[RFC PATCH 14/22] perf bpf: config eBPF programs based on their names.

[Wang Nan]

This patch partially implements bpf_obj_config(), which is used for
define k(ret)probe positions which will be attached eBPF programs.

parse_perf_probe_command() is used to do the main parsing works.
Parsing result is stored into a global array. This is because
add_perf_probe_events() is non-reentrantable. In following patch,
add_perf_probe_events will be introduced to insert kprobes. It accepts
an array of 'struct perf_probe_event' and do works together.

This patch deals programs with 'kprobe/myprobe' like name only by
generating perf probe command string then calling
parse_perf_probe_command().

Signed-off-by: Wang Nan <wangnan0@xxxxxxxxxx>
---
 tools/perf/util/bpf-loader.c | 201 +++++++++++++++++++++++++++++++++++++++++++
 tools/perf/util/bpf-loader.h |   2 +
 2 files changed, 203 insertions(+)

diff --git a/tools/perf/util/bpf-loader.c b/tools/perf/util/bpf-loader.c
index 66fbca2..b2871fc 100644
--- a/tools/perf/util/bpf-loader.c
+++ b/tools/perf/util/bpf-loader.c
@@ -22,6 +22,38 @@
 
 static LIST_HEAD(bpf_obj_list);
 
+#define MAX_CMDLEN 256
+#define PERF_BPF_PROBE_GROUP "perf_bpf_probe"
+/*
+ * perf probe is no non-reentrantable, so we must group all events
+ * together and call add_perf_probe_events only once.
+ */
+
+struct params {
+	struct perf_probe_event event_array[MAX_PROBES];
+	size_t nr_events;
+};
+static struct params params = {
+	.nr_events = 0,
+};
+
+static struct perf_probe_event *
+alloc_perf_probe_event(void)
+{
+	struct perf_probe_event *pev;
+	int n = params.nr_events;
+
+	if (n >= MAX_PROBES) {
+		pr_err("bpf: too many events, increase MAX_PROBES\n");
+		return NULL;
+	}
+
+	params.nr_events = n + 1;
+	pev = &params.event_array[n];
+	bzero(pev, sizeof(*pev));
+	return pev;
+}
+
 static struct bpf_obj *__bpf_obj_alloc(const char *path)
 {
 	struct bpf_obj *obj;
@@ -279,6 +311,10 @@ bpf_perf_prog_free(struct bpf_perf_prog *prog)
 		free(prog->name);
 	if (prog->insns)
 		free(prog->insns);
+	if (prog->pev) {
+		clear_perf_probe_event(prog->pev);
+		bzero(prog->pev, sizeof(*prog->pev));
+	}
 	free(prog);
 }
 
@@ -448,6 +484,169 @@ static int bpf_obj_validate(struct bpf_obj *obj)
 	return 0;
 }
 
+static struct bpf_perf_prog *
+bpf_find_prog_by_name(struct bpf_obj *obj, const char *name)
+{
+	struct bpf_perf_prog *prog;
+
+	list_for_each_entry(prog, &obj->progs_list, list)
+		if (strcmp(name, prog->name) == 0)
+			return prog;
+	return NULL;
+}
+
+/*
+ * Use config_str to config program. If prog is NULL, find a
+ * prog based on config_str. config_str should not be NULL.
+ */
+static int __bpf_perf_prog_config(struct bpf_obj *obj,
+				  struct bpf_perf_prog *prog,
+				  char *config_str)
+{
+	struct perf_probe_event *pev = alloc_perf_probe_event();
+	int err = 0;
+	
+	if (!pev)
+		return -ENOMEM;
+
+	if ((err = parse_perf_probe_command(config_str, pev)) < 0) {
+		pr_err("bpf config: %s is not a valid config string\n",
+			config_str);
+		/* parse failed, don't need clear pev. */
+		return -EINVAL;
+	}
+
+	if (pev->group && strcmp(pev->group, PERF_BPF_PROBE_GROUP)) {
+		pr_err("bpf config: '%s': group for event is set "
+		       "and not '%s'.\n", config_str,
+		       PERF_BPF_PROBE_GROUP);
+		err = -EINVAL;
+		goto errout;
+	} else if (!pev->group)
+		pev->group = strdup(PERF_BPF_PROBE_GROUP);
+
+	if (!pev->group) {
+		pr_err("bpf config: strdup failed\n");
+		err = -ENOMEM;
+		goto errout;
+	}
+
+	if (!pev->event) {
+		pr_err("bpf config: '%s': event name is missing\n",
+				config_str);
+		err = -EINVAL;
+		goto errout;
+	}
+
+	if (!prog)
+		prog = bpf_find_prog_by_name(obj, pev->event);
+	if (!prog) {
+		pr_err("bpf config: section %s not found for"
+		       " config '%s'\n", pev->event, config_str);
+		err = -ENOENT;
+		goto errout;
+	}
+
+	if (prog->pev) {
+		pr_err("bpf config: duplicate config for section %s\n",
+			prog->name);
+		err = -EEXIST;
+		goto errout;
+	}
+
+	prog->pev = pev;
+	pr_debug("bpf config: config %s ok\n", prog->name);
+	return 0;
+errout:
+	if (pev)
+		clear_perf_probe_event(pev);
+	return err;
+}
+
+/*
+ * Config specific prog using config_str. Both prog and config_str
+ * can be set to NULL, but not both. If prog is NULL, search prog
+ * based on config_str. If config_str is NULL, try to generate a
+ * config_str using prog->name.
+ */
+static int bpf_perf_prog_config(struct bpf_obj *obj,
+				struct bpf_perf_prog *prog,
+				char *config_str)
+{
+	char __config_str[MAX_CMDLEN];
+	char *func_str;
+	char *name = NULL;
+
+	if (!prog && !config_str) {
+		pr_err("bpf config: internal error\n");
+		return -EINVAL;
+	}
+
+	if (prog)
+		name = prog->name;
+
+	if (name && (func_str = strchr(name, '/'))) {
+		const char *ret_str;
+		int err = 0;
+
+		/* try to config prog based on its name */
+		if (config_str) {
+			pr_err("bpf config: bad config %s for %s\n",
+			       config_str, name);
+			return -EINVAL;
+		}
+		config_str = __config_str;
+
+		if (memcmp(name, "kprobe/", 7) == 0)
+			ret_str = "";
+		else if (memcmp(name, "kretprobe/", 10) == 0)
+			ret_str = "%return";
+		else {
+			pr_err("bpf: bad section name: '%s'\n", name);
+			return -EINVAL;
+		}
+
+		/* skip '/' */
+		func_str += 1;
+		err = snprintf(config_str, MAX_CMDLEN, "%s=%s%s",
+			       func_str, func_str, ret_str);
+		if (err >= MAX_CMDLEN) {
+			pr_err("bpf: function name %s too long\n", func_str);
+			return -EINVAL;
+		}
+
+		err = __bpf_perf_prog_config(obj, prog, config_str);
+		if (err)
+			return err;
+		return 0;
+	}
+
+	if (config_str)
+		/* prog should be NULL in this case. */
+		return __bpf_perf_prog_config(obj, prog, config_str);
+
+	/*
+	 * prog->name is a symbol and config_str is NULL.
+	 * Return normally. It will be config again with config_str.
+	 */
+	return 0;
+}
+
+static int bpf_obj_config(struct bpf_obj *obj)
+{
+	struct bpf_perf_prog *prog;
+	int err;
+
+	/* try to config progs based on their names */
+	list_for_each_entry(prog, &obj->progs_list, list) {
+		err = bpf_perf_prog_config(obj, prog, NULL);
+		if (err)
+			return err;
+	}
+
+	return 0;
+}
+
 int bpf__load(const char *path)
 {
 	struct bpf_obj *obj;
@@ -474,6 +673,8 @@ int bpf__load(const char *path)
 		goto out;
 	if ((err = bpf_obj_validate(obj)))
 		goto out;
+	if ((err = bpf_obj_config(obj)))
+		goto out;
 
 	list_add(&obj->list, &bpf_obj_list);
 	return 0;
diff --git a/tools/perf/util/bpf-loader.h b/tools/perf/util/bpf-loader.h
index 1417c0d..09f77a5 100644
--- a/tools/perf/util/bpf-loader.h
+++ b/tools/perf/util/bpf-loader.h
@@ -27,6 +27,8 @@ struct bpf_perf_prog {
 	char *name;
 	struct bpf_insn *insns;
 	size_t insns_cnt;
+
+	struct perf_probe_event *pev;
 };
 
 struct bpf_obj {
-- 
1.8.3.4

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