[PATCH bpf-next v4 1/2] trace_helpers.c: Add helpers to poll multiple perf FDs for events

[PATCH bpf-next v4 1/2] trace_helpers.c: Add helpers to poll multiple perf FDs for events

[Toke Høiland-Jørgensen]

Add two new helper functions to trace_helpers that supports polling
multiple perf file descriptors for events. These are used to the XDP
perf_event_output example, which needs to work with one perf fd per CPU.

Signed-off-by: Toke Høiland-Jørgensen <toke@toke.dk>
---
 tools/testing/selftests/bpf/trace_helpers.c |   47 ++++++++++++++++++++++++++-
 tools/testing/selftests/bpf/trace_helpers.h |    4 ++
 2 files changed, 49 insertions(+), 2 deletions(-)

diff --git a/tools/testing/selftests/bpf/trace_helpers.c b/tools/testing/selftests/bpf/trace_helpers.c
index 3868dcb63420..1e62d89f34cf 100644
--- a/tools/testing/selftests/bpf/trace_helpers.c
+++ b/tools/testing/selftests/bpf/trace_helpers.c
@@ -88,7 +88,7 @@ static int page_size;
 static int page_cnt = 8;
 static struct perf_event_mmap_page *header;
 
-int perf_event_mmap(int fd)
+int perf_event_mmap_header(int fd, struct perf_event_mmap_page **header)
 {
 	void *base;
 	int mmap_size;
@@ -102,10 +102,15 @@ int perf_event_mmap(int fd)
 		return -1;
 	}
 
-	header = base;
+	*header = base;
 	return 0;
 }
 
+int perf_event_mmap(int fd)
+{
+	return perf_event_mmap_header(fd, &header);
+}
+
 static int perf_event_poll(int fd)
 {
 	struct pollfd pfd = { .fd = fd, .events = POLLIN };
@@ -163,3 +168,41 @@ int perf_event_poller(int fd, perf_event_print_fn output_fn)
 
 	return ret;
 }
+
+int perf_event_poller_multi(int *fds, struct perf_event_mmap_page **headers,
+			    int num_fds, perf_event_print_fn output_fn)
+{
+	enum bpf_perf_event_ret ret;
+	struct pollfd *pfds;
+	void *buf = NULL;
+	size_t len = 0;
+	int i;
+
+	pfds = malloc(sizeof(*pfds) * num_fds);
+	if (!pfds)
+		return -1;
+
+	memset(pfds, 0, sizeof(*pfds) * num_fds);
+	for (i = 0; i < num_fds; i++) {
+		pfds[i].fd = fds[i];
+		pfds[i].events = POLLIN;
+	}
+
+	for (;;) {
+		poll(pfds, num_fds, 1000);
+		for (i = 0; i < num_fds; i++) {
+			if (pfds[i].revents) {
+				ret = bpf_perf_event_read_simple(headers[i], page_cnt * page_size,
+								page_size, &buf, &len,
+								bpf_perf_event_print,
+								output_fn);
+				if (ret != LIBBPF_PERF_EVENT_CONT)
+					break;
+			}
+		}
+	}
+	free(buf);
+	free(pfds);
+
+	return ret;
+}
diff --git a/tools/testing/selftests/bpf/trace_helpers.h b/tools/testing/selftests/bpf/trace_helpers.h
index 3b4bcf7f5084..18924f23db1b 100644
--- a/tools/testing/selftests/bpf/trace_helpers.h
+++ b/tools/testing/selftests/bpf/trace_helpers.h
@@ -3,6 +3,7 @@
 #define __TRACE_HELPER_H
 
 #include <libbpf.h>
+#include <linux/perf_event.h>
 
 struct ksym {
 	long addr;
@@ -16,6 +17,9 @@ long ksym_get_addr(const char *name);
 typedef enum bpf_perf_event_ret (*perf_event_print_fn)(void *data, int size);
 
 int perf_event_mmap(int fd);
+int perf_event_mmap_header(int fd, struct perf_event_mmap_page **header);
 /* return LIBBPF_PERF_EVENT_DONE or LIBBPF_PERF_EVENT_ERROR */
 int perf_event_poller(int fd, perf_event_print_fn output_fn);
+int perf_event_poller_multi(int *fds, struct perf_event_mmap_page **headers,
+			    int num_fds, perf_event_print_fn output_fn);
 #endif

[PATCH bpf-next v4 2/2] samples/bpf: Add xdp_sample_pkts example

[Toke Høiland-Jørgensen]

Add an example program showing how to sample packets from XDP using the
perf event buffer. The example userspace program just prints the ethernet
header for every packet sampled.

Signed-off-by: Toke Høiland-Jørgensen <toke@toke.dk>
---
 samples/bpf/Makefile               |    4 +
 samples/bpf/xdp_sample_pkts_kern.c |   62 +++++++++++++
 samples/bpf/xdp_sample_pkts_user.c |  176 ++++++++++++++++++++++++++++++++++++
 3 files changed, 242 insertions(+)
 create mode 100644 samples/bpf/xdp_sample_pkts_kern.c
 create mode 100644 samples/bpf/xdp_sample_pkts_user.c

diff --git a/samples/bpf/Makefile b/samples/bpf/Makefile
index 1303af10e54d..9ea2f7b64869 100644
--- a/samples/bpf/Makefile
+++ b/samples/bpf/Makefile
@@ -52,6 +52,7 @@ hostprogs-y += xdp_adjust_tail
 hostprogs-y += xdpsock
 hostprogs-y += xdp_fwd
 hostprogs-y += task_fd_query
+hostprogs-y += xdp_sample_pkts
 
 # Libbpf dependencies
 LIBBPF = $(TOOLS_PATH)/lib/bpf/libbpf.a
@@ -107,6 +108,7 @@ xdp_adjust_tail-objs := xdp_adjust_tail_user.o
 xdpsock-objs := bpf_load.o xdpsock_user.o
 xdp_fwd-objs := bpf_load.o xdp_fwd_user.o
 task_fd_query-objs := bpf_load.o task_fd_query_user.o $(TRACE_HELPERS)
+xdp_sample_pkts-objs := xdp_sample_pkts_user.o $(TRACE_HELPERS)
 
 # Tell kbuild to always build the programs
 always := $(hostprogs-y)
@@ -163,6 +165,7 @@ always += xdp_adjust_tail_kern.o
 always += xdpsock_kern.o
 always += xdp_fwd_kern.o
 always += task_fd_query_kern.o
+always += xdp_sample_pkts_kern.o
 
 HOSTCFLAGS += -I$(objtree)/usr/include
 HOSTCFLAGS += -I$(srctree)/tools/lib/
@@ -179,6 +182,7 @@ HOSTCFLAGS_spintest_user.o += -I$(srctree)/tools/lib/bpf/
 HOSTCFLAGS_trace_event_user.o += -I$(srctree)/tools/lib/bpf/
 HOSTCFLAGS_sampleip_user.o += -I$(srctree)/tools/lib/bpf/
 HOSTCFLAGS_task_fd_query_user.o += -I$(srctree)/tools/lib/bpf/
+HOSTCFLAGS_xdp_sample_pkts_user.o += -I$(srctree)/tools/lib/bpf/
 
 HOST_LOADLIBES		+= $(LIBBPF) -lelf
 HOSTLOADLIBES_tracex4		+= -lrt
diff --git a/samples/bpf/xdp_sample_pkts_kern.c b/samples/bpf/xdp_sample_pkts_kern.c
new file mode 100644
index 000000000000..4560522ca015
--- /dev/null
+++ b/samples/bpf/xdp_sample_pkts_kern.c
@@ -0,0 +1,62 @@
+#include <linux/ptrace.h>
+#include <linux/version.h>
+#include <uapi/linux/bpf.h>
+#include "bpf_helpers.h"
+
+#define SAMPLE_SIZE 64ul
+#define MAX_CPUS 24
+
+#define bpf_printk(fmt, ...)					\
+({								\
+	       char ____fmt[] = fmt;				\
+	       bpf_trace_printk(____fmt, sizeof(____fmt),	\
+				##__VA_ARGS__);			\
+})
+
+struct bpf_map_def SEC("maps") my_map = {
+	.type = BPF_MAP_TYPE_PERF_EVENT_ARRAY,
+	.key_size = sizeof(int),
+	.value_size = sizeof(u32),
+	.max_entries = MAX_CPUS,
+};
+
+SEC("xdp_sample")
+int xdp_sample_prog(struct xdp_md *ctx)
+{
+	void *data_end = (void *)(long)ctx->data_end;
+	void *data = (void *)(long)ctx->data;
+
+        /* Metadata will be in the perf event before the packet data. */
+	struct S {
+		u16 cookie;
+		u16 pkt_len;
+	} __attribute__((packed)) metadata;
+
+	if (data + SAMPLE_SIZE < data_end) {
+		/* The XDP perf_event_output handler will use the upper 32 bits
+		 * of the flags argument as a number of bytes to include of the
+		 * packet payload in the event data. If the size is too big, the
+		 * call to bpf_perf_event_output will fail and return -EFAULT.
+		 *
+		 * See bpf_xdp_event_output in net/core/filter.c.
+		 *
+		 * The BPF_F_CURRENT_CPU flag means that the event output fd
+		 * will be indexed by the CPU number in the event map.
+		 */
+		u64 flags = (SAMPLE_SIZE << 32) | BPF_F_CURRENT_CPU;
+		int ret;
+
+		metadata.cookie = 0xdead;
+		metadata.pkt_len = (u16)(data_end - data);
+
+		ret = bpf_perf_event_output(ctx, &my_map, flags,
+				      &metadata, sizeof(metadata));
+		if(ret)
+			bpf_printk("perf_event_output failed: %d\n", ret);
+	}
+
+	return XDP_PASS;
+}
+
+char _license[] SEC("license") = "GPL";
+u32 _version SEC("version") = LINUX_VERSION_CODE;
diff --git a/samples/bpf/xdp_sample_pkts_user.c b/samples/bpf/xdp_sample_pkts_user.c
new file mode 100644
index 000000000000..672392d48ce3
--- /dev/null
+++ b/samples/bpf/xdp_sample_pkts_user.c
@@ -0,0 +1,176 @@
+/* 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 <stdio.h>
+#include <unistd.h>
+#include <stdlib.h>
+#include <stdbool.h>
+#include <string.h>
+#include <fcntl.h>
+#include <poll.h>
+#include <linux/perf_event.h>
+#include <linux/bpf.h>
+#include <net/if.h>
+#include <errno.h>
+#include <assert.h>
+#include <sys/sysinfo.h>
+#include <sys/syscall.h>
+#include <sys/ioctl.h>
+#include <sys/mman.h>
+#include <time.h>
+#include <signal.h>
+#include <libbpf.h>
+#include <bpf/bpf.h>
+
+#include "perf-sys.h"
+#include "trace_helpers.h"
+
+#define MAX_CPUS 24
+static int pmu_fds[MAX_CPUS], if_idx = 0;
+static struct perf_event_mmap_page *headers[MAX_CPUS];
+static char *if_name;
+
+static int do_attach(int idx, int fd, const char *name)
+{
+	int err;
+
+	err = bpf_set_link_xdp_fd(idx, fd, 0);
+	if (err < 0)
+		printf("ERROR: failed to attach program to %s\n", name);
+
+	return err;
+}
+
+static int do_detach(int idx, const char *name)
+{
+	int err;
+
+	err = bpf_set_link_xdp_fd(idx, -1, 0);
+	if (err < 0)
+		printf("ERROR: failed to detach program from %s\n", name);
+
+	return err;
+}
+
+#define SAMPLE_SIZE 64
+
+static int print_bpf_output(void *data, int size)
+{
+	struct {
+		__u16 cookie;
+		__u16 pkt_len;
+		__u8  pkt_data[SAMPLE_SIZE];
+	} __attribute__((packed)) *e = data;
+	int i;
+
+	if (e->cookie != 0xdead) {
+		printf("BUG cookie %x sized %d\n",
+		       e->cookie, size);
+		return LIBBPF_PERF_EVENT_ERROR;
+	}
+
+	printf("Pkt len: %-5d bytes. Ethernet hdr: ", e->pkt_len);
+	for (i = 0; i < 14 && i < e->pkt_len; i++)
+		printf("%02x ", e->pkt_data[i]);
+	printf("\n");
+
+	return LIBBPF_PERF_EVENT_CONT;
+}
+
+static void test_bpf_perf_event(int map_fd, int num)
+{
+	struct perf_event_attr attr = {
+		.sample_type = PERF_SAMPLE_RAW,
+		.type = PERF_TYPE_SOFTWARE,
+		.config = PERF_COUNT_SW_BPF_OUTPUT,
+		.wakeup_events = 1, /* get an fd notification for every event */
+	};
+	int i;
+
+	for (i = 0; i < num; i++) {
+		int key = i;
+
+		pmu_fds[i] = sys_perf_event_open(&attr, -1/*pid*/, i/*cpu*/, -1/*group_fd*/, 0);
+
+		assert(pmu_fds[i] >= 0);
+		assert(bpf_map_update_elem(map_fd, &key, &pmu_fds[i], BPF_ANY) == 0);
+		ioctl(pmu_fds[i], PERF_EVENT_IOC_ENABLE, 0);
+	}
+}
+
+static void sig_handler(int signo)
+{
+	do_detach(if_idx, if_name);
+	exit(0);
+}
+
+int main(int argc, char **argv)
+{
+	struct bpf_prog_load_attr prog_load_attr = {
+		.prog_type	= BPF_PROG_TYPE_XDP,
+	};
+	struct bpf_object *obj;
+	struct bpf_map *map;
+	int prog_fd, map_fd;
+	char filename[256];
+	int ret, err, i;
+	int numcpus;
+
+	if (argc < 2) {
+		printf("Usage: %s <ifname>\n", argv[0]);
+		return 1;
+	}
+
+	numcpus = get_nprocs();
+	if (numcpus > MAX_CPUS)
+		numcpus = MAX_CPUS;
+
+	snprintf(filename, sizeof(filename), "%s_kern.o", argv[0]);
+	prog_load_attr.file = filename;
+
+	if (bpf_prog_load_xattr(&prog_load_attr, &obj, &prog_fd))
+		return 1;
+
+	if (!prog_fd) {
+		printf("load_bpf_file: %s\n", strerror(errno));
+		return 1;
+	}
+
+	map = bpf_map__next(NULL, obj);
+	if (!map) {
+		printf("finding a map in obj file failed\n");
+		return 1;
+	}
+	map_fd = bpf_map__fd(map);
+
+	if_idx = if_nametoindex(argv[1]);
+	if (!if_idx)
+		if_idx = strtoul(argv[1], NULL, 0);
+
+	if (!if_idx) {
+		fprintf(stderr, "Invalid ifname\n");
+		return 1;
+	}
+	if_name = argv[1];
+	err = do_attach(if_idx, prog_fd, argv[1]);
+	if (err)
+		return err;
+
+	if (signal(SIGINT, sig_handler) ||
+	    signal(SIGHUP, sig_handler) ||
+	    signal(SIGTERM, sig_handler)) {
+		perror("signal");
+		return 1;
+	}
+
+	test_bpf_perf_event(map_fd, numcpus);
+
+	for (i = 0; i < numcpus; i++)
+		if (perf_event_mmap_header(pmu_fds[i], &headers[i]) < 0)
+			return 1;
+
+	ret = perf_event_poller_multi(pmu_fds, headers, numcpus, print_bpf_output);
+	kill(0, SIGINT);
+	return ret;
+}

Re: [PATCH bpf-next v4 1/2] trace_helpers.c: Add helpers to poll multiple perf FDs for events

[Jakub Kicinski]

On Tue, 05 Jun 2018 16:50:00 +0200, Toke Høiland-Jørgensen wrote:
> Add two new helper functions to trace_helpers that supports polling
> multiple perf file descriptors for events. These are used to the XDP
> perf_event_output example, which needs to work with one perf fd per CPU.
> 
> Signed-off-by: Toke Høiland-Jørgensen <toke@toke.dk>
> ---
>  tools/testing/selftests/bpf/trace_helpers.c |   47 ++++++++++++++++++++++++++-
>  tools/testing/selftests/bpf/trace_helpers.h |    4 ++
>  2 files changed, 49 insertions(+), 2 deletions(-)
> 
> diff --git a/tools/testing/selftests/bpf/trace_helpers.c b/tools/testing/selftests/bpf/trace_helpers.c
> index 3868dcb63420..1e62d89f34cf 100644
> --- a/tools/testing/selftests/bpf/trace_helpers.c
> +++ b/tools/testing/selftests/bpf/trace_helpers.c
> @@ -88,7 +88,7 @@ static int page_size;
>  static int page_cnt = 8;
>  static struct perf_event_mmap_page *header;
>  
> -int perf_event_mmap(int fd)
> +int perf_event_mmap_header(int fd, struct perf_event_mmap_page **header)
>  {
>  	void *base;
>  	int mmap_size;
> @@ -102,10 +102,15 @@ int perf_event_mmap(int fd)
>  		return -1;
>  	}
>  
> -	header = base;
> +	*header = base;
>  	return 0;
>  }
>  
> +int perf_event_mmap(int fd)
> +{
> +	return perf_event_mmap_header(fd, &header);
> +}
> +
>  static int perf_event_poll(int fd)
>  {
>  	struct pollfd pfd = { .fd = fd, .events = POLLIN };
> @@ -163,3 +168,41 @@ int perf_event_poller(int fd, perf_event_print_fn output_fn)
>  
>  	return ret;
>  }
> +
> +int perf_event_poller_multi(int *fds, struct perf_event_mmap_page **headers,
> +			    int num_fds, perf_event_print_fn output_fn)
> +{
> +	enum bpf_perf_event_ret ret;
> +	struct pollfd *pfds;
> +	void *buf = NULL;
> +	size_t len = 0;
> +	int i;
> +
> +	pfds = malloc(sizeof(*pfds) * num_fds);
> +	if (!pfds)
> +		return -1;

nit: this is correct, but better use LIBBPF_PERF_EVENT_ERROR?  This
function is supposed to return enum bpf_perf_event_ret values I assume?
In case someone moves this code to libbpf later on...

> +	memset(pfds, 0, sizeof(*pfds) * num_fds);
> +	for (i = 0; i < num_fds; i++) {
> +		pfds[i].fd = fds[i];
> +		pfds[i].events = POLLIN;
> +	}
> +
> +	for (;;) {
> +		poll(pfds, num_fds, 1000);
> +		for (i = 0; i < num_fds; i++) {
> +			if (pfds[i].revents) {

nit: save yourself a lever of indentation by doing:

if (!pfds[i].revents)
	continue;

and you won't have to go over 80 chars.

> +				ret = bpf_perf_event_read_simple(headers[i], page_cnt * page_size,
> +								page_size, &buf, &len,
> +								bpf_perf_event_print,
> +								output_fn);
> +				if (ret != LIBBPF_PERF_EVENT_CONT)
> +					break;
> +			}
> +		}
> +	}
> +	free(buf);
> +	free(pfds);
> +
> +	return ret;
> +}

Re: [PATCH bpf-next v4 2/2] samples/bpf: Add xdp_sample_pkts example

[Jakub Kicinski]

On Tue, 05 Jun 2018 16:50:00 +0200, Toke Høiland-Jørgensen wrote:
> Add an example program showing how to sample packets from XDP using the
> perf event buffer. The example userspace program just prints the ethernet
> header for every packet sampled.
> 
> Signed-off-by: Toke Høiland-Jørgensen <toke@toke.dk>

> diff --git a/samples/bpf/xdp_sample_pkts_kern.c b/samples/bpf/xdp_sample_pkts_kern.c
> new file mode 100644
> index 000000000000..4560522ca015
> --- /dev/null
> +++ b/samples/bpf/xdp_sample_pkts_kern.c
> @@ -0,0 +1,62 @@
> +#include <linux/ptrace.h>
> +#include <linux/version.h>
> +#include <uapi/linux/bpf.h>
> +#include "bpf_helpers.h"
> +
> +#define SAMPLE_SIZE 64ul
> +#define MAX_CPUS 24

That may be a lil' too few for modern HW with hyper-threading on ;)  
My development machine says:

$ ncpus
28

128, maybe?

> +#define bpf_printk(fmt, ...)					\
> +({								\
> +	       char ____fmt[] = fmt;				\
> +	       bpf_trace_printk(____fmt, sizeof(____fmt),	\
> +				##__VA_ARGS__);			\
> +})
> +
> +struct bpf_map_def SEC("maps") my_map = {
> +	.type = BPF_MAP_TYPE_PERF_EVENT_ARRAY,
> +	.key_size = sizeof(int),
> +	.value_size = sizeof(u32),
> +	.max_entries = MAX_CPUS,
> +};
> +
> +SEC("xdp_sample")
> +int xdp_sample_prog(struct xdp_md *ctx)
> +{
> +	void *data_end = (void *)(long)ctx->data_end;
> +	void *data = (void *)(long)ctx->data;
> +
> +        /* Metadata will be in the perf event before the packet data. */
> +	struct S {
> +		u16 cookie;
> +		u16 pkt_len;
> +	} __attribute__((packed)) metadata;
> +
> +	if (data + SAMPLE_SIZE < data_end) {
> +		/* The XDP perf_event_output handler will use the upper 32 bits
> +		 * of the flags argument as a number of bytes to include of the
> +		 * packet payload in the event data. If the size is too big, the
> +		 * call to bpf_perf_event_output will fail and return -EFAULT.
> +		 *
> +		 * See bpf_xdp_event_output in net/core/filter.c.
> +		 *
> +		 * The BPF_F_CURRENT_CPU flag means that the event output fd
> +		 * will be indexed by the CPU number in the event map.
> +		 */
> +		u64 flags = (SAMPLE_SIZE << 32) | BPF_F_CURRENT_CPU;
> +		int ret;
> +
> +		metadata.cookie = 0xdead;
> +		metadata.pkt_len = (u16)(data_end - data);
> +
> +		ret = bpf_perf_event_output(ctx, &my_map, flags,
> +				      &metadata, sizeof(metadata));
> +		if(ret)

Please run checkpatch --strict on the samples.

> +			bpf_printk("perf_event_output failed: %d\n", ret);
> +	}
> +
> +	return XDP_PASS;
> +}
> +
> +char _license[] SEC("license") = "GPL";
> +u32 _version SEC("version") = LINUX_VERSION_CODE;

Re: [PATCH bpf-next v4 2/2] samples/bpf: Add xdp_sample_pkts example

[Toke Høiland-Jørgensen]

Jakub Kicinski <jakub.kicinski@netronome.com> writes:

> On Tue, 05 Jun 2018 16:50:00 +0200, Toke Høiland-Jørgensen wrote:
>> Add an example program showing how to sample packets from XDP using the
>> perf event buffer. The example userspace program just prints the ethernet
>> header for every packet sampled.
>> 
>> Signed-off-by: Toke Høiland-Jørgensen <toke@toke.dk>
>
>> diff --git a/samples/bpf/xdp_sample_pkts_kern.c b/samples/bpf/xdp_sample_pkts_kern.c
>> new file mode 100644
>> index 000000000000..4560522ca015
>> --- /dev/null
>> +++ b/samples/bpf/xdp_sample_pkts_kern.c
>> @@ -0,0 +1,62 @@
>> +#include <linux/ptrace.h>
>> +#include <linux/version.h>
>> +#include <uapi/linux/bpf.h>
>> +#include "bpf_helpers.h"
>> +
>> +#define SAMPLE_SIZE 64ul
>> +#define MAX_CPUS 24
>
> That may be a lil' too few for modern HW with hyper-threading on ;)  
> My development machine says:
>
> $ ncpus
> 28
>
> 128, maybe?

What? 24 CPUs should be enough for everyone, surely? ;)

(I just took twice the number of CPUs in my largest machine; but fair
point, other people have access to more expensive toys I guess... will fix)

>> +#define bpf_printk(fmt, ...)					\
>> +({								\
>> +	       char ____fmt[] = fmt;				\
>> +	       bpf_trace_printk(____fmt, sizeof(____fmt),	\
>> +				##__VA_ARGS__);			\
>> +})
>> +
>> +struct bpf_map_def SEC("maps") my_map = {
>> +	.type = BPF_MAP_TYPE_PERF_EVENT_ARRAY,
>> +	.key_size = sizeof(int),
>> +	.value_size = sizeof(u32),
>> +	.max_entries = MAX_CPUS,
>> +};
>> +
>> +SEC("xdp_sample")
>> +int xdp_sample_prog(struct xdp_md *ctx)
>> +{
>> +	void *data_end = (void *)(long)ctx->data_end;
>> +	void *data = (void *)(long)ctx->data;
>> +
>> +        /* Metadata will be in the perf event before the packet data. */
>> +	struct S {
>> +		u16 cookie;
>> +		u16 pkt_len;
>> +	} __attribute__((packed)) metadata;
>> +
>> +	if (data + SAMPLE_SIZE < data_end) {
>> +		/* The XDP perf_event_output handler will use the upper 32 bits
>> +		 * of the flags argument as a number of bytes to include of the
>> +		 * packet payload in the event data. If the size is too big, the
>> +		 * call to bpf_perf_event_output will fail and return -EFAULT.
>> +		 *
>> +		 * See bpf_xdp_event_output in net/core/filter.c.
>> +		 *
>> +		 * The BPF_F_CURRENT_CPU flag means that the event output fd
>> +		 * will be indexed by the CPU number in the event map.
>> +		 */
>> +		u64 flags = (SAMPLE_SIZE << 32) | BPF_F_CURRENT_CPU;
>> +		int ret;
>> +
>> +		metadata.cookie = 0xdead;
>> +		metadata.pkt_len = (u16)(data_end - data);
>> +
>> +		ret = bpf_perf_event_output(ctx, &my_map, flags,
>> +				      &metadata, sizeof(metadata));
>> +		if(ret)
>
> Please run checkpatch --strict on the samples.

Will do!

>> +			bpf_printk("perf_event_output failed: %d\n", ret);
>> +	}
>> +
>> +	return XDP_PASS;
>> +}
>> +
>> +char _license[] SEC("license") = "GPL";
>> +u32 _version SEC("version") = LINUX_VERSION_CODE;

Re: [PATCH bpf-next v4 2/2] samples/bpf: Add xdp_sample_pkts example

[Jesper Dangaard Brouer]

On Wed, 06 Jun 2018 13:01:52 +0200
Toke Høiland-Jørgensen <toke@toke.dk> wrote:

> Jakub Kicinski <jakub.kicinski@netronome.com> writes:
> 
> > On Tue, 05 Jun 2018 16:50:00 +0200, Toke Høiland-Jørgensen wrote:  
> >> Add an example program showing how to sample packets from XDP using the
> >> perf event buffer. The example userspace program just prints the ethernet
> >> header for every packet sampled.
> >> 
> >> Signed-off-by: Toke Høiland-Jørgensen <toke@toke.dk>  
> >  
> >> diff --git a/samples/bpf/xdp_sample_pkts_kern.c b/samples/bpf/xdp_sample_pkts_kern.c
> >> new file mode 100644
> >> index 000000000000..4560522ca015
> >> --- /dev/null
> >> +++ b/samples/bpf/xdp_sample_pkts_kern.c
> >> @@ -0,0 +1,62 @@
> >> +#include <linux/ptrace.h>
> >> +#include <linux/version.h>
> >> +#include <uapi/linux/bpf.h>
> >> +#include "bpf_helpers.h"
> >> +
> >> +#define SAMPLE_SIZE 64ul
> >> +#define MAX_CPUS 24  
> >
> > That may be a lil' too few for modern HW with hyper-threading on ;)  
> > My development machine says:
> >
> > $ ncpus
> > 28
> >
> > 128, maybe?  
> 
> What? 24 CPUs should be enough for everyone, surely? ;)
> 
> (I just took twice the number of CPUs in my largest machine; but fair
> point, other people have access to more expensive toys I guess... will fix)
> 
> >> +#define bpf_printk(fmt, ...)					\
> >> +({								\
> >> +	       char ____fmt[] = fmt;				\
> >> +	       bpf_trace_printk(____fmt, sizeof(____fmt),	\
> >> +				##__VA_ARGS__);			\
> >> +})
> >> +
> >> +struct bpf_map_def SEC("maps") my_map = {
> >> +	.type = BPF_MAP_TYPE_PERF_EVENT_ARRAY,
> >> +	.key_size = sizeof(int),
> >> +	.value_size = sizeof(u32),
> >> +	.max_entries = MAX_CPUS,
> >> +};

I agree, we should increase it to something larger than 24, just to
avoid people getting surprised, but this is only sample code.

At some point I want us to add another example, that show how to adjust
this runtime, which is actually possible with bpf_load.c via a map
callback that Martin added.  I've not look at how libbpf can support
this.  I do have sample code[1] that could be adjusted to do this, but
I don't want to create dependencies to bpf_load.c, as we all agree that
everything should be moved to use libbpf (tools/lib/bpf).

[1] https://github.com/netoptimizer/prototype-kernel/blob/master/kernel/samples/bpf/xdp_ddos01_blacklist_user.c#L186-L218

-- 
Best regards,
  Jesper Dangaard Brouer
  MSc.CS, Principal Kernel Engineer at Red Hat
  LinkedIn: http://www.linkedin.com/in/brouer