On Sat, 27 Sep 2008 14:17:47 +0200
If I understand you suggestion, it looks like the right thing to do.
Here is a tentative fix, which has not even been compile-tested.
Is it so that the problem is triggered by consuming a trace entry
which does not produce any output? If that entry is all there is
in the ring at a time of a read call, then the last call to
trace_seq_to_user() returns -EBUSY, because there is nothing to
copy to user. What I failed to understand when I wrote that
piece of code, is that returning 0 means EOF. The only cases
when we do want to return an EOF are near the
while (trace_empty(iter)) {
loop.
Frederic, could you test the fix, and if it works, send it to Ingo?
Thanks.
---
diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index 6ada059..d85659a 100644
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -2616,6 +2616,7 @@ tracing_read_pipe(struct file *filp, char __user *ubuf,
goto out;
}
+waitagain:
while (trace_empty(iter)) {
if ((filp->f_flags & O_NONBLOCK)) {
@@ -2749,8 +2750,13 @@ tracing_read_pipe(struct file *filp, char __user *ubuf,
sret = trace_seq_to_user(&iter->seq, ubuf, cnt);
if (iter->seq.readpos >= iter->seq.len)
trace_seq_reset(&iter->seq);
+
+ /*
+ * If there was nothing to send to user, inspite of consuming trace
+ * entries, go back to wait for more entries.
+ */
if (sret == -EBUSY)
- sret = 0;
+ goto waitagain;
out:
mutex_unlock(&trace_types_lock);
--
