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, 389 insertions, 0 deletions

diff --git a/nbd/client-connection.c b/nbd/client-connection.c
new file mode 100644
index 000000000..695f85575
--- /dev/null
+++ b/nbd/client-connection.c
@@ -0,0 +1,389 @@
+/*
+ * QEMU Block driver for  NBD
+ *
+ * Copyright (c) 2021 Virtuozzo International GmbH.
+ *
+ * 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/osdep.h"
+
+#include "block/nbd.h"
+
+#include "qapi/qapi-visit-sockets.h"
+#include "qapi/clone-visitor.h"
+
+struct NBDClientConnection {
+    /* Initialization constants, never change */
+    SocketAddress *saddr; /* address to connect to */
+    QCryptoTLSCreds *tlscreds;
+    NBDExportInfo initial_info;
+    bool do_negotiation;
+    bool do_retry;
+
+    QemuMutex mutex;
+
+    /*
+     * @sioc and @err represent a connection attempt.  While running
+     * is true, they are only used by the connection thread, and mutex
+     * locking is not needed.  Once the thread finishes,
+     * nbd_co_establish_connection then steals these pointers while
+     * under the mutex.
+     */
+    NBDExportInfo updated_info;
+    QIOChannelSocket *sioc;
+    QIOChannel *ioc;
+    Error *err;
+
+    /* All further fields are accessed only under mutex */
+    bool running; /* thread is running now */
+    bool detached; /* thread is detached and should cleanup the state */
+
+    /*
+     * wait_co: if non-NULL, which coroutine to wake in
+     * nbd_co_establish_connection() after yield()
+     */
+    Coroutine *wait_co;
+};
+
+/*
+ * The function isn't protected by any mutex, only call it when the client
+ * connection attempt has not yet started.
+ */
+void nbd_client_connection_enable_retry(NBDClientConnection *conn)
+{
+    conn->do_retry = true;
+}
+
+NBDClientConnection *nbd_client_connection_new(const SocketAddress *saddr,
+                                               bool do_negotiation,
+                                               const char *export_name,
+                                               const char *x_dirty_bitmap,
+                                               QCryptoTLSCreds *tlscreds)
+{
+    NBDClientConnection *conn = g_new(NBDClientConnection, 1);
+
+    object_ref(OBJECT(tlscreds));
+    *conn = (NBDClientConnection) {
+        .saddr = QAPI_CLONE(SocketAddress, saddr),
+        .tlscreds = tlscreds,
+        .do_negotiation = do_negotiation,
+
+        .initial_info.request_sizes = true,
+        .initial_info.structured_reply = true,
+        .initial_info.base_allocation = true,
+        .initial_info.x_dirty_bitmap = g_strdup(x_dirty_bitmap),
+        .initial_info.name = g_strdup(export_name ?: "")
+    };
+
+    qemu_mutex_init(&conn->mutex);
+
+    return conn;
+}
+
+static void nbd_client_connection_do_free(NBDClientConnection *conn)
+{
+    if (conn->sioc) {
+        qio_channel_close(QIO_CHANNEL(conn->sioc), NULL);
+        object_unref(OBJECT(conn->sioc));
+    }
+    error_free(conn->err);
+    qapi_free_SocketAddress(conn->saddr);
+    object_unref(OBJECT(conn->tlscreds));
+    g_free(conn->initial_info.x_dirty_bitmap);
+    g_free(conn->initial_info.name);
+    g_free(conn);
+}
+
+/*
+ * Connect to @addr and do NBD negotiation if @info is not null. If @tlscreds
+ * are given @outioc is returned. @outioc is provided only on success.  The call
+ * may be cancelled from other thread by simply qio_channel_shutdown(sioc).
+ */
+static int nbd_connect(QIOChannelSocket *sioc, SocketAddress *addr,
+                       NBDExportInfo *info, QCryptoTLSCreds *tlscreds,
+                       QIOChannel **outioc, Error **errp)
+{
+    int ret;
+
+    if (outioc) {
+        *outioc = NULL;
+    }
+
+    ret = qio_channel_socket_connect_sync(sioc, addr, errp);
+    if (ret < 0) {
+        return ret;
+    }
+
+    qio_channel_set_delay(QIO_CHANNEL(sioc), false);
+
+    if (!info) {
+        return 0;
+    }
+
+    ret = nbd_receive_negotiate(NULL, QIO_CHANNEL(sioc), tlscreds,
+                                tlscreds ? addr->u.inet.host : NULL,
+                                outioc, info, errp);
+    if (ret < 0) {
+        /*
+         * nbd_receive_negotiate() may setup tls ioc and return it even on
+         * failure path. In this case we should use it instead of original
+         * channel.
+         */
+        if (outioc && *outioc) {
+            qio_channel_close(QIO_CHANNEL(*outioc), NULL);
+            object_unref(OBJECT(*outioc));
+            *outioc = NULL;
+        } else {
+            qio_channel_close(QIO_CHANNEL(sioc), NULL);
+        }
+
+        return ret;
+    }
+
+    return 0;
+}
+
+static void *connect_thread_func(void *opaque)
+{
+    NBDClientConnection *conn = opaque;
+    int ret;
+    bool do_free;
+    uint64_t timeout = 1;
+    uint64_t max_timeout = 16;
+
+    qemu_mutex_lock(&conn->mutex);
+    while (!conn->detached) {
+        assert(!conn->sioc);
+        conn->sioc = qio_channel_socket_new();
+
+        qemu_mutex_unlock(&conn->mutex);
+
+        error_free(conn->err);
+        conn->err = NULL;
+        conn->updated_info = conn->initial_info;
+
+        ret = nbd_connect(conn->sioc, conn->saddr,
+                          conn->do_negotiation ? &conn->updated_info : NULL,
+                          conn->tlscreds, &conn->ioc, &conn->err);
+
+        /*
+         * conn->updated_info will finally be returned to the user. Clear the
+         * pointers to our internally allocated strings, which are IN parameters
+         * of nbd_receive_negotiate() and therefore nbd_connect(). Caller
+         * shoudn't be interested in these fields.
+         */
+        conn->updated_info.x_dirty_bitmap = NULL;
+        conn->updated_info.name = NULL;
+
+        qemu_mutex_lock(&conn->mutex);
+
+        if (ret < 0) {
+            object_unref(OBJECT(conn->sioc));
+            conn->sioc = NULL;
+            if (conn->do_retry && !conn->detached) {
+                qemu_mutex_unlock(&conn->mutex);
+
+                sleep(timeout);
+                if (timeout < max_timeout) {
+                    timeout *= 2;
+                }
+
+                qemu_mutex_lock(&conn->mutex);
+                continue;
+            }
+        }
+
+        break;
+    }
+
+    /* mutex is locked */
+
+    assert(conn->running);
+    conn->running = false;
+    if (conn->wait_co) {
+        aio_co_wake(conn->wait_co);
+        conn->wait_co = NULL;
+    }
+    do_free = conn->detached;
+
+    qemu_mutex_unlock(&conn->mutex);
+
+    if (do_free) {
+        nbd_client_connection_do_free(conn);
+    }
+
+    return NULL;
+}
+
+void nbd_client_connection_release(NBDClientConnection *conn)
+{
+    bool do_free = false;
+
+    if (!conn) {
+        return;
+    }
+
+    WITH_QEMU_LOCK_GUARD(&conn->mutex) {
+        assert(!conn->detached);
+        if (conn->running) {
+            conn->detached = true;
+        } else {
+            do_free = true;
+        }
+        if (conn->sioc) {
+            qio_channel_shutdown(QIO_CHANNEL(conn->sioc),
+                                 QIO_CHANNEL_SHUTDOWN_BOTH, NULL);
+        }
+    }
+
+    if (do_free) {
+        nbd_client_connection_do_free(conn);
+    }
+}
+
+/*
+ * Get a new connection in context of @conn:
+ *   if the thread is running, wait for completion
+ *   if the thread already succeeded in the background, and user didn't get the
+ *     result, just return it now
+ *   otherwise the thread is not running, so start a thread and wait for
+ *     completion
+ *
+ * If @blocking is false, don't wait for the thread, return immediately.
+ *
+ * If @info is not NULL, also do nbd-negotiation after successful connection.
+ * In this case info is used only as out parameter, and is fully initialized by
+ * nbd_co_establish_connection(). "IN" fields of info as well as related only to
+ * nbd_receive_export_list() would be zero (see description of NBDExportInfo in
+ * include/block/nbd.h).
+ */
+QIOChannel *coroutine_fn
+nbd_co_establish_connection(NBDClientConnection *conn, NBDExportInfo *info,
+                            bool blocking, Error **errp)
+{
+    QemuThread thread;
+
+    if (conn->do_negotiation) {
+        assert(info);
+    }
+
+    WITH_QEMU_LOCK_GUARD(&conn->mutex) {
+        /*
+         * Don't call nbd_co_establish_connection() in several coroutines in
+         * parallel. Only one call at once is supported.
+         */
+        assert(!conn->wait_co);
+
+        if (!conn->running) {
+            if (conn->sioc) {
+                /* Previous attempt finally succeeded in background */
+                if (conn->do_negotiation) {
+                    memcpy(info, &conn->updated_info, sizeof(*info));
+                    if (conn->ioc) {
+                        /* TLS channel now has own reference to parent */
+                        object_unref(OBJECT(conn->sioc));
+                        conn->sioc = NULL;
+
+                        return g_steal_pointer(&conn->ioc);
+                    }
+                }
+
+                assert(!conn->ioc);
+
+                return QIO_CHANNEL(g_steal_pointer(&conn->sioc));
+            }
+
+            conn->running = true;
+            error_free(conn->err);
+            conn->err = NULL;
+            qemu_thread_create(&thread, "nbd-connect",
+                               connect_thread_func, conn, QEMU_THREAD_DETACHED);
+        }
+
+        if (!blocking) {
+            error_setg(errp, "No connection at the moment");
+            return NULL;
+        }
+
+        conn->wait_co = qemu_coroutine_self();
+    }
+
+    /*
+     * We are going to wait for connect-thread finish, but
+     * nbd_co_establish_connection_cancel() can interrupt.
+     */
+    qemu_coroutine_yield();
+
+    WITH_QEMU_LOCK_GUARD(&conn->mutex) {
+        if (conn->running) {
+            /*
+             * The connection attempt was canceled and the coroutine resumed
+             * before the connection thread finished its job.  Report the
+             * attempt as failed, but leave the connection thread running,
+             * to reuse it for the next connection attempt.
+             */
+            error_setg(errp, "Connection attempt cancelled by other operation");
+            return NULL;
+        } else {
+            error_propagate(errp, conn->err);
+            conn->err = NULL;
+            if (!conn->sioc) {
+                return NULL;
+            }
+            if (conn->do_negotiation) {
+                memcpy(info, &conn->updated_info, sizeof(*info));
+                if (conn->ioc) {
+                    /* TLS channel now has own reference to parent */
+                    object_unref(OBJECT(conn->sioc));
+                    conn->sioc = NULL;
+
+                    return g_steal_pointer(&conn->ioc);
+                }
+            }
+
+            assert(!conn->ioc);
+
+            return QIO_CHANNEL(g_steal_pointer(&conn->sioc));
+        }
+    }
+
+    abort(); /* unreachable */
+}
+
+/*
+ * nbd_co_establish_connection_cancel
+ * Cancel nbd_co_establish_connection() asynchronously.
+ *
+ * Note that this function neither directly stops the thread nor closes the
+ * socket, but rather safely wakes nbd_co_establish_connection() which is
+ * sleeping in yield()
+ */
+void nbd_co_establish_connection_cancel(NBDClientConnection *conn)
+{
+    Coroutine *wait_co;
+
+    WITH_QEMU_LOCK_GUARD(&conn->mutex) {
+        wait_co = g_steal_pointer(&conn->wait_co);
+    }
+
+    if (wait_co) {
+        aio_co_wake(wait_co);
+    }
+}