[[!toc levels=2]] # Rationale For [[automated testing|todo/automated_builds_and_tests]] purposes, we need to use removable USB mass storage devices, e.g. to test USB-only features such as the USB installer or persistence. On a headless test server in a datacenter, one does not want to rely on a set of physical USB sticks being plugged in. Therefore, these USB mass storage devices must be emulated in software, and should probably use files as underlying storage. # Tools ## g-file-storage * obsoleted by `g-mass-storage` * not in Debian kernel as of 3.2.21-3 ## g-mass-storage Works fine with qemu-kvm (1.0+dfsg-11) and libvirt (0.9.12-3): modprobe dummy-hcd is_high_speed=1 modprobe g_mass_storage file=/tmp/test.usb removable=1 Then I use qemu-kvm + libvirt USB 2.0 passthrough to lend that virtual USB mass storage device to a qemu-kvm VM, which I boot from a Tails 0.12 ISO, that I clone onto the virtual USB device using the Tails USB installer. Then I unplug the virtual CD drive, and boot the same VM from the virtual USB mass storage device, onto which I successfully setup a Tails persistent volume. Rebooting, enabling the persistent volume does work. ### Drawbacks * **Not in Debian** kernel as of 3.2.21-3, asked in [[!debbug 678731]] * **All underlying files must be listed at module load time**; this should not be a problem, but still a limitation to be kept in mind. ## qemu qemu (1.1.0+dfsg-1) and qemu-kvm (1.0+dfsg-11) know how to emulate a USB mass storage device, using `-usbdevice` (deprecated) or (roughly) a combination of `-drive file=path_to_test_file.usb,if=none` and `-device usb-storage,drive=DRIVE-ID`. At least with qemu-kvm: * one can boot from such a USB device * virt-manager (0.9.1-4) and libvirt (0.9.12-3) allow to add and configure such a device, and plug it into a virtual USB 2.0 controller ### Drawbacks * **removable property**: by default the emulated USB disk is *not* marked as removable; qemu and qemu-kvm from Wheezy support emulating removable USB devices, but libvirt has no way to pass this option. - [upstream ticket](https://bugzilla.redhat.com/show_bug.cgi?id=922495) - The qemu part was [discussed on Launchpad](https://bugs.launchpad.net/qemu/+bug/686613) already. - A patch that adds the missing feature is being upstream'd, see [[contribute/release_process/test/setup]] for details.

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