Re: [PATCH net-next 2/3] bpf: introduce bpf_perf_event_output() helper

From: Wangnan (F)
Date: Wed Oct 21 2015 - 07:06:49 EST



On 2015/10/21 18:01, He Kuang wrote:
hi, Alexei

I've tested the sample in next patch and it works well. I think more work on
the perf side needs to be done for parsing PERF_COUNT_SW_BPF_OUTPUT event type,
are you working on that?

Thank you.

We need to add something into parse-event.y/l to let it know the new software event.
We can do this simple task. However, as I gussed before, perf is unable to print
this new event so there is some work need to be done to let 'perf report' and
'perf script' know it.

One thing I can still remember is finding a way to inject format information through
those output so 'perf script' and 'perf data convert --to-ctf' can decode the raw data
without extra work. Can you remember that we have discussed a solution which connects
debuginfo and output raw data using a builtin function in LLVM/clang? We already have
clang/LLVM patch on it, but on perf side I haven't do start working on it. I think we can
make perf output raw data hexadamically at first.

I'll do the above work and put related patch at the end of my eBPF patchset because
they shouldn't be merged until this patchset upstreamed.

Thank you.


On 2015/10/21 11:02, Alexei Starovoitov wrote:
This helper is used to send raw data from eBPF program into
special PERF_TYPE_SOFTWARE/PERF_COUNT_SW_BPF_OUTPUT perf_event.
User space needs to perf_event_open() it (either for one or all cpus) and
store FD into perf_event_array (similar to bpf_perf_event_read() helper)
before eBPF program can send data into it.

Today the programs triggered by kprobe collect the data and either store
it into the maps or print it via bpf_trace_printk() where latter is the debug
facility and not suitable to stream the data. This new helper replaces
such bpf_trace_printk() usage and allows programs to have dedicated
channel into user space for post-processing of the raw data collected.

Signed-off-by: Alexei Starovoitov <ast@xxxxxxxxxx>
---
include/uapi/linux/bpf.h | 11 ++++++++++
include/uapi/linux/perf_event.h | 1 +
kernel/bpf/arraymap.c | 2 ++
kernel/bpf/verifier.c | 3 ++-
kernel/trace/bpf_trace.c | 46 +++++++++++++++++++++++++++++++++++++++
5 files changed, 62 insertions(+), 1 deletion(-)

diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
index 564f1f091991..2e032426cfb7 100644
--- a/include/uapi/linux/bpf.h
+++ b/include/uapi/linux/bpf.h
@@ -287,6 +287,17 @@ enum bpf_func_id {
* Return: realm if != 0
*/
BPF_FUNC_get_route_realm,
+
+ /**
+ * bpf_perf_event_output(ctx, map, index, data, size) - output perf raw sample
+ * @ctx: struct pt_regs*
+ * @map: pointer to perf_event_array map
+ * @index: index of event in the map
+ * @data: data on stack to be output as raw data
+ * @size: size of data
+ * Return: 0 on success
+ */
+ BPF_FUNC_perf_event_output,
__BPF_FUNC_MAX_ID,
};

diff --git a/include/uapi/linux/perf_event.h b/include/uapi/linux/perf_event.h
index 2881145cda86..d3c417615361 100644
--- a/include/uapi/linux/perf_event.h
+++ b/include/uapi/linux/perf_event.h
@@ -110,6 +110,7 @@ enum perf_sw_ids {
PERF_COUNT_SW_ALIGNMENT_FAULTS = 7,
PERF_COUNT_SW_EMULATION_FAULTS = 8,
PERF_COUNT_SW_DUMMY = 9,
+ PERF_COUNT_SW_BPF_OUTPUT = 10,

PERF_COUNT_SW_MAX, /* non-ABI */
};
diff --git a/kernel/bpf/arraymap.c b/kernel/bpf/arraymap.c
index f2d9e698c753..e3cfe46b074f 100644
--- a/kernel/bpf/arraymap.c
+++ b/kernel/bpf/arraymap.c
@@ -295,6 +295,8 @@ static void *perf_event_fd_array_get_ptr(struct bpf_map *map, int fd)
return (void *)attr;

if (attr->type != PERF_TYPE_RAW &&
+ !(attr->type == PERF_TYPE_SOFTWARE &&
+ attr->config == PERF_COUNT_SW_BPF_OUTPUT) &&
attr->type != PERF_TYPE_HARDWARE) {
perf_event_release_kernel(event);
return ERR_PTR(-EINVAL);
diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index 1d6b97be79e1..b56cf51f8d42 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -245,6 +245,7 @@ static const struct {
} func_limit[] = {
{BPF_MAP_TYPE_PROG_ARRAY, BPF_FUNC_tail_call},
{BPF_MAP_TYPE_PERF_EVENT_ARRAY, BPF_FUNC_perf_event_read},
+ {BPF_MAP_TYPE_PERF_EVENT_ARRAY, BPF_FUNC_perf_event_output},
};

static void print_verifier_state(struct verifier_env *env)
@@ -910,7 +911,7 @@ static int check_map_func_compatibility(struct bpf_map *map, int func_id)
* don't allow any other map type to be passed into
* the special func;
*/
- if (bool_map != bool_func)
+ if (bool_func && bool_map != bool_func)
return -EINVAL;
}

diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c
index 0fe96c7c8803..47febbe7998e 100644
--- a/kernel/trace/bpf_trace.c
+++ b/kernel/trace/bpf_trace.c
@@ -215,6 +215,50 @@ const struct bpf_func_proto bpf_perf_event_read_proto = {
.arg2_type = ARG_ANYTHING,
};

+static u64 bpf_perf_event_output(u64 r1, u64 r2, u64 index, u64 r4, u64 size)
+{
+ struct pt_regs *regs = (struct pt_regs *) (long) r1;
+ struct bpf_map *map = (struct bpf_map *) (long) r2;
+ struct bpf_array *array = container_of(map, struct bpf_array, map);
+ void *data = (void *) (long) r4;
+ struct perf_sample_data sample_data;
+ struct perf_event *event;
+ struct perf_raw_record raw = {
+ .size = size,
+ .data = data,
+ };
+
+ if (unlikely(index >= array->map.max_entries))
+ return -E2BIG;
+
+ event = (struct perf_event *)array->ptrs[index];
+ if (unlikely(!event))
+ return -ENOENT;
+
+ if (unlikely(event->attr.type != PERF_TYPE_SOFTWARE ||
+ event->attr.config != PERF_COUNT_SW_BPF_OUTPUT))
+ return -EINVAL;
+
+ if (unlikely(event->oncpu != smp_processor_id()))
+ return -EOPNOTSUPP;
+
+ perf_sample_data_init(&sample_data, 0, 0);
+ sample_data.raw = &raw;
+ perf_event_output(event, &sample_data, regs);
+ return 0;
+}
+
+static const struct bpf_func_proto bpf_perf_event_output_proto = {
+ .func = bpf_perf_event_output,
+ .gpl_only = false,
+ .ret_type = RET_INTEGER,
+ .arg1_type = ARG_PTR_TO_CTX,
+ .arg2_type = ARG_CONST_MAP_PTR,
+ .arg3_type = ARG_ANYTHING,
+ .arg4_type = ARG_PTR_TO_STACK,
+ .arg5_type = ARG_CONST_STACK_SIZE,
+};
+
static const struct bpf_func_proto *kprobe_prog_func_proto(enum bpf_func_id func_id)
{
switch (func_id) {
@@ -242,6 +286,8 @@ static const struct bpf_func_proto *kprobe_prog_func_proto(enum bpf_func_id func
return &bpf_get_smp_processor_id_proto;
case BPF_FUNC_perf_event_read:
return &bpf_perf_event_read_proto;
+ case BPF_FUNC_perf_event_output:
+ return &bpf_perf_event_output_proto;
default:
return NULL;
}




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