util/defer-call: move defer_call() to util/

The networking subsystem may wish to use defer_call(), so move the code
to util/ where it can be reused.

As a reminder of what defer_call() does:

This API defers a function call within a defer_call_begin()/defer_call_end()
section, allowing multiple calls to batch up. This is a performance
optimization that is used in the block layer to submit several I/O requests
at once instead of individually:

  defer_call_begin(); <-- start of section
  ...
  defer_call(my_func, my_obj); <-- deferred my_func(my_obj) call
  defer_call(my_func, my_obj); <-- another
  defer_call(my_func, my_obj); <-- another
  ...
  defer_call_end(); <-- end of section, my_func(my_obj) is called once

Suggested-by: Ilya Maximets <i.maximets@ovn.org>
Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
Message-ID: <20230913200045.1024233-3-stefanha@redhat.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Reviewed-by: Kevin Wolf <kwolf@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>

MAINTAINERS

@@ -2755,12 +2755,13 @@ S: Supported
 F: util/async.c
 F: util/aio-*.c
 F: util/aio-*.h
+F: util/defer-call.c
 F: util/fdmon-*.c
 F: block/io.c
-F: block/plug.c
 F: migration/block*
 F: include/block/aio.h
 F: include/block/aio-wait.h
+F: include/qemu/defer-call.h
 F: scripts/qemugdb/aio.py
 F: tests/unit/test-fdmon-epoll.c
 T: git https://github.com/stefanha/qemu.git block

block/blkio.c

@@ -13,6 +13,7 @@
 #include "block/block_int.h"
 #include "exec/memory.h"
 #include "exec/cpu-common.h" /* for qemu_ram_get_fd() */
+#include "qemu/defer-call.h"
 #include "qapi/error.h"
 #include "qemu/error-report.h"
 #include "qapi/qmp/qdict.h"

block/io_uring.c

@@ -15,6 +15,7 @@
 #include "block/block.h"
 #include "block/raw-aio.h"
 #include "qemu/coroutine.h"
+#include "qemu/defer-call.h"
 #include "qapi/error.h"
 #include "sysemu/block-backend.h"
 #include "trace.h"

block/linux-aio.c

@@ -14,6 +14,7 @@
 #include "block/raw-aio.h"
 #include "qemu/event_notifier.h"
 #include "qemu/coroutine.h"
+#include "qemu/defer-call.h"
 #include "qapi/error.h"
 #include "sysemu/block-backend.h"
 

block/meson.build

@@ -21,7 +21,6 @@ block_ss.add(files(
   'mirror.c',
   'nbd.c',
   'null.c',
-  'plug.c',
   'preallocate.c',
   'progress_meter.c',
   'qapi.c',

block/nvme.c

@@ -16,6 +16,7 @@
 #include "qapi/error.h"
 #include "qapi/qmp/qdict.h"
 #include "qapi/qmp/qstring.h"
+#include "qemu/defer-call.h"
 #include "qemu/error-report.h"
 #include "qemu/main-loop.h"
 #include "qemu/module.h"

hw/block/dataplane/xen-block.c

@@ -19,6 +19,7 @@
  */
 
 #include "qemu/osdep.h"
+#include "qemu/defer-call.h"
 #include "qemu/error-report.h"
 #include "qemu/main-loop.h"
 #include "qemu/memalign.h"

hw/block/virtio-blk.c

@@ -12,6 +12,7 @@
  */
 
 #include "qemu/osdep.h"
+#include "qemu/defer-call.h"
 #include "qapi/error.h"
 #include "qemu/iov.h"
 #include "qemu/module.h"

hw/scsi/virtio-scsi.c

@@ -18,6 +18,7 @@
 #include "standard-headers/linux/virtio_ids.h"
 #include "hw/virtio/virtio-scsi.h"
 #include "migration/qemu-file-types.h"
+#include "qemu/defer-call.h"
 #include "qemu/error-report.h"
 #include "qemu/iov.h"
 #include "qemu/module.h"

include/qemu/defer-call.h

@@ -0,0 +1,16 @@
+/* SPDX-License-Identifier: GPL-2.0-or-later */
+/*
+ * Deferred calls
+ *
+ * Copyright Red Hat.
+ */
+
+#ifndef QEMU_DEFER_CALL_H
+#define QEMU_DEFER_CALL_H
+
+/* See documentation in util/defer-call.c */
+void defer_call_begin(void);
+void defer_call_end(void);
+void defer_call(void (*fn)(void *), void *opaque);
+
+#endif /* QEMU_DEFER_CALL_H */

include/sysemu/block-backend-io.h

@@ -100,10 +100,6 @@ void blk_iostatus_set_err(BlockBackend *blk, int error);
 int blk_get_max_iov(BlockBackend *blk);
 int blk_get_max_hw_iov(BlockBackend *blk);
 
-void defer_call_begin(void);
-void defer_call_end(void);
-void defer_call(void (*fn)(void *), void *opaque);
-
 AioContext *blk_get_aio_context(BlockBackend *blk);
 BlockAcctStats *blk_get_stats(BlockBackend *blk);
 void *blk_aio_get(const AIOCBInfo *aiocb_info, BlockBackend *blk,

block/plug.c → util/defer-call.c

@@ -22,7 +22,7 @@
 #include "qemu/coroutine-tls.h"
 #include "qemu/notify.h"
 #include "qemu/thread.h"
-#include "sysemu/block-backend.h"
+#include "qemu/defer-call.h"
 
 /* A function call that has been deferred until defer_call_end() */
 typedef struct {

util/meson.build

@@ -28,6 +28,7 @@ util_ss.add(when: 'CONFIG_WIN32', if_true: pathcch)
 if glib_has_gslice
   util_ss.add(files('qtree.c'))
 endif
+util_ss.add(files('defer-call.c'))
 util_ss.add(files('envlist.c', 'path.c', 'module.c'))
 util_ss.add(files('host-utils.c'))
 util_ss.add(files('bitmap.c', 'bitops.c'))