Multiple partitions in buildroot? - embedded-linux

Question

Let's discuss a very common case in building up a system image, in which, we need our rootfs as SquashFs to be read-only indeed, and another ext4 partition(let's say home) for general read-write storage.
The system image layout(genimage.cfg) looks like this in a buildroot environment:
image sdcard.img {
hdimage {}
partition boot {
partition-type = 0xC
bootable = "true"
image = "boot.vfat"
}
partition rootfs {
partition-type = 0x83
image = "rootfs.squashfs"
}
partition home {
partition-type = 0x83
image = "home.ext4"
}
}
image boot.vfat {
vfat {
files = {
"bcm2711-rpi-4-b.dtb",
"rpi-firmware/cmdline.txt",
"rpi-firmware/config.txt",
"rpi-firmware/fixup4.dat",
"rpi-firmware/start4.elf",
"rpi-firmware/overlays",
"zImage"
}
}
size = 16M
}
image home.ext4 {
name = "home"
mountpoint = "/home"
ext4 {}
size = 32M
}
But in final stage of creating image, we end up with an error:
>> Executing post-image script ~/rpi4/post-image.sh
INFO: cmd: "mkdir -p "/home/iman/rpi4/genimage.tmp"" (stderr+stdout):
INFO: cmd: "rm -rf "/home/iman/rpi4/genimage.tmp"/*" (stderr+stdout):
DEBUG: hdimage(sdcard.img): adding implicit file rule for 'rootfs.squashfs'
DEBUG: vfat(boot.vfat): adding implicit file rule for 'bcm2711-rpi-4-b.dtb'
DEBUG: vfat(boot.vfat): adding implicit file rule for 'rpi-firmware/cmdline.txt'
DEBUG: vfat(boot.vfat): adding implicit file rule for 'rpi-firmware/config.txt'
DEBUG: vfat(boot.vfat): adding implicit file rule for 'rpi-firmware/fixup4.dat'
DEBUG: vfat(boot.vfat): adding implicit file rule for 'rpi-firmware/start4.elf'
DEBUG: vfat(boot.vfat): adding implicit file rule for 'rpi-firmware/overlays'
DEBUG: vfat(boot.vfat): adding implicit file rule for 'zImage'
INFO: cmd: "mkdir -p "/home/iman/rpi4/genimage.tmp"" (stderr+stdout):
INFO: cmd: "cp -a "/tmp/tmp.dMfSigyUwW" "/home/iman/rpi4/genimage.tmp/root"" (stderr+stdout):
INFO: cmd: "mv "/home/iman/rpi4/genimage.tmp/root/home" "/home/iman/rpi4/genimage.tmp/home"" (stderr+stdout):
mv: cannot stat '/home/iman/rpi4/genimage.tmp/root/home': No such file or directory
Makefile:809: recipe for target 'target-post-image' failed
make[1]: *** [target-post-image] Error 1
Makefile:84: recipe for target '_all' failed
make: *** [_all] Error 2
What other steps should be taken care of?
Or in more general, what is the way to creating + mounting new partition in buildroot?

Answer 1

If you want an empty /home directory then you should not use the mountpoint keyword:
image home.ext4 {
name = "home"
ext4 {}
size = 32M
}
The mountpoint keyword does not tell where the partition will be mounted. See The genimage docs for an explanation of what it does.
If you want to mount your partition from your rootfs then you can add it to /etc/fstab, perhaps in a rootfs overlay (BR2_ROOTFS_OVERLAY). genimage has no control on what will be actually mounted.

Answer 2

There are a lot of examples in test/ folder. For example it's about How add empty partition in your image:
image test.hdimage {
hdimage {
align = 1M
disk-signature = 0x12345678
}
partition part1 {
image = "part2.img"
size = 5k
partition-type = 0x83
}
partition extraimage {
image = "diskEmpty.ext2"
}
}
image diskEmpty.ext2 {
size = 10M //space for user, real space = (space for user + space for filesystem) > 10M
empty = true
temporary = true
ext2 {
label = "my_empty"
use-mke2fs = true
}
}