[Spice-devel] RFC: Lightweight tracing mechanism

[Frediano Ziglio]

> > On 23 May 2017, at 12:55, Victor Toso < victortoso at redhat.com > wrote:
> 

> > On Tue, May 23, 2017 at 11:51:01AM +0200, Christophe Fergeau wrote:
> 

> > > or something like glib (SPICE_XXX_DEBUG=alignment:foo:bar)
> > 
> 

> > Just to point out that we have a bug for this [0] and IMHO it would be
> 
> > the best approach but it would take some effort to have it besides the
> 
> > glib that we would need is 2.50 (current required is 2.36)
> 
> > [0] https://bugs.freedesktop.org/show_bug.cgi?id=91838
> 

These seems to suggest the usage of glib for more refined control. 

> Pavel also recently commented on having some trouble with --spice-debug and
> SPICE_DEBUG and…

Would be helpful if you had recap Pavel problems. I don't remember. 

> For what it’s worth, I’ve implemented in several of my own projects a low-key
> tracing facility which for Spice would basically look like this:

> https://github.com/c3d/spice-common/compare/cast-warnings...c3d:traces
> https://github.com/c3d/spice-gtk/compare/cast-warnings...c3d:traces

> Specifically:

> - Define available traces in spice-traces.def file, e.g.:

> // SPICE_TRACE(name, default_value, info)
> SPICE_TRACE(foo, false, “Talk about foo")
> SPICE_TRACE(bar, true, “A bar is a good thing, enabled by default")
> #undef SPICE_TRACE

> - Declare a structure holding one bit per trace flag, as follows:

> extern struct spice_traces {
> #define SPICE_TRACE(name, init, info) bool name:1;
> #include “spice-traces.def”
> } spice_traces;

> - Initialize it in log.c, as follows:

> struct spice_traces spice_traces = {
> #define SPICE_TRACE(name, init, info) init,
> #include “spice-traces.def"
> };

> - In log.c, add a function to deal with passing trace options either from
> command-line or environemnt

> - In log.h, add macros to quickly test traces:

> #define TRACE(name) (spice_traces.name)
> #define IFTRACE(name) if (TRACE(name))
> #define spice_trace(name, …) IFTRACE(name) spice_debug(__VA_ARGS__)

> - In spice-option.c, add code to deal with testing the options.

> Would you find this useful? The most difficult part being to connect that to
> existing tracing mechanisms to avoid replication of traces, while at the
> same time ensuring that the existing enabling mechanisms work as before.

> Christophe

The main questions are: 
- what are the original problems exactly? 
- why your solution is good in your opinion? 
- did you try other options (like Marc-andre' suggested) ? 

Reading the code is not clear where exactly you implemented the different domains 
suggested by the bug report. Did you just coded SSL as an example? 
Also you introduced a new "TRACE" logging level; why DEBUG was not enough? 

Frediano 
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