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I've made my own kernel package for a custom iMX8M board, which passes lintian without warnings or errors.

The top three layers of the package tree are:

/tmp/my-kernel_5.10.9-2lEIW6BD_arm64 |-- DEBIAN | |-- control | `-- preinst |-- boot | |-- Image | `-- dtbs | `-- imx8mq-smarc.dtb |-- lib | `-- modules `-- usr `-- share `-- doc

preinst makes sure that /boot is mounted:

fadedbee@box ~ $ sudo cat /tmp/my-kernel_5.10.9-2lEIW6BD_arm64/DEBIAN/preinst #!/bin/bash set -e if grep -qs '/dev/mmcblk1p1 /boot' /proc/mounts; then echo "/boot is mounted." else echo "/boot is not yet mounted, mounting..." mount /dev/mmcblk1p1 /boot fi exit 0

It mounts /boot, if not already mounted and relies on the dpkg to put all of the files in place.

It currently fails.

root@arm:~# dpkg -i /tmp/my-kernel_5.10.9-2lEIW6BD_arm64.deb (Reading database ... 45956 files and directories currently installed.) Preparing to unpack .../my-kernel_5.10.9-2lEIW6BD_arm64.deb ... /boot is not yet mounted, mounting... Unpacking my-kernel (5.10.9) ... dpkg: error processing archive /tmp/my-kernel_5.10.9-2lEIW6BD_arm64.deb (--install): unable to make backup link of './boot/Image' before installing new version: Operation not permitted Errors were encountered while processing: /tmp/my-kernel_5.10.9-2lEIW6BD_arm64.deb

The permissions on /boot/Image are as expected:

root@arm:~# ls -lsa /boot/Image 28680 -rwxr-xr-x 1 root root 29366784 Mar 25 11:48 /boot/Image

The /boot partition is vfat and mounted R/W:

root@arm:~# mount | grep boot /dev/mmcblk1p1 on /boot type vfat (rw,relatime,fmask=0022,dmask=0022,codepage=437,iocharset=iso8859-1,shortname=mixed,errors=remount-ro)

Why might this operation be failing?

Is there a work-around?

Update: I've checked what's inside a "normal" debian kernel package. It also relies on normal behaviour to install the kernel image in /boot.

root@debian:/tmp/tmp# tree -L 3 . ├── boot │   ├── config-6.1.0-18-amd64 │   ├── System.map-6.1.0-18-amd64 │   └── vmlinuz-6.1.0-18-amd64 ├── lib │   └── modules │   └── 6.1.0-18-amd64 └── usr └── share ├── bug ├── doc └── lintian 10 directories, 3 files
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    I've been helped to see that "link" is the critical word. FAT filesystems may not support symbolic and/or hard links. I will try using ext2 for boot instead of FAT. Commented Mar 26, 2024 at 11:58

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I needed to fix two problems to make this work.

  1. I amended my disk-image build system to create a ext4 /boot instead of the vendor-provided vfat /boot. This allows dpkg to make symlinks and hardlinks. Unfortunately this led to u-boot failing to load uEnv.txt, the kernel Image and the device-tree blob. I was able to use the u-boot monitor to list the files on /boot, so I was confused for an hour or two, until I did a "print env" and noticed that there were some "loadfat" calls in the compiled-in environment.
u-boot$ ext4ls mmc 1:1 <DIR> 1024 . <DIR> 1024 .. <DIR> 12288 lost+found <DIR> 1024 dtbs 29366784 Image 1163 uEnv.txt u-boot$ printenv ... loadaddr=0x40480000 loadbootenv=fatload mmc ${mmcdev}:${mmcpart} ${loadaddr} uEnv.txt loadbootscript=fatload mmc ${mmcdev}:${mmcpart} ${loadaddr} ${script}; loadfdt=fatload mmc ${mmcdev}:${mmcpart} ${fdt_addr} /dtbs/${fdt_file} loadimage=fatload mmc ${mmcdev}:${mmcpart} ${loadaddr} ${image} ...
  1. To fix that, I first confirmed that I could manually fix the environment and boot from ext4. Then I found the correct source file and edited u-boot's smarcimx8mq.h:
fadedbee@box ~/my_build/src/uboot $ git diff diff --git a/include/configs/smarcimx8mq.h b/include/configs/smarcimx8mq.h index 7eb93677cd..43ce2636eb 100644 --- a/include/configs/smarcimx8mq.h +++ b/include/configs/smarcimx8mq.h @@ -101,8 +101,8 @@ "mmcroot=" CONFIG_MMCROOT " rootwait rw\0" \ "usbroot=/dev/sda2 rootwait ro\0" \ "mmcrootfstype=ext4 rootwait\0" \ - "loadbootenv=fatload mmc ${mmcdev}:${mmcpart} ${loadaddr} uEnv.txt\0" \ + "loadbootenv=ext4load mmc ${mmcdev}:${mmcpart} ${loadaddr} uEnv.txt\0" \ "loadusbbootenv=fatload usb 0:1 ${loadaddr} uEnv.txt\0" \ "mmcautodetect=yes\0" \ "importbootenv=echo Importing environment from mmc (uEnv.txt)...; " \ "env import -t $loadaddr $filesize\0" \ @@ -112,13 +112,13 @@ "rootfstype=${mmcrootfstype} root=${mmcroot}\0 " \ "usbargs=setenv bootargs ${jh_clk} console=${console} ${optargs} " \ "rootfsusbtype=${usbrootfstype} root=${usbroot}\0 " \ - "loadbootscript=fatload mmc ${mmcdev}:${mmcpart} ${loadaddr} ${script};\0" \ + "loadbootscript=ext4load mmc ${mmcdev}:${mmcpart} ${loadaddr} ${script};\0" \ "bootscript=echo Running bootscript from mmc ...; " \ "source\0" \ - "loadimage=fatload mmc ${mmcdev}:${mmcpart} ${loadaddr} ${image}\0" \ + "loadimage=ext4load mmc ${mmcdev}:${mmcpart} ${loadaddr} ${image}\0" \ "loadm4bin=load mmc ${mmcdev}:${mmcpart} ${m4_addr_tmp} ${m4_bin}\0" \ "loadusbimage=fatload usb 0:1 ${loadaddr} ${image}\0" \ - "loadfdt=fatload mmc ${mmcdev}:${mmcpart} ${fdt_addr} /dtbs/${fdt_file}\0" \ + "loadfdt=ext4load mmc ${mmcdev}:${mmcpart} ${fdt_addr} /dtbs/${fdt_file}\0" \ "loadusbfdt=fatload usb 0:1 ${fdt_addr} /dtbs/${fdt_file}\0" \ "cpm4mem=cp.b ${m4_addr_tmp} ${m4_addr} 20000\0" \ "mmcboot=echo Booting from mmc ...; " \

and recompiled u-boot.

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