Build enhancements

[nalajcie]

WORK IN PROGRES | DO NOT MERGE

This PR includes many buildscript enhancements and fixes to make it possible building with docker environment.

This also adds github workflow to automatically test building for supported targets (experimental).

[nalajcie]

Actually, this will probably be changed tomorrow to branch instead of pull request, as github actions configured in pull request are not triggered.

Unfortunately this PR introduces CI for 'push' and 'pull_request' only on main repo, it will look like that:
nalajcie#1

[kemonats]

maybe cut instead awk

sz=$(du -k "$IMG" | cut -f1)

[kemonats]

This can be simpliefied to:

TARGET_FAMILY=$(echo "$TARGET" | cut -d- -f1)
TARGET_SUBFAMILY=$(echo "$TARGET" | awk -F- '{ print $1"-"$2 }')

or without creating processes:

TARGET_FAMILY=${TARGET%%-*}
tmp=${TARGET#*-}
TARGET_SUBFAMILY="$TARGET_FAMILY-${tmp%%-*}"
unset tmp

[nalajcie]

Yeah, I wanted to do something with that ugly one-liner but ended with using printf in awk - which was not better by any means.

I think we can use string substitution as You suggested (as it's POSIX sh compliant), but I would prefer to do it separately from this PR (probably introduce it as a function to phoenix-rtos-build/build.subr?).

For now I've used Your version of awk script as it's tidier than the previous solution.

[kemonats]

shorter

 mkdir -p "$PREFIX_ROOTFS/"{dev,/local,data,mnt,var}

[kemonats]

Instead of executing du for each file, maybe it will be better:

size=$(find "${PREFIX_ROOTFS}" -type f -print0 | du -c -k --files0-from - | awk 'END{print $1}')

You can do arithmetic in awk:

awk 'END{print($1 * 150) / 100}'

[nalajcie]

I think leaving it as is is better - the first line computes the real sum of file sizes and the second just estimates the partition size to be 1.5x larger than that.

Maybe it would increase readability to change variables naming to fileSizeSum and partSize, but it can be done in a separate PR if desirable.

[kemonats]

du -k does not show the actual size of the files, but the size of the blocks used
e.g.
filesystem ETX4

du -b test.txt 
1       test.txt

du -k test.txt 
4       test.txt

[nalajcie]

You're right - I didn't dig into the ext2 image creation too much, the main point of this PR is to make all targets compilable, introduce docker-based build and basic CI using Github Actions.

The ext2 creation needs to be probably revised, as genext2fs takes size -b in blocks, and we should take into account that block size on host filesystem (eg. Your EXT4) might be different than on the target image.

For now I think we don't have the ability to mount ext2 partition on riscv64 targets, it would be better to focus on ia32-generic on which mounting ext2 works (can be tested under qemu).

This is not related to the buildsystem enhancements, should be done as a separate PR.

[nalajcie]

edit: I've checked that default block size in genext2fs is 1024, so we should probably get the ceil of file_size / 1024, eg:

echo $((($(stat -c "%s" file.txt) + 1023) / 1024))

But I'm not proficient enough to make the change and currently don't have the means to test it, so I'm leaving it as-is.

I think @Maxez is more knowledgeable in this topic, maybe our comments would help him.