[17/21] qdev: Add a hook for a bus to device if it can add devices

From: Benjamin Herrenschmidt <benh@kernel.crashing.org>

This allows a bus class to tell whether a given bus has room for
any new device. max_dev isn't sufficient as the rules can depend
on some arguments or can differ between instances of a bus. This
will be used by PCI in subsequent patches

Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
[clg: updated for qemu-2.9 ]
Signed-off-by: Cédric Le Goater <clg@kaod.org>
---
 include/hw/qdev-core.h |  1 +
 qdev-monitor.c         | 14 +++++++++-----
 2 files changed, 10 insertions(+), 5 deletions(-)

On Wed, Apr 05, 2017 at 02:41:42PM +0200, Cédric Le Goater wrote:
> From: Benjamin Herrenschmidt <benh@kernel.crashing.org>
> 
> This allows a bus class to tell whether a given bus has room for
> any new device. max_dev isn't sufficient as the rules can depend
> on some arguments or can differ between instances of a bus. This
> will be used by PCI in subsequent patches
> 
> Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
> [clg: updated for qemu-2.9 ]
> Signed-off-by: Cédric Le Goater <clg@kaod.org>
> ---
>  include/hw/qdev-core.h |  1 +
>  qdev-monitor.c         | 14 +++++++++-----
>  2 files changed, 10 insertions(+), 5 deletions(-)
> 
> diff --git a/include/hw/qdev-core.h b/include/hw/qdev-core.h
> index b44b47676576..867662ba5352 100644
> --- a/include/hw/qdev-core.h
> +++ b/include/hw/qdev-core.h
> @@ -201,6 +201,7 @@ struct BusClass {
>       */
>      char *(*get_fw_dev_path)(DeviceState *dev);
>      void (*reset)(BusState *bus);
> +    bool (*can_add_device)(BusState *bus, QemuOpts *opts);
>      BusRealize realize;
>      BusUnrealize unrealize;
>  
> diff --git a/qdev-monitor.c b/qdev-monitor.c
> index 5f2fcdfc4551..c6eca929c473 100644
> --- a/qdev-monitor.c
> +++ b/qdev-monitor.c
> @@ -415,7 +415,7 @@ static inline bool qbus_is_full(BusState *bus)
>   * Return the bus if found, else %NULL.
>   */
>  static BusState *qbus_find_recursive(BusState *bus, const char *name,
> -                                     const char *bus_typename)
> +                                     const char *bus_typename, QemuOpts *opts)
>  {
>      BusChild *kid;
>      BusState *pick, *child, *ret;
> @@ -429,7 +429,10 @@ static BusState *qbus_find_recursive(BusState *bus, const char *name,
>      }
>  
>      if (match && !qbus_is_full(bus)) {
> -        return bus;             /* root matches and isn't full */
> +        BusClass *bc = BUS_GET_CLASS(bus);
> +        if (!bc->can_add_device || bc->can_add_device(bus, opts)) {
> +            return bus;             /* root matches and isn't full */

Seems like qbus_is_full() should be changed to use the can_add_device
hook, rather than changing the caller here.  Essentially the current
max_devs implementation would become the fallback if the bus doesn't
define a bus specific test.

> +        }
>      }
>  
>      pick = match ? bus : NULL;
> @@ -437,7 +440,7 @@ static BusState *qbus_find_recursive(BusState *bus, const char *name,
>      QTAILQ_FOREACH(kid, &bus->children, sibling) {
>          DeviceState *dev = kid->child;
>          QLIST_FOREACH(child, &dev->child_bus, sibling) {
> -            ret = qbus_find_recursive(child, name, bus_typename);
> +            ret = qbus_find_recursive(child, name, bus_typename, opts);
>              if (ret && !qbus_is_full(ret)) {
>                  return ret;     /* a descendant matches and isn't full */
>              }
> @@ -467,7 +470,7 @@ static BusState *qbus_find(const char *path, Error **errp)
>              assert(!path[0]);
>              elem[0] = len = 0;
>          }
> -        bus = qbus_find_recursive(sysbus_get_default(), elem, NULL);
> +        bus = qbus_find_recursive(sysbus_get_default(), elem, NULL, NULL);
>          if (!bus) {
>              error_setg(errp, "Bus '%s' not found", elem);
>              return NULL;
> @@ -591,7 +594,8 @@ DeviceState *qdev_device_add(QemuOpts *opts, Error **errp)
>              return NULL;
>          }
>      } else if (dc->bus_type != NULL) {
> -        bus = qbus_find_recursive(sysbus_get_default(), NULL, dc->bus_type);
> +        bus = qbus_find_recursive(sysbus_get_default(), NULL, dc->bus_type,
> +                                  opts);
>          if (!bus || qbus_is_full(bus)) {
>              error_setg(errp, "No '%s' bus found for device '%s'",
>                         dc->bus_type, driver);