block: rename blk_io_plug_call() API to defer_call()

Prepare to move the blk_io_plug_call() API out of the block layer so
that other subsystems call use this deferred call mechanism. Rename it
to defer_call() but leave the code in block/plug.c.

The next commit will move the code out of the block layer.

Suggested-by: Ilya Maximets <i.maximets@ovn.org>
Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Reviewed-by: Paul Durrant <paul@xen.org>
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
Message-ID: <20230913200045.1024233-2-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>

block/blkio.c

@@ -312,10 +312,10 @@ static void blkio_detach_aio_context(BlockDriverState *bs)
 }
 
 /*
- * Called by blk_io_unplug() or immediately if not plugged. Called without
- * blkio_lock.
+ * Called by defer_call_end() or immediately if not in a deferred section.
+ * Called without blkio_lock.
  */
-static void blkio_unplug_fn(void *opaque)
+static void blkio_deferred_fn(void *opaque)
 {
     BDRVBlkioState *s = opaque;
 
@@ -332,7 +332,7 @@ static void blkio_submit_io(BlockDriverState *bs)
 {
     BDRVBlkioState *s = bs->opaque;
 
-    blk_io_plug_call(blkio_unplug_fn, s);
+    defer_call(blkio_deferred_fn, s);
 }
 
 static int coroutine_fn

block/io_uring.c

@@ -306,7 +306,7 @@ static void ioq_init(LuringQueue *io_q)
     io_q->blocked = false;
 }
 
-static void luring_unplug_fn(void *opaque)
+static void luring_deferred_fn(void *opaque)
 {
     LuringState *s = opaque;
     trace_luring_unplug_fn(s, s->io_q.blocked, s->io_q.in_queue,
@@ -367,7 +367,7 @@ static int luring_do_submit(int fd, LuringAIOCB *luringcb, LuringState *s,
             return ret;
         }
 
-        blk_io_plug_call(luring_unplug_fn, s);
+        defer_call(luring_deferred_fn, s);
     }
     return 0;
 }

block/linux-aio.c

@@ -353,7 +353,7 @@ static uint64_t laio_max_batch(LinuxAioState *s, uint64_t dev_max_batch)
     return max_batch;
 }
 
-static void laio_unplug_fn(void *opaque)
+static void laio_deferred_fn(void *opaque)
 {
     LinuxAioState *s = opaque;
 
@@ -393,7 +393,7 @@ static int laio_do_submit(int fd, struct qemu_laiocb *laiocb, off_t offset,
         if (s->io_q.in_queue >= laio_max_batch(s, dev_max_batch)) {
             ioq_submit(s);
         } else {
-            blk_io_plug_call(laio_unplug_fn, s);
+            defer_call(laio_deferred_fn, s);
         }
     }
 

block/nvme.c

@@ -476,7 +476,7 @@ static void nvme_trace_command(const NvmeCmd *cmd)
     }
 }
 
-static void nvme_unplug_fn(void *opaque)
+static void nvme_deferred_fn(void *opaque)
 {
     NVMeQueuePair *q = opaque;
 
@@ -503,7 +503,7 @@ static void nvme_submit_command(NVMeQueuePair *q, NVMeRequest *req,
     q->need_kick++;
     qemu_mutex_unlock(&q->lock);
 
-    blk_io_plug_call(nvme_unplug_fn, q);
+    defer_call(nvme_deferred_fn, q);
 }
 
 static void nvme_admin_cmd_sync_cb(void *opaque, int ret)

block/plug.c

@@ -1,24 +1,21 @@
 /* SPDX-License-Identifier: GPL-2.0-or-later */
 /*
- * Block I/O plugging
+ * Deferred calls
  *
  * Copyright Red Hat.
  *
- * This API defers a function call within a blk_io_plug()/blk_io_unplug()
+ * 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:
  *
- *   blk_io_plug(); <-- start of plugged region
+ *   defer_call_begin(); <-- start of section
  *   ...
- *   blk_io_plug_call(my_func, my_obj); <-- deferred my_func(my_obj) call
- *   blk_io_plug_call(my_func, my_obj); <-- another
- *   blk_io_plug_call(my_func, my_obj); <-- another
+ *   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
  *   ...
- *   blk_io_unplug(); <-- end of plugged region, my_func(my_obj) is called once
- *
- * This code is actually generic and not tied to the block layer. If another
- * subsystem needs this functionality, it could be renamed.
+ *   defer_call_end(); <-- end of section, my_func(my_obj) is called once
  */
 
 #include "qemu/osdep.h"
@@ -27,66 +24,66 @@
 #include "qemu/thread.h"
 #include "sysemu/block-backend.h"
 
-/* A function call that has been deferred until unplug() */
+/* A function call that has been deferred until defer_call_end() */
 typedef struct {
     void (*fn)(void *);
     void *opaque;
-} UnplugFn;
+} DeferredCall;
 
 /* Per-thread state */
 typedef struct {
-    unsigned count;       /* how many times has plug() been called? */
-    GArray *unplug_fns;   /* functions to call at unplug time */
-} Plug;
+    unsigned nesting_level;
+    GArray *deferred_call_array;
+} DeferCallThreadState;
 
-/* Use get_ptr_plug() to fetch this thread-local value */
-QEMU_DEFINE_STATIC_CO_TLS(Plug, plug);
+/* 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 blk_io_plug_atexit(Notifier *n, void *value)
+static void defer_call_atexit(Notifier *n, void *value)
 {
-    Plug *plug = get_ptr_plug();
-    g_array_free(plug->unplug_fns, TRUE);
+    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 blk_io_plug_atexit_notifier;
+static __thread Notifier defer_call_atexit_notifier;
 
 /**
- * blk_io_plug_call:
+ * defer_call:
  * @fn: a function pointer to be invoked
  * @opaque: a user-defined argument to @fn()
  *
- * Call @fn(@opaque) immediately if not within a blk_io_plug()/blk_io_unplug()
- * section.
+ * 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
- * blk_io_plug()/blk_io_unplug() section in this thread. If the same
+ * 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
- * blk_io_unplug() so that accumulated calls are batched into a single call.
+ * 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 blk_io_plug_call(void (*fn)(void *), void *opaque)
+void defer_call(void (*fn)(void *), void *opaque)
 {
-    Plug *plug = get_ptr_plug();
+    DeferCallThreadState *thread_state = get_ptr_defer_call_thread_state();
 
-    /* Call immediately if we're not plugged */
-    if (plug->count == 0) {
+    /* Call immediately if we're not deferring calls */
+    if (thread_state->nesting_level == 0) {
         fn(opaque);
         return;
     }
 
-    GArray *array = plug->unplug_fns;
+    GArray *array = thread_state->deferred_call_array;
     if (!array) {
-        array = g_array_new(FALSE, FALSE, sizeof(UnplugFn));
-        plug->unplug_fns = array;
-        blk_io_plug_atexit_notifier.notify = blk_io_plug_atexit;
-        qemu_thread_atexit_add(&blk_io_plug_atexit_notifier);
+        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);
     }
 
-    UnplugFn *fns = (UnplugFn *)array->data;
-    UnplugFn new_fn = {
+    DeferredCall *fns = (DeferredCall *)array->data;
+    DeferredCall new_fn = {
         .fn = fn,
         .opaque = opaque,
     };
@@ -106,46 +103,46 @@ void blk_io_plug_call(void (*fn)(void *), void *opaque)
 }
 
 /**
- * blk_io_plug: Defer blk_io_plug_call() functions until blk_io_unplug()
+ * defer_call_begin: Defer defer_call() functions until defer_call_end()
  *
- * blk_io_plug/unplug are thread-local operations. This means that multiple
- * threads can simultaneously call plug/unplug, but the caller must ensure that
- * each unplug() is called in the same thread of the matching plug().
+ * 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. blk_io_plug_call() functions are only called at the
- * outermost blk_io_unplug().
+ * Nesting is supported. defer_call() functions are only called at the
+ * outermost defer_call_end().
  */
-void blk_io_plug(void)
+void defer_call_begin(void)
 {
-    Plug *plug = get_ptr_plug();
+    DeferCallThreadState *thread_state = get_ptr_defer_call_thread_state();
 
-    assert(plug->count < UINT32_MAX);
+    assert(thread_state->nesting_level < UINT32_MAX);
 
-    plug->count++;
+    thread_state->nesting_level++;
 }
 
 /**
- * blk_io_unplug: Run any pending blk_io_plug_call() functions
+ * defer_call_end: Run any pending defer_call() functions
  *
- * There must have been a matching blk_io_plug() call in the same thread prior
- * to this blk_io_unplug() call.
+ * There must have been a matching defer_call_begin() call in the same thread
+ * prior to this defer_call_end() call.
  */
-void blk_io_unplug(void)
+void defer_call_end(void)
 {
-    Plug *plug = get_ptr_plug();
+    DeferCallThreadState *thread_state = get_ptr_defer_call_thread_state();
 
-    assert(plug->count > 0);
+    assert(thread_state->nesting_level > 0);
 
-    if (--plug->count > 0) {
+    if (--thread_state->nesting_level > 0) {
         return;
     }
 
-    GArray *array = plug->unplug_fns;
+    GArray *array = thread_state->deferred_call_array;
     if (!array) {
         return;
     }
 
-    UnplugFn *fns = (UnplugFn *)array->data;
+    DeferredCall *fns = (DeferredCall *)array->data;
 
     for (guint i = 0; i < array->len; i++) {
         fns[i].fn(fns[i].opaque);

hw/block/dataplane/xen-block.c

@@ -509,7 +509,7 @@ static int xen_block_get_request(XenBlockDataPlane *dataplane,
 
 /*
  * Threshold of in-flight requests above which we will start using
- * blk_io_plug()/blk_io_unplug() to batch requests.
+ * defer_call_begin()/defer_call_end() to batch requests.
  */
 #define IO_PLUG_THRESHOLD 1
 
@@ -537,7 +537,7 @@ static bool xen_block_handle_requests(XenBlockDataPlane *dataplane)
      * is below us.
      */
     if (inflight_atstart > IO_PLUG_THRESHOLD) {
-        blk_io_plug();
+        defer_call_begin();
     }
     while (rc != rp) {
         /* pull request from ring */
@@ -577,12 +577,12 @@ static bool xen_block_handle_requests(XenBlockDataPlane *dataplane)
 
         if (inflight_atstart > IO_PLUG_THRESHOLD &&
             batched >= inflight_atstart) {
-            blk_io_unplug();
+            defer_call_end();
         }
         xen_block_do_aio(request);
         if (inflight_atstart > IO_PLUG_THRESHOLD) {
             if (batched >= inflight_atstart) {
-                blk_io_plug();
+                defer_call_begin();
                 batched = 0;
             } else {
                 batched++;
@@ -590,7 +590,7 @@ static bool xen_block_handle_requests(XenBlockDataPlane *dataplane)
         }
     }
     if (inflight_atstart > IO_PLUG_THRESHOLD) {
-        blk_io_unplug();
+        defer_call_end();
     }
 
     return done_something;

hw/block/virtio-blk.c

@@ -1134,7 +1134,7 @@ void virtio_blk_handle_vq(VirtIOBlock *s, VirtQueue *vq)
     bool suppress_notifications = virtio_queue_get_notification(vq);
 
     aio_context_acquire(blk_get_aio_context(s->blk));
-    blk_io_plug();
+    defer_call_begin();
 
     do {
         if (suppress_notifications) {
@@ -1158,7 +1158,7 @@ void virtio_blk_handle_vq(VirtIOBlock *s, VirtQueue *vq)
         virtio_blk_submit_multireq(s, &mrb);
     }
 
-    blk_io_unplug();
+    defer_call_end();
     aio_context_release(blk_get_aio_context(s->blk));
 }
 

hw/scsi/virtio-scsi.c

@@ -799,7 +799,7 @@ static int virtio_scsi_handle_cmd_req_prepare(VirtIOSCSI *s, VirtIOSCSIReq *req)
         return -ENOBUFS;
     }
     scsi_req_ref(req->sreq);
-    blk_io_plug();
+    defer_call_begin();
     object_unref(OBJECT(d));
     return 0;
 }
@@ -810,7 +810,7 @@ static void virtio_scsi_handle_cmd_req_submit(VirtIOSCSI *s, VirtIOSCSIReq *req)
     if (scsi_req_enqueue(sreq)) {
         scsi_req_continue(sreq);
     }
-    blk_io_unplug();
+    defer_call_end();
     scsi_req_unref(sreq);
 }
 
@@ -836,7 +836,7 @@ static void virtio_scsi_handle_cmd_vq(VirtIOSCSI *s, VirtQueue *vq)
                 while (!QTAILQ_EMPTY(&reqs)) {
                     req = QTAILQ_FIRST(&reqs);
                     QTAILQ_REMOVE(&reqs, req, next);
-                    blk_io_unplug();
+                    defer_call_end();
                     scsi_req_unref(req->sreq);
                     virtqueue_detach_element(req->vq, &req->elem, 0);
                     virtio_scsi_free_req(req);

include/sysemu/block-backend-io.h

@@ -100,9 +100,9 @@ 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 blk_io_plug(void);
-void blk_io_unplug(void);
-void blk_io_plug_call(void (*fn)(void *), void *opaque);
+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);