job mutex will be used to protect the job struct elements and list,
replacing AioContext locks.
Right now use a shared lock for all jobs, in order to keep things
simple. Once the AioContext lock is gone, we can introduce per-job
locks.
To simplify the switch from aiocontext to job lock, introduce
*nop* lock/unlock functions and macros.
We want to always call job_lock/unlock outside the AioContext locks,
and not vice-versa, otherwise we might get a deadlock. This is not
straightforward to do, and that's why we start with nop functions.
Once everything is protected by job_lock/unlock, we can change the nop into
an actual mutex and remove the aiocontext lock.
Since job_mutex is already being used, add static
real_job_{lock/unlock} for the existing usage.
Signed-off-by: Emanuele Giuseppe Esposito<eesposit@redhat.com>
Reviewed-by: Stefan Hajnoczi<stefanha@redhat.com>