[yocto] setcap using postinst

[Ibtsam Ul-Haq]

Hi all,

I need help to set capabilities for certain binaries at build time.

I have followed this discussion from 2016:
https://lists.yoctoproject.org/pipermail/yocto/2016-July/030942.html

I am currently using Yocto Krogoth (not allowed to upgrade that for now),
but I have updated pseudo to 1.9.0.

In my image file I have added:
IMAGE_DEPENDS_tar_append = " tar-replacement-native"
EXTRANATIVEPATH += "tar-native"
IMAGE_CMD_TAR = "tar --xattrs --xattrs-include=*"

In my recipe file I have added postinst script:
pkg_postinst_${PN} () {
    setcap cap_sys_time,cap_ipc_owner+ep "$D/${bindir}/mybin"
}

My target device uses an sdcard image, which is created using dd from
the rootfs.ext4 image.

Apparently the postinst script approach is not working for me, I do
not get the capabilities on mybin in a running system. I need the
postinst script to work at rootfs creation time as I do not plan to
keep setcap in the final image, and also want to switch to a read-only
rootfs soon.

I would appreciate if someone could help me to make this work.

Best regards,
Ibtsam Haq