Re: [PATCH 05/11] qdev: Make DeviceState.id independent of QemuOpts

[Kevin Wolf <kwolf@redhat.com>]

Am 24.09.2021 um 16:02 hat Vladimir Sementsov-Ogievskiy geschrieben:
> 24.09.2021 12:04, Kevin Wolf wrote:
> > DeviceState.id is a pointer to a string that is stored in the QemuOpts
> > object DeviceState.opts and freed together with it. We want to create
> > devices without going through QemuOpts in the future, so make this a
> > separately allocated string.
> > 
> > Signed-off-by: Kevin Wolf <kwolf@redhat.com>
> 
> Interesting that in hw/xen/xen-legacy-backend.c
> g_strdup_printf-allocated id is passed to qdev_set_id prior this
> patch. So, the patch seems to fix that small leak. Worth to mention?

Ok, I can mention it explicitly.

> > ---
> >   include/hw/qdev-core.h              | 2 +-
> >   include/monitor/qdev.h              | 2 +-
> >   hw/arm/virt.c                       | 2 +-
> >   hw/core/qdev.c                      | 1 +
> >   hw/pci-bridge/pci_expander_bridge.c | 2 +-
> >   hw/ppc/e500.c                       | 2 +-
> >   softmmu/qdev-monitor.c              | 5 +++--
> >   7 files changed, 9 insertions(+), 7 deletions(-)
> > 
> > diff --git a/include/hw/qdev-core.h b/include/hw/qdev-core.h
> > index 34c8a7506a..1857d9698e 100644
> > --- a/include/hw/qdev-core.h
> > +++ b/include/hw/qdev-core.h
> > @@ -176,7 +176,7 @@ struct DeviceState {
> >       Object parent_obj;
> >       /*< public >*/
> > -    const char *id;
> > +    char *id;
> >       char *canonical_path;
> >       bool realized;
> >       bool pending_deleted_event;
> > diff --git a/include/monitor/qdev.h b/include/monitor/qdev.h
> > index eaa947d73a..389287eb44 100644
> > --- a/include/monitor/qdev.h
> > +++ b/include/monitor/qdev.h
> > @@ -9,6 +9,6 @@ void qmp_device_add(QDict *qdict, QObject **ret_data, Error **errp);
> >   int qdev_device_help(QemuOpts *opts);
> >   DeviceState *qdev_device_add(QemuOpts *opts, Error **errp);
> > -void qdev_set_id(DeviceState *dev, const char *id);
> > +void qdev_set_id(DeviceState *dev, char *id);
> >   #endif
> > diff --git a/hw/arm/virt.c b/hw/arm/virt.c
> > index 1d59f0e59f..f933d48d3b 100644
> > --- a/hw/arm/virt.c
> > +++ b/hw/arm/virt.c
> > @@ -1459,7 +1459,7 @@ static void create_platform_bus(VirtMachineState *vms)
> >       MemoryRegion *sysmem = get_system_memory();
> >       dev = qdev_new(TYPE_PLATFORM_BUS_DEVICE);
> > -    dev->id = TYPE_PLATFORM_BUS_DEVICE;
> > +    dev->id = g_strdup(TYPE_PLATFORM_BUS_DEVICE);
> >       qdev_prop_set_uint32(dev, "num_irqs", PLATFORM_BUS_NUM_IRQS);
> >       qdev_prop_set_uint32(dev, "mmio_size", vms->memmap[VIRT_PLATFORM_BUS].size);
> >       sysbus_realize_and_unref(SYS_BUS_DEVICE(dev), &error_fatal);
> > diff --git a/hw/core/qdev.c b/hw/core/qdev.c
> > index cefc5eaa0a..d918b50a1d 100644
> > --- a/hw/core/qdev.c
> > +++ b/hw/core/qdev.c
> > @@ -956,6 +956,7 @@ static void device_finalize(Object *obj)
> >       }
> >       qemu_opts_del(dev->opts);
> > +    g_free(dev->id);
> >   }
> >   static void device_class_base_init(ObjectClass *class, void *data)
> > diff --git a/hw/pci-bridge/pci_expander_bridge.c b/hw/pci-bridge/pci_expander_bridge.c
> > index 7112dc3062..10e6e7c2ab 100644
> > --- a/hw/pci-bridge/pci_expander_bridge.c
> > +++ b/hw/pci-bridge/pci_expander_bridge.c
> > @@ -245,7 +245,7 @@ static void pxb_dev_realize_common(PCIDevice *dev, bool pcie, Error **errp)
> >       } else {
> >           bus = pci_root_bus_new(ds, "pxb-internal", NULL, NULL, 0, TYPE_PXB_BUS);
> >           bds = qdev_new("pci-bridge");
> > -        bds->id = dev_name;
> > +        bds->id = g_strdup(dev_name);
> >           qdev_prop_set_uint8(bds, PCI_BRIDGE_DEV_PROP_CHASSIS_NR, pxb->bus_nr);
> >           qdev_prop_set_bit(bds, PCI_BRIDGE_DEV_PROP_SHPC, false);
> >       }
> > diff --git a/hw/ppc/e500.c b/hw/ppc/e500.c
> > index 95451414dd..960e7efcd3 100644
> > --- a/hw/ppc/e500.c
> > +++ b/hw/ppc/e500.c
> > @@ -1006,7 +1006,7 @@ void ppce500_init(MachineState *machine)
> >       /* Platform Bus Device */
> >       if (pmc->has_platform_bus) {
> >           dev = qdev_new(TYPE_PLATFORM_BUS_DEVICE);
> > -        dev->id = TYPE_PLATFORM_BUS_DEVICE;
> > +        dev->id = g_strdup(TYPE_PLATFORM_BUS_DEVICE);
> >           qdev_prop_set_uint32(dev, "num_irqs", pmc->platform_bus_num_irqs);
> >           qdev_prop_set_uint32(dev, "mmio_size", pmc->platform_bus_size);
> >           sysbus_realize_and_unref(SYS_BUS_DEVICE(dev), &error_fatal);
> > diff --git a/softmmu/qdev-monitor.c b/softmmu/qdev-monitor.c
> > index 034b999401..1207e57a46 100644
> > --- a/softmmu/qdev-monitor.c
> > +++ b/softmmu/qdev-monitor.c
> > @@ -592,7 +592,8 @@ static BusState *qbus_find(const char *path, Error **errp)
> >       return bus;
> >   }
> > -void qdev_set_id(DeviceState *dev, const char *id)
> > +/* Takes ownership of @id, will be freed when deleting the device */
> > +void qdev_set_id(DeviceState *dev, char *id)
> >   {
> >       if (id) {
> >           dev->id = id;
> > @@ -690,7 +691,7 @@ DeviceState *qdev_device_add(QemuOpts *opts, Error **errp)
> >           }
> >       }
> > -    qdev_set_id(dev, qemu_opts_id(opts));
> > +    qdev_set_id(dev, g_strdup(qemu_opts_id(opts)));
> >       /* set properties */
> >       if (qemu_opt_foreach(opts, set_property, dev, errp)) {
> > 
> 
> In hw/pci/pci_bridge.c
> 
> we do
> 
>    br->bus_name = dev->qdev.id
> 
> It seems bad, as we now stole dynamic pointer, that may be freed later.

If it's bad now, it was as bad before because previously it was just a
pointer stolen from the QemuOpts that is freed in the same function as
dev->id after this patch.

I think the code is correct (it's just another field of the same device,
the real bus name is just a copy of it, and the bus can't outlive the
device that owns it anyway), but it might be bad style.

Kevin