Re: [Qemu-devel] [Qemu-block] [PATCH 2/2] trace: Forbid event format ending with newline character

[John Snow <jsnow@redhat.com>]

On 9/13/19 5:00 PM, Philippe Mathieu-Daudé wrote:
> On 9/13/19 10:01 PM, John Snow wrote:
>> On 9/13/19 6:52 AM, Philippe Mathieu-Daudé wrote:
>>> Event format ending with newlines confuse the trace reports.
>>> Forbid them.
>>>
>>> Add a check to refuse new format added with trailing newline:
>>>
>>>   $ make
>>>   [...]
>>>     GEN     hw/misc/trace.h
>>>   Traceback (most recent call last):
>>>     File "scripts/tracetool.py", line 152, in <module>
>>>       main(sys.argv)
>>>     File "scripts/tracetool.py", line 143, in main
>>>       events.extend(tracetool.read_events(fh, arg))
>>>     File "scripts/tracetool/__init__.py", line 367, in read_events
>>>       event = Event.build(line)
>>>     File "scripts/tracetool/__init__.py", line 281, in build
>>>       raise ValueError("Event format can not end with a newline character")
>>>   ValueError: Error at hw/misc/trace-events:121: Event format can not end with a newline character
>>>
>>> Signed-off-by: Philippe Mathieu-Daudé <philmd@redhat.com>
>>> ---
>>>  docs/devel/tracing.txt        | 2 ++
>>>  scripts/tracetool/__init__.py | 3 +++
>>>  2 files changed, 5 insertions(+)
>>>
>>> diff --git a/docs/devel/tracing.txt b/docs/devel/tracing.txt
>>> index 76e492a489..8231bbf5d1 100644
>>> --- a/docs/devel/tracing.txt
>>> +++ b/docs/devel/tracing.txt
>>> @@ -112,6 +112,8 @@ Trace events should use types as follows:
>>>  Format strings should reflect the types defined in the trace event.  Take
>>>  special care to use PRId64 and PRIu64 for int64_t and uint64_t types,
>>>  respectively.  This ensures portability between 32- and 64-bit platforms.
>>> +Format strings must not end with a newline character.  It is the responsibility
>>> +of backends to adapt line ending for proper logging.
>>>  
>>>  Each event declaration will start with the event name, then its arguments,
>>>  finally a format string for pretty-printing. For example:
>>> diff --git a/scripts/tracetool/__init__.py b/scripts/tracetool/__init__.py
>>> index 6fca674936..57df74e67c 100644
>>> --- a/scripts/tracetool/__init__.py
>>> +++ b/scripts/tracetool/__init__.py
>>> @@ -277,6 +277,9 @@ class Event(object):
>>>          if fmt.find("%m") != -1 or fmt_trans.find("%m") != -1:
>>>              raise ValueError("Event format '%m' is forbidden, pass the error "
>>>                               "as an explicit trace argument")
>>> +        if fmt.endswith("\\n\""):
>>> +            raise ValueError("Event format must not end with a newline "
>>
>> It's barely worth mentioning, but you can use r"\n" for cases like this,
>> if it makes it easier to read.
> 
> TIL Python r"" :)
> 
> This would be r"\n\"", right? We need to match the trailing '"'.
> Same length, not sure which string is easier to review =)
> 

Ah, wow, I did misread this. It's confusing!

In this case, you can use r'\n"' to get the job done.

(My r-b stands, anyway.)

--js