Re: [PATCH v6 11/27] util: introduce some API docs for logging APIs

Daniel P. Berrangé <berrange@redhat.com> writes:

There is a gotcha with qemu_log() usage in a threaded process. If fragments of a log message are output via qemu_log() it is possible for messages from two threads to get mixed up. To prevent this qemu_log_trylock() should be used, along with fprintf(f) calls.

This is a subtle problem that needs to be explained in the API docs to ensure correct usage.

In the Rust code, the log_mask_ln method which is conceptually equivalent to the C qemu_log() call will unconditionally append a newline so must only ever be used for complete log messages.

Reported-by: Markus Armbruster <armbru@redhat.com> Signed-off-by: Daniel P. Berrangé <berrange@redhat.com>

Reviewed-by: Markus Armbruster <armbru@redhat.com>