[yocto] ROOTFS_RPM_DEBUG undocumented

[Paulo Neves]

Hello all,

I recently had the problem where the do_rootfs task seemed to hang.
The output where it hang looked like [1] and stayed that way for the
better part of an hour.

When I ran bitbake with -vD arguments not more relevant output was
given [2], also hanging for a lot of time.

As noted in another mailing list post about rootfs hanging[3], the
culprit was the enormous amount of kernel modules which were being
built. I only discovered this because I was able to strace and see
that actually bitbake was not hanging but actually running dnf
install.

When I searched for the code responsible for the invocation of dnf I
notice there is an undocumented variable called ROOTFS_RPM_DEBUG that
enables verbosity of the dnf and prints it out. This would have been
very helpful output for my 'bitbake -vD' invocation, and truly
debugging information would have helped.

What I ask is a decision on which option would better suite this issue:

# Add ROOTFS_RPM_DEBUG to the documentation;
# Detect if we are running with debug output and enable the debugging
output. This is the most elegant solution but I do not know how to
detect if debug log level is turned on;
# Have dnf always print in verbose mode and print the output to
bb.debug instead of bb.note.

I am happy to provide a patch upon decision or suggestions.

Paulo Neves

[1] NOTE: recipe drotag-cloud-image-debug-1.0-r0: task do_rootfs: Started

[2] DEBUG: drotag-cloud-image-debug-1.0-r0 do_rootfs: Executing python
function do_rootfs

[3] https://lists.yoctoproject.org/pipermail/yocto/2017-May/036293.html