upstream: Move bottom-half handlers to async.c

Change-Id: Ibd4321edb2abe349d32483a60fdb94a282f22240

1 files changed, 216 insertions, 0 deletions

diff --git a/async.c b/async.c
new file mode 100644
index 0000000..57ac3a8
--- /dev/null
+++ b/async.c
@@ -0,0 +1,216 @@
+/*
+ * QEMU System Emulator
+ *
+ * Copyright (c) 2003-2008 Fabrice Bellard
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL
+ * THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+ * THE SOFTWARE.
+ */
+
+#include "qemu-common.h"
+#include "qemu-aio.h"
+
+/*
+ * An AsyncContext protects the callbacks of AIO requests and Bottom Halves
+ * against interfering with each other. A typical example is qcow2 that accepts
+ * asynchronous requests, but relies for manipulation of its metadata on
+ * synchronous bdrv_read/write that doesn't trigger any callbacks.
+ *
+ * However, these functions are often emulated using AIO which means that AIO
+ * callbacks must be run - but at the same time we must not run callbacks of
+ * other requests as they might start to modify metadata and corrupt the
+ * internal state of the caller of bdrv_read/write.
+ *
+ * To achieve the desired semantics we switch into a new AsyncContext.
+ * Callbacks must only be run if they belong to the current AsyncContext.
+ * Otherwise they need to be queued until their own context is active again.
+ * This is how you can make qemu_aio_wait() wait only for your own callbacks.
+ *
+ * The AsyncContexts form a stack. When you leave a AsyncContexts, you always
+ * return to the old ("parent") context.
+ */
+struct AsyncContext {
+    /* Consecutive number of the AsyncContext (position in the stack) */
+    int id;
+
+    /* Anchor of the list of Bottom Halves belonging to the context */
+    struct QEMUBH *first_bh;
+
+    /* Link to parent context */
+    struct AsyncContext *parent;
+};
+
+/* The currently active AsyncContext */
+static struct AsyncContext *async_context = &(struct AsyncContext) { 0 };
+
+/*
+ * Enter a new AsyncContext. Already scheduled Bottom Halves and AIO callbacks
+ * won't be called until this context is left again.
+ */
+void async_context_push(void)
+{
+    struct AsyncContext *new = qemu_mallocz(sizeof(*new));
+    new->parent = async_context;
+    new->id = async_context->id + 1;
+    async_context = new;
+}
+
+/* Run queued AIO completions and destroy Bottom Half */
+static void bh_run_aio_completions(void *opaque)
+{
+    QEMUBH **bh = opaque;
+    qemu_bh_delete(*bh);
+    qemu_free(bh);
+    qemu_aio_process_queue();
+}
+/*
+ * Leave the currently active AsyncContext. All Bottom Halves belonging to the
+ * old context are executed before changing the context.
+ */
+void async_context_pop(void)
+{
+    struct AsyncContext *old = async_context;
+    QEMUBH **bh;
+
+    /* Flush the bottom halves, we don't want to lose them */
+    while (qemu_bh_poll());
+
+    /* Switch back to the parent context */
+    async_context = async_context->parent;
+    qemu_free(old);
+
+    if (async_context == NULL) {
+        abort();
+    }
+
+    /* Schedule BH to run any queued AIO completions as soon as possible */
+    bh = qemu_malloc(sizeof(*bh));
+    *bh = qemu_bh_new(bh_run_aio_completions, bh);
+    qemu_bh_schedule(*bh);
+}
+
+/*
+ * Returns the ID of the currently active AsyncContext
+ */
+int get_async_context_id(void)
+{
+    return async_context->id;
+}
+
+/***********************************************************/
+/* bottom halves (can be seen as timers which expire ASAP) */
+
+struct QEMUBH {
+    QEMUBHFunc *cb;
+    void *opaque;
+    int scheduled;
+    int idle;
+    int deleted;
+    QEMUBH *next;
+};
+
+QEMUBH *qemu_bh_new(QEMUBHFunc *cb, void *opaque)
+{
+    QEMUBH *bh;
+    bh = qemu_mallocz(sizeof(QEMUBH));
+    bh->cb = cb;
+    bh->opaque = opaque;
+    bh->next = async_context->first_bh;
+    async_context->first_bh = bh;
+    return bh;
+}
+
+int qemu_bh_poll(void)
+{
+    QEMUBH *bh, **bhp;
+    int ret;
+
+    ret = 0;
+    for (bh = async_context->first_bh; bh; bh = bh->next) {
+        if (!bh->deleted && bh->scheduled) {
+            bh->scheduled = 0;
+            if (!bh->idle)
+                ret = 1;
+            bh->idle = 0;
+            bh->cb(bh->opaque);
+        }
+    }
+
+    /* remove deleted bhs */
+    bhp = &async_context->first_bh;
+    while (*bhp) {
+        bh = *bhp;
+        if (bh->deleted) {
+            *bhp = bh->next;
+            qemu_free(bh);
+        } else
+            bhp = &bh->next;
+    }
+
+    return ret;
+}
+
+void qemu_bh_schedule_idle(QEMUBH *bh)
+{
+    if (bh->scheduled)
+        return;
+    bh->scheduled = 1;
+    bh->idle = 1;
+}
+
+void qemu_bh_schedule(QEMUBH *bh)
+{
+    if (bh->scheduled)
+        return;
+    bh->scheduled = 1;
+    bh->idle = 0;
+    /* stop the currently executing CPU to execute the BH ASAP */
+    qemu_notify_event();
+}
+
+void qemu_bh_cancel(QEMUBH *bh)
+{
+    bh->scheduled = 0;
+}
+
+void qemu_bh_delete(QEMUBH *bh)
+{
+    bh->scheduled = 0;
+    bh->deleted = 1;
+}
+
+void qemu_bh_update_timeout(int *timeout)
+{
+    QEMUBH *bh;
+
+    for (bh = async_context->first_bh; bh; bh = bh->next) {
+        if (!bh->deleted && bh->scheduled) {
+            if (bh->idle) {
+                /* idle bottom halves will be polled at least
+                 * every 10ms */
+                *timeout = MIN(10, *timeout);
+            } else {
+                /* non-idle bottom halves will be executed
+                 * immediately */
+                *timeout = 0;
+                break;
+            }
+        }
+    }
+}
+