[Qemu-devel] debug logging (was: Re: [PATCHv2 3/4] qxl: add debug_cs and cmdlog_cs)

[Gerd Hoffmann <kraxel@redhat.com>]

   Hi,

> The bigger hack called "qxl_terse" I didn't even send :) ok, so now I get
> to either keep this in my closet or think of how to do a minimal acceptable
> qemu logging infrastructure that would let me register a logging handle and
> use that to redirect to a chardev (they would all default to being muxed over
> stdio?)
>
> QemuLogger *qemu_create_logger(const char *logger_id);
>   - logger_id is used to match to the chardev given on the command line
>   - need to prevent collision, so probably easier to have a logger_id be an int
>   and have that looked up to a string in an automatically generated table?

What I have in mind is a simple dbg_print() function, integrated with 
qdev and simliar to what the linux kernel has, i.e. something like:

int dbg_print(DeviceState *qdev, int loglevel, const char *fmt, ...);

This can basically be used that as drop-in replacement for the 
fprintf(stderr, fmt, ...) style found in many drivers.

dbg_print would get the driver name via qdev->info->name, get the 
instance via qdev->parent_bus->info->get_dev_path(), get a timestamp, 
then create a standard prefix for all messages for easy grepping.  It 
would also check qdev->loglevel to figure whenever the message should be 
printed or not.  All devices get a property to set qdev->loglevel, so 
all logging can be configured at runtime per device.

Messages go to stderr by default.  A -debug switch could be added to 
route them another way.

Comments in the idea?

cheers,
   Gerd