When aio_context_new() -> aio_context_setup() fails at startup it
doesn't really matter whether errors are returned to the caller or the
process terminates immediately.

However, it is not acceptable to terminate when hotplugging --object
iothread at runtime. Refactor aio_context_setup() so that errors can be
propagated. The next commit will set errp when fdmon_io_uring_setup()
fails.

Suggested-by: Kevin Wolf <kwolf@redhat.com>
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Reviewed-by: Kevin Wolf <kwolf@redhat.com>
---
v5:
- Indicate error in return value from function with Error *errp arg [Kevin]
---
 include/block/aio.h | 5 ++++-
 util/aio-posix.c    | 5 +++--
 util/aio-win32.c    | 3 ++-
 util/async.c        | 6 +++++-
 4 files changed, 14 insertions(+), 5 deletions(-)

diff --git a/include/block/aio.h b/include/block/aio.h
index 2760f308f5..9562733fa7 100644
--- a/include/block/aio.h
+++ b/include/block/aio.h
@@ -718,10 +718,13 @@ void qemu_set_current_aio_context(AioContext *ctx);
 /**
  * aio_context_setup:
  * @ctx: the aio context
+ * @errp: error pointer
  *
  * Initialize the aio context.
+ *
+ * Returns: true on success, false otherwise
  */
-void aio_context_setup(AioContext *ctx);
+bool aio_context_setup(AioContext *ctx, Error **errp);
 
 /**
  * aio_context_destroy:
diff --git a/util/aio-posix.c b/util/aio-posix.c
index bebd9ce3a2..9806a75c12 100644
--- a/util/aio-posix.c
+++ b/util/aio-posix.c
@@ -718,7 +718,7 @@ bool aio_poll(AioContext *ctx, bool blocking)
     return progress;
 }
 
-void aio_context_setup(AioContext *ctx)
+bool aio_context_setup(AioContext *ctx, Error **errp)
 {
     ctx->fdmon_ops = &fdmon_poll_ops;
     ctx->epollfd = -1;
@@ -726,10 +726,11 @@ void aio_context_setup(AioContext *ctx)
 
     /* Use the fastest fd monitoring implementation if available */
     if (fdmon_io_uring_setup(ctx)) {
-        return;
+        return true;
     }
 
     fdmon_epoll_setup(ctx);
+    return true;
 }
 
 void aio_context_destroy(AioContext *ctx)
diff --git a/util/aio-win32.c b/util/aio-win32.c
index 18cc9fb7a9..6e6f699e4b 100644
--- a/util/aio-win32.c
+++ b/util/aio-win32.c
@@ -419,8 +419,9 @@ bool aio_poll(AioContext *ctx, bool blocking)
     return progress;
 }
 
-void aio_context_setup(AioContext *ctx)
+bool aio_context_setup(AioContext *ctx, Error **errp)
 {
+    return true;
 }
 
 void aio_context_destroy(AioContext *ctx)
diff --git a/util/async.c b/util/async.c
index 7d06ff98f3..00e46b99f9 100644
--- a/util/async.c
+++ b/util/async.c
@@ -580,6 +580,7 @@ static void co_schedule_bh_cb(void *opaque)
 
 AioContext *aio_context_new(Error **errp)
 {
+    ERRP_GUARD();
     int ret;
     AioContext *ctx;
 
@@ -610,7 +611,10 @@ AioContext *aio_context_new(Error **errp)
      * you add any new resources to AioContext, it's probably best to acquire
      * them before aio_context_setup().
      */
-    aio_context_setup(ctx);
+    if (!aio_context_setup(ctx, errp)) {
+        event_notifier_cleanup(&ctx->notifier);
+        goto fail;
+    }
 
     g_source_set_can_recurse(&ctx->source, true);
     qemu_lockcnt_init(&ctx->list_lock);
-- 
2.51.0