Reading rootfs partition from kernel parameter 'root'

[j0zzy]

Small improvements to init script. This will allow to set root partition in uEnv.txt. Script waits 20 second for the partition, if it doesn't show up it tries to boot from sd card (/dev/mmcblk0p2).

Sample uEnv.txt

console=tty0 console=ttyS0,115200n8 no_console_suspend
kernel_filename=pine64/Image
initrd_filename=initrdwait.img 
root=/dev/sdb2
ethaddr=##:##:##:##:##:##

UART output

[  172.346109] Freeing unused kernel memory: 492K (ffffffc00097a000 - ffffffc0009f5000)
Kernel params: console=tty0 console=ttyS0,115200n8 no_console_suspend earlycon=uart,mmio32,0x01c28000 mac_addr=##:##:##:##:##:## root=/dev/sdb2 ro rootwait
Waiting for root system /dev/sdb2, countdown : 20
[  172.468887]
[  172.468887]
[.....]
[  172.976050] scene_lock_init name=ohci_standby
[  172.986656] host_chose finished 86!
Waiting for root system /dev/sdb2, countdown : 19
Waiting for root system /dev/sdb2, countdown : 18
Waiting for root system /dev/sdb2, countdown : 17
Waiting for root system /dev/sdb2, countdown : 16
Waiting for root system /dev/sdb2, countdown : 15
[  177.438461] scsi 1:0:0:0: Direct-Access     ATA      HGST HTS541010A9 A560 PQ: 0 ANSI: 6
[  177.454878] sd 1:0:0:0: [sdb] 1953525168 512-byte logical blocks: (1.00 TB/931 GiB)
[  177.470117] sd 1:0:0:0: [sdb] Write Protect is off
[  177.482171] sd 1:0:0:0: [sdb] Write cache: disabled, read cache: enabled, doesn't support DPO or FUA
[  177.559890]  sdb: sdb1 sdb2 sdb3 sdb4 sdb5 sdb6
[  177.576276] sd 1:0:0:0: [sdb] Attached SCSI disk
Waiting for root system /dev/sdb2, countdown : 14
Rootfs: /dev/sdb2
Welcome to Ubuntu 16.04 LTS!

[longsleep]

Why these single quotes? Looks strange.

[j0zzy]

Without quotes interpreter tries to evaluate all $(...) inside <<EOF ... EOF.
Example:

cat > some.txt <<EOF
echo $(uname)
EOF

File content:
Linux

cat > some.txt <<'EOF'
echo $(uname)
EOF

File content:
echo $(uname)

[longsleep]

I made some comments. I like the overall idea - let me know if you want to handle my comments, else i will eventually change some things myself and merge then.

[j0zzy]

I fixed local variables.

[longsleep]

Squashed and merged in 5c7d199 - thanks!