60 lines
2.5 KiB
Text
60 lines
2.5 KiB
Text
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qemu usb storage emulation
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--------------------------
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QEMU has three devices for usb storage emulation.
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Number one emulates the classic bulk-only transport protocol which is
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used by 99% of the usb sticks on the market today and is called
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"usb-storage". Usage (hooking up to xhci, other host controllers work
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too):
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qemu ${other_vm_args} \
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-drive if=none,id=stick,file=/path/to/file.img \
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-device nec-usb-xhci,id=xhci \
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-device usb-storage,bus=xhci.0,drive=stick
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Number two is the newer usb attached scsi transport. This one doesn't
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automagically create a scsi disk, so you have to explicitly attach one
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manually. Multiple logical units are supported. Here is an example
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with tree logical units:
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qemu ${other_vm_args} \
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-drive if=none,id=uas-disk1,file=/path/to/file1.img \
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-drive if=none,id=uas-disk2,file=/path/to/file2.img \
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-drive if=none,id=uas-cdrom,media=cdrom,file=/path/to/image.iso \
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-device nec-usb-xhci,id=xhci \
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-device usb-uas,id=uas,bus=xhci.0 \
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-device scsi-hd,bus=uas.0,scsi-id=0,lun=0,drive=uas-disk1 \
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-device scsi-hd,bus=uas.0,scsi-id=0,lun=1,drive=uas-disk2 \
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-device scsi-cd,bus=uas.0,scsi-id=0,lun=5,drive=uas-cdrom
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Number three emulates the classic bulk-only transport protocol too.
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It's called "usb-bot". It shares most code with "usb-storage", and
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the guest will not be able to see the difference. The qemu command
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line interface is similar to usb-uas though, i.e. no automatic scsi
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disk creation. It also features support for up to 16 LUNs. The LUN
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numbers must be continuous, i.e. for three devices you must use 0+1+2.
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The 0+1+5 numbering from the "usb-uas" example isn't going to work
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with "usb-bot".
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Starting with qemu version 2.7 usb-bot and usb-uas devices can be
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hotplugged. In the hotplug case they are added with "attached =
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false" so the guest will not see the device until the "attached"
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property is explicitly set to true. That allows to attach one or more
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scsi devices before making the device visible to the guest, i.e. the
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workflow looks like this:
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(1) device-add usb-bot,id=foo
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(2) device-add scsi-{hd,cd},bus=foo.0,lun=0
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(2b) optionally add more devices (luns 1 ... 15).
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(3) scripts/qmp/qom-set foo.attached = true
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enjoy,
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Gerd
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--
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Gerd Hoffmann <kraxel@redhat.com>
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