hw/ide: Fix crash when plugging a piix3-ide device into the x-remote machine

QEMU currently crashes when the user tries to do something like:

 qemu-system-x86_64 -M x-remote -device piix3-ide

This happens because the "isabus" variable is not initialized with
the x-remote machine yet. Add a proper check for this condition
and propagate the error to the caller, so we can fail there gracefully.

Message-Id: <20210416125256.2039734-1-thuth@redhat.com>
Reviewed-by: John Snow <jsnow@redhat.com>
Signed-off-by: Thomas Huth <thuth@redhat.com>

1 files changed, 8 insertions, 5 deletions

diff --git a/include/hw/isa/isa.h b/include/hw/isa/isa.h
index ddaae89a85..d4417b34b6 100644
--- a/include/hw/isa/isa.h
+++ b/include/hw/isa/isa.h
@@ -132,12 +132,15 @@ void isa_register_ioport(ISADevice *dev, MemoryRegion *io, uint16_t start);
  * @portio: the ports, sorted by offset.
  * @opaque: passed into the portio callbacks.
  * @name: passed into memory_region_init_io.
+ *
+ * Returns: 0 on success, negative error code otherwise (e.g. if the
+ *          ISA bus is not available)
  */
-void isa_register_portio_list(ISADevice *dev,
-                              PortioList *piolist,
-                              uint16_t start,
-                              const MemoryRegionPortio *portio,
-                              void *opaque, const char *name);
+int isa_register_portio_list(ISADevice *dev,
+                             PortioList *piolist,
+                             uint16_t start,
+                             const MemoryRegionPortio *portio,
+                             void *opaque, const char *name);
 
 static inline ISABus *isa_bus_from_device(ISADevice *d)
 {