[RFC PATCH v2 01/14] job.c: make job_lock/unlock public

[Emanuele Giuseppe Esposito]

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. Once everything is protected
by jobs, we can add the mutex and remove the aiocontext.
Since job_mutex is already being used, add static
_job_{lock/unlock}.

Signed-off-by: Emanuele Giuseppe Esposito <eespo...@redhat.com>
Reviewed-by: Stefan Hajnoczi <stefa...@redhat.com>
---
 include/qemu/job.h | 18 ++++++++++++++++++
 job.c              | 39 +++++++++++++++++++++++++++------------
 2 files changed, 45 insertions(+), 12 deletions(-)

diff --git a/include/qemu/job.h b/include/qemu/job.h
index 7e9e59f4b8..ccf7826426 100644
--- a/include/qemu/job.h
+++ b/include/qemu/job.h
@@ -297,6 +297,24 @@ typedef enum JobCreateFlags {
     JOB_MANUAL_DISMISS = 0x04,
 } JobCreateFlags;
 
+/**
+ * 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().
diff --git a/job.c b/job.c
index 94b142684f..0e4dacf028 100644
--- a/job.c
+++ b/job.c
@@ -32,6 +32,12 @@
 #include "trace/trace-root.h"
 #include "qapi/qapi-events-job.h"
 
+/*
+ * job_mutex protects the jobs list, but also makes the
+ * struct job fields thread-safe.
+ */
+static QemuMutex job_mutex;
+
 static QLIST_HEAD(, Job) jobs = QLIST_HEAD_INITIALIZER(jobs);
 
 /* Job State Transition Table */
@@ -74,17 +80,26 @@ struct JobTxn {
     int refcnt;
 };
 
-/* Right now, this mutex is only needed to synchronize accesses to job->busy
- * and job->sleep_timer, such as concurrent calls to job_do_yield and
- * job_enter. */
-static QemuMutex job_mutex;
+#define JOB_LOCK_GUARD() /* QEMU_LOCK_GUARD(&job_mutex) */
+
+#define WITH_JOB_LOCK_GUARD() /* WITH_QEMU_LOCK_GUARD(&job_mutex) */
+
+void job_lock(void)
+{
+    /* nop */
+}
+
+void job_unlock(void)
+{
+    /* nop */
+}
 
-static void job_lock(void)
+static void _job_lock(void)
 {
     qemu_mutex_lock(&job_mutex);
 }
 
-static void job_unlock(void)
+static void _job_unlock(void)
 {
     qemu_mutex_unlock(&job_mutex);
 }
@@ -449,21 +464,21 @@ void job_enter_cond(Job *job, bool(*fn)(Job *job))
         return;
     }
 
-    job_lock();
+    _job_lock();
     if (job->busy) {
-        job_unlock();
+        _job_unlock();
         return;
     }
 
     if (fn && !fn(job)) {
-        job_unlock();
+        _job_unlock();
         return;
     }
 
     assert(!job->deferred_to_main_loop);
     timer_del(&job->sleep_timer);
     job->busy = true;
-    job_unlock();
+    _job_unlock();
     aio_co_enter(job->aio_context, job->co);
 }
 
@@ -480,13 +495,13 @@ void job_enter(Job *job)
  * called explicitly. */
 static void coroutine_fn job_do_yield(Job *job, uint64_t ns)
 {
-    job_lock();
+    _job_lock();
     if (ns != -1) {
         timer_mod(&job->sleep_timer, ns);
     }
     job->busy = false;
     job_event_idle(job);
-    job_unlock();
+    _job_unlock();
     qemu_coroutine_yield();
 
     /* Set by job_enter_cond() before re-entering the coroutine.  */
-- 
2.27.0