job.c: make job_mutex and job_lock/unlock() public

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>
Reviewed-by: Vladimir Sementsov-Ogievskiy <vsementsov@yandex-team.ru>
Message-Id: <20220926093214.506243-2-eesposit@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>

1 files changed, 24 insertions, 0 deletions

diff --git a/include/qemu/job.h b/include/qemu/job.h
index 397ac39608..e625547bdb 100644
--- a/include/qemu/job.h
+++ b/include/qemu/job.h
@@ -303,6 +303,30 @@ typedef enum JobCreateFlags {
     JOB_MANUAL_DISMISS = 0x04,
 } JobCreateFlags;
 
+extern QemuMutex job_mutex;
+
+#define JOB_LOCK_GUARD() /* QEMU_LOCK_GUARD(&job_mutex) */
+
+#define WITH_JOB_LOCK_GUARD() /* WITH_QEMU_LOCK_GUARD(&job_mutex) */
+
+/**
+ * job_lock:
+ *
+ * Take the mutex protecting the list of jobs and their status.
+ * Most functions called by the monitor need to call job_lock
+ * and job_unlock manually.  On the other hand, function called
+ * by the block jobs themselves and by the block layer will take the
+ * lock for you.
+ */
+void job_lock(void);
+
+/**
+ * job_unlock:
+ *
+ * Release the mutex protecting the list of jobs and their status.
+ */
+void job_unlock(void);
+
 /**
  * Allocate and return a new job transaction. Jobs can be added to the
  * transaction using job_txn_add_job().