Messages in this thread Patch in this message | | | Date | Sun, 28 Sep 2008 20:12:59 +0300 | From | Pekka Paalanen <> | Subject | trace_pipe tentative fix (Re: [PATCH -tip 2/3] Tracing/ftrace: Adapt mmiotrace to the new type of print_line) |
| |
On Sat, 27 Sep 2008 14:17:47 +0200 "Frédéric Weisbecker" <fweisbec@gmail.com> wrote:
> 2008/9/26 Pekka Paalanen <pq@iki.fi>: > > Yes, I do disagree about printing stuff that doesn't belong there. > > First, I doubt printing bogus text is a right way to fix the > > early pipe EOF problem. Second, if you really have to do that, > > do it so that it obeys the mmiotrace log format specification. > > (I'd recommend a MARK entry.) The spec is in > > Documentation/tracers/mmiotrace.txt. > > No problem, I have one other option: ignoring and sleep again before > receiving another entries. > I can do another patch this week end to implement that. > The third patch only concerns the boot tracer. It relays to other > output functions. > > Just tell me if you agree with the ignoring...
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); -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
| |