RFC: Enable CONFIG_USB_GADGET_DUMMY_HCD ?
 

We currently have the USB Gadget interface enabled with the peripheral
controller CONFIG_USB_GADGET_NET2280. We also have
CONFIG_USB_FILE_STORAGE which gives us the g_file_storage module.

So far I haven't found anything in the changelog or git commits to
indicate if CONFIG_USB_GADGET_NET2280 is an inherited default or choice
based on some scenario we need.

If we were to enable CONFIG_USB_GADGET_DUMMY_HCD instead of
CONFIG_USB_GADGET_NET2280 to give us the dummy-hcd module, we can
provide the ability for the user to create virtual USB mass-storage
devices on the host from a backing file-store.

This can be very useful especially for VMs such as KVM, VMWARE and so
forth because it presents a virtual USB mass storage device to the
guest.

This is a quite separate facility from using a loop mount for creating
block devices on a file backing-store.

For example:

modprobe dummy-hcd
modprobe g_file_storage file=/home/all/VirtualMachines/usb-storage.img

kvm ... -usb -usbdevice host:X.Y

E.g.
dd if=/dev/zero of=/home/all/VirtualMachines/usb-storage.img bs=1024
count=2048

nc -l -p 9999 >boot.log &

kvm -name Ubuntu-Jaunty-Desktop -serial tcp:127.0.0.1:9999 -monitor
stdio -m 512 -hda ubuntu-jaunty-desktop.qcow2 -boot c -k en-gb -net
nic,model=rtl8139,macaddr=56:44:45:30:31:32,vlan=0 -net
tap,ifname=tap0,script=no,vlan=0 -soundhw es1370 -usbdevice
host:0525:a4a5

[ 5.536627] usb 1-2: new full speed USB device using uhci_hcd and address 2
[ 6.181501] usb 1-2: configuration #1 chosen from 1 choice
[ 6.299703] Initializing USB Mass Storage driver...
[ 6.317778] scsi2 : SCSI emulation for USB Mass Storage devices
[ 6.324037] usbcore: registered new interface driver usb-storage
[ 6.339894] USB Mass Storage support registered.
[ 11.356923] scsi 2:0:0:0: Direct-Access Linux File-Stor Gadget 0302 PQ: 0 ANSI: 2
[ 11.436330] sd 2:0:0:0: [sdb] 4096 512-byte hardware sectors: (2.09 MB/2.00 MiB)



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RFC: Enable CONFIG_USB_GADGET_DUMMY_HCD ?
 

TJ wrote:
> We currently have the USB Gadget interface enabled with the peripheral
> controller CONFIG_USB_GADGET_NET2280. We also have
> CONFIG_USB_FILE_STORAGE which gives us the g_file_storage module.
>
> So far I haven't found anything in the changelog or git commits to
> indicate if CONFIG_USB_GADGET_NET2280 is an inherited default or choice
> based on some scenario we need.
>
> If we were to enable CONFIG_USB_GADGET_DUMMY_HCD instead of
> CONFIG_USB_GADGET_NET2280 to give us the dummy-hcd module, we can
> provide the ability for the user to create virtual USB mass-storage
> devices on the host from a backing file-store.
>
> This can be very useful especially for VMs such as KVM, VMWARE and so
> forth because it presents a virtual USB mass storage device to the
> guest.
>
> This is a quite separate facility from using a loop mount for creating
> block devices on a file backing-store.
>
> For example:
>
> modprobe dummy-hcd
> modprobe g_file_storage file=/home/all/VirtualMachines/usb-storage.img
>
> kvm ... -usb -usbdevice host:X.Y
>
> E.g.
> dd if=/dev/zero of=/home/all/VirtualMachines/usb-storage.img bs=1024
> count=2048
>
> nc -l -p 9999 >boot.log &
>
> kvm -name Ubuntu-Jaunty-Desktop -serial tcp:127.0.0.1:9999 -monitor
> stdio -m 512 -hda ubuntu-jaunty-desktop.qcow2 -boot c -k en-gb -net
> nic,model=rtl8139,macaddr=56:44:45:30:31:32,vlan=0 -net
> tap,ifname=tap0,script=no,vlan=0 -soundhw es1370 -usbdevice
> host:0525:a4a5
>
> [ 5.536627] usb 1-2: new full speed USB device using uhci_hcd and address 2
> [ 6.181501] usb 1-2: configuration #1 chosen from 1 choice
> [ 6.299703] Initializing USB Mass Storage driver...
> [ 6.317778] scsi2 : SCSI emulation for USB Mass Storage devices
> [ 6.324037] usbcore: registered new interface driver usb-storage
> [ 6.339894] USB Mass Storage support registered.
> [ 11.356923] scsi 2:0:0:0: Direct-Access Linux File-Stor Gadget 0302 PQ: 0 ANSI: 2
> [ 11.436330] sd 2:0:0:0: [sdb] 4096 512-byte hardware sectors: (2.09 MB/2.00 MiB)
>
>
>

Frankly, I cannot think of a single reason why CONFIG_USB_GADGET_NET2280
is enabled. PC platforms certainly don't contain the USB slave hardware
that this driver requires.

On the other hand, Ubuntu _does_ profess to be a VM friendly platform,
so CONFIG_USB_GADGET_DUMMY_HCD makes a lot of sense.

http://kernel.ubuntu.com/git?p=ubuntu/ubuntu-jaunty.git;a=commit;h=fc19cf886204da09de45cf2db227 5335a5974f93

rtg
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Tim Gardner tim.gardner@canonical.com

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