It's useful to know kprobe's nmissed and nhit stats. For example with
tracing tools, it's important to know when events may have been lost.
There is currently no way to get that information from the perf API.
This patch adds a new ioctl that lets users query this information.
---
include/linux/trace_events.h | 6 ++++++
include/uapi/linux/perf_event.h | 23 +++++++++++++++++++++++
kernel/events/core.c | 11 +++++++++++
kernel/trace/trace_kprobe.c | 25 +++++++++++++++++++++++++
4 files changed, 65 insertions(+)
diff --git a/include/linux/trace_events.h b/include/linux/trace_events.h
index 5150436783e8..28faf115e0b8 100644
--- a/include/linux/trace_events.h
+++ b/include/linux/trace_events.h
@@ -586,6 +586,12 @@ extern int bpf_get_kprobe_info(const struct perf_event *event,
u32 *fd_type, const char **symbol,
u64 *probe_offset, u64 *probe_addr,
bool perf_type_tracepoint);
+extern int perf_event_query_kprobe(struct perf_event *event, void __user *info);
+#else
+int perf_event_query_kprobe(struct perf_event *event, void __user *info)
+{
+ return -EOPNOTSUPP;
+}
#endif
#ifdef CONFIG_UPROBE_EVENTS
extern int perf_uprobe_init(struct perf_event *event,
diff --git a/include/uapi/linux/perf_event.h b/include/uapi/linux/perf_event.h
index 7198ddd0c6b1..4a5e18606baf 100644
--- a/include/uapi/linux/perf_event.h
+++ b/include/uapi/linux/perf_event.h
@@ -447,6 +447,28 @@ struct perf_event_query_bpf {
__u32 ids[0];
};
+/*
+ * Structure used by below PERF_EVENT_IOC_QUERY_KPROE command
+ * to query information about the kprobe attached to the perf
+ * event.
+ */
+struct perf_event_query_kprobe {
+ /*
+ * Size of structure for forward/backward compatibility
+ */
+ __u32 size;
+ /*
+ * Set by the kernel to indicate number of times this kprobe
+ * was temporarily disabled
+ */
+ __u64 nmissed;
+ /*
+ * Set by the kernel to indicate number of times this kprobe
+ * was hit
+ */
+ __u64 nhit;
+};
+
/*
* Ioctls that can be done on a perf event fd:
*/
@@ -462,6 +484,7 @@ struct perf_event_query_bpf {
#define PERF_EVENT_IOC_PAUSE_OUTPUT _IOW('$', 9, __u32)
#define PERF_EVENT_IOC_QUERY_BPF _IOWR('$', 10, struct perf_event_query_bpf *)
#define PERF_EVENT_IOC_MODIFY_ATTRIBUTES _IOW('$', 11, struct perf_event_attr *)
+#define PERF_EVENT_IOC_QUERY_KPROBE _IOWR('$', 12, struct perf_event_query_kprobe *)
enum perf_event_ioc_flags {
PERF_IOC_FLAG_GROUP = 1U << 0,
diff --git a/kernel/events/core.c b/kernel/events/core.c
index 026a14541a38..d61c3ac5da4f 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -5061,6 +5061,10 @@ static int perf_event_set_bpf_prog(struct perf_event *event, u32 prog_fd);
static int perf_copy_attr(struct perf_event_attr __user *uattr,
struct perf_event_attr *attr);
+#ifdef CONFIG_KPROBE_EVENTS
+static struct pmu perf_kprobe;
+#endif /* CONFIG_KPROBE_EVENTS */
+
static long _perf_ioctl(struct perf_event *event, unsigned int cmd, unsigned long arg)
{
void (*func)(struct perf_event *);
@@ -5143,6 +5147,13 @@ static long _perf_ioctl(struct perf_event *event, unsigned int cmd, unsigned lon
return perf_event_modify_attr(event, &new_attr);
}
+#ifdef CONFIG_KPROBE_EVENTS
+ case PERF_EVENT_IOC_QUERY_KPROBE:
+ if (event->attr.type != perf_kprobe.type)
+ return -EINVAL;
+
+ return perf_event_query_kprobe(event, (void __user *)arg);
+#endif /* CONFIG_KPROBE_EVENTS */
default:
return -ENOTTY;
}
diff --git a/kernel/trace/trace_kprobe.c b/kernel/trace/trace_kprobe.c
index 9d483ad9bb6c..5449182f3056 100644
--- a/kernel/trace/trace_kprobe.c
+++ b/kernel/trace/trace_kprobe.c
@@ -196,6 +196,31 @@ bool trace_kprobe_error_injectable(struct trace_event_call *call)
return within_error_injection_list(trace_kprobe_address(tk));
}
+int perf_event_query_kprobe(struct perf_event *event, void __user *info)
+{
+ struct perf_event_query_kprobe __user *uquery = info;
+ struct perf_event_query_kprobe query = {};
+ struct trace_event_call *call = event->tp_event;
+ struct trace_kprobe *tk = (struct trace_kprobe *)call->data;
+ u64 nmissed, nhit;
+
+ if (!capable(CAP_SYS_ADMIN))
+ return -EPERM;
+ if (copy_from_user(&query, uquery, sizeof(query)))
+ return -EFAULT;
+ if (query.size != sizeof(query))
+ return -EINVAL;
+
+ nhit = trace_kprobe_nhit(tk);
+ nmissed = tk->rp.kp.nmissed;
+
+ if (copy_to_user(&uquery->nmissed, &nmissed, sizeof(nmissed)) ||
+ copy_to_user(&uquery->nhit, &nhit, sizeof(nhit)))
+ return -EFAULT;
+
+ return 0;
+}
+
static int register_kprobe_event(struct trace_kprobe *tk);
static int unregister_kprobe_event(struct trace_kprobe *tk);
--
2.20.1
