Support kfunc in vfsstat.py

Adding kfunc return trampoline probe if available instead of
kprobe/kretprobe probes.

The kfunc trampolines are faster - less intrusive.

Below are stats for running perf bench sched pipe benchamark while
running vfsstat.py on the background for kprobes and kfuncs.

With kprobes:
         Performance counter stats for './perf bench sched pipe -l 5000000' (3 runs):

           112,520,853,574      cycles:k

                    48.674 +- 0.672 seconds time elapsed  ( +-  1.38% )

With kfuncs:
         Performance counter stats for './perf bench sched pipe -l 5000000' (3 runs):

           106,304,165,424      cycles:k

                    46.820 +- 0.197 seconds time elapsed  ( +-  0.42% )

Signed-off-by: Jiri Olsa <jolsa@kernel.org>

tools/vfsstat.py

@@ -37,7 +37,7 @@ def usage():
         usage()
 
 # load BPF program
-b = BPF(text="""
+bpf_text = """
 #include <uapi/linux/ptrace.h>
 
 enum stat_types {
@@ -55,18 +55,38 @@ def usage():
     u64 *leaf = stats.lookup(&key);
     if (leaf) (*leaf)++;
 }
+"""
 
+bpf_text_kprobe = """
 void do_read(struct pt_regs *ctx) { stats_increment(S_READ); }
 void do_write(struct pt_regs *ctx) { stats_increment(S_WRITE); }
 void do_fsync(struct pt_regs *ctx) { stats_increment(S_FSYNC); }
 void do_open(struct pt_regs *ctx) { stats_increment(S_OPEN); }
 void do_create(struct pt_regs *ctx) { stats_increment(S_CREATE); }
-""")
-b.attach_kprobe(event="vfs_read", fn_name="do_read")
-b.attach_kprobe(event="vfs_write", fn_name="do_write")
-b.attach_kprobe(event="vfs_fsync", fn_name="do_fsync")
-b.attach_kprobe(event="vfs_open", fn_name="do_open")
-b.attach_kprobe(event="vfs_create", fn_name="do_create")
+"""
+
+bpf_text_kfunc = """
+KFUNC_PROBE(vfs_read, int unused)   { stats_increment(S_READ); }
+KFUNC_PROBE(vfs_write, int unused)  { stats_increment(S_WRITE); }
+KFUNC_PROBE(vfs_fsync, int unused)  { stats_increment(S_FSYNC); }
+KFUNC_PROBE(vfs_open, int unused)   { stats_increment(S_OPEN); }
+KFUNC_PROBE(vfs_create, int unused) { stats_increment(S_CREATE); }
+"""
+
+is_support_kfunc = BPF.support_kfunc()
+#is_support_kfunc = False #BPF.support_kfunc()
+if is_support_kfunc:
+    bpf_text += bpf_text_kfunc
+else:
+    bpf_text += bpf_text_kprobe
+
+b = BPF(text=bpf_text)
+if not is_support_kfunc:
+    b.attach_kprobe(event="vfs_read",   fn_name="do_read")
+    b.attach_kprobe(event="vfs_write",  fn_name="do_write")
+    b.attach_kprobe(event="vfs_fsync",  fn_name="do_fsync")
+    b.attach_kprobe(event="vfs_open",   fn_name="do_open")
+    b.attach_kprobe(event="vfs_create", fn_name="do_create")
 
 # stat column labels and indexes
 stat_types = {