U-boot boot script
by Mike Krinkin
To wrap up my explorations of U-boot I’d like show how to automatically load a kernel with U-boot on startup.
Boot script
In the past posts to load my toy binary using U-boot I had to run the following commands in the U-boot shell:
fatload virtio 0:1 0x40000000 kernel.bin
fatload virtio 0:1 0x41000000 virt.dtb
booti 0x40000000 - 0x41000000
That’s not a big deal, but it would be better if U-boot could do all that automatically and, naturally, U-boot should be able to do that.
NOTE: U-boot is used in multiple consumer hardware systems, for example, some Wi-Fi routers use U-boot as a bootloader and you don’t have to type some shell commands when using those - you just power up the device and then U-boot does the rest automatically.
So how can we tell U-boot to execute command above automatically?
First, we need to prepare the script. When I built U-boot with it I also
built a bunch of useful tools, one of them is mkimage. This tool takes
some image or data as an input, attaches a header to it and produces an
image in format that U-boot is familiar with.
Let’s save the commands above in a text file, let’s call it boot.txt,
though the name does not matter as much. Now, we can use mkimage to
produce a U-boot image from it as follows:
~/ws/u-boot/tools/mkimage -T script -d boot.txt boot.scr
Image Name:
Created: Sun Nov 19 20:54:48 2023
Image Type: PowerPC Linux Script (gzip compressed)
Data Size: 118 Bytes = 0.12 KiB = 0.00 MiB
Load Address: 00000000
Entry Point: 00000000
Contents:
Image 0: 110 Bytes = 0.11 KiB = 0.00 MiB
NOTE:
~/ws/u-boot/is where U-boot sources I downloaded live and where the U-boot build results are, so that’s wheremkimageis as well.
This command should have prodiced a file boot.scr. The content of this file
is mostly the text of our script, but it also contains an additional binary
header:
cat boot.scr
'V�$��eZvPv�jպnfatload virtio 0:1 0x40000000 kernel.bin
fatload virtio 0:1 0x41000000 virt.dtb
booti 0x40000000 - 0x41000000
So now, I will place this boot.scr file in the root file system used by QEMU:
mkdir rootfs/boot
cp boot.scr rootfs/boot
NOTE:
rootfsis the directory that QEMU will use as a root file system on the emulated device.
So if we start QEMU now, it will load U-boot and U-boot will load our toy binary automatically auto some wait time unless we interrupt it:
qemu-system-aarch64 \
-machine virt,virtualization=on,secure=off \
-cpu max \
-bios u-boot.bin \
-nographic \
-drive file=fat:rw:./rootfs,format=raw,media=disk
U-Boot 2023.10-rc1-00323-gb1a8ef746f (Aug 07 2023 - 13:43:27 +0100)
DRAM: 128 MiB
Core: 51 devices, 14 uclasses, devicetree: board
Flash: 64 MiB
Loading Environment from Flash... *** Warning - bad CRC, using default environment
In: pl011@9000000
Out: pl011@9000000
Err: pl011@9000000
Net: eth0: virtio-net#32
Hit any key to stop autoboot: 0
Scanning for bootflows in all bootdevs
Seq Method State Uclass Part Name Filename
--- ----------- ------ -------- ---- ------------------------ ----------------
Scanning global bootmeth 'efi_mgr':
Scanning bootdev 'fw-cfg@9020000.bootdev':
fatal: no kernel available
No working controllers found
scanning bus for devices...
Scanning bootdev 'virtio-blk#33.bootdev':
0 script ready virtio 1 virtio-blk#33.bootdev.par /boot/boot.scr
** Booting bootflow 'virtio-blk#33.bootdev.part_1' with script
4608 bytes read in 1 ms (4.4 MiB/s)
1048576 bytes read in 1 ms (1000 MiB/s)
## Flattened Device Tree blob at 41000000
Booting using the fdt blob at 0x41000000
Working FDT set to 41000000
Loading Device Tree to 0000000045c8c000, end 0000000045d8efff ... OK
Working FDT set to 45c8c000
Starting kernel ...
Hello, World
Standard Boot Process
So let’s try to understand a little bit more how U-boot actually finds the kernel to boot and the specifc commands. U-boot has a few relevant concepts that are relevant to the boot process:
- Boot Device - disk, memory card, network device, etc from which we get the binaries, device tree, scripts and other things we need to boot the system;
- Boot Method - it’s a method/algorithm/process used to scan the Boot Device extract the configs and binaries we need;
- Boot Flow - a configuration of how to actually boot an OS, I will ignore it for my simplistic example as I don’t actually need it.
U-boot supports multiple differnt types of boot devices and boot methods. For example, in the U-boot build that I use on QEMU I can see the following boot devices:
bootdev list
Seq Probed Status Uclass Name
--- ------ ------ -------- ------------------
0 [ ] OK qfw fw-cfg@9020000.bootdev
1 [ ] OK ethernet virtio-net#32.bootdev
2 [ ] OK virtio virtio-blk#33.bootdev
--- ------ ------ -------- ------------------
(3 bootdevs)
And here are the available boot methods:
bootmeth list -a
Order Seq Name Description
----- --- ------------------ ------------------
0 0 efi EFI boot from an .efi file
glob 1 efi_mgr EFI bootmgr flow
2 2 extlinux Extlinux boot from a block device
3 3 pxe PXE boot from a network device
4 4 qfw QEMU boot using firmware interface
5 5 script Script boot from a block device
glob 6 vbe_simple VBE simple
----- --- ------------------ ------------------
(7 bootmeths)
In the example above I used virtio-blk#33.bootdev as a boot device and
script as a boot method. Though, U-boot tried multiple different options
before it figured out that those boot device and method work.
Boot Order
As you saw above virtio-blk#33.bootdev was not the first device in the list
and script was far from the first method, so U-boot tried multiple different
options before it found that that combination worked.
We can actually see what things and in what order U-boot would try on startup using the following command in U-boot shell:
bootflow scan -lae
Scanning for bootflows in all bootdevs
Seq Method State Uclass Part Name Filename
--- ----------- ------ -------- ---- ------------------------ ----------------
Scanning global bootmeth 'efi_mgr':
0 efi_mgr base (none) 0 <NULL> <NULL>
** No media/partition found, err=-22E
Scanning bootdev 'fw-cfg@9020000.bootdev':
1 efi base qfw 0 <NULL> <NULL>
** No media/partition found, err=-524E
2 extlinux base qfw 0 <NULL> <NULL>
** No media/partition found, err=-524E
3 pxe base qfw 0 <NULL> <NULL>
** No media/partition found, err=-524E
fatal: no kernel available
4 qfw base qfw 0 qfw <NULL>
** No media/partition found, err=-5E
5 script base qfw 0 <NULL> /boot/boot.scr
** No media/partition found, err=-1E
No working controllers found
scanning bus for devices...
Scanning bootdev 'virtio-blk#33.bootdev':
6 efi media virtio 0 virtio-blk#33.bootdev.who <NULL>
** No partition found, err=-2E
7 extlinux media virtio 0 virtio-blk#33.bootdev.who <NULL>
** No partition found, err=-2E
8 pxe base virtio 0 virtio-blk#33.bootdev.who <NULL>
** No media/partition found, err=-524E
9 qfw base virtio 0 virtio-blk#33.bootdev.who <NULL>
** No media/partition found, err=-524E
a script media virtio 0 virtio-blk#33.bootdev.who <NULL>
** No partition found, err=-2E
b efi fs virtio 1 virtio-blk#33.bootdev.par efi/boot/bootaa64.efi
** File not found, err=-2E
c extlinux fs virtio 1 virtio-blk#33.bootdev.par /boot/extlinux/extlinux.conf
** File not found, err=-2E
d pxe base virtio 1 virtio-blk#33.bootdev.par <NULL>
** No media/partition found, err=-524E
e qfw base virtio 1 virtio-blk#33.bootdev.par <NULL>
** No media/partition found, err=-524E
f script ready virtio 1 virtio-blk#33.bootdev.par /boot/boot.scr
10 efi media virtio 2 virtio-blk#33.bootdev.par <NULL>
** No partition found, err=-2E
11 extlinux media virtio 2 virtio-blk#33.bootdev.par <NULL>
** No partition found, err=-2E
12 pxe base virtio 2 virtio-blk#33.bootdev.par <NULL>
** No media/partition found, err=-524E
13 qfw base virtio 2 virtio-blk#33.bootdev.par <NULL>
** No media/partition found, err=-524E
14 script media virtio 2 virtio-blk#33.bootdev.par <NULL>
** No partition found, err=-2E
15 efi media virtio 3 virtio-blk#33.bootdev.par <NULL>
** No partition found, err=-2E
16 extlinux media virtio 3 virtio-blk#33.bootdev.par <NULL>
** No partition found, err=-2E
17 pxe base virtio 3 virtio-blk#33.bootdev.par <NULL>
** No media/partition found, err=-524E
18 qfw base virtio 3 virtio-blk#33.bootdev.par <NULL>
** No media/partition found, err=-524E
19 script media virtio 3 virtio-blk#33.bootdev.par <NULL>
** No partition found, err=-2E
1a efi media virtio 4 virtio-blk#33.bootdev.par <NULL>
** No partition found, err=-2E
1b extlinux media virtio 4 virtio-blk#33.bootdev.par <NULL>
** No partition found, err=-2E
1c pxe base virtio 4 virtio-blk#33.bootdev.par <NULL>
** No media/partition found, err=-524E
1d qfw base virtio 4 virtio-blk#33.bootdev.par <NULL>
** No media/partition found, err=-524E
1e script media virtio 4 virtio-blk#33.bootdev.par <NULL>
** No partition found, err=-2E
1f efi media virtio 5 virtio-blk#33.bootdev.par <NULL>
** No partition found, err=-2E
20 extlinux media virtio 5 virtio-blk#33.bootdev.par <NULL>
** No partition found, err=-2E
21 pxe base virtio 5 virtio-blk#33.bootdev.par <NULL>
** No media/partition found, err=-524E
22 qfw base virtio 5 virtio-blk#33.bootdev.par <NULL>
** No media/partition found, err=-524E
23 script media virtio 5 virtio-blk#33.bootdev.par <NULL>
** No partition found, err=-2E
24 efi media virtio 6 virtio-blk#33.bootdev.par <NULL>
** No partition found, err=-2E
25 extlinux media virtio 6 virtio-blk#33.bootdev.par <NULL>
** No partition found, err=-2E
26 pxe base virtio 6 virtio-blk#33.bootdev.par <NULL>
** No media/partition found, err=-524E
27 qfw base virtio 6 virtio-blk#33.bootdev.par <NULL>
** No media/partition found, err=-524E
28 script media virtio 6 virtio-blk#33.bootdev.par <NULL>
** No partition found, err=-2E
29 efi media virtio 7 virtio-blk#33.bootdev.par <NULL>
** No partition found, err=-2E
2a extlinux media virtio 7 virtio-blk#33.bootdev.par <NULL>
** No partition found, err=-2E
2b pxe base virtio 7 virtio-blk#33.bootdev.par <NULL>
** No media/partition found, err=-524E
2c qfw base virtio 7 virtio-blk#33.bootdev.par <NULL>
** No media/partition found, err=-524E
2d script media virtio 7 virtio-blk#33.bootdev.par <NULL>
** No partition found, err=-2E
2e efi media virtio 8 virtio-blk#33.bootdev.par <NULL>
** No partition found, err=-2E
2f extlinux media virtio 8 virtio-blk#33.bootdev.par <NULL>
** No partition found, err=-2E
30 pxe base virtio 8 virtio-blk#33.bootdev.par <NULL>
** No media/partition found, err=-524E
31 qfw base virtio 8 virtio-blk#33.bootdev.par <NULL>
** No media/partition found, err=-524E
32 script media virtio 8 virtio-blk#33.bootdev.par <NULL>
** No partition found, err=-2E
33 efi media virtio 9 virtio-blk#33.bootdev.par <NULL>
** No partition found, err=-2E
34 extlinux media virtio 9 virtio-blk#33.bootdev.par <NULL>
** No partition found, err=-2E
35 pxe base virtio 9 virtio-blk#33.bootdev.par <NULL>
** No media/partition found, err=-524E
36 qfw base virtio 9 virtio-blk#33.bootdev.par <NULL>
** No media/partition found, err=-524E
37 script media virtio 9 virtio-blk#33.bootdev.par <NULL>
** No partition found, err=-2E
38 efi media virtio a virtio-blk#33.bootdev.par <NULL>
** No partition found, err=-2E
39 extlinux media virtio a virtio-blk#33.bootdev.par <NULL>
** No partition found, err=-2E
3a pxe base virtio a virtio-blk#33.bootdev.par <NULL>
** No media/partition found, err=-524E
3b qfw base virtio a virtio-blk#33.bootdev.par <NULL>
** No media/partition found, err=-524E
3c script media virtio a virtio-blk#33.bootdev.par <NULL>
** No partition found, err=-2E
3d efi media virtio b virtio-blk#33.bootdev.par <NULL>
** No partition found, err=-2E
3e extlinux media virtio b virtio-blk#33.bootdev.par <NULL>
** No partition found, err=-2E
3f pxe base virtio b virtio-blk#33.bootdev.par <NULL>
** No media/partition found, err=-524E
40 qfw base virtio b virtio-blk#33.bootdev.par <NULL>
** No media/partition found, err=-524E
41 script media virtio b virtio-blk#33.bootdev.par <NULL>
** No partition found, err=-2E
42 efi media virtio c virtio-blk#33.bootdev.par <NULL>
** No partition found, err=-2E
43 extlinux media virtio c virtio-blk#33.bootdev.par <NULL>
** No partition found, err=-2E
44 pxe base virtio c virtio-blk#33.bootdev.par <NULL>
** No media/partition found, err=-524E
45 qfw base virtio c virtio-blk#33.bootdev.par <NULL>
** No media/partition found, err=-524E
46 script media virtio c virtio-blk#33.bootdev.par <NULL>
** No partition found, err=-2E
47 efi media virtio d virtio-blk#33.bootdev.par <NULL>
** No partition found, err=-2E
48 extlinux media virtio d virtio-blk#33.bootdev.par <NULL>
** No partition found, err=-2E
49 pxe base virtio d virtio-blk#33.bootdev.par <NULL>
** No media/partition found, err=-524E
4a qfw base virtio d virtio-blk#33.bootdev.par <NULL>
** No media/partition found, err=-524E
4b script media virtio d virtio-blk#33.bootdev.par <NULL>
** No partition found, err=-2E
4c efi media virtio e virtio-blk#33.bootdev.par <NULL>
** No partition found, err=-2E
4d extlinux media virtio e virtio-blk#33.bootdev.par <NULL>
** No partition found, err=-2E
4e pxe base virtio e virtio-blk#33.bootdev.par <NULL>
** No media/partition found, err=-524E
4f qfw base virtio e virtio-blk#33.bootdev.par <NULL>
** No media/partition found, err=-524E
50 script media virtio e virtio-blk#33.bootdev.par <NULL>
** No partition found, err=-2E
51 efi media virtio f virtio-blk#33.bootdev.par <NULL>
** No partition found, err=-2E
52 extlinux media virtio f virtio-blk#33.bootdev.par <NULL>
** No partition found, err=-2E
53 pxe base virtio f virtio-blk#33.bootdev.par <NULL>
** No media/partition found, err=-524E
54 qfw base virtio f virtio-blk#33.bootdev.par <NULL>
** No media/partition found, err=-524E
55 script media virtio f virtio-blk#33.bootdev.par <NULL>
** No partition found, err=-2E
56 efi media virtio 10 virtio-blk#33.bootdev.par <NULL>
** No partition found, err=-2E
57 extlinux media virtio 10 virtio-blk#33.bootdev.par <NULL>
** No partition found, err=-2E
58 pxe base virtio 10 virtio-blk#33.bootdev.par <NULL>
** No media/partition found, err=-524E
59 qfw base virtio 10 virtio-blk#33.bootdev.par <NULL>
** No media/partition found, err=-524E
5a script media virtio 10 virtio-blk#33.bootdev.par <NULL>
** No partition found, err=-2E
5b efi media virtio 11 virtio-blk#33.bootdev.par <NULL>
** No partition found, err=-2E
5c extlinux media virtio 11 virtio-blk#33.bootdev.par <NULL>
** No partition found, err=-2E
5d pxe base virtio 11 virtio-blk#33.bootdev.par <NULL>
** No media/partition found, err=-524E
5e qfw base virtio 11 virtio-blk#33.bootdev.par <NULL>
** No media/partition found, err=-524E
5f script media virtio 11 virtio-blk#33.bootdev.par <NULL>
** No partition found, err=-2E
60 efi media virtio 12 virtio-blk#33.bootdev.par <NULL>
** No partition found, err=-2E
61 extlinux media virtio 12 virtio-blk#33.bootdev.par <NULL>
** No partition found, err=-2E
62 pxe base virtio 12 virtio-blk#33.bootdev.par <NULL>
** No media/partition found, err=-524E
63 qfw base virtio 12 virtio-blk#33.bootdev.par <NULL>
** No media/partition found, err=-524E
64 script media virtio 12 virtio-blk#33.bootdev.par <NULL>
** No partition found, err=-2E
65 efi media virtio 13 virtio-blk#33.bootdev.par <NULL>
** No partition found, err=-2E
66 extlinux media virtio 13 virtio-blk#33.bootdev.par <NULL>
** No partition found, err=-2E
67 pxe base virtio 13 virtio-blk#33.bootdev.par <NULL>
** No media/partition found, err=-524E
68 qfw base virtio 13 virtio-blk#33.bootdev.par <NULL>
** No media/partition found, err=-524E
69 script media virtio 13 virtio-blk#33.bootdev.par <NULL>
** No partition found, err=-2E
6a efi media virtio 14 virtio-blk#33.bootdev.par <NULL>
** No partition found, err=-2E
6b extlinux media virtio 14 virtio-blk#33.bootdev.par <NULL>
** No partition found, err=-2E
6c pxe base virtio 14 virtio-blk#33.bootdev.par <NULL>
** No media/partition found, err=-524E
6d qfw base virtio 14 virtio-blk#33.bootdev.par <NULL>
** No media/partition found, err=-524E
6e script media virtio 14 virtio-blk#33.bootdev.par <NULL>
** No partition found, err=-2E
6f efi media virtio 15 virtio-blk#33.bootdev.par <NULL>
** No partition found, err=-2E
70 extlinux media virtio 15 virtio-blk#33.bootdev.par <NULL>
** No partition found, err=-2E
71 pxe base virtio 15 virtio-blk#33.bootdev.par <NULL>
** No media/partition found, err=-524E
72 qfw base virtio 15 virtio-blk#33.bootdev.par <NULL>
** No media/partition found, err=-524E
73 script media virtio 15 virtio-blk#33.bootdev.par <NULL>
** No partition found, err=-2E
74 efi media virtio 16 virtio-blk#33.bootdev.par <NULL>
** No partition found, err=-2E
75 extlinux media virtio 16 virtio-blk#33.bootdev.par <NULL>
** No partition found, err=-2E
76 pxe base virtio 16 virtio-blk#33.bootdev.par <NULL>
** No media/partition found, err=-524E
77 qfw base virtio 16 virtio-blk#33.bootdev.par <NULL>
** No media/partition found, err=-524E
78 script media virtio 16 virtio-blk#33.bootdev.par <NULL>
** No partition found, err=-2E
79 efi media virtio 17 virtio-blk#33.bootdev.par <NULL>
** No partition found, err=-2E
7a extlinux media virtio 17 virtio-blk#33.bootdev.par <NULL>
** No partition found, err=-2E
7b pxe base virtio 17 virtio-blk#33.bootdev.par <NULL>
** No media/partition found, err=-524E
7c qfw base virtio 17 virtio-blk#33.bootdev.par <NULL>
** No media/partition found, err=-524E
7d script media virtio 17 virtio-blk#33.bootdev.par <NULL>
** No partition found, err=-2E
7e efi media virtio 18 virtio-blk#33.bootdev.par <NULL>
** No partition found, err=-2E
7f extlinux media virtio 18 virtio-blk#33.bootdev.par <NULL>
** No partition found, err=-2E
80 pxe base virtio 18 virtio-blk#33.bootdev.par <NULL>
** No media/partition found, err=-524E
81 qfw base virtio 18 virtio-blk#33.bootdev.par <NULL>
** No media/partition found, err=-524E
82 script media virtio 18 virtio-blk#33.bootdev.par <NULL>
** No partition found, err=-2E
83 efi media virtio 19 virtio-blk#33.bootdev.par <NULL>
** No partition found, err=-2E
84 extlinux media virtio 19 virtio-blk#33.bootdev.par <NULL>
** No partition found, err=-2E
85 pxe base virtio 19 virtio-blk#33.bootdev.par <NULL>
** No media/partition found, err=-524E
86 qfw base virtio 19 virtio-blk#33.bootdev.par <NULL>
** No media/partition found, err=-524E
87 script media virtio 19 virtio-blk#33.bootdev.par <NULL>
** No partition found, err=-2E
88 efi media virtio 1a virtio-blk#33.bootdev.par <NULL>
** No partition found, err=-2E
89 extlinux media virtio 1a virtio-blk#33.bootdev.par <NULL>
** No partition found, err=-2E
8a pxe base virtio 1a virtio-blk#33.bootdev.par <NULL>
** No media/partition found, err=-524E
8b qfw base virtio 1a virtio-blk#33.bootdev.par <NULL>
** No media/partition found, err=-524E
8c script media virtio 1a virtio-blk#33.bootdev.par <NULL>
** No partition found, err=-2E
8d efi media virtio 1b virtio-blk#33.bootdev.par <NULL>
** No partition found, err=-2E
8e extlinux media virtio 1b virtio-blk#33.bootdev.par <NULL>
** No partition found, err=-2E
8f pxe base virtio 1b virtio-blk#33.bootdev.par <NULL>
** No media/partition found, err=-524E
90 qfw base virtio 1b virtio-blk#33.bootdev.par <NULL>
** No media/partition found, err=-524E
91 script media virtio 1b virtio-blk#33.bootdev.par <NULL>
** No partition found, err=-2E
92 efi media virtio 1c virtio-blk#33.bootdev.par <NULL>
** No partition found, err=-2E
93 extlinux media virtio 1c virtio-blk#33.bootdev.par <NULL>
** No partition found, err=-2E
94 pxe base virtio 1c virtio-blk#33.bootdev.par <NULL>
** No media/partition found, err=-524E
95 qfw base virtio 1c virtio-blk#33.bootdev.par <NULL>
** No media/partition found, err=-524E
96 script media virtio 1c virtio-blk#33.bootdev.par <NULL>
** No partition found, err=-2E
97 efi media virtio 1d virtio-blk#33.bootdev.par <NULL>
** No partition found, err=-2E
98 extlinux media virtio 1d virtio-blk#33.bootdev.par <NULL>
** No partition found, err=-2E
99 pxe base virtio 1d virtio-blk#33.bootdev.par <NULL>
** No media/partition found, err=-524E
9a qfw base virtio 1d virtio-blk#33.bootdev.par <NULL>
** No media/partition found, err=-524E
9b script media virtio 1d virtio-blk#33.bootdev.par <NULL>
** No partition found, err=-2E
BOOTP broadcast 1
DHCP client bound to address 10.0.2.15 (2 ms)
Scanning bootdev 'virtio-net#32.bootdev':
BOOTP broadcast 1
DHCP client bound to address 10.0.2.15 (0 ms)
*** Warning: no boot file name; using '0A00020F.img'
Using virtio-net#32 device
TFTP from server 10.0.2.2; our IP address is 10.0.2.15
Filename '0A00020F.img'.
Load address: 0x40400000
Loading: *
TFTP error: 'Access violation' (2)
Not retrying...
9c efi base ethernet 0 virtio-net#32.bootdev.0 <NULL>
** No media/partition found, err=-2E
9d extlinux base ethernet 0 <NULL> <NULL>
** No media/partition found, err=-524E
9e pxe base ethernet 0 <NULL> <NULL>
** No media/partition found, err=-524E
9f qfw base ethernet 0 <NULL> <NULL>
** No media/partition found, err=-524E
a0 script base ethernet 0 virtio-net#32.bootdev.0 <NULL>
** No media/partition found, err=-22E
No more bootdevs
--- ----------- ------ -------- ---- ------------------------ ----------------
(161 bootflows, 1 valid)
Excluding so called global boot methods, the logic U-boot uses is pretty straighforward - it just itreatates over all the possible boot devices and tries all the possible boot methods on each device in order.
So what is the order of those boot devices? It appears that the order is
controlled by an environment variable boot_targets. It seems that the default
value of the boot_targets variable is board specific, but it can be changed.
For example, in my case the default value looks like:
env print boot_targets
boot_targets=qfw usb scsi virtio nvme dhcp
And given that I know that my boot script lives on a Virtio block device I can override it this way:
setenv boot_targets "virtio"
And once I do that, the boot process will actually start by looking at the
virtio block device first reducing the number of options to consider:
bootflow scan -lae
Scanning for bootflows in all bootdevs
Seq Method State Uclass Part Name Filename
--- ----------- ------ -------- ---- ------------------------ ----------------
Scanning global bootmeth 'efi_mgr':
0 efi_mgr base (none) 0 <NULL> <NULL>
** No media/partition found, err=-22E
Scanning bootdev 'virtio-blk#33.bootdev':
1 efi media virtio 0 virtio-blk#33.bootdev.who <NULL>
** No partition found, err=-2E
2 extlinux media virtio 0 virtio-blk#33.bootdev.who <NULL>
** No partition found, err=-2E
3 pxe base virtio 0 virtio-blk#33.bootdev.who <NULL>
** No media/partition found, err=-524E
4 qfw base virtio 0 virtio-blk#33.bootdev.who <NULL>
** No media/partition found, err=-524E
5 script media virtio 0 virtio-blk#33.bootdev.who <NULL>
** No partition found, err=-2E
6 efi fs virtio 1 virtio-blk#33.bootdev.par efi/boot/bootaa64.efi
** File not found, err=-2E
7 extlinux fs virtio 1 virtio-blk#33.bootdev.par /boot/extlinux/extlinux.conf
** File not found, err=-2E
8 pxe base virtio 1 virtio-blk#33.bootdev.par <NULL>
** No media/partition found, err=-524E
9 qfw base virtio 1 virtio-blk#33.bootdev.par <NULL>
** No media/partition found, err=-524E
a script ready virtio 1 virtio-blk#33.bootdev.par /boot/boot.scr
b efi media virtio 2 virtio-blk#33.bootdev.par <NULL>
** No partition found, err=-2E
c extlinux media virtio 2 virtio-blk#33.bootdev.par <NULL>
** No partition found, err=-2E
d pxe base virtio 2 virtio-blk#33.bootdev.par <NULL>
** No media/partition found, err=-524E
e qfw base virtio 2 virtio-blk#33.bootdev.par <NULL>
** No media/partition found, err=-524E
f script media virtio 2 virtio-blk#33.bootdev.par <NULL>
** No partition found, err=-2E
10 efi media virtio 3 virtio-blk#33.bootdev.par <NULL>
** No partition found, err=-2E
11 extlinux media virtio 3 virtio-blk#33.bootdev.par <NULL>
** No partition found, err=-2E
12 pxe base virtio 3 virtio-blk#33.bootdev.par <NULL>
** No media/partition found, err=-524E
13 qfw base virtio 3 virtio-blk#33.bootdev.par <NULL>
** No media/partition found, err=-524E
14 script media virtio 3 virtio-blk#33.bootdev.par <NULL>
** No partition found, err=-2E
15 efi media virtio 4 virtio-blk#33.bootdev.par <NULL>
** No partition found, err=-2E
16 extlinux media virtio 4 virtio-blk#33.bootdev.par <NULL>
** No partition found, err=-2E
17 pxe base virtio 4 virtio-blk#33.bootdev.par <NULL>
** No media/partition found, err=-524E
18 qfw base virtio 4 virtio-blk#33.bootdev.par <NULL>
** No media/partition found, err=-524E
19 script media virtio 4 virtio-blk#33.bootdev.par <NULL>
** No partition found, err=-2E
1a efi media virtio 5 virtio-blk#33.bootdev.par <NULL>
** No partition found, err=-2E
1b extlinux media virtio 5 virtio-blk#33.bootdev.par <NULL>
** No partition found, err=-2E
1c pxe base virtio 5 virtio-blk#33.bootdev.par <NULL>
** No media/partition found, err=-524E
1d qfw base virtio 5 virtio-blk#33.bootdev.par <NULL>
** No media/partition found, err=-524E
1e script media virtio 5 virtio-blk#33.bootdev.par <NULL>
** No partition found, err=-2E
1f efi media virtio 6 virtio-blk#33.bootdev.par <NULL>
** No partition found, err=-2E
20 extlinux media virtio 6 virtio-blk#33.bootdev.par <NULL>
** No partition found, err=-2E
21 pxe base virtio 6 virtio-blk#33.bootdev.par <NULL>
** No media/partition found, err=-524E
22 qfw base virtio 6 virtio-blk#33.bootdev.par <NULL>
** No media/partition found, err=-524E
23 script media virtio 6 virtio-blk#33.bootdev.par <NULL>
** No partition found, err=-2E
24 efi media virtio 7 virtio-blk#33.bootdev.par <NULL>
** No partition found, err=-2E
25 extlinux media virtio 7 virtio-blk#33.bootdev.par <NULL>
** No partition found, err=-2E
26 pxe base virtio 7 virtio-blk#33.bootdev.par <NULL>
** No media/partition found, err=-524E
27 qfw base virtio 7 virtio-blk#33.bootdev.par <NULL>
** No media/partition found, err=-524E
28 script media virtio 7 virtio-blk#33.bootdev.par <NULL>
** No partition found, err=-2E
29 efi media virtio 8 virtio-blk#33.bootdev.par <NULL>
** No partition found, err=-2E
2a extlinux media virtio 8 virtio-blk#33.bootdev.par <NULL>
** No partition found, err=-2E
2b pxe base virtio 8 virtio-blk#33.bootdev.par <NULL>
** No media/partition found, err=-524E
2c qfw base virtio 8 virtio-blk#33.bootdev.par <NULL>
** No media/partition found, err=-524E
2d script media virtio 8 virtio-blk#33.bootdev.par <NULL>
** No partition found, err=-2E
2e efi media virtio 9 virtio-blk#33.bootdev.par <NULL>
** No partition found, err=-2E
2f extlinux media virtio 9 virtio-blk#33.bootdev.par <NULL>
** No partition found, err=-2E
30 pxe base virtio 9 virtio-blk#33.bootdev.par <NULL>
** No media/partition found, err=-524E
31 qfw base virtio 9 virtio-blk#33.bootdev.par <NULL>
** No media/partition found, err=-524E
32 script media virtio 9 virtio-blk#33.bootdev.par <NULL>
** No partition found, err=-2E
33 efi media virtio a virtio-blk#33.bootdev.par <NULL>
** No partition found, err=-2E
34 extlinux media virtio a virtio-blk#33.bootdev.par <NULL>
** No partition found, err=-2E
35 pxe base virtio a virtio-blk#33.bootdev.par <NULL>
** No media/partition found, err=-524E
36 qfw base virtio a virtio-blk#33.bootdev.par <NULL>
** No media/partition found, err=-524E
37 script media virtio a virtio-blk#33.bootdev.par <NULL>
** No partition found, err=-2E
38 efi media virtio b virtio-blk#33.bootdev.par <NULL>
** No partition found, err=-2E
39 extlinux media virtio b virtio-blk#33.bootdev.par <NULL>
** No partition found, err=-2E
3a pxe base virtio b virtio-blk#33.bootdev.par <NULL>
** No media/partition found, err=-524E
3b qfw base virtio b virtio-blk#33.bootdev.par <NULL>
** No media/partition found, err=-524E
3c script media virtio b virtio-blk#33.bootdev.par <NULL>
** No partition found, err=-2E
3d efi media virtio c virtio-blk#33.bootdev.par <NULL>
** No partition found, err=-2E
3e extlinux media virtio c virtio-blk#33.bootdev.par <NULL>
** No partition found, err=-2E
3f pxe base virtio c virtio-blk#33.bootdev.par <NULL>
** No media/partition found, err=-524E
40 qfw base virtio c virtio-blk#33.bootdev.par <NULL>
** No media/partition found, err=-524E
41 script media virtio c virtio-blk#33.bootdev.par <NULL>
** No partition found, err=-2E
42 efi media virtio d virtio-blk#33.bootdev.par <NULL>
** No partition found, err=-2E
43 extlinux media virtio d virtio-blk#33.bootdev.par <NULL>
** No partition found, err=-2E
44 pxe base virtio d virtio-blk#33.bootdev.par <NULL>
** No media/partition found, err=-524E
45 qfw base virtio d virtio-blk#33.bootdev.par <NULL>
** No media/partition found, err=-524E
46 script media virtio d virtio-blk#33.bootdev.par <NULL>
** No partition found, err=-2E
47 efi media virtio e virtio-blk#33.bootdev.par <NULL>
** No partition found, err=-2E
48 extlinux media virtio e virtio-blk#33.bootdev.par <NULL>
** No partition found, err=-2E
49 pxe base virtio e virtio-blk#33.bootdev.par <NULL>
** No media/partition found, err=-524E
4a qfw base virtio e virtio-blk#33.bootdev.par <NULL>
** No media/partition found, err=-524E
4b script media virtio e virtio-blk#33.bootdev.par <NULL>
** No partition found, err=-2E
4c efi media virtio f virtio-blk#33.bootdev.par <NULL>
** No partition found, err=-2E
4d extlinux media virtio f virtio-blk#33.bootdev.par <NULL>
** No partition found, err=-2E
4e pxe base virtio f virtio-blk#33.bootdev.par <NULL>
** No media/partition found, err=-524E
4f qfw base virtio f virtio-blk#33.bootdev.par <NULL>
** No media/partition found, err=-524E
50 script media virtio f virtio-blk#33.bootdev.par <NULL>
** No partition found, err=-2E
51 efi media virtio 10 virtio-blk#33.bootdev.par <NULL>
** No partition found, err=-2E
52 extlinux media virtio 10 virtio-blk#33.bootdev.par <NULL>
** No partition found, err=-2E
53 pxe base virtio 10 virtio-blk#33.bootdev.par <NULL>
** No media/partition found, err=-524E
54 qfw base virtio 10 virtio-blk#33.bootdev.par <NULL>
** No media/partition found, err=-524E
55 script media virtio 10 virtio-blk#33.bootdev.par <NULL>
** No partition found, err=-2E
56 efi media virtio 11 virtio-blk#33.bootdev.par <NULL>
** No partition found, err=-2E
57 extlinux media virtio 11 virtio-blk#33.bootdev.par <NULL>
** No partition found, err=-2E
58 pxe base virtio 11 virtio-blk#33.bootdev.par <NULL>
** No media/partition found, err=-524E
59 qfw base virtio 11 virtio-blk#33.bootdev.par <NULL>
** No media/partition found, err=-524E
5a script media virtio 11 virtio-blk#33.bootdev.par <NULL>
** No partition found, err=-2E
5b efi media virtio 12 virtio-blk#33.bootdev.par <NULL>
** No partition found, err=-2E
5c extlinux media virtio 12 virtio-blk#33.bootdev.par <NULL>
** No partition found, err=-2E
5d pxe base virtio 12 virtio-blk#33.bootdev.par <NULL>
** No media/partition found, err=-524E
5e qfw base virtio 12 virtio-blk#33.bootdev.par <NULL>
** No media/partition found, err=-524E
5f script media virtio 12 virtio-blk#33.bootdev.par <NULL>
** No partition found, err=-2E
60 efi media virtio 13 virtio-blk#33.bootdev.par <NULL>
** No partition found, err=-2E
61 extlinux media virtio 13 virtio-blk#33.bootdev.par <NULL>
** No partition found, err=-2E
62 pxe base virtio 13 virtio-blk#33.bootdev.par <NULL>
** No media/partition found, err=-524E
63 qfw base virtio 13 virtio-blk#33.bootdev.par <NULL>
** No media/partition found, err=-524E
64 script media virtio 13 virtio-blk#33.bootdev.par <NULL>
** No partition found, err=-2E
65 efi media virtio 14 virtio-blk#33.bootdev.par <NULL>
** No partition found, err=-2E
66 extlinux media virtio 14 virtio-blk#33.bootdev.par <NULL>
** No partition found, err=-2E
67 pxe base virtio 14 virtio-blk#33.bootdev.par <NULL>
** No media/partition found, err=-524E
68 qfw base virtio 14 virtio-blk#33.bootdev.par <NULL>
** No media/partition found, err=-524E
69 script media virtio 14 virtio-blk#33.bootdev.par <NULL>
** No partition found, err=-2E
6a efi media virtio 15 virtio-blk#33.bootdev.par <NULL>
** No partition found, err=-2E
6b extlinux media virtio 15 virtio-blk#33.bootdev.par <NULL>
** No partition found, err=-2E
6c pxe base virtio 15 virtio-blk#33.bootdev.par <NULL>
** No media/partition found, err=-524E
6d qfw base virtio 15 virtio-blk#33.bootdev.par <NULL>
** No media/partition found, err=-524E
6e script media virtio 15 virtio-blk#33.bootdev.par <NULL>
** No partition found, err=-2E
6f efi media virtio 16 virtio-blk#33.bootdev.par <NULL>
** No partition found, err=-2E
70 extlinux media virtio 16 virtio-blk#33.bootdev.par <NULL>
** No partition found, err=-2E
71 pxe base virtio 16 virtio-blk#33.bootdev.par <NULL>
** No media/partition found, err=-524E
72 qfw base virtio 16 virtio-blk#33.bootdev.par <NULL>
** No media/partition found, err=-524E
73 script media virtio 16 virtio-blk#33.bootdev.par <NULL>
** No partition found, err=-2E
74 efi media virtio 17 virtio-blk#33.bootdev.par <NULL>
** No partition found, err=-2E
75 extlinux media virtio 17 virtio-blk#33.bootdev.par <NULL>
** No partition found, err=-2E
76 pxe base virtio 17 virtio-blk#33.bootdev.par <NULL>
** No media/partition found, err=-524E
77 qfw base virtio 17 virtio-blk#33.bootdev.par <NULL>
** No media/partition found, err=-524E
78 script media virtio 17 virtio-blk#33.bootdev.par <NULL>
** No partition found, err=-2E
79 efi media virtio 18 virtio-blk#33.bootdev.par <NULL>
** No partition found, err=-2E
7a extlinux media virtio 18 virtio-blk#33.bootdev.par <NULL>
** No partition found, err=-2E
7b pxe base virtio 18 virtio-blk#33.bootdev.par <NULL>
** No media/partition found, err=-524E
7c qfw base virtio 18 virtio-blk#33.bootdev.par <NULL>
** No media/partition found, err=-524E
7d script media virtio 18 virtio-blk#33.bootdev.par <NULL>
** No partition found, err=-2E
7e efi media virtio 19 virtio-blk#33.bootdev.par <NULL>
** No partition found, err=-2E
7f extlinux media virtio 19 virtio-blk#33.bootdev.par <NULL>
** No partition found, err=-2E
80 pxe base virtio 19 virtio-blk#33.bootdev.par <NULL>
** No media/partition found, err=-524E
81 qfw base virtio 19 virtio-blk#33.bootdev.par <NULL>
** No media/partition found, err=-524E
82 script media virtio 19 virtio-blk#33.bootdev.par <NULL>
** No partition found, err=-2E
83 efi media virtio 1a virtio-blk#33.bootdev.par <NULL>
** No partition found, err=-2E
84 extlinux media virtio 1a virtio-blk#33.bootdev.par <NULL>
** No partition found, err=-2E
85 pxe base virtio 1a virtio-blk#33.bootdev.par <NULL>
** No media/partition found, err=-524E
86 qfw base virtio 1a virtio-blk#33.bootdev.par <NULL>
** No media/partition found, err=-524E
87 script media virtio 1a virtio-blk#33.bootdev.par <NULL>
** No partition found, err=-2E
88 efi media virtio 1b virtio-blk#33.bootdev.par <NULL>
** No partition found, err=-2E
89 extlinux media virtio 1b virtio-blk#33.bootdev.par <NULL>
** No partition found, err=-2E
8a pxe base virtio 1b virtio-blk#33.bootdev.par <NULL>
** No media/partition found, err=-524E
8b qfw base virtio 1b virtio-blk#33.bootdev.par <NULL>
** No media/partition found, err=-524E
8c script media virtio 1b virtio-blk#33.bootdev.par <NULL>
** No partition found, err=-2E
8d efi media virtio 1c virtio-blk#33.bootdev.par <NULL>
** No partition found, err=-2E
8e extlinux media virtio 1c virtio-blk#33.bootdev.par <NULL>
** No partition found, err=-2E
8f pxe base virtio 1c virtio-blk#33.bootdev.par <NULL>
** No media/partition found, err=-524E
90 qfw base virtio 1c virtio-blk#33.bootdev.par <NULL>
** No media/partition found, err=-524E
91 script media virtio 1c virtio-blk#33.bootdev.par <NULL>
** No partition found, err=-2E
92 efi media virtio 1d virtio-blk#33.bootdev.par <NULL>
** No partition found, err=-2E
93 extlinux media virtio 1d virtio-blk#33.bootdev.par <NULL>
** No partition found, err=-2E
94 pxe base virtio 1d virtio-blk#33.bootdev.par <NULL>
** No media/partition found, err=-524E
95 qfw base virtio 1d virtio-blk#33.bootdev.par <NULL>
** No media/partition found, err=-524E
96 script media virtio 1d virtio-blk#33.bootdev.par <NULL>
** No partition found, err=-2E
No more bootdevs
--- ----------- ------ -------- ---- ------------------------ ----------------
(151 bootflows, 1 valid)
Addtionally, I can change the order of boot methods as well even further reducing the number of options U-boot will have to try:
setenv bootmeths "script"
bootflow scan -lae
Scanning for bootflows in all bootdevs
Seq Method State Uclass Part Name Filename
--- ----------- ------ -------- ---- ------------------------ ----------------
Scanning bootdev 'virtio-blk#33.bootdev':
0 script media virtio 0 virtio-blk#33.bootdev.who <NULL>
** No partition found, err=-2E
1 script ready virtio 1 virtio-blk#33.bootdev.par /boot/boot.scr
2 script media virtio 2 virtio-blk#33.bootdev.par <NULL>
** No partition found, err=-2E
3 script media virtio 3 virtio-blk#33.bootdev.par <NULL>
** No partition found, err=-2E
4 script media virtio 4 virtio-blk#33.bootdev.par <NULL>
** No partition found, err=-2E
5 script media virtio 5 virtio-blk#33.bootdev.par <NULL>
** No partition found, err=-2E
6 script media virtio 6 virtio-blk#33.bootdev.par <NULL>
** No partition found, err=-2E
7 script media virtio 7 virtio-blk#33.bootdev.par <NULL>
** No partition found, err=-2E
8 script media virtio 8 virtio-blk#33.bootdev.par <NULL>
** No partition found, err=-2E
9 script media virtio 9 virtio-blk#33.bootdev.par <NULL>
** No partition found, err=-2E
a script media virtio a virtio-blk#33.bootdev.par <NULL>
** No partition found, err=-2E
b script media virtio b virtio-blk#33.bootdev.par <NULL>
** No partition found, err=-2E
c script media virtio c virtio-blk#33.bootdev.par <NULL>
** No partition found, err=-2E
d script media virtio d virtio-blk#33.bootdev.par <NULL>
** No partition found, err=-2E
e script media virtio e virtio-blk#33.bootdev.par <NULL>
** No partition found, err=-2E
f script media virtio f virtio-blk#33.bootdev.par <NULL>
** No partition found, err=-2E
10 script media virtio 10 virtio-blk#33.bootdev.par <NULL>
** No partition found, err=-2E
11 script media virtio 11 virtio-blk#33.bootdev.par <NULL>
** No partition found, err=-2E
12 script media virtio 12 virtio-blk#33.bootdev.par <NULL>
** No partition found, err=-2E
13 script media virtio 13 virtio-blk#33.bootdev.par <NULL>
** No partition found, err=-2E
14 script media virtio 14 virtio-blk#33.bootdev.par <NULL>
** No partition found, err=-2E
15 script media virtio 15 virtio-blk#33.bootdev.par <NULL>
** No partition found, err=-2E
16 script media virtio 16 virtio-blk#33.bootdev.par <NULL>
** No partition found, err=-2E
17 script media virtio 17 virtio-blk#33.bootdev.par <NULL>
** No partition found, err=-2E
18 script media virtio 18 virtio-blk#33.bootdev.par <NULL>
** No partition found, err=-2E
19 script media virtio 19 virtio-blk#33.bootdev.par <NULL>
** No partition found, err=-2E
1a script media virtio 1a virtio-blk#33.bootdev.par <NULL>
** No partition found, err=-2E
1b script media virtio 1b virtio-blk#33.bootdev.par <NULL>
** No partition found, err=-2E
1c script media virtio 1c virtio-blk#33.bootdev.par <NULL>
** No partition found, err=-2E
1d script media virtio 1d virtio-blk#33.bootdev.par <NULL>
** No partition found, err=-2E
No more bootdevs
--- ----------- ------ -------- ---- ------------------------ ----------------
(30 bootflows, 1 valid)
Instead of conclusion
Instead of the conclusion I will provide some code references to where this boot logic implementation lives in U-boot:
- the implementation of the
bootflowshell command lives inu-boot/cmd/bootflow.c - the implementation of the boot device iterators is located in
u-boot/boot/bootflow.c - logic of different boot methods is split bettwen multiple files in
u-boot/bootdirectory, but the common routines for iteration through the available boot methods live inu-boot/boot/bootmeth-uclass.c - spefically
scriptboot method implementation details live inu-boot/boot/bootmeth-script.cand by looking around for similarly named files you can find what other boot methods can U-boot support in principle.
Finally, environment variables boot_targets and bootmeths that control what
boot devices and methods to try and in which order handled a little bit
differently from each other.
boot_targets environment variable is read directly when needed and that’s why
it’s relatively easy to find a reference to it in
u-boot/boot/bootstd-uclass.c.
bootmeths variable is not accessed directly and instead there is a callback
that gets called when this variable get changed. It’s registered via
U_BOOT_ENV_CALLBACK macro in u-boot/boot/bootmeth-uclass.c.