Feather-trace: let userspace add overhead events

This is useful for measuring locking-related overheads
that are partially recorded in userspace.

1 files changed, 40 insertions, 0 deletions

diff --git a/litmus/trace.c b/litmus/trace.c
index f0eb2c706488..5d77806da647 100644
--- a/litmus/trace.c
+++ b/litmus/trace.c
@@ -1,5 +1,6 @@
 #include <linux/sched.h>
 #include <linux/module.h>
+#include <linux/uaccess.h>
 
 #include <litmus/ftdev.h>
 #include <litmus/litmus.h>
@@ -31,6 +32,18 @@ static inline void __save_timestamp_cpu(unsigned long event,
         }
 }
 
+static void __add_timestamp_user(struct timestamp *pre_recorded)
+{
+        unsigned int seq_no;
+        struct timestamp *ts;
+        seq_no = fetch_and_inc((int *) &ts_seq_no);
+        if (ft_buffer_start_write(trace_ts_buf, (void**)  &ts)) {
+                *ts = *pre_recorded;
+                ts->seq_no = seq_no;
+                ft_buffer_finish_write(trace_ts_buf, ts);
+        }
+}
+
 static inline void __save_timestamp(unsigned long event,
                                    uint8_t type)
 {
@@ -108,6 +121,32 @@ static void free_timestamp_buffer(struct ftdev* ftdev, unsigned int idx)
         ftdev->minor[idx].buf = NULL;
 }
 
+static ssize_t write_timestamp_from_user(struct ft_buffer* buf, size_t len,
+                                         const char __user *from)
+{
+        ssize_t consumed = 0;
+        struct timestamp ts;
+
+        /* don't give us partial timestamps */
+        if (len % sizeof(ts))
+                return -EINVAL;
+
+        while (len >= sizeof(ts)) {
+                if (copy_from_user(&ts, from, sizeof(ts))) {
+                        consumed = -EFAULT;
+                        goto out;
+                }
+                len  -= sizeof(ts);
+                from += sizeof(ts);
+                consumed += sizeof(ts);
+
+                __add_timestamp_user(&ts);
+        }
+
+out:
+        return consumed;
+}
+
 static int __init init_ft_overhead_trace(void)
 {
         int err;
@@ -119,6 +158,7 @@ static int __init init_ft_overhead_trace(void)
 
         overhead_dev.alloc = alloc_timestamp_buffer;
         overhead_dev.free  = free_timestamp_buffer;
+        overhead_dev.write = write_timestamp_from_user;
 
         err = register_ftdev(&overhead_dev);
         if (err)