[PATCH V2 2/2] bpf: control a set of perf events by creating a new ioctl PERF_EVENT_IOC_SET_ENABLER

Kaixu Xia
2015-10-14T12:38:23Z

This patch creates a new ioctl PERF_EVENT_IOC_SET_ENABLER to let
perf to select an event as 'enabler'. So we can set this 'enabler'
event to enable/disable a set of events. The event on CPU 0 is
treated as the 'enabler' event by default.

Signed-off-by: Kaixu Xia <xiakaixu@huawei.com>
---
include/linux/perf_event.h | 1 +
include/uapi/linux/perf_event.h | 1 +
kernel/events/core.c | 42 ++++++++++++++++++++++++++++++++++++++++-
kernel/trace/bpf_trace.c | 5 ++++-
4 files changed, 47 insertions(+), 2 deletions(-)

diff --git a/include/linux/perf_event.h b/include/linux/perf_event.h
index dcbf7d5..bc9fe77 100644
--- a/include/linux/perf_event.h
+++ b/include/linux/perf_event.h
@@ -473,6 +473,7 @@ struct perf_event {

atomic_t event_limit;
atomic_t sample_disable;
+ atomic_t *p_sample_disable;

void (*destroy)(struct perf_event *);
struct rcu_head rcu_head;
diff --git a/include/uapi/linux/perf_event.h b/include/uapi/linux/perf_event.h
index a2b9dd7..3b4fb90 100644
--- a/include/uapi/linux/perf_event.h
+++ b/include/uapi/linux/perf_event.h
@@ -393,6 +393,7 @@ struct perf_event_attr {
#define PERF_EVENT_IOC_SET_FILTER _IOW('$', 6, char *)
#define PERF_EVENT_IOC_ID _IOR('$', 7, __u64 *)
#define PERF_EVENT_IOC_SET_BPF _IOW('$', 8, __u32)
+#define PERF_EVENT_IOC_SET_ENABLER _IO ('$', 9)

enum perf_event_ioc_flags {
PERF_IOC_FLAG_GROUP = 1U << 0,
diff --git a/kernel/events/core.c b/kernel/events/core.c
index 942351c..03d2594 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -4152,6 +4152,7 @@ static int perf_event_set_output(struct perf_event *event,
struct perf_event *output_event);
static int perf_event_set_filter(struct perf_event *event, void __user *arg);
static int perf_event_set_bpf_prog(struct perf_event *event, u32 prog_fd);
+static int perf_event_set_sample_enabler(struct perf_event *event, u32 enabler_fd);

static long _perf_ioctl(struct perf_event *event, unsigned int cmd, unsigned long arg)
{
@@ -4208,6 +4209,9 @@ static long _perf_ioctl(struct perf_event *event, unsigned int cmd, unsigned lon
case PERF_EVENT_IOC_SET_BPF:
return perf_event_set_bpf_prog(event, arg);

+ case PERF_EVENT_IOC_SET_ENABLER:
+ return perf_event_set_sample_enabler(event, arg);
+
default:
return -ENOTTY;
}
@@ -6337,7 +6341,7 @@ static int __perf_event_overflow(struct perf_event *event,
irq_work_queue(&event->pending);
}

- if (!atomic_read(&event->sample_disable))
+ if (!atomic_read(event->p_sample_disable))
return ret;

if (event->overflow_handler)
@@ -6989,6 +6993,35 @@ static int perf_event_set_bpf_prog(struct perf_event *event, u32 prog_fd)
return 0;
}

+static int perf_event_set_sample_enabler(struct perf_event *event, u32 enabler_fd)
+{
+ int ret;
+ struct fd enabler;
+ struct perf_event *enabler_event;
+
+ if (enabler_fd == -1)
+ return 0;
+
+ ret = perf_fget_light(enabler_fd, &enabler);
+ if (ret)
+ return ret;
+ enabler_event = enabler.file->private_data;
+ if (event == enabler_event) {
+ fdput(enabler);
+ return 0;
+ }
+
+ /* they must be on the same PMU*/
+ if (event->pmu != enabler_event->pmu) {
+ fdput(enabler);
+ return -EINVAL;
+ }
+
+ event->p_sample_disable = &enabler_event->sample_disable;
+ fdput(enabler);
+ return 0;
+}
+
static void perf_event_free_bpf_prog(struct perf_event *event)
{
struct bpf_prog *prog;
@@ -7023,6 +7056,11 @@ static int perf_event_set_bpf_prog(struct perf_event *event, u32 prog_fd)
return -ENOENT;
}

+static int perf_event_set_sample_enabler(struct perf_event *event, u32 group_fd)
+{
+ return -ENOENT;
+}
+
static void perf_event_free_bpf_prog(struct perf_event *event)
{
}
@@ -7718,6 +7756,8 @@ static void perf_event_check_sample_flag(struct perf_event *event)
atomic_set(&event->sample_disable, 0);
else
atomic_set(&event->sample_disable, 1);
+
+ event->p_sample_disable = &event->sample_disable;
}

/*
diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c
index f261333..d012be3 100644
--- a/kernel/trace/bpf_trace.c
+++ b/kernel/trace/bpf_trace.c
@@ -221,9 +221,12 @@ static u64 bpf_perf_event_sample_control(u64 r1, u64 index, u64 flag, u64 r4, u6
struct bpf_array *array = container_of(map, struct bpf_array, map);
struct perf_event *event;

- if (unlikely(index >= array->map.max_entries))
+ if (unlikely(index > array->map.max_entries))
return -E2BIG;

+ if (index == array->map.max_entries)
+ index = 0;
+
event = (struct perf_event *)array->ptrs[index];
if (!event)
return -ENOENT;
--
1.8.3.4