| Message ID | 20220919231720.163121-4-shentey@gmail.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | Deprecate sysbus_get_default() and get_system_memory() et. al | expand |
On 20/9/22 01:17, Bernhard Beschow wrote: > In QEMU, a machine and the main_system_bus always go togehter. Usually > the bus is part of the machine which suggsts to host it there. "together", "suggests" > Since tere is already a current_machine singleton, all code that > accesses the main_system_bus can be changed (behind the scenes) to go > through current_machine. This resolves a singleton. Futhermore, by "Furthermore" > reifying it in code, the every-machine-has-exactly-one-main-system-bus > relationship becomes very obvious. > > Note that the main_system_bus attribute is a value rather than a > pointer. This trades pointer dereferences for pointer arithmetic. The > idea is to reduce cache misses - a rule of thumb says that > every pointer dereference causes a cache miss while arithmetic is > basically free. > > Signed-off-by: Bernhard Beschow <shentey@gmail.com> > --- > hw/core/bus.c | 5 ++++- > hw/core/machine.c | 3 +++ > hw/core/sysbus.c | 22 +++++----------------- > include/hw/boards.h | 1 + > 4 files changed, 13 insertions(+), 18 deletions(-) > diff --git a/include/hw/boards.h b/include/hw/boards.h > index 311ed17e18..7af940102d 100644 > --- a/include/hw/boards.h > +++ b/include/hw/boards.h Likely missing the BusState declaration: #include "hw/qdev-core.h" > @@ -346,6 +346,7 @@ struct MachineState { > */ > MemoryRegion *ram; > DeviceMemoryState *device_memory; > + BusState main_system_bus; > > ram_addr_t ram_size; > ram_addr_t maxram_size;
diff --git a/hw/core/bus.c b/hw/core/bus.c index c7831b5293..e3e807946c 100644 --- a/hw/core/bus.c +++ b/hw/core/bus.c @@ -129,9 +129,12 @@ static void qbus_init_internal(BusState *bus, DeviceState *parent, bus->parent->num_child_bus++; object_property_add_child(OBJECT(bus->parent), bus->name, OBJECT(bus)); object_unref(OBJECT(bus)); + + /* The only bus without a parent is the main system bus */ + assert(sysbus_get_default()); } else { /* The only bus without a parent is the main system bus */ - assert(bus == sysbus_get_default()); + assert(!sysbus_get_default()); } } diff --git a/hw/core/machine.c b/hw/core/machine.c index aa520e74a8..ebd3e0ff08 100644 --- a/hw/core/machine.c +++ b/hw/core/machine.c @@ -1097,6 +1097,9 @@ static void machine_initfn(Object *obj) ms->smp.threads = 1; machine_copy_boot_config(ms, &(BootConfiguration){ 0 }); + + qbus_init(&ms->main_system_bus, sizeof(ms->main_system_bus), + TYPE_SYSTEM_BUS, NULL, "main-system-bus"); } static void machine_finalize(Object *obj) diff --git a/hw/core/sysbus.c b/hw/core/sysbus.c index 05c1da3d31..16a9b4d7a0 100644 --- a/hw/core/sysbus.c +++ b/hw/core/sysbus.c @@ -20,6 +20,7 @@ #include "qemu/osdep.h" #include "qapi/error.h" #include "qemu/module.h" +#include "hw/boards.h" #include "hw/sysbus.h" #include "monitor/monitor.h" #include "exec/address-spaces.h" @@ -336,26 +337,13 @@ static const TypeInfo sysbus_device_type_info = { .class_init = sysbus_device_class_init, }; -static BusState *main_system_bus; - -static void main_system_bus_create(void) -{ - /* - * assign main_system_bus before qbus_init() - * in order to make "if (bus != sysbus_get_default())" work - */ - main_system_bus = g_malloc0(system_bus_info.instance_size); - qbus_init(main_system_bus, system_bus_info.instance_size, - TYPE_SYSTEM_BUS, NULL, "main-system-bus"); - OBJECT(main_system_bus)->free = g_free; -} - BusState *sysbus_get_default(void) { - if (!main_system_bus) { - main_system_bus_create(); + if (!current_machine) { + return NULL; } - return main_system_bus; + + return ¤t_machine->main_system_bus; } static void sysbus_register_types(void) diff --git a/include/hw/boards.h b/include/hw/boards.h index 311ed17e18..7af940102d 100644 --- a/include/hw/boards.h +++ b/include/hw/boards.h @@ -346,6 +346,7 @@ struct MachineState { */ MemoryRegion *ram; DeviceMemoryState *device_memory; + BusState main_system_bus; ram_addr_t ram_size; ram_addr_t maxram_size;
In QEMU, a machine and the main_system_bus always go togehter. Usually the bus is part of the machine which suggsts to host it there. Since tere is already a current_machine singleton, all code that accesses the main_system_bus can be changed (behind the scenes) to go through current_machine. This resolves a singleton. Futhermore, by reifying it in code, the every-machine-has-exactly-one-main-system-bus relationship becomes very obvious. Note that the main_system_bus attribute is a value rather than a pointer. This trades pointer dereferences for pointer arithmetic. The idea is to reduce cache misses - a rule of thumb says that every pointer dereference causes a cache miss while arithmetic is basically free. Signed-off-by: Bernhard Beschow <shentey@gmail.com> --- hw/core/bus.c | 5 ++++- hw/core/machine.c | 3 +++ hw/core/sysbus.c | 22 +++++----------------- include/hw/boards.h | 1 + 4 files changed, 13 insertions(+), 18 deletions(-)