xen: add a mechanism to automatically create XenDevice-s...

...that maintains compatibility with existing Xen toolstacks.

Xen toolstacks instantiate PV backends by simply writing information into
xenstore and expecting a backend implementation to be watching for this.

This patch adds a new 'xen-backend' module to allow individual XenDevice
implementations to register create and destroy functions. The creator
will be called when a tool-stack instantiates a new backend in this way,
and the destructor will then be called after the resulting XenDevice
object is unrealized.

To support this it is also necessary to add new watchers into the XenBus
implementation to handle enumeration of new backends and also destruction
of XenDevice-s when the toolstack sets the backend 'online' key to 0.

NOTE: This patch only adds the framework. A subsequent patch will add a
      creator function for xen-block devices.

Signed-off-by: Paul Durrant <paul.durrant@citrix.com>
Reviewed-by: Anthony Perard <anthony.perard@citrix.com>
Signed-off-by: Anthony PERARD <anthony.perard@citrix.com>

4 files changed, 332 insertions, 2 deletions

diff --git a/hw/xen/Makefile.objs b/hw/xen/Makefile.objs
index 77c0868..84df60a 100644
--- a/hw/xen/Makefile.objs
+++ b/hw/xen/Makefile.objs
@@ -1,5 +1,5 @@
 # xen backend driver support
-common-obj-$(CONFIG_XEN) += xen-legacy-backend.o xen_devconfig.o xen_pvdev.o xen-common.o xen-bus.o xen-bus-helper.o
+common-obj-$(CONFIG_XEN) += xen-legacy-backend.o xen_devconfig.o xen_pvdev.o xen-common.o xen-bus.o xen-bus-helper.o xen-backend.o
 
 obj-$(CONFIG_XEN_PCI_PASSTHROUGH) += xen-host-pci-device.o
 obj-$(CONFIG_XEN_PCI_PASSTHROUGH) += xen_pt.o xen_pt_config_init.o xen_pt_graphics.o xen_pt_msi.o
diff --git a/hw/xen/trace-events b/hw/xen/trace-events
index d4651bd..f694462 100644
--- a/hw/xen/trace-events
+++ b/hw/xen/trace-events
@@ -16,6 +16,9 @@ xen_domid_restrict(int err) "err: %u"
 # include/hw/xen/xen-bus.c
 xen_bus_realize(void) ""
 xen_bus_unrealize(void) ""
+xen_bus_enumerate(void) ""
+xen_bus_type_enumerate(const char *type) "type: %s"
+xen_bus_backend_create(const char *type, const char *path) "type: %s path: %s"
 xen_bus_add_watch(const char *node, const char *key, char *token) "node: %s key: %s token: %s"
 xen_bus_remove_watch(const char *node, const char *key, char *token) "node: %s key: %s token: %s"
 xen_bus_watch(const char *token) "token: %s"
diff --git a/hw/xen/xen-backend.c b/hw/xen/xen-backend.c
new file mode 100644
index 0000000..da065f8
--- /dev/null
+++ b/hw/xen/xen-backend.c
@@ -0,0 +1,165 @@
+/*
+ * Copyright (c) 2018  Citrix Systems Inc.
+ *
+ * This work is licensed under the terms of the GNU GPL, version 2 or later.
+ * See the COPYING file in the top-level directory.
+ */
+
+#include "qemu/osdep.h"
+#include "qemu/error-report.h"
+#include "qapi/error.h"
+#include "hw/xen/xen-backend.h"
+#include "hw/xen/xen-bus.h"
+
+typedef struct XenBackendImpl {
+    const char *type;
+    XenBackendDeviceCreate create;
+    XenBackendDeviceDestroy destroy;
+} XenBackendImpl;
+
+struct XenBackendInstance {
+    QLIST_ENTRY(XenBackendInstance) entry;
+    const XenBackendImpl *impl;
+    XenBus *xenbus;
+    char *name;
+    XenDevice *xendev;
+};
+
+static GHashTable *xen_backend_table_get(void)
+{
+    static GHashTable *table;
+
+    if (table == NULL) {
+        table = g_hash_table_new(g_str_hash, g_str_equal);
+    }
+
+    return table;
+}
+
+static void xen_backend_table_add(XenBackendImpl *impl)
+{
+    g_hash_table_insert(xen_backend_table_get(), (void *)impl->type, impl);
+}
+
+static const XenBackendImpl *xen_backend_table_lookup(const char *type)
+{
+    return g_hash_table_lookup(xen_backend_table_get(), type);
+}
+
+void xen_backend_register(const XenBackendInfo *info)
+{
+    XenBackendImpl *impl = g_new0(XenBackendImpl, 1);
+
+    g_assert(info->type);
+
+    if (xen_backend_table_lookup(info->type)) {
+        error_report("attempt to register duplicate Xen backend type '%s'",
+                     info->type);
+        abort();
+    }
+
+    if (!info->create) {
+        error_report("backend type '%s' has no creator", info->type);
+        abort();
+    }
+
+    impl->type = info->type;
+    impl->create = info->create;
+    impl->destroy = info->destroy;
+
+    xen_backend_table_add(impl);
+}
+
+static QLIST_HEAD(, XenBackendInstance) backend_list;
+
+static void xen_backend_list_add(XenBackendInstance *backend)
+{
+    QLIST_INSERT_HEAD(&backend_list, backend, entry);
+}
+
+static XenBackendInstance *xen_backend_list_find(XenDevice *xendev)
+{
+    XenBackendInstance *backend;
+
+    QLIST_FOREACH(backend, &backend_list, entry) {
+        if (backend->xendev == xendev) {
+            return backend;
+        }
+    }
+
+    return NULL;
+}
+
+static void xen_backend_list_remove(XenBackendInstance *backend)
+{
+    QLIST_REMOVE(backend, entry);
+}
+
+void xen_backend_device_create(XenBus *xenbus, const char *type,
+                               const char *name, QDict *opts, Error **errp)
+{
+    const XenBackendImpl *impl = xen_backend_table_lookup(type);
+    XenBackendInstance *backend;
+    Error *local_error = NULL;
+
+    if (!impl) {
+        return;
+    }
+
+    backend = g_new0(XenBackendInstance, 1);
+    backend->xenbus = xenbus;
+    backend->name = g_strdup(name);
+
+    impl->create(backend, opts, &local_error);
+    if (local_error) {
+        error_propagate(errp, local_error);
+        g_free(backend->name);
+        g_free(backend);
+        return;
+    }
+
+    backend->impl = impl;
+    xen_backend_list_add(backend);
+}
+
+XenBus *xen_backend_get_bus(XenBackendInstance *backend)
+{
+    return backend->xenbus;
+}
+
+const char *xen_backend_get_name(XenBackendInstance *backend)
+{
+    return backend->name;
+}
+
+void xen_backend_set_device(XenBackendInstance *backend,
+                            XenDevice *xendev)
+{
+    g_assert(!backend->xendev);
+    backend->xendev = xendev;
+}
+
+XenDevice *xen_backend_get_device(XenBackendInstance *backend)
+{
+    return backend->xendev;
+}
+
+
+bool xen_backend_try_device_destroy(XenDevice *xendev, Error **errp)
+{
+    XenBackendInstance *backend = xen_backend_list_find(xendev);
+    const XenBackendImpl *impl;
+
+    if (!backend) {
+        return false;
+    }
+
+    impl = backend->impl;
+    impl->destroy(backend, errp);
+
+    xen_backend_list_remove(backend);
+    g_free(backend->name);
+    g_free(backend);
+
+    return true;
+}
diff --git a/hw/xen/xen-bus.c b/hw/xen/xen-bus.c
index 6861ce1..3aeccec 100644
--- a/hw/xen/xen-bus.c
+++ b/hw/xen/xen-bus.c
@@ -11,10 +11,12 @@
 #include "hw/hw.h"
 #include "hw/sysbus.h"
 #include "hw/xen/xen.h"
+#include "hw/xen/xen-backend.h"
 #include "hw/xen/xen-bus.h"
 #include "hw/xen/xen-bus-helper.h"
 #include "monitor/monitor.h"
 #include "qapi/error.h"
+#include "qapi/qmp/qdict.h"
 #include "sysemu/sysemu.h"
 #include "trace.h"
 
@@ -190,12 +192,151 @@ static void xen_bus_remove_watch(XenBus *xenbus, XenWatch *watch,
     free_watch(watch);
 }
 
+static void xen_bus_backend_create(XenBus *xenbus, const char *type,
+                                   const char *name, char *path,
+                                   Error **errp)
+{
+    xs_transaction_t tid;
+    char **key;
+    QDict *opts;
+    unsigned int i, n;
+    Error *local_err = NULL;
+
+    trace_xen_bus_backend_create(type, path);
+
+again:
+    tid = xs_transaction_start(xenbus->xsh);
+    if (tid == XBT_NULL) {
+        error_setg(errp, "failed xs_transaction_start");
+        return;
+    }
+
+    key = xs_directory(xenbus->xsh, tid, path, &n);
+    if (!key) {
+        if (!xs_transaction_end(xenbus->xsh, tid, true)) {
+            error_setg_errno(errp, errno, "failed xs_transaction_end");
+        }
+        return;
+    }
+
+    opts = qdict_new();
+    for (i = 0; i < n; i++) {
+        char *val;
+
+        /*
+         * Assume anything found in the xenstore backend area, other than
+         * the keys created for a generic XenDevice, are parameters
+         * to be used to configure the backend.
+         */
+        if (!strcmp(key[i], "state") ||
+            !strcmp(key[i], "online") ||
+            !strcmp(key[i], "frontend") ||
+            !strcmp(key[i], "frontend-id") ||
+            !strcmp(key[i], "hotplug-status"))
+            continue;
+
+        if (xs_node_scanf(xenbus->xsh, tid, path, key[i], NULL, "%ms",
+                          &val) == 1) {
+            qdict_put_str(opts, key[i], val);
+            free(val);
+        }
+    }
+
+    free(key);
+
+    if (!xs_transaction_end(xenbus->xsh, tid, false)) {
+        qobject_unref(opts);
+
+        if (errno == EAGAIN) {
+            goto again;
+        }
+
+        error_setg_errno(errp, errno, "failed xs_transaction_end");
+        return;
+    }
+
+    xen_backend_device_create(xenbus, type, name, opts, &local_err);
+    qobject_unref(opts);
+
+    if (local_err) {
+        error_propagate_prepend(errp, local_err,
+                                "failed to create '%s' device '%s': ",
+                                type, name);
+    }
+}
+
+static void xen_bus_type_enumerate(XenBus *xenbus, const char *type)
+{
+    char *domain_path = g_strdup_printf("backend/%s/%u", type, xen_domid);
+    char **backend;
+    unsigned int i, n;
+
+    trace_xen_bus_type_enumerate(type);
+
+    backend = xs_directory(xenbus->xsh, XBT_NULL, domain_path, &n);
+    if (!backend) {
+        goto out;
+    }
+
+    for (i = 0; i < n; i++) {
+        char *backend_path = g_strdup_printf("%s/%s", domain_path,
+                                             backend[i]);
+        enum xenbus_state backend_state;
+
+        if (xs_node_scanf(xenbus->xsh, XBT_NULL, backend_path, "state",
+                          NULL, "%u", &backend_state) != 1)
+            backend_state = XenbusStateUnknown;
+
+        if (backend_state == XenbusStateInitialising) {
+            Error *local_err = NULL;
+
+            xen_bus_backend_create(xenbus, type, backend[i], backend_path,
+                                   &local_err);
+            if (local_err) {
+                error_report_err(local_err);
+            }
+        }
+
+        g_free(backend_path);
+    }
+
+    free(backend);
+
+out:
+    g_free(domain_path);
+}
+
+static void xen_bus_enumerate(void *opaque)
+{
+    XenBus *xenbus = opaque;
+    char **type;
+    unsigned int i, n;
+
+    trace_xen_bus_enumerate();
+
+    type = xs_directory(xenbus->xsh, XBT_NULL, "backend", &n);
+    if (!type) {
+        return;
+    }
+
+    for (i = 0; i < n; i++) {
+        xen_bus_type_enumerate(xenbus, type[i]);
+    }
+
+    free(type);
+}
+
 static void xen_bus_unrealize(BusState *bus, Error **errp)
 {
     XenBus *xenbus = XEN_BUS(bus);
 
     trace_xen_bus_unrealize();
 
+    if (xenbus->backend_watch) {
+        xen_bus_remove_watch(xenbus, xenbus->backend_watch, NULL);
+        xenbus->backend_watch = NULL;
+    }
+
     if (!xenbus->xsh) {
         return;
     }
@@ -231,6 +372,7 @@ static void xen_bus_realize(BusState *bus, Error **errp)
 {
     XenBus *xenbus = XEN_BUS(bus);
     unsigned int domid;
+    Error *local_err = NULL;
 
     trace_xen_bus_realize();
 
@@ -250,6 +392,18 @@ static void xen_bus_realize(BusState *bus, Error **errp)
     notifier_list_init(&xenbus->watch_notifiers);
     qemu_set_fd_handler(xs_fileno(xenbus->xsh), xen_bus_watch, NULL,
                         xenbus);
+
+    module_call_init(MODULE_INIT_XEN_BACKEND);
+
+    xenbus->backend_watch =
+        xen_bus_add_watch(xenbus, "", /* domain root node */
+                          "backend", xen_bus_enumerate, xenbus, &local_err);
+    if (local_err) {
+        /* This need not be treated as a hard error so don't propagate */
+        error_reportf_err(local_err,
+                          "failed to set up enumeration watch: ");
+    }
+
     return;
 
 fail:
@@ -407,7 +561,15 @@ static void xen_device_backend_changed(void *opaque)
                 xendev->backend_state == XenbusStateInitialising ||
                 xendev->backend_state == XenbusStateInitWait ||
                 xendev->backend_state == XenbusStateUnknown)) {
-        object_unparent(OBJECT(xendev));
+        Error *local_err = NULL;
+
+        if (!xen_backend_try_device_destroy(xendev, &local_err)) {
+            object_unparent(OBJECT(xendev));
+        }
+
+        if (local_err) {
+            error_report_err(local_err);
+        }
     }
 }