From c4583c8c394ee49ce7d5271f572abd3b000fa9e4 Mon Sep 17 00:00:00 2001 From: Paul Durrant Date: Thu, 1 Oct 2020 09:15:00 +0100 Subject: [PATCH] xen-bus: reduce scope of backend watch Currently a single watch on /local/domain/X/backend is registered by each QEMU process running in service domain X (where X is usually 0). The purpose of this watch is to ensure that QEMU is notified when the Xen toolstack creates a new device backend area. Such a backend area is specific to a single frontend area created for a specific guest domain and, since each QEMU process is also created to service a specfic guest domain, it is unnecessary and inefficient to notify all QEMU processes. Only the QEMU process associated with the same guest domain need receive the notification. This patch re-factors the watch registration code such that notifications are targetted appropriately. Reported-by: Jerome Leseinne Signed-off-by: Paul Durrant Reviewed-by: Anthony PERARD Message-Id: <20201001081500.1026-1-paul@xen.org> Signed-off-by: Anthony PERARD --- hw/xen/xen-backend.c | 11 ++++++++++ hw/xen/xen-bus.c | 40 ++++++++++++++++++++++++++++-------- include/hw/xen/xen-backend.h | 1 + include/hw/xen/xen-bus.h | 3 ++- 4 files changed, 46 insertions(+), 9 deletions(-) diff --git a/hw/xen/xen-backend.c b/hw/xen/xen-backend.c index 10199fb58d..5b0fb76eae 100644 --- a/hw/xen/xen-backend.c +++ b/hw/xen/xen-backend.c @@ -41,6 +41,12 @@ static void xen_backend_table_add(XenBackendImpl *impl) g_hash_table_insert(xen_backend_table_get(), (void *)impl->type, impl); } +static const char **xen_backend_table_keys(unsigned int *count) +{ + return (const char **)g_hash_table_get_keys_as_array( + xen_backend_table_get(), count); +} + static const XenBackendImpl *xen_backend_table_lookup(const char *type) { return g_hash_table_lookup(xen_backend_table_get(), type); @@ -70,6 +76,11 @@ void xen_backend_register(const XenBackendInfo *info) xen_backend_table_add(impl); } +const char **xen_backend_get_types(unsigned int *count) +{ + return xen_backend_table_keys(count); +} + static QLIST_HEAD(, XenBackendInstance) backend_list; static void xen_backend_list_add(XenBackendInstance *backend) diff --git a/hw/xen/xen-bus.c b/hw/xen/xen-bus.c index 9ce1c9540b..8c588920d9 100644 --- a/hw/xen/xen-bus.c +++ b/hw/xen/xen-bus.c @@ -430,7 +430,15 @@ static void xen_bus_unrealize(BusState *bus) trace_xen_bus_unrealize(); if (xenbus->backend_watch) { - xen_bus_remove_watch(xenbus, xenbus->backend_watch, NULL); + unsigned int i; + + for (i = 0; i < xenbus->backend_types; i++) { + if (xenbus->backend_watch[i]) { + xen_bus_remove_watch(xenbus, xenbus->backend_watch[i], NULL); + } + } + + g_free(xenbus->backend_watch); xenbus->backend_watch = NULL; } @@ -446,8 +454,11 @@ static void xen_bus_unrealize(BusState *bus) static void xen_bus_realize(BusState *bus, Error **errp) { + char *key = g_strdup_printf("%u", xen_domid); XenBus *xenbus = XEN_BUS(bus); unsigned int domid; + const char **type; + unsigned int i; Error *local_err = NULL; trace_xen_bus_realize(); @@ -469,19 +480,32 @@ static void xen_bus_realize(BusState *bus, Error **errp) module_call_init(MODULE_INIT_XEN_BACKEND); - xenbus->backend_watch = - xen_bus_add_watch(xenbus, "", /* domain root node */ - "backend", xen_bus_backend_changed, &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: "); + type = xen_backend_get_types(&xenbus->backend_types); + xenbus->backend_watch = g_new(XenWatch *, xenbus->backend_types); + + for (i = 0; i < xenbus->backend_types; i++) { + char *node = g_strdup_printf("backend/%s", type[i]); + + xenbus->backend_watch[i] = + xen_bus_add_watch(xenbus, node, key, xen_bus_backend_changed, + &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 '%s' enumeration watch: ", + type[i]); + } + + g_free(node); } + g_free(type); + g_free(key); return; fail: xen_bus_unrealize(bus); + g_free(key); } static void xen_bus_unplug_request(HotplugHandler *hotplug, diff --git a/include/hw/xen/xen-backend.h b/include/hw/xen/xen-backend.h index 010d712638..aac2fd454d 100644 --- a/include/hw/xen/xen-backend.h +++ b/include/hw/xen/xen-backend.h @@ -31,6 +31,7 @@ void xen_backend_set_device(XenBackendInstance *backend, XenDevice *xen_backend_get_device(XenBackendInstance *backend); void xen_backend_register(const XenBackendInfo *info); +const char **xen_backend_get_types(unsigned int *nr); void xen_backend_device_create(XenBus *xenbus, const char *type, const char *name, QDict *opts, Error **errp); diff --git a/include/hw/xen/xen-bus.h b/include/hw/xen/xen-bus.h index 3df696136f..6bdbf3ff82 100644 --- a/include/hw/xen/xen-bus.h +++ b/include/hw/xen/xen-bus.h @@ -66,7 +66,8 @@ struct XenBus { domid_t backend_id; struct xs_handle *xsh; XenWatchList *watch_list; - XenWatch *backend_watch; + unsigned int backend_types; + XenWatch **backend_watch; QLIST_HEAD(, XenDevice) inactive_devices; };