Re: [yocto] Fw: Reducing rootfs size in yocto

["Mikko Rapeli" <mikko.rapeli@bmw.de>]

Hi,

Generic approaches for reducing yocto target image size where buildhistory
is an important source of information:

 * review and minimize distro features, enable only what you need
   https://www.yoctoproject.org/docs/latest/mega-manual/mega-manual.html#ref-features-distro

 * review and minimize image recipe, install only those image features and packages
   which you need
   https://www.yoctoproject.org/docs/latest/mega-manual/mega-manual.html#ref-features-image

 * review the needed binary packages: traverse the tree of dependencies what you need,
   review every single recipe and change PACKAGECONFIG or build flags to remove
   features which you do not need. This it may be possible to remove large set
   of dependencies from images, e.g. language bindings, debug tools. In some cases
   one just needs a single binary executable or shared library but it is bundled
   in a larger binary package with more complex dependencies. For these cases
   add a bbappend to custom layers to change the packaging to only include what
   you need.
   https://www.yoctoproject.org/docs/latest/mega-manual/mega-manual.html#var-PACKAGECONFIG

 * change compiler flags from default O2 to Os optimization. This can work for
   some recipes which are not prerformance critical or to the whole build. Note
   that many SW components break this in their own build scripts by adding
   O2 or even O3 by default. Check from buildhistory that binary sizes go smaller
   after switch from O2 to Os and review every important recipe which did not.
   You may be able to save up to 15% in rootfs size this way, but all depends
   on the details of SW components and image contents.
   see poky/meta/conf/bitbake.conf

I've followed this for multiple products and found out that poky is nice to work with
but BSP layers add or depend on all kinds of extra things that products do not need.
Thus I have ended by BBMASK'ing away large parts of BSP layer recipes in distro
configs. This with multiple x86 and ARM BSP layers from various SoC vendors.

Also, RTFM :)

https://www.yoctoproject.org/docs/latest/mega-manual/mega-manual.html#building-a-tiny-system

Hope this helps,

-Mikko