Re: [Qemu-block] [Qemu-devel] [PATCH v2 1/2] trace: Remove trailing newline in events

[Stefan Hajnoczi]

On Mon, Sep 16, 2019 at 12:41:44PM -0400, John Snow wrote:
> On 9/16/19 12:40 PM, Philippe Mathieu-Daudé wrote:
> > On 9/16/19 6:36 PM, Eric Blake wrote:
> >> On 9/16/19 4:51 AM, Philippe Mathieu-Daudé wrote:
> >>> While the tracing frawework does not forbid trailing newline in
> >>
> >> framework
> >>
> >>> events format string, using them lead to confuse output.
> >>> It is the responsibility of the backend to properly end an event
> >>> line.
> >>
> >> Why just trailing newline? Should we not forbid ALL use of newline in a
> >> trace message?
> > 
> > I thought about it and forgot to add a comment when respining.
> > Yes, I think this is the right thing to enforce.
> > However it requires more cleanup, affecting more subsystems, so I'd
> > rather keep it for a follow-up series.
> 
> What's the problem with using multi-line trace statements?

I agree with avoiding trailing newlines in format strings in the
./trace-events files for consistency.

Although non-trailing newlines in format strings are unusual, they could
make trace logs easier to read in complex cases.  I don't see a reason
to forbid them since we support trace backends that emit a binary log
with a parsing API - there's no need to write scripts that parse the
text output.

> (I think I intentionally use these for AHCI in a few places.)

hw/ide/ahci.c format strings do not contain newlines, so they are
technically in compliance.

ahci_pretty_buffer_fis() is used to generate a hex dump with newlines
but it's a %s format string argument to trace_handle_reg_h2d_fis_dump()
and trace_handle_cmd_fis_dump().

Stefan

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