support xz compressed images

[chombourger]

use https://github.com/Rogdham/python-xz to support .xz images

[vj-kumar]

Not sure if someone is looking into to it. If not planing to take it.

[chombourger]

Not sure if someone is looking into to it. If not planing to take it.

Thanks!

[vj-kumar]

@chombourger Any specific reason for using python-xz? Looks like lzma can do it too. I do see some benefits mentioned in python-xz, but currently not sure whether it will have an impact.

[jan-kiszka]

If you are talking about isar image compression: Adriaan has started porting over the OE image compression features. That will obsolete the currently needed custom image classes.

[vj-kumar]

@jan-kiszka This is about mtda's storage writer supporting xz compressed images.

mtda/mtda/storage/writer.py

Lines 49 to 60 in a13e98c

	compression = CONSTS.IMAGE(compression)
	if compression == CONSTS.IMAGE.RAW:
	self._write = self.write_raw
	elif compression == CONSTS.IMAGE.BZ2:
	self._write = self.write_bz2
	elif compression == CONSTS.IMAGE.GZ:
	self._write = self.write_gz
	elif compression == CONSTS.IMAGE.ZST:
	self._write = self.write_zst
	else:
	raise ValueError("unsupported image compression!")
	self._compression = compression

[vj-kumar]

Bz2 write is broken. Tested in Qemu, Richa also validated in an actual board. XZ similar implementation to BZ2 also doesnot work. Checking.

[chombourger]

Thanks for the info. We will get a framework to test our APIs and features With #146 and hopefully avoid regressions in the future

[vj-kumar]

Related to #147

Planning to address #147 before getting here.