Jakub Kicinski <jakub.kicin...@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 <t...@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;
