[PATCH libinput] tools: prefix debug output with '.' on device changes

[Eric Engestrom]

On Thu, Sep 08, 2016 at 03:55:47PM +1000, Peter Hutterer wrote:
> We print the sysname, but it's not always obvious when there's an event from
> another device within the stream from another device. Prefix it so it's easier
> to spot and search for.
> 
> See https://bugzilla.redhat.com/show_bug.cgi?id=1364850#c3 for an example of
> how such an event can hide.
> 
> We only use last_device for comparing pointer values so we don't need a
> reference to the device, it doesn't matter if the device itself goes out of
> scope.
> 
> Signed-off-by: Peter Hutterer <peter.hutterer at who-t.net>
> ---
>  tools/event-debug.c | 12 +++++++++++-
>  1 file changed, 11 insertions(+), 1 deletion(-)
> 
> diff --git a/tools/event-debug.c b/tools/event-debug.c
> index 67432b7..0e95611 100644
> --- a/tools/event-debug.c
> +++ b/tools/event-debug.c
> @@ -49,8 +49,11 @@ static unsigned int stop = 0;
>  static void
>  print_event_header(struct libinput_event *ev)
>  {
> +	/* use for pointer value only, do not dereference */
> +	static struct libinput_device *last_device = NULL;

I would make that a void* to make it clear that it's not meant to be
dereferenced.

>  	struct libinput_device *dev = libinput_event_get_device(ev);
>  	const char *type = NULL;
> +	char prefix;
>  
>  	switch(libinput_event_get_type(ev)) {
>  	case LIBINPUT_EVENT_NONE:
> @@ -132,7 +135,14 @@ print_event_header(struct libinput_event *ev)
>  		break;
>  	}
>  
> -	printf("%-7s	%-16s ", libinput_device_get_sysname(dev), type);
> +	prefix = (last_device != dev) ? '-' : ' ';

Nit: that line would be even shorter within the printf than here on
its own :)

Reviewed-by: Eric Engestrom <eric.engestrom at imgtec.com>

> +
> +	printf("%c%-7s	%-16s ",
> +	       prefix,
> +	       libinput_device_get_sysname(dev),
> +	       type);
> +
> +	last_device = dev;
>  }
>  
>  static void
> -- 
> 2.7.4