Openwrt x86_64 grub2 fallback feature

[Alex Nikitenko]

Hello.

I was trying to bring up GRUB fallback feature on x86_64 based OpenWRT build.

I used this article as a reference. http://www.linuxscrew.com/2012/04/24/grub-fallback-boot-good-kernel-if-new-one-crashes/

It's for Fedora, but I hope, that I can do something similar for openwrt.

Here's my config:

serial --unit=0 --speed=38400 --word=8 --parity=no --stop=1
terminal_input console serial; terminal_output console serial


set default="saved"
set timeout="5"
set root='(hd0,msdos1)'
set fallback="0 1"

menuentry "OpenWrt" {
        linux /boot/vmlinuz root=/dev/sda2 rootfstype=ext4 rootwait console=tty0 console=ttyS0,38400n8 noinitrd
        savedefault fallback
}

menuentry "OpenWrt-backup" {
        linux /boot/vmlinuz-backup root=/dev/sda3 rootfstype=ext4 rootwait console=tty0 console=ttyS0,38400n8 noinitrd
        savedefault fallback
}

menuentry "OpenWrt (failsafe)" {
        linux /boot/vmlinuz failsafe=true root=/dev/sda2 rootfstype=ext4 rootwait console=tty0 console=ttyS0,38400n8 noinitrd
}

But, when I try to boot  openwrt with this config I get message, that command is not recognized.

Booting `OpenWrt'
error: can't find command `savedefault'.
Press any key to continue...

I believe, that in order to make fallback feature work, I need loadenv module enabled. I enabled it, but it didn't help.
I also found an information, that I might be getting troubles with savedefault because my kernel and rootfs are stored on 4GB USB stick. Is this a problem?
Can I reconfigure a grub somehow in order to have this feature?

Thanks,

Alex