USBDevice's realize method usb_qdev_realize() automatically creates a
usb-hub when only one port is left. Creating devices in realize
methods is questionable, but works.
If usb-hub creation fails, an error is reported to stderr, but the
failure is otherwise ignored. We then create the actual device using
the last port, which may well succeed.
Example:
$ qemu -nodefaults -S -display none -machine usb=on -monitor stdio
QEMU 2.2.50 monitor - type 'help' for more information
(qemu) device_add usb-mouse
[Repeat 36 times]
(qemu) info usb
Device 0.0, Port 1, Speed 12 Mb/s, Product QEMU USB Mouse
Device 0.0, Port 2, Speed 12 Mb/s, Product QEMU USB Hub
Device 0.0, Port 2.1, Speed 12 Mb/s, Product QEMU USB Mouse
[More mice and hubs omitted...]
Device 0.0, Port 2.8.8.8.8.7, Speed 12 Mb/s, Product QEMU USB Mouse
(qemu) device_add usb-mouse
usb hub chain too deep
Failed to initialize USB device 'usb-hub'
(qemu) info usb
[...]
Device 0.0, Port 2.8.8.8.8.7, Speed 12 Mb/s, Product QEMU USB Mouse
Device 0.0, Port 2.8.8.8.8.8, Speed 12 Mb/s, Product QEMU USB Mouse
Despite the "Failed" message, the command actually succeeded.
In QMP, it's worse. When adding the 37th mouse via QMP, the command
fails with
{"error": {"class": "GenericError", "desc": "usb hub chain too deep"}}
Additionally, "Failed to initialize USB device 'usb-hub'" is reported
on stderr. Despite the command failure, the device was created. This
is wrong.
Fix by avoiding qdev_init() for usb-hub creation, so we can ignore
errors cleanly.
Signed-off-by: Markus Armbruster <armbru@redhat.com>
Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
bd8b92d5c8