trace_usb_port_attach prints junk data

Running qemu with tracing (-D ~/qemu_trace -d trace:\*) will result in a trace file with unprintable characters.

example: usb_port_attach bus 0, port 1, devspeed <90>l<DB>.<D8>U, portspeed full+high

The problem is in hw/usb/bus.c usb_mask_to_str. If speedmask doesn't match any of the defined speed nothing is written to *dest and uninitialized data is printed to the log.

This happens with a real usb device that is forwarded into the machine.

My qemu version is 2.6.0 but it looks like the problem exists in latest git also.

This bug is still present in current head of git; I've just sent a patch: http://patchwork.ozlabs.org/patch/1068196/


Patch has been included here:
https://git.qemu.org/?p=qemu.git;a=commitdiff;h=5189e30b146ab39f9d