[RFC][PATCH 08/10] samples/bpf: Add support for trace events to the eBPF loading code

[Tom Zanussi]

Because we now have two types of eBPF programs that can attach to
kprobes, we need to add a way to distinguish them.

BPF_PROG_TYPE_KPROBE programs are defined the same as they were
before:

SEC("kprobe/...")

BPF_PROG_TYPE_TRACE_EVENT programs always start with 'event/'.  A
TRACE_EVENT program on a kprobe would be defined in the same way as a
KPROBE program but would prepend the 'event/':
before bu can be applied to kprobes by

SEC("event/kprobe/...")
SEC("event/kretprobe/...")

BPF_PROG_TYPE_TRACE_EVENT program on a static trace event simply
specifies 'event/' plus the colon-separated subsys:event name:

SEC("event/subsys:event")

Also, add a couple helper declarations for the new field-reading
helper functions.

Signed-off-by: Tom Zanussi <tom.zanussi@xxxxxxxxxxxxxxx>
---
 samples/bpf/bpf_helpers.h |  4 ++++
 samples/bpf/bpf_load.c    | 46 +++++++++++++++++++++++++++++++++++++++++-----
 2 files changed, 45 insertions(+), 5 deletions(-)

diff --git a/samples/bpf/bpf_helpers.h b/samples/bpf/bpf_helpers.h
index 7ad19e1..a2fe8df 100644
--- a/samples/bpf/bpf_helpers.h
+++ b/samples/bpf/bpf_helpers.h
@@ -39,6 +39,10 @@ static int (*bpf_redirect)(int ifindex, int flags) =
 	(void *) BPF_FUNC_redirect;
 static int (*bpf_perf_event_output)(void *ctx, void *map, int index, void *data, int size) =
 	(void *) BPF_FUNC_perf_event_output;
+static int (*bpf_trace_event_field_read)(void *ctx, const char *field_name) =
+	(void *) BPF_FUNC_trace_event_field_read;
+static int (*bpf_trace_event_field_read_string)(void *ctx, const char *field_name, void *buf, int size) =
+	(void *) BPF_FUNC_trace_event_field_read_string;
 
 /* llvm builtin functions that eBPF C program may use to
  * emit BPF_LD_ABS and BPF_LD_IND instructions
diff --git a/samples/bpf/bpf_load.c b/samples/bpf/bpf_load.c
index da86a8e..006a139 100644
--- a/samples/bpf/bpf_load.c
+++ b/samples/bpf/bpf_load.c
@@ -46,14 +46,39 @@ static int populate_prog_array(const char *event, int prog_fd)
 
 static int load_and_attach(const char *event, struct bpf_insn *prog, int size)
 {
+	bool is_trace_event = strncmp(event, "event/", 6) == 0;
 	bool is_socket = strncmp(event, "socket", 6) == 0;
-	bool is_kprobe = strncmp(event, "kprobe/", 7) == 0;
-	bool is_kretprobe = strncmp(event, "kretprobe/", 10) == 0;
+	bool is_kretprobe = false;
+	bool is_kprobe = false;
+
 	enum bpf_prog_type prog_type;
-	char buf[256];
+	char buf[256], event_buf[256];
 	int fd, efd, err, id;
 	struct perf_event_attr attr = {};
 
+	char *event_name = NULL;
+	char *subsys_name = NULL;
+
+	if (is_trace_event)
+		event += 6;
+
+	is_kprobe = strncmp(event, "kprobe/", 7) == 0;
+	is_kretprobe = strncmp(event, "kretprobe/", 10) == 0;
+
+	if (is_trace_event) {
+		if (!(is_kprobe || is_kretprobe)) {
+			strncpy(event_buf, event, 255);
+			event_buf[255] = '\0';
+
+			event_name = event_buf;
+			subsys_name = strsep(&event_name, ":");
+			if (!subsys_name || !event_name) {
+				printf("Unknown trace event '%s'\n", event);
+				return -1;
+			}
+		}
+	}
+
 	attr.type = PERF_TYPE_TRACEPOINT;
 	attr.sample_type = PERF_SAMPLE_RAW;
 	attr.sample_period = 1;
@@ -61,6 +86,8 @@ static int load_and_attach(const char *event, struct bpf_insn *prog, int size)
 
 	if (is_socket) {
 		prog_type = BPF_PROG_TYPE_SOCKET_FILTER;
+	} else if (is_trace_event) {
+		prog_type = BPF_PROG_TYPE_TRACE_EVENT;
 	} else if (is_kprobe || is_kretprobe) {
 		prog_type = BPF_PROG_TYPE_KPROBE;
 	} else {
@@ -114,8 +141,15 @@ static int load_and_attach(const char *event, struct bpf_insn *prog, int size)
 	}
 
 	strcpy(buf, DEBUGFS);
-	strcat(buf, "events/kprobes/");
-	strcat(buf, event);
+	if (is_kprobe || is_kretprobe) {
+		strcat(buf, "events/kprobes/");
+		strcat(buf, event);
+	} else {
+		strcat(buf, "events/");
+		strcat(buf, subsys_name);
+		strcat(buf, "/");
+		strcat(buf, event_name);
+	}
 	strcat(buf, "/id");
 
 	efd = open(buf, O_RDONLY, 0);
@@ -300,6 +334,7 @@ int load_bpf_file(char *path)
 
 			if (memcmp(shname_prog, "kprobe/", 7) == 0 ||
 			    memcmp(shname_prog, "kretprobe/", 10) == 0 ||
+			    memcmp(shname_prog, "event/", 6) == 0 ||
 			    memcmp(shname_prog, "socket", 6) == 0)
 				load_and_attach(shname_prog, insns, data_prog->d_size);
 		}
@@ -316,6 +351,7 @@ int load_bpf_file(char *path)
 
 		if (memcmp(shname, "kprobe/", 7) == 0 ||
 		    memcmp(shname, "kretprobe/", 10) == 0 ||
+		    memcmp(shname, "event/", 6) == 0 ||
 		    memcmp(shname, "socket", 6) == 0)
 			load_and_attach(shname, data->d_buf, data->d_size);
 	}
-- 
1.9.3