[RFC PATCH v8 39/49] bpf tools: Load a program with different instance using preprocessor

[Wang Nan]

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.

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 function. Caller
should pass libbpf the number of instance should be created and a
preprocessor function which will be called when doing real loading.
The callback should return instructions arrays for each instances.

nr_instance and instance_fds are appended into bpf_programs to support
multiple instances. bpf_program__get_nth_fd() is introduced for
read fd of instances. Old interface bpf_program__get_fd() won't work
for program which has preprocessor hooked.

Signed-off-by: Wang Nan <wangnan0@xxxxxxxxxx>
Signed-off-by: He Kuang <hekuang@xxxxxxxxxx>
---
 tools/lib/bpf/libbpf.c | 135 +++++++++++++++++++++++++++++++++++++++++++++++--
 tools/lib/bpf/libbpf.h |  22 ++++++++
 2 files changed, 152 insertions(+), 5 deletions(-)

diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
index a2f2991..c581bf6 100644
--- a/tools/lib/bpf/libbpf.c
+++ b/tools/lib/bpf/libbpf.c
@@ -100,6 +100,10 @@ struct bpf_program {
 
 	int fd;
 
+	int nr_instance;
+	int *instance_fds;
+	bpf_program_prep_t preprocessor;
+
 	struct bpf_object *obj;
 	void *priv;
 	bpf_program_clear_priv_t clear_priv;
@@ -156,6 +160,19 @@ static void bpf_program__unload(struct bpf_program *prog)
 		return;
 
 	zclose(prog->fd);
+
+	if (prog->preprocessor) {
+		int i;
+
+		if (prog->nr_instance <= 0)
+			pr_warning("Internal error when unloading: instance is %d\n",
+				   prog->nr_instance);
+		else
+			for (i = 0; i < prog->nr_instance; i++)
+				zclose(prog->instance_fds[i]);
+		prog->nr_instance = -1;
+		zfree(&prog->instance_fds);
+	}
 }
 
 static void bpf_program__clear(struct bpf_program *prog)
@@ -231,6 +248,8 @@ bpf_program__new(struct bpf_object *obj, void *data, size_t size,
 	prog->idx = idx;
 	prog->fd = -1;
 	prog->obj = obj;
+	prog->nr_instance = -1;
+	prog->instance_fds = NULL;
 
 	return prog;
 out:
@@ -786,13 +805,57 @@ static int
 bpf_program__load(struct bpf_program *prog,
 		  char *license, u32 kern_version)
 {
-	int err, fd;
+	int err = 0, fd, i;
+
+	if (!prog->preprocessor) {
+		err = load_program(prog->insns, prog->insns_cnt,
+				license, kern_version, &fd);
+		if (!err)
+			prog->fd = fd;
+		goto out;
+	}
+
+	if (prog->nr_instance <= 0 || !prog->instance_fds) {
+		pr_warning("Internal error when loading '%s'\n",
+				prog->section_name);
+		return -EINVAL;
+	}
+
+	for (i = 0; i < prog->nr_instance; 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);
 
-	err = load_program(prog->insns, prog->insns_cnt,
-			   license, kern_version, &fd);
-	if (!err)
-		prog->fd = 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);
@@ -1043,6 +1106,68 @@ int bpf_program__get_fd(struct bpf_program *prog, int *pfd)
 	if (!pfd)
 		return -EINVAL;
 
+	if (prog->preprocessor) {
+		pr_warning("Invalid using bpf_program__get_fd() on program %s\n",
+			   prog->section_name);
+		return -EINVAL;
+	}
+
 	*pfd = prog->fd;
 	return 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;
+
+	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->nr_instance = nr_instance;
+	prog->instance_fds = instance_fds;
+	prog->preprocessor = prep;
+	return 0;
+}
+
+int bpf_program__get_nth_fd(struct bpf_program *prog, int n, int *pfd)
+{
+	int fd;
+
+	if (!pfd)
+		return -EINVAL;
+
+	if (!prog->preprocessor ||
+		prog->nr_instance <= 0 ||
+		!prog->instance_fds) {
+
+		pr_warning("Invalid using bpf_program__get_nth_fd() on program %s\n",
+			   prog->section_name);
+		return -EINVAL;
+	}
+
+	if (n >= prog->nr_instance || n < 0) {
+		pr_warning("Can't get the %dth fd from program %s: only %d instances\n",
+			   n, prog->section_name, prog->nr_instance);
+		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 -EEXIST;
+	}
+
+	*pfd = fd;
+	return 0;
+}
diff --git a/tools/lib/bpf/libbpf.h b/tools/lib/bpf/libbpf.h
index 61ea96d..b6e8f3a 100644
--- a/tools/lib/bpf/libbpf.h
+++ b/tools/lib/bpf/libbpf.h
@@ -69,6 +69,28 @@ int bpf_program__get_title(struct bpf_program *prog,
 
 int bpf_program__get_fd(struct bpf_program *prog, int *pfd);
 
+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__get_nth_fd(struct bpf_program *prog, int n, int *pfd);
+
 /*
  * 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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