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>

6 files changed, 4 insertions, 157 deletions

diff --git a/block/blkio.c b/block/blkio.c
index 7cf6d61f47..0a0a6c0f5f 100644
--- a/block/blkio.c
+++ b/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"
diff --git a/block/io_uring.c b/block/io_uring.c
index 8429f341be..3a1e1f45b3 100644
--- a/block/io_uring.c
+++ b/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"
diff --git a/block/linux-aio.c b/block/linux-aio.c
index 49a37174c2..a2670b3e46 100644
--- a/block/linux-aio.c
+++ b/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"
 
diff --git a/block/meson.build b/block/meson.build
index f351b9d0d3..59ff6d380c 100644
--- a/block/meson.build
+++ b/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',
diff --git a/block/nvme.c b/block/nvme.c
index dfbd1085fd..96b3f8f2fa 100644
--- a/block/nvme.c
+++ b/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"
diff --git a/block/plug.c b/block/plug.c
deleted file mode 100644
index f26173559c..0000000000
--- a/block/plug.c
+++ /dev/null
@@ -1,156 +0,0 @@
-/* SPDX-License-Identifier: GPL-2.0-or-later */
-/*
- * Deferred calls
- *
- * Copyright Red Hat.
- *
- * 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
- */
-
-#include "qemu/osdep.h"
-#include "qemu/coroutine-tls.h"
-#include "qemu/notify.h"
-#include "qemu/thread.h"
-#include "sysemu/block-backend.h"
-
-/* A function call that has been deferred until defer_call_end() */
-typedef struct {
-    void (*fn)(void *);
-    void *opaque;
-} DeferredCall;
-
-/* Per-thread state */
-typedef struct {
-    unsigned nesting_level;
-    GArray *deferred_call_array;
-} DeferCallThreadState;
-
-/* Use get_ptr_defer_call_thread_state() to fetch this thread-local value */
-QEMU_DEFINE_STATIC_CO_TLS(DeferCallThreadState, defer_call_thread_state);
-
-/* Called at thread cleanup time */
-static void defer_call_atexit(Notifier *n, void *value)
-{
-    DeferCallThreadState *thread_state = get_ptr_defer_call_thread_state();
-    g_array_free(thread_state->deferred_call_array, TRUE);
-}
-
-/* This won't involve coroutines, so use __thread */
-static __thread Notifier defer_call_atexit_notifier;
-
-/**
- * defer_call:
- * @fn: a function pointer to be invoked
- * @opaque: a user-defined argument to @fn()
- *
- * Call @fn(@opaque) immediately if not within a
- * defer_call_begin()/defer_call_end() section.
- *
- * Otherwise defer the call until the end of the outermost
- * defer_call_begin()/defer_call_end() section in this thread. If the same
- * @fn/@opaque pair has already been deferred, it will only be called once upon
- * defer_call_end() so that accumulated calls are batched into a single call.
- *
- * The caller must ensure that @opaque is not freed before @fn() is invoked.
- */
-void defer_call(void (*fn)(void *), void *opaque)
-{
-    DeferCallThreadState *thread_state = get_ptr_defer_call_thread_state();
-
-    /* Call immediately if we're not deferring calls */
-    if (thread_state->nesting_level == 0) {
-        fn(opaque);
-        return;
-    }
-
-    GArray *array = thread_state->deferred_call_array;
-    if (!array) {
-        array = g_array_new(FALSE, FALSE, sizeof(DeferredCall));
-        thread_state->deferred_call_array = array;
-        defer_call_atexit_notifier.notify = defer_call_atexit;
-        qemu_thread_atexit_add(&defer_call_atexit_notifier);
-    }
-
-    DeferredCall *fns = (DeferredCall *)array->data;
-    DeferredCall new_fn = {
-        .fn = fn,
-        .opaque = opaque,
-    };
-
-    /*
-     * There won't be many, so do a linear search. If this becomes a bottleneck
-     * then a binary search (glib 2.62+) or different data structure could be
-     * used.
-     */
-    for (guint i = 0; i < array->len; i++) {
-        if (memcmp(&fns[i], &new_fn, sizeof(new_fn)) == 0) {
-            return; /* already exists */
-        }
-    }
-
-    g_array_append_val(array, new_fn);
-}
-
-/**
- * defer_call_begin: Defer defer_call() functions until defer_call_end()
- *
- * defer_call_begin() and defer_call_end() are thread-local operations. The
- * caller must ensure that each defer_call_begin() has a matching
- * defer_call_end() in the same thread.
- *
- * Nesting is supported. defer_call() functions are only called at the
- * outermost defer_call_end().
- */
-void defer_call_begin(void)
-{
-    DeferCallThreadState *thread_state = get_ptr_defer_call_thread_state();
-
-    assert(thread_state->nesting_level < UINT32_MAX);
-
-    thread_state->nesting_level++;
-}
-
-/**
- * defer_call_end: Run any pending defer_call() functions
- *
- * There must have been a matching defer_call_begin() call in the same thread
- * prior to this defer_call_end() call.
- */
-void defer_call_end(void)
-{
-    DeferCallThreadState *thread_state = get_ptr_defer_call_thread_state();
-
-    assert(thread_state->nesting_level > 0);
-
-    if (--thread_state->nesting_level > 0) {
-        return;
-    }
-
-    GArray *array = thread_state->deferred_call_array;
-    if (!array) {
-        return;
-    }
-
-    DeferredCall *fns = (DeferredCall *)array->data;
-
-    for (guint i = 0; i < array->len; i++) {
-        fns[i].fn(fns[i].opaque);
-    }
-
-    /*
-     * This resets the array without freeing memory so that appending is cheap
-     * in the future.
-     */
-    g_array_set_size(array, 0);
-}