[PATCH for-6.1? 4/6] job: Add job_cancel_requested()

[Max Reitz]

Most callers of job_is_cancelled() actually want to know whether the job
is on its way to immediate termination.  For example, we refuse to pause
jobs that are cancelled; but this only makes sense for jobs that are
really actually cancelled.

A mirror job that is cancelled during READY with force=false should
absolutely be allowed to pause.  This "cancellation" (which is actually
a kind of completion) may take an indefinite amount of time, and so
should behave like any job during normal operation.  For example, with
on-target-error=stop, the job should stop on write errors.  (In
contrast, force-cancelled jobs should not get write errors, as they
should just terminate and not do further I/O.)

Therefore, redefine job_is_cancelled() to only return true for jobs that
are force-cancelled (which as of HEAD^ means any job that interprets the
cancellation request as a request for immediate termination), and add
job_cancel_request() as the general variant, which returns true for any
jobs which have been requested to be cancelled, whether it be
immediately or after an arbitrarily long completion phase.

Buglink: https://gitlab.com/qemu-project/qemu/-/issues/462
Signed-off-by: Max Reitz <mreitz@redhat.com>
---
 include/qemu/job.h |  8 +++++++-
 block/mirror.c     |  9 ++++-----
 job.c              | 13 +++++++++----
 3 files changed, 20 insertions(+), 10 deletions(-)

diff --git a/include/qemu/job.h b/include/qemu/job.h
index 8aa90f7395..032edf3c5f 100644
--- a/include/qemu/job.h
+++ b/include/qemu/job.h
@@ -436,9 +436,15 @@ const char *job_type_str(const Job *job);
 /** Returns true if the job should not be visible to the management layer. */
 bool job_is_internal(Job *job);
 
-/** Returns whether the job is scheduled for cancellation. */
+/** Returns whether the job is being cancelled. */
 bool job_is_cancelled(Job *job);
 
+/**
+ * Returns whether the job is scheduled for cancellation (at an
+ * indefinite point).
+ */
+bool job_cancel_requested(Job *job);
+
 /** Returns whether the job is in a completed state. */
 bool job_is_completed(Job *job);
 
diff --git a/block/mirror.c b/block/mirror.c
index c3514f4196..291d2ed040 100644
--- a/block/mirror.c
+++ b/block/mirror.c
@@ -938,7 +938,7 @@ static int coroutine_fn mirror_run(Job *job, Error **errp)
         job_transition_to_ready(&s->common.job);
         s->synced = true;
         s->actively_synced = true;
-        while (!job_is_cancelled(&s->common.job) && !s->should_complete) {
+        while (!job_cancel_requested(&s->common.job) && !s->should_complete) {
             job_yield(&s->common.job);
         }
         s->common.job.cancelled = false;
@@ -1046,7 +1046,7 @@ static int coroutine_fn mirror_run(Job *job, Error **errp)
             }
 
             should_complete = s->should_complete ||
-                job_is_cancelled(&s->common.job);
+                job_cancel_requested(&s->common.job);
             cnt = bdrv_get_dirty_count(s->dirty_bitmap);
         }
 
@@ -1089,7 +1089,7 @@ static int coroutine_fn mirror_run(Job *job, Error **errp)
         }
         trace_mirror_before_sleep(s, cnt, s->synced, delay_ns);
         job_sleep_ns(&s->common.job, delay_ns);
-        if (job_is_cancelled(&s->common.job) && s->common.job.force_cancel) {
+        if (job_is_cancelled(&s->common.job)) {
             break;
         }
         s->last_pause_ns = qemu_clock_get_ns(QEMU_CLOCK_REALTIME);
@@ -1101,8 +1101,7 @@ immediate_exit:
          * or it was cancelled prematurely so that we do not guarantee that
          * the target is a copy of the source.
          */
-        assert(ret < 0 || (s->common.job.force_cancel &&
-               job_is_cancelled(&s->common.job)));
+        assert(ret < 0 || job_is_cancelled(&s->common.job));
         assert(need_drain);
         mirror_wait_for_all_io(s);
     }
diff --git a/job.c b/job.c
index e78d893a9c..c51c8077cb 100644
--- a/job.c
+++ b/job.c
@@ -216,6 +216,11 @@ const char *job_type_str(const Job *job)
 }
 
 bool job_is_cancelled(Job *job)
+{
+    return job->cancelled && job->force_cancel;
+}
+
+bool job_cancel_requested(Job *job)
 {
     return job->cancelled;
 }
@@ -650,7 +655,7 @@ static void job_conclude(Job *job)
 
 static void job_update_rc(Job *job)
 {
-    if (!job->ret && job_is_cancelled(job)) {
+    if (!job->ret && job_cancel_requested(job)) {
         job->ret = -ECANCELED;
     }
     if (job->ret) {
@@ -704,7 +709,7 @@ static int job_finalize_single(Job *job)
 
     /* Emit events only if we actually started */
     if (job_started(job)) {
-        if (job_is_cancelled(job)) {
+        if (job_cancel_requested(job)) {
             job_event_cancelled(job);
         } else {
             job_event_completed(job);
@@ -1015,7 +1020,7 @@ void job_complete(Job *job, Error **errp)
     if (job_apply_verb(job, JOB_VERB_COMPLETE, errp)) {
         return;
     }
-    if (job_is_cancelled(job) || !job->driver->complete) {
+    if (job_cancel_requested(job) || !job->driver->complete) {
         error_setg(errp, "The active block job '%s' cannot be completed",
                    job->id);
         return;
@@ -1043,7 +1048,7 @@ int job_finish_sync(Job *job, void (*finish)(Job *, Error 
**errp), Error **errp)
     AIO_WAIT_WHILE(job->aio_context,
                    (job_enter(job), !job_is_completed(job)));
 
-    ret = (job_is_cancelled(job) && job->ret == 0) ? -ECANCELED : job->ret;
+    ret = (job_cancel_requested(job) && job->ret == 0) ? -ECANCELED : job->ret;
     job_unref(job);
     return ret;
 }
-- 
2.31.1