[Openembedded-architecture] Changes that switching from smart to dnf will cause

[Anders Darander]

Hi,

I'm primarily responding to your proposed pkg_postinst_ontarget_${PN},
as I'm a little bit worried.

* Alexander Kanavin <alexander.kanavin at linux.intel.com> [170214 15:04]:

> 2. Rpm 5.x is replaced with rpm 4.x. This is done for two major reasons:

> - DNF is API incompatible with Rpm 5.x and porting it and maintaining the
> port is non-trivial.

> - rpm 5.x itself is more or less unmaintained both in the upstream and in
> Yocto. There is no community around it, and Yocto is the sole remaining
> user. I think this is a stronger argument for moving away from it, than any
> technically superior features rpm 5.x may have over 4.x (not sure what those
> would be).

Mark Hatle should comment on this one. I know that there's been quite
some issues with RPM4 and cross-compilation / embedded usage...

> 6. Things that need to run on target during package installation should go
> into pkg_postinst_ontarget()

> Previously, the way to achieve this was:

> pkg_postinst_PACKAGENAME() {
>      if [ x"$D" = "x" ]; then
>           # Actions to carry out on the device go here
>      else
>           exit 1
>      fi
> }

> The new way is simply:

> pkg_postinst_ontarget_PACKAGENAME() {
>      # Actions to carry out on the device go here
> }

Do you plan to convert the old pkg_postinst_${PN} to this one?
How are they supposed to work on a read-only rootfs?

I'd say, ensure that the pkg_postinst_${PN} actually fails if something
goes wrong, i.e. add `set -e`, and fix up everything that fails during
rootfs...

Regarding your examples with fontconfig etc, luckily, I've not had to
use those yet, but I mmight have to do that in the near future. If so,
they'll have to run during rootfs creation and not on the target.

> The old way still works, but is deprecated and will produce a warning. I
> understand this change is orthogonal to dnf, but the current design is
> flawed and now is a chance to fix it. The reasons are:

> 1) Code is hard to read; it is not obvious that 'if D is defined then exit
> 1' means 'defer what follows to first boot during package cross-install'.

As with everything, documentation and experience helps... But sure, for
a newcomer this might look strange.

> 2) Worse, this hides actual errors in the scriptlets; there is no difference
> between scriptlet failing because it's intended to be run on target and
> scriptlet failing because there's a bug or a regression somewhere. I've
> already found broken scriptlets where the brokenness was hidden this way (in
> meta-selftest/recipes-test/postinst/postinst_1.0.bb)

Ensure that they're run under `set -e`...

> Plain pkg_postinst() without special tricks works exactly as before.

In the worst case, there might be followup patches trying to convert
pkg_postinst_ontarget_${PN} back to pkg_postinst_${PN}, for the
ro-rootfs case.

Cheers,
Anders

-- 
Anders Darander, Senior System Architect
ChargeStorm AB / eStorm AB