Linux guest cannot perform large USB requests

[Andreas Müller]

I have a Starlight Express Trius SX-56 astrophotography camera. This camera performs image transfers as single USB bulk transfers. Due to the large sensor size, these transfers are 32MB in size. While this is larger than the default memory size for usbfs in the kernel (16MB), by writing a larger number to /sys/module/usbcore/parameters/usbfs_memory_mb, this limit can easily be extended. However, that does not make the camera work in a VirtualBox virtual machine. It turns out that the 32MB request formulated in the guest arrives as a 5MB request in the host (tested on MacOS mojave, USB packets inspected with Wireshark on MacOS host and Linux guest). The camera cannot handle this short request and locks up.