From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754548AbYI2JVT (ORCPT ); Mon, 29 Sep 2008 05:21:19 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1752681AbYI2JVE (ORCPT ); Mon, 29 Sep 2008 05:21:04 -0400 Received: from fg-out-1718.google.com ([72.14.220.156]:51873 "EHLO fg-out-1718.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752003AbYI2JVC convert rfc822-to-8bit (ORCPT ); Mon, 29 Sep 2008 05:21:02 -0400 DomainKey-Signature: a=rsa-sha1; c=nofws; d=gmail.com; s=gamma; h=message-id:date:from:to:subject:cc:in-reply-to:mime-version :content-type:content-transfer-encoding:content-disposition :references; b=EoHtTh0N+O40423Zi8TeA7/EGNej321GTU225mkWHYwZY9YarqrQDJe2AzSmp2nnZN xWYATlRUlQXBg48edgfsWe4S3YF+8by1h19YiAQlQ9gQIqdtkf6+waTrv7DbVXUNzBcJ 1kus0MH0+efgk6Lr4B9ExBtNm+cuoruXKMXsk= Message-ID: Date: Mon, 29 Sep 2008 11:20:59 +0200 From: "=?ISO-8859-1?Q?Fr=E9d=E9ric_Weisbecker?=" To: "Pekka Paalanen" Subject: Re: trace_pipe tentative fix (Re: [PATCH -tip 2/3] Tracing/ftrace: Adapt mmiotrace to the new type of print_line) Cc: mingo@elte.hu, rostedt@goodmis.org, linux-kernel@vger.kernel.org In-Reply-To: <20080928201259.09bbac54@daedalus.pq.iki.fi> MIME-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 8BIT Content-Disposition: inline References: <48DD0347.5070008@gmail.com> <20080927002121.0038cdfe@daedalus.pq.iki.fi> <20080928201259.09bbac54@daedalus.pq.iki.fi> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 2008/9/28 Pekka Paalanen : > On Sat, 27 Sep 2008 14:17:47 +0200 > "Frédéric Weisbecker" wrote: > >> 2008/9/26 Pekka Paalanen : >> > 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.