samples/bpf: Add counting example for kfree_skb() function calls and the write() syscall

this example has two probes in one C file that attach to
different kprove events and use two different maps.

1st probe is x64 specific equivalent of dropmon. It attaches to
kfree_skb, retrevies 'ip' address of kfree_skb() caller and
counts number of packet drops at that 'ip' address. User space
prints 'location - count' map every second.

2nd probe attaches to kprobe:sys_write and computes a histogram
of different write sizes

Usage:
	$ sudo tracex2
	location 0xffffffff81695995 count 1
	location 0xffffffff816d0da9 count 2

	location 0xffffffff81695995 count 2
	location 0xffffffff816d0da9 count 2

	location 0xffffffff81695995 count 3
	location 0xffffffff816d0da9 count 2

	557145+0 records in
	557145+0 records out
	285258240 bytes (285 MB) copied, 1.02379 s, 279 MB/s
		   syscall write() stats
	     byte_size       : count     distribution
	       1 -> 1        : 3        |                                      |
	       2 -> 3        : 0        |                                      |
	       4 -> 7        : 0        |                                      |
	       8 -> 15       : 0        |                                      |
	      16 -> 31       : 2        |                                      |
	      32 -> 63       : 3        |                                      |
	      64 -> 127      : 1        |                                      |
	     128 -> 255      : 1        |                                      |
	     256 -> 511      : 0        |                                      |
	     512 -> 1023     : 1118968  |************************************* |

Ctrl-C at any time. Kernel will auto cleanup maps and programs

	$ addr2line -ape ./bld_x64/vmlinux 0xffffffff81695995
	0xffffffff816d0da9 0xffffffff81695995:
	./bld_x64/../net/ipv4/icmp.c:1038 0xffffffff816d0da9:
	./bld_x64/../net/unix/af_unix.c:1231

Signed-off-by: Alexei Starovoitov <ast@plumgrid.com>
Cc: Arnaldo Carvalho de Melo <acme@infradead.org>
Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Daniel Borkmann <daniel@iogearbox.net>
Cc: David S. Miller <davem@davemloft.net>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Steven Rostedt <rostedt@goodmis.org>
Link: http://lkml.kernel.org/r/1427312966-8434-8-git-send-email-ast@plumgrid.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>

3 files changed, 185 insertions, 0 deletions

diff --git a/samples/bpf/Makefile b/samples/bpf/Makefile
index 51f6f01e5a3a..6dd272143733 100644
--- a/samples/bpf/Makefile
+++ b/samples/bpf/Makefile
@@ -7,6 +7,7 @@ hostprogs-y += sock_example
 hostprogs-y += sockex1
 hostprogs-y += sockex2
 hostprogs-y += tracex1
+hostprogs-y += tracex2
 
 test_verifier-objs := test_verifier.o libbpf.o
 test_maps-objs := test_maps.o libbpf.o
@@ -14,12 +15,14 @@ sock_example-objs := sock_example.o libbpf.o
 sockex1-objs := bpf_load.o libbpf.o sockex1_user.o
 sockex2-objs := bpf_load.o libbpf.o sockex2_user.o
 tracex1-objs := bpf_load.o libbpf.o tracex1_user.o
+tracex2-objs := bpf_load.o libbpf.o tracex2_user.o
 
 # Tell kbuild to always build the programs
 always := $(hostprogs-y)
 always += sockex1_kern.o
 always += sockex2_kern.o
 always += tracex1_kern.o
+always += tracex2_kern.o
 
 HOSTCFLAGS += -I$(objtree)/usr/include
 
@@ -27,6 +30,7 @@ HOSTCFLAGS_bpf_load.o += -I$(objtree)/usr/include -Wno-unused-variable
 HOSTLOADLIBES_sockex1 += -lelf
 HOSTLOADLIBES_sockex2 += -lelf
 HOSTLOADLIBES_tracex1 += -lelf
+HOSTLOADLIBES_tracex2 += -lelf
 
 # point this to your LLVM backend with bpf support
 LLC=$(srctree)/tools/bpf/llvm/bld/Debug+Asserts/bin/llc
diff --git a/samples/bpf/tracex2_kern.c b/samples/bpf/tracex2_kern.c
new file mode 100644
index 000000000000..19ec1cfc45db
--- /dev/null
+++ b/samples/bpf/tracex2_kern.c
@@ -0,0 +1,86 @@
+/* Copyright (c) 2013-2015 PLUMgrid, http://plumgrid.com
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of version 2 of the GNU General Public
+ * License as published by the Free Software Foundation.
+ */
+#include <linux/skbuff.h>
+#include <linux/netdevice.h>
+#include <linux/version.h>
+#include <uapi/linux/bpf.h>
+#include "bpf_helpers.h"
+
+struct bpf_map_def SEC("maps") my_map = {
+        .type = BPF_MAP_TYPE_HASH,
+        .key_size = sizeof(long),
+        .value_size = sizeof(long),
+        .max_entries = 1024,
+};
+
+/* kprobe is NOT a stable ABI. If kernel internals change this bpf+kprobe
+ * example will no longer be meaningful
+ */
+SEC("kprobe/kfree_skb")
+int bpf_prog2(struct pt_regs *ctx)
+{
+        long loc = 0;
+        long init_val = 1;
+        long *value;
+
+        /* x64 specific: read ip of kfree_skb caller.
+         * non-portable version of __builtin_return_address(0)
+         */
+        bpf_probe_read(&loc, sizeof(loc), (void *)ctx->sp);
+
+        value = bpf_map_lookup_elem(&my_map, &loc);
+        if (value)
+                *value += 1;
+        else
+                bpf_map_update_elem(&my_map, &loc, &init_val, BPF_ANY);
+        return 0;
+}
+
+static unsigned int log2(unsigned int v)
+{
+        unsigned int r;
+        unsigned int shift;
+
+        r = (v > 0xFFFF) << 4; v >>= r;
+        shift = (v > 0xFF) << 3; v >>= shift; r |= shift;
+        shift = (v > 0xF) << 2; v >>= shift; r |= shift;
+        shift = (v > 0x3) << 1; v >>= shift; r |= shift;
+        r |= (v >> 1);
+        return r;
+}
+
+static unsigned int log2l(unsigned long v)
+{
+        unsigned int hi = v >> 32;
+        if (hi)
+                return log2(hi) + 32;
+        else
+                return log2(v);
+}
+
+struct bpf_map_def SEC("maps") my_hist_map = {
+        .type = BPF_MAP_TYPE_ARRAY,
+        .key_size = sizeof(u32),
+        .value_size = sizeof(long),
+        .max_entries = 64,
+};
+
+SEC("kprobe/sys_write")
+int bpf_prog3(struct pt_regs *ctx)
+{
+        long write_size = ctx->dx; /* arg3 */
+        long init_val = 1;
+        long *value;
+        u32 index = log2l(write_size);
+
+        value = bpf_map_lookup_elem(&my_hist_map, &index);
+        if (value)
+                __sync_fetch_and_add(value, 1);
+        return 0;
+}
+char _license[] SEC("license") = "GPL";
+u32 _version SEC("version") = LINUX_VERSION_CODE;
diff --git a/samples/bpf/tracex2_user.c b/samples/bpf/tracex2_user.c
new file mode 100644
index 000000000000..91b8d0896fbb
--- /dev/null
+++ b/samples/bpf/tracex2_user.c
@@ -0,0 +1,95 @@
+#include <stdio.h>
+#include <unistd.h>
+#include <stdlib.h>
+#include <signal.h>
+#include <linux/bpf.h>
+#include "libbpf.h"
+#include "bpf_load.h"
+
+#define MAX_INDEX       64
+#define MAX_STARS       38
+
+static void stars(char *str, long val, long max, int width)
+{
+        int i;
+
+        for (i = 0; i < (width * val / max) - 1 && i < width - 1; i++)
+                str[i] = '*';
+        if (val > max)
+                str[i - 1] = '+';
+        str[i] = '\0';
+}
+
+static void print_hist(int fd)
+{
+        int key;
+        long value;
+        long data[MAX_INDEX] = {};
+        char starstr[MAX_STARS];
+        int i;
+        int max_ind = -1;
+        long max_value = 0;
+
+        for (key = 0; key < MAX_INDEX; key++) {
+                bpf_lookup_elem(fd, &key, &value);
+                data[key] = value;
+                if (value && key > max_ind)
+                        max_ind = key;
+                if (value > max_value)
+                        max_value = value;
+        }
+
+        printf("           syscall write() stats\n");
+        printf("     byte_size       : count     distribution\n");
+        for (i = 1; i <= max_ind + 1; i++) {
+                stars(starstr, data[i - 1], max_value, MAX_STARS);
+                printf("%8ld -> %-8ld : %-8ld |%-*s|\n",
+                       (1l << i) >> 1, (1l << i) - 1, data[i - 1],
+                       MAX_STARS, starstr);
+        }
+}
+static void int_exit(int sig)
+{
+        print_hist(map_fd[1]);
+        exit(0);
+}
+
+int main(int ac, char **argv)
+{
+        char filename[256];
+        long key, next_key, value;
+        FILE *f;
+        int i;
+
+        snprintf(filename, sizeof(filename), "%s_kern.o", argv[0]);
+
+        signal(SIGINT, int_exit);
+
+        /* start 'ping' in the background to have some kfree_skb events */
+        f = popen("ping -c5 localhost", "r");
+        (void) f;
+
+        /* start 'dd' in the background to have plenty of 'write' syscalls */
+        f = popen("dd if=/dev/zero of=/dev/null count=5000000", "r");
+        (void) f;
+
+        if (load_bpf_file(filename)) {
+                printf("%s", bpf_log_buf);
+                return 1;
+        }
+
+        for (i = 0; i < 5; i++) {
+                key = 0;
+                while (bpf_get_next_key(map_fd[0], &key, &next_key) == 0) {
+                        bpf_lookup_elem(map_fd[0], &next_key, &value);
+                        printf("location 0x%lx count %ld\n", next_key, value);
+                        key = next_key;
+                }
+                if (key)
+                        printf("\n");
+                sleep(1);
+        }
+        print_hist(map_fd[1]);
+
+        return 0;
+}