Re: How to solve: 'Please append a correct "root=" boot option' ?

[Thomas Huth]

On 20/04/2023 04.40, Freitas GDH wrote:
> Hi there!
>
> I'm using a customized qemu-4.0.0 with SOC RT3352 (implemented by Firmguide 
> <https://github.com/cyruscyliu/firmguide>) in order to emulate D-Link 
> DIR-615 firmware. Using an openwrt file I got a dtb file and compiled qemu 
> successfully. But when I'm trying to emulate the firmware, I'm not able to 
> identify the right mapping for my FS image file. I used two different 
> squashfs files, one extracted from stock firmware and the other from openwrt 
> lede-17.01.7 image. In both cases I got the same error. The following are 
> the command syntax used.
>
> //tmp/qemu-4.0.0/mipsel-softmmu/qemu-system-mipsel \
> -D /dev/null \
> -M fg_DIR_615_H1_ralink_rt3352_soc \
> -kernel 
> /home/fenix/firmguide/_lede-17.01.7-ramips-rt305x-dir-615-h1-squashfs-sysupgrade.bin.extracted/0.uimage \
> -dtb 
> /home/fenix/firmguide/_lede-17.01.7-ramips-rt305x-dir-615-h1-squashfs-sysupgrade.bin.extracted/_40.extracted/410.dtb,offset=0x410 \
> -nographic \
> -drive file=/tmp/dir-615_H1/lede-17.01.7_dir-615.squashfs,if=none,format=raw \
> -append "root=/dev/vda"/

With "-drive ...,if=none,..." you only configure a *backend* for a block 
device, but it is not automatically wired to any of the emulated devices.
You need to know which hardware device in your emulated machine should be 
used as block device *frontend*.
Then you either have to use "-drive ...,if=ide,..." or "if=scsi" or 
"if=virtio" or whatever, or add an "id=xxx" parameter to the drive option 
and configure the device with "-device yyy,drive=xxx". It all depends on the 
implementation of the machine that you are using. No clue about that 
fg_DIR_615_H1_ralink_rt3352_soc machine, though, since it is not an upstream 
machine, I guess you have to look at the source code if there is no 
documentation available.

 HTH,
  Thomas

PS: If you feel lost in the QEMU parameter jungle, I recommend 
https://archive.fosdem.org/2018/schedule/event/vai_qemu_jungle/ ... block 
devices start around minute 25:23 in the presentation.

> I used: vda, vda1, sda, sda1.
>
> Piece of log:
>
> [    1.544687] rt2880_wdt 10000120.watchdog: Initialized
> [    1.546636] NET: Registered protocol family 10
> [    1.558513] NET: Registered protocol family 17
> [    1.559810] bridge: automatic filtering via arp/ip/ip6tables has been 
> deprecated. Update your scripts to load br_netfilter if you need this.
> [    1.560308] 8021q: 802.1Q VLAN Support v1.8
> [    1.564650] fdt: not creating '/sys/firmware/fdt': CRC check failed
> *[    1.579213] VFS: Cannot open root device "vda" or unknown-block(0,0): 
> error -6
> [    1.579566] Please append a correct "root=" boot option; here are the 
> available partitions:
> [    1.580137] Kernel panic - not syncing: VFS: Unable to mount root fs on 
> unknown-block(0,0)*
> [    1.582285] Rebooting in 1 seconds..
> [    3.551589] Reboot failed -- System halted
>
>
> But if instead of /-drive /I use -/initrd/ the emulation runs successfully.
> -initrd 0.cpio \
> -append "console=ttyS0 nowatchdog nokaslr"
>
> O also tried to create a cpio file from the squashfs files, but I got the 
> same error 'cannot open root device...'.
>
> Thank you !