Introduce Virtio-loopback epsilon release:

Epsilon release introduces a new compatibility layer which make virtio-loopback
design to work with QEMU and rust-vmm vhost-user backend without require any
changes.

Signed-off-by: Timos Ampelikiotis <t.ampelikiotis@virtualopensystems.com>
Change-Id: I52e57563e08a7d0bdc002f8e928ee61ba0c53dd9

1 files changed, 149 insertions, 0 deletions

diff --git a/include/block/aio-wait.h b/include/block/aio-wait.h
new file mode 100644
index 000000000..b39eefb38
--- /dev/null
+++ b/include/block/aio-wait.h
@@ -0,0 +1,149 @@
+/*
+ * AioContext wait support
+ *
+ * Copyright (C) 2018 Red Hat, Inc.
+ *
+ * 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.
+ */
+
+#ifndef QEMU_AIO_WAIT_H
+#define QEMU_AIO_WAIT_H
+
+#include "block/aio.h"
+#include "qemu/main-loop.h"
+
+/**
+ * AioWait:
+ *
+ * An object that facilitates synchronous waiting on a condition. A single
+ * global AioWait object (global_aio_wait) is used internally.
+ *
+ * The main loop can wait on an operation running in an IOThread as follows:
+ *
+ *   AioContext *ctx = ...;
+ *   MyWork work = { .done = false };
+ *   schedule_my_work_in_iothread(ctx, &work);
+ *   AIO_WAIT_WHILE(ctx, !work.done);
+ *
+ * The IOThread must call aio_wait_kick() to notify the main loop when
+ * work.done changes:
+ *
+ *   static void do_work(...)
+ *   {
+ *       ...
+ *       work.done = true;
+ *       aio_wait_kick();
+ *   }
+ */
+typedef struct {
+    /* Number of waiting AIO_WAIT_WHILE() callers. Accessed with atomic ops. */
+    unsigned num_waiters;
+} AioWait;
+
+extern AioWait global_aio_wait;
+
+/**
+ * AIO_WAIT_WHILE:
+ * @ctx: the aio context, or NULL if multiple aio contexts (for which the
+ *       caller does not hold a lock) are involved in the polling condition.
+ * @cond: wait while this conditional expression is true
+ *
+ * Wait while a condition is true.  Use this to implement synchronous
+ * operations that require event loop activity.
+ *
+ * The caller must be sure that something calls aio_wait_kick() when the value
+ * of @cond might have changed.
+ *
+ * The caller's thread must be the IOThread that owns @ctx or the main loop
+ * thread (with @ctx acquired exactly once).  This function cannot be used to
+ * wait on conditions between two IOThreads since that could lead to deadlock,
+ * go via the main loop instead.
+ */
+#define AIO_WAIT_WHILE(ctx, cond) ({                               \
+    bool waited_ = false;                                          \
+    AioWait *wait_ = &global_aio_wait;                             \
+    AioContext *ctx_ = (ctx);                                      \
+    /* Increment wait_->num_waiters before evaluating cond. */     \
+    qatomic_inc(&wait_->num_waiters);                              \
+    if (ctx_ && in_aio_context_home_thread(ctx_)) {                \
+        while ((cond)) {                                           \
+            aio_poll(ctx_, true);                                  \
+            waited_ = true;                                        \
+        }                                                          \
+    } else {                                                       \
+        assert(qemu_get_current_aio_context() ==                   \
+               qemu_get_aio_context());                            \
+        while ((cond)) {                                           \
+            if (ctx_) {                                            \
+                aio_context_release(ctx_);                         \
+            }                                                      \
+            aio_poll(qemu_get_aio_context(), true);                \
+            if (ctx_) {                                            \
+                aio_context_acquire(ctx_);                         \
+            }                                                      \
+            waited_ = true;                                        \
+        }                                                          \
+    }                                                              \
+    qatomic_dec(&wait_->num_waiters);                              \
+    waited_; })
+
+/**
+ * aio_wait_kick:
+ * Wake up the main thread if it is waiting on AIO_WAIT_WHILE().  During
+ * synchronous operations performed in an IOThread, the main thread lets the
+ * IOThread's event loop run, waiting for the operation to complete.  A
+ * aio_wait_kick() call will wake up the main thread.
+ */
+void aio_wait_kick(void);
+
+/**
+ * aio_wait_bh_oneshot:
+ * @ctx: the aio context
+ * @cb: the BH callback function
+ * @opaque: user data for the BH callback function
+ *
+ * Run a BH in @ctx and wait for it to complete.
+ *
+ * Must be called from the main loop thread with @ctx acquired exactly once.
+ * Note that main loop event processing may occur.
+ */
+void aio_wait_bh_oneshot(AioContext *ctx, QEMUBHFunc *cb, void *opaque);
+
+/**
+ * in_aio_context_home_thread:
+ * @ctx: the aio context
+ *
+ * Return whether we are running in the thread that normally runs @ctx.  Note
+ * that acquiring/releasing ctx does not affect the outcome, each AioContext
+ * still only has one home thread that is responsible for running it.
+ */
+static inline bool in_aio_context_home_thread(AioContext *ctx)
+{
+    if (ctx == qemu_get_current_aio_context()) {
+        return true;
+    }
+
+    if (ctx == qemu_get_aio_context()) {
+        return qemu_mutex_iothread_locked();
+    } else {
+        return false;
+    }
+}
+
+#endif /* QEMU_AIO_WAIT_H */