
> index f16170c..d82b89e 100644
> --- a/tools/lib/bpf/libbpf.h
> +++ b/tools/lib/bpf/libbpf.h
> @@ -67,6 +67,28 @@ const char *bpf_program__title(struct bpf_program *prog, bool dup);
>
> int bpf_program__fd(struct bpf_program *prog);
>
> +struct bpf_insn;
> +struct bpf_prog_prep_result {
> + /*
> + * If not NULL, load new instruction array.
> + * If set to NULL, don't load this instance.
> + */
> + struct bpf_insn *new_insn_ptr;
> + int new_insn_cnt;
> +
> + /* If not NULL, result fd is set to it */
> + int *pfd;
> +};
> +
> +typedef int (*bpf_program_prep_t)(struct bpf_program *, int n,
> + struct bpf_insn *, int insn_cnt,
> + struct bpf_prog_prep_result *res);
> +
> +int bpf_program__set_prep(struct bpf_program *prog, int nr_instance,
> + bpf_program_prep_t prep);
> +
> +int bpf_program__nth_fd(struct bpf_program *prog, int n);
> +
> /*
> * We don't need __attribute__((packed)) now since it is
> * unnecessary for 'bpf_map_def' because they are all aligned.
> --
> 1.8.3.4
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Next message: Arnaldo Carvalho de Melo: "Re: [PATCH 14/31] perf tools: Add BPF_PROLOGUE config options for further patches"
Previous message: Arnaldo Carvalho de Melo: "Re: [PATCH 12/31] perf probe: Reset args and nargs for probe_trace_event when failure"
Next in thread: Wangnan (F): "Re: [PATCH 13/31] bpf tools: Load a program with different instances using preprocessor"
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