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Date: Sun, 24 Aug 2014 13:21:24 -0700
From: Alexei Starovoitov <ast@...mgrid.com>
To: "David S. Miller" <davem@...emloft.net>
Cc: Ingo Molnar <mingo@...nel.org>,
Linus Torvalds <torvalds@...ux-foundation.org>,
Andy Lutomirski <luto@...capital.net>,
Steven Rostedt <rostedt@...dmis.org>,
Daniel Borkmann <dborkman@...hat.com>,
Chema Gonzalez <chema@...gle.com>,
Eric Dumazet <edumazet@...gle.com>,
Peter Zijlstra <a.p.zijlstra@...llo.nl>,
Brendan Gregg <brendan.d.gregg@...il.com>,
Namhyung Kim <namhyung@...nel.org>,
"H. Peter Anvin" <hpa@...or.com>,
Andrew Morton <akpm@...ux-foundation.org>,
Kees Cook <keescook@...omium.org>, linux-api@...r.kernel.org,
netdev@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: [PATCH v5 net-next 23/29] samples: bpf: example of tracing filters with eBPF
simple packet drop monitor:
- in-kernel eBPF program attaches to kfree_skb() event and records number
of packet drops at given location
- userspace iterates over the map every second and prints stats
Signed-off-by: Alexei Starovoitov <ast@...mgrid.com>
---
samples/bpf/Makefile | 12 +++++
samples/bpf/dropmon.c | 122 +++++++++++++++++++++++++++++++++++++++++++++++++
2 files changed, 134 insertions(+)
create mode 100644 samples/bpf/Makefile
create mode 100644 samples/bpf/dropmon.c
diff --git a/samples/bpf/Makefile b/samples/bpf/Makefile
new file mode 100644
index 000000000000..8dfbacaef9ba
--- /dev/null
+++ b/samples/bpf/Makefile
@@ -0,0 +1,12 @@
+# kbuild trick to avoid linker error. Can be omitted if a module is built.
+obj- := dummy.o
+
+# List of programs to build
+hostprogs-y := dropmon
+
+dropmon-objs := dropmon.o libbpf.o
+
+# Tell kbuild to always build the programs
+always := $(hostprogs-y)
+
+HOSTCFLAGS += -I$(objtree)/usr/include
diff --git a/samples/bpf/dropmon.c b/samples/bpf/dropmon.c
new file mode 100644
index 000000000000..3b921e2f4c8f
--- /dev/null
+++ b/samples/bpf/dropmon.c
@@ -0,0 +1,122 @@
+/* simple packet drop monitor:
+ * - in-kernel eBPF program attaches to kfree_skb() event and records number
+ * of packet drops at given location
+ * - userspace iterates over the map every second and prints stats
+ */
+#include <stdio.h>
+#include <unistd.h>
+#include <linux/bpf.h>
+#include <errno.h>
+#include <linux/unistd.h>
+#include <string.h>
+#include <linux/filter.h>
+#include <stdlib.h>
+#include <sys/types.h>
+#include <sys/stat.h>
+#include <fcntl.h>
+#include <stdbool.h>
+#include "libbpf.h"
+
+#define TRACEPOINT "/sys/kernel/debug/tracing/events/skb/kfree_skb/"
+
+static int write_to_file(const char *file, const char *str, bool keep_open)
+{
+ int fd, err;
+
+ fd = open(file, O_WRONLY);
+ err = write(fd, str, strlen(str));
+ (void) err;
+
+ if (keep_open) {
+ return fd;
+ } else {
+ close(fd);
+ return -1;
+ }
+}
+
+static int dropmon(void)
+{
+ /* the following eBPF program is equivalent to C:
+ * void filter(struct bpf_context *ctx)
+ * {
+ * long loc = ctx->arg2;
+ * long init_val = 1;
+ * void *value;
+ *
+ * value = bpf_map_lookup_elem(MAP_ID, &loc);
+ * if (value) {
+ * (*(long *) value) += 1;
+ * } else {
+ * bpf_map_update_elem(MAP_ID, &loc, &init_val);
+ * }
+ * }
+ */
+ static struct bpf_insn prog[] = {
+ BPF_LDX_MEM(BPF_DW, BPF_REG_2, BPF_REG_1, 8), /* r2 = *(u64 *)(r1 + 8) */
+ BPF_STX_MEM(BPF_DW, BPF_REG_10, BPF_REG_2, -8), /* *(u64 *)(fp - 8) = r2 */
+ BPF_MOV64_REG(BPF_REG_2, BPF_REG_10),
+ BPF_ALU64_IMM(BPF_ADD, BPF_REG_2, -8), /* r2 = fp - 8 */
+ BPF_LD_MAP_FD(BPF_REG_1, 0),
+ BPF_RAW_INSN(BPF_JMP | BPF_CALL, 0, 0, 0, BPF_FUNC_map_lookup_elem),
+ BPF_JMP_IMM(BPF_JEQ, BPF_REG_0, 0, 3),
+ BPF_MOV64_IMM(BPF_REG_1, 1), /* r1 = 1 */
+ BPF_RAW_INSN(BPF_STX | BPF_XADD | BPF_DW, BPF_REG_0, BPF_REG_1, 0, 0), /* xadd r0 += r1 */
+ BPF_EXIT_INSN(),
+ BPF_ST_MEM(BPF_DW, BPF_REG_10, -16, 1), /* *(u64 *)(fp - 16) = 1 */
+ BPF_MOV64_REG(BPF_REG_3, BPF_REG_10),
+ BPF_ALU64_IMM(BPF_ADD, BPF_REG_3, -16), /* r3 = fp - 16 */
+ BPF_MOV64_REG(BPF_REG_2, BPF_REG_10),
+ BPF_ALU64_IMM(BPF_ADD, BPF_REG_2, -8), /* r2 = fp - 8 */
+ BPF_LD_MAP_FD(BPF_REG_1, 0),
+ BPF_RAW_INSN(BPF_JMP | BPF_CALL, 0, 0, 0, BPF_FUNC_map_update_elem),
+ BPF_EXIT_INSN(),
+ };
+
+ long long key, next_key, value = 0;
+ int prog_fd, map_fd, i;
+ char fmt[32];
+
+ map_fd = bpf_create_map(BPF_MAP_TYPE_HASH, sizeof(key), sizeof(value), 1024);
+ if (map_fd < 0) {
+ printf("failed to create map '%s'\n", strerror(errno));
+ goto cleanup;
+ }
+
+ prog[4].imm = map_fd;
+ prog[16].imm = map_fd;
+
+ prog_fd = bpf_prog_load(BPF_PROG_TYPE_TRACING_FILTER, prog,
+ sizeof(prog), "GPL");
+ if (prog_fd < 0) {
+ printf("failed to load prog '%s'\n", strerror(errno));
+ return -1;
+ }
+
+ sprintf(fmt, "bpf_%d", prog_fd);
+
+ write_to_file(TRACEPOINT "filter", fmt, true);
+
+ for (i = 0; i < 10; i++) {
+ key = 0;
+ while (bpf_get_next_key(map_fd, &key, &next_key) == 0) {
+ bpf_lookup_elem(map_fd, &next_key, &value);
+ printf("location 0x%llx count %lld\n", next_key, value);
+ key = next_key;
+ }
+ if (key)
+ printf("\n");
+ sleep(1);
+ }
+
+cleanup:
+ /* maps, programs, tracepoint filters will auto cleanup on process exit */
+
+ return 0;
+}
+
+int main(void)
+{
+ dropmon();
+ return 0;
+}
--
1.7.9.5
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