linux-kernel - Re: [PATCH 2/2] tracing: add checks for printing pci devices in mmiotrace.

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Message-ID: <20090213201932.2dd07f93@daedalus.pq.iki.fi>
Date:	Fri, 13 Feb 2009 20:19:32 +0200
From:	Pekka Paalanen <pq@....fi>
To:	wenji.huang@...cle.com
Cc:	Steven Rostedt <rostedt@...dmis.org>, linux-kernel@...r.kernel.org,
	mingo@...e.hu
Subject: Re: [PATCH 2/2] tracing: add checks for printing pci devices in
 mmiotrace.

On Fri, 13 Feb 2009 14:09:52 +0800
Wenji Huang <wenji.huang@...cle.com> wrote:

> Steven Rostedt wrote:
> > On Thu, 12 Feb 2009, Wenji Huang wrote:
> > 
> >> This patch is to provide checking return value of trace_seq_printf
> >> so as to keep completeness of mmio_print_pcidev.
> >>
> >> Signed-off-by: Wenji Huang <wenji.huang@...cle.com>
> >> ---
> >>  kernel/trace/trace_mmiotrace.c |   26 ++++++++++++++++----------
> >>  1 files changed, 16 insertions(+), 10 deletions(-)
> >>
> >> diff --git a/kernel/trace/trace_mmiotrace.c b/kernel/trace/trace_mmiotrace.c
> >> index c401b90..ebb0b61 100644
> >> --- a/kernel/trace/trace_mmiotrace.c
> >> +++ b/kernel/trace/trace_mmiotrace.c
> >> @@ -56,17 +56,19 @@ static void mmio_trace_start(struct trace_array *tr)
> >>  	mmio_reset_data(tr);
> >>  }
> >>  
> >> -static int mmio_print_pcidev(struct trace_seq *s, const struct pci_dev *dev)
> >> +static enum print_line_t mmio_print_pcidev(struct trace_seq *s,
> >> +					   const struct pci_dev *dev)
> >>  {
> >>  	int ret = 0;
> >>  	int i;
> >>  	resource_size_t start, end;
> >>  	const struct pci_driver *drv = pci_dev_driver(dev);
> >>  
> >> -	/* XXX: incomplete checks for trace_seq_printf() return value */
> >> -	ret += trace_seq_printf(s, "PCIDEV %02x%02x %04x%04x %x",
> >> +	ret = trace_seq_printf(s, "PCIDEV %02x%02x %04x%04x %x",
> >>  				dev->bus->number, dev->devfn,
> >>  				dev->vendor, dev->device, dev->irq);
> >> +	if (!ret)
> >> +		return TRACE_TYPE_PARTIAL_LINE;
> >>  	/*
> >>  	 * XXX: is pci_resource_to_user() appropriate, since we are
> >>  	 * supposed to interpret the __ioremap() phys_addr argument based on
> >> @@ -74,21 +76,25 @@ static int mmio_print_pcidev(struct trace_seq *s, const struct pci_dev *dev)
> >>  	 */
> >>  	for (i = 0; i < 7; i++) {
> >>  		pci_resource_to_user(dev, i, &dev->resource[i], &start, &end);
> >> -		ret += trace_seq_printf(s, " %llx",
> >> +		ret = trace_seq_printf(s, " %llx",
> >>  			(unsigned long long)(start |
> >>  			(dev->resource[i].flags & PCI_REGION_FLAG_MASK)));
> >> -	}
> >> -	for (i = 0; i < 7; i++) {
> >> +		if (!ret)
> >> +			return TRACE_TYPE_PARTIAL_LINE;
> > 
> > The above looks like a change of logic to me. I'm a bit tired so I can be 
> > wrong. But it looks like the original was:
> > 
> >      for (i = 0; i < 7; i++) {
> >              pci_resource_to_user(dev, i, &dev->resource[i], &start, &end);
> >              ret += trace_seq_printf(s, " %llx",
> >                      (unsigned long long)(start |
> >                      (dev->resource[i].flags & PCI_REGION_FLAG_MASK)));
> >      }
> >      for (i = 0; i < 7; i++) {
> >              pci_resource_to_user(dev, i, &dev->resource[i], &start, &end);
> >              ret += trace_seq_printf(s, " %llx",
> >                      dev->resource[i].start < dev->resource[i].end ?
> >                      (unsigned long long)(end - start) + 1 : 0);
> >      }
> > 
> > And the new is:
> > 
> >      for (i = 0; i < 7; i++) {
> >              pci_resource_to_user(dev, i, &dev->resource[i], &start, &end);
> >              ret = trace_seq_printf(s, " %llx",   
> >                      (unsigned long long)(start |
> >                      (dev->resource[i].flags & PCI_REGION_FLAG_MASK)));
> >              if (!ret)
> >                      return TRACE_TYPE_PARTIAL_LINE;
> >              pci_resource_to_user(dev, i, &dev->resource[i], &start, &end);
> >              ret = trace_seq_printf(s, " %llx",
> >                      dev->resource[i].start < dev->resource[i].end ?
> >                      (unsigned long long)(end - start) + 1 : 0);
> >              if (!ret)
> >                      return TRACE_TYPE_PARTIAL_LINE;
> >      }
> > 
> > This changes the output format.
> > 
> > Pekka,
> > 
> > Is this OK?
> > 
> > -- Steve
> 
> oops, output format is changed. Need to update it.

Indeed, don't change the output format, please.

These checks are not enough to actually handle the case, mmio_read()
needs to be updated, too, to do the right thing (I'm looking at Ingo's
tip/master). I.e. it should skip to print_out to flush out old data.
Shouldn't also *ppos be updated in mmio_read()?


Thanks for looking into this.
-- 
Pekka Paalanen
http://www.iki.fi/pq/
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