Re: [Qemu-devel] Where to log xen_platform_log data

[Stefano Stabellini]

On Sat, 3 Sep 2011, Stefan Hajnoczi wrote:
> Hi Steven,
> The Xen platform PCI device has a logging feature that is currently
> implemented using trace_xen_platform_log(s->log_buffer).  String
> arguments may not be supported by all trace backends so they should be
> avoided.  For example, the simple trace backend logs 8-byte arguments
> and therefore cannot log strings - it will simply log the char *
> pointer value, not the actual log message.  Here is what
> docs/tracing.txt says:
> 
>    Pointers (including char *) cannot be dereferenced easily (or at all) in
>    some trace backends.  If pointers are used, ensure they are meaningful by
>    themselves and do not assume the data they point to will be traced.  Do
>    not pass in string arguments.
> 
> Is there a better place to send the log output?

Ideally they would go to syslog: the idea was to write a syslog trace
backend but it hasn't been done yet.

It seems to me that having the ability to trace a string would be very
useful; we could implement a fallback tracing function to those backends
that don't support char* logging natively.