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xen-bus: reduce scope of backend watch

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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 <jerome.leseinne@gmail.com>
Signed-off-by: Paul Durrant <pdurrant@amazon.com>
Reviewed-by: Anthony PERARD <anthony.perard@citrix.com>
Message-Id: <20201001081500.1026-1-paul@xen.org>
Signed-off-by: Anthony PERARD <anthony.perard@citrix.com>
This commit is contained in:
Paul Durrant 2020-10-01 09:15:00 +01:00 • committed by Anthony PERARD
parent 2211118a2a
commit c4583c8c39
4 changed files with 46 additions and 9 deletions
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40
hw/xen/xen-bus.c
View file

@ -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,