qemu/hw/xen/xen-backend.c
David Woodhouse eb6ae7a682 hw/xen: do not repeatedly try to create a failing backend device
If xen_backend_device_create() fails to instantiate a device, the XenBus
code will just keep trying over and over again each time the bus is
re-enumerated, as long as the backend appears online and in
XenbusStateInitialising.

The only thing which prevents the XenBus code from recreating duplicates
of devices which already exist, is the fact that xen_device_realize()
sets the backend state to XenbusStateInitWait. If the attempt to create
the device doesn't get *that* far, that's when it will keep getting
retried.

My first thought was to handle errors by setting the backend state to
XenbusStateClosed, but that doesn't work for XenConsole which wants to
*ignore* any device of type != "ioemu" completely.

So, make xen_backend_device_create() *keep* the XenBackendInstance for a
failed device, and provide a new xen_backend_exists() function to allow
xen_bus_type_enumerate() to check whether one already exists before
creating a new one.

Signed-off-by: David Woodhouse <dwmw@amazon.co.uk>
Reviewed-by: Paul Durrant <paul@xen.org>
2023-11-07 08:54:20 +00:00

191 lines
4.2 KiB
C

/*
* 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 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);
}
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);
}
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)
{
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;
}
bool xen_backend_exists(const char *type, const char *name)
{
const XenBackendImpl *impl = xen_backend_table_lookup(type);
XenBackendInstance *backend;
if (!impl) {
return false;
}
QLIST_FOREACH(backend, &backend_list, entry) {
if (backend->impl == impl && !strcmp(backend->name, name)) {
return true;
}
}
return false;
}
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)
{
ERRP_GUARD();
const XenBackendImpl *impl = xen_backend_table_lookup(type);
XenBackendInstance *backend;
if (!impl) {
return;
}
backend = g_new0(XenBackendInstance, 1);
backend->xenbus = xenbus;
backend->name = g_strdup(name);
impl->create(backend, opts, errp);
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;
if (backend->xendev) {
impl->destroy(backend, errp);
}
xen_backend_list_remove(backend);
g_free(backend->name);
g_free(backend);
return true;
}