Hi Alexei,
On Tue, Jan 27, 2015 at 08:06:06PM -0800, Alexei Starovoitov wrote:
User interface:
fd = open("/sys/kernel/debug/tracing/__event__/filter")
write(fd, "bpf_123")
where 123 is process local FD associated with eBPF program previously loaded.
__event__ is static tracepoint event or syscall.
(kprobe support is in next patch)
Once program is successfully attached to tracepoint event, the tracepoint
will be auto-enabled
close(fd)
auto-disables tracepoint event and detaches eBPF program from it
eBPF programs can call in-kernel helper functions to:
- lookup/update/delete elements in maps
- memcmp
- fetch_ptr/u64/u32/u16/u8 values from unsafe address via probe_kernel_read(),
so that eBPF program can walk any kernel data structures
Signed-off-by: Alexei Starovoitov <redacted>
---
[SNIP]
quoted hunk ↗ jump to hunk
diff --git a/kernel/trace/trace_events.c b/kernel/trace/trace_events.c
index b03a0ea77b99..70482817231a 100644
--- a/kernel/trace/trace_events.c
+++ b/kernel/trace/trace_events.c
@@ -1084,6 +1084,26 @@ event_filter_read(struct file *filp, char __user *ubuf, size_t cnt,
return r;
}
+static int event_filter_release(struct inode *inode, struct file *filp)
+{
+ struct ftrace_event_file *file;
+ char buf[2] = "0";
+
+ mutex_lock(&event_mutex);
+ file = event_file_data(filp);
+ if (file) {
+ if (file->flags & TRACE_EVENT_FL_BPF) {
+ /* auto-disable the filter */
+ ftrace_event_enable_disable(file, 0);
Hmm.. what if user already enabled an event, attached a bpf filter and
then detached the filter - I'm not sure we can always auto-disable
it..
quoted hunk ↗ jump to hunk
+
+ /* if BPF filter was used, clear it on fd close */
+ apply_event_filter(file, buf);
+ }
+ }
+ mutex_unlock(&event_mutex);
+ return 0;
+}
+
static ssize_t
event_filter_write(struct file *filp, const char __user *ubuf, size_t cnt,
loff_t *ppos)
@@ -1107,8 +1127,18 @@ event_filter_write(struct file *filp, const char __user *ubuf, size_t cnt,
mutex_lock(&event_mutex);
file = event_file_data(filp);
- if (file)
+ if (file) {
+ /*
+ * note to user space tools:
+ * write() into debugfs/tracing/events/xxx/filter file
+ * must be done with the same privilege level as open()
+ */
err = apply_event_filter(file, buf);
+ if (!err && file->flags & TRACE_EVENT_FL_BPF)
+ /* once filter is applied, auto-enable it */
+ ftrace_event_enable_disable(file, 1);
+ }
+
mutex_unlock(&event_mutex);
free_page((unsigned long) buf);@@ -1363,6 +1393,7 @@ static const struct file_operations ftrace_event_filter_fops = {
.open = tracing_open_generic,
.read = event_filter_read,
.write = event_filter_write,
+ .release = event_filter_release,
.llseek = default_llseek,
};
diff --git a/kernel/trace/trace_events_filter.c b/kernel/trace/trace_events_filter.c
index ced69da0ff55..e0303b3cc9fb 100644
--- a/kernel/trace/trace_events_filter.c
+++ b/kernel/trace/trace_events_filter.c
@@ -23,6 +23,9 @@
#include <linux/mutex.h>
#include <linux/perf_event.h>
#include <linux/slab.h>
+#include <linux/bpf.h>
+#include <trace/bpf_trace.h>
+#include <linux/filter.h>
#include "trace.h"
#include "trace_output.h"
@@ -541,6 +544,21 @@ static int filter_match_preds_cb(enum move_type move, struct filter_pred *pred,
return WALK_PRED_DEFAULT;
}
+unsigned int trace_filter_call_bpf(struct event_filter *filter, void *ctx)
+{
+ unsigned int ret;
+
+ if (in_nmi()) /* not supported yet */
+ return 0;
But doesn't this mean to auto-disable all attached events during NMI
as returning 0 will prevent the event going to ring buffer?
I think it'd be better to keep an attached event in a soft-disabled
state like event trigger and give control of enabling to users..
Thanks,
Namhyung
quoted hunk ↗ jump to hunk
+
+ rcu_read_lock();
+ ret = BPF_PROG_RUN(filter->prog, ctx);
+ rcu_read_unlock();
+
+ return ret;
+}
+EXPORT_SYMBOL_GPL(trace_filter_call_bpf);