Messages in this thread | | | Date | Mon, 29 Sep 2008 11:20:59 +0200 | From | "Frédéric Weisbecker" <> | Subject | Re: trace_pipe tentative fix (Re: [PATCH -tip 2/3] Tracing/ftrace: Adapt mmiotrace to the new type of print_line) |
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2008/9/28 Pekka Paalanen <pq@iki.fi>: > 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); >
Ok I will test it this evening. -- 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/
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