armqemuubifs

Problems mounting a ubi image using QEMU

I'm trying to emulate a nand flash with qemu and use that to mount an existent ubifs image on the virtual machine.

I added a nand device and a drive of the type mtd, resulting on the following command:

$ qemu-system-arm -nographic -M virt -m 64 -device nand,chip_id=0x59  -drive if=mtd,format=raw,file=data.ubi -kernel openwrt-armvirt-32-zImage-initramfs 
Warning: Orphaned drive without device: id=mtd0,file=data.ubi,if=mtd,bus=0,unit=0
[    0.000000] Booting Linux on physical CPU 0x0
[    0.000000] Linux version 4.19.56 (buildbot@builds) (gcc version 7.4.0 (OpenWrt GCC 7.4.0 r10348-577174cf60)) #0 SMP Tue Jun 25 14:46:01 2019
[    0.000000] CPU: ARMv7 Processor [412fc0f1] revision 1 (ARMv7), cr=30c5387d
[    0.000000] CPU: div instructions available: patching division code
[    0.000000] CPU: PIPT / VIPT nonaliasing data cache, PIPT instruction cache
[    0.000000] OF: fdt: Machine model: linux,dummy-virt
[    0.000000] Memory policy: Data cache writealloc
[    0.000000] psci: probing for conduit method from DT.
[    0.000000] psci: PSCIv0.2 detected in firmware.
...

I can't access to the data.ubi probably because of the following warning:

"Warning: Orphaned drive without device"

How can I add the ubi image to the nand device correctly?

Solution

  • You have to link the -drive and -device via an id parameter:

    qemu-system-arm \
  `: [...]` \
  -device nand,chip_id=0x59,id=myubiflash \
  -drive if=mtd,format=raw,file=data.ubi,id=myubiflash \
  `: [...]`

    If you really read the message carefully, you'll notice that the drive id defaults to mtd0:

    Warning: Orphaned drive without device: id=mtd0,file=data.ubi,if=mtd,bus=0,unit=0

    And of course qemu can't magically guess that you meant to define the -device nand for the drive.

    The error message is exactly on the spot here.

    Edit

    I'll admit, no perfect understanding of the layers of syntax in QEMU commandline on my side either. Also, the QEMU doc isn't the easiest to read; however it has this passage:

    A block driver node created with -blockdev can be used for a guest device by specifying its node name for the drive property in a -device argument that defines a block device.

    -blockdev is synonym to -drive in this context.

    If I can interpret it right, the meaning of this is that instead of

    you're supposed to use

    Can't test this ATM, but either of those should make it work for you.