[oe] [RFC] cpio.lzma compression level in bitbake.conf

[Andrea Adami]

Hello,

in bitbake.conf we use the maximum lzma compression level (-c -9) for
the initramfs:

IMAGE_CMD_cpio.lzma = "type cpio >/dev/null; cd ${IMAGE_ROOTFS} &&
(find . | cpio -o -H newc | lzma -c -9
>${DEPLOY_DIR_IMAGE}/${IMAGE_NAME}.rootfs.cpio.lzma)
${EXTRA_IMAGECMD}"

This makes decompressor fail on devices with 32Mb RAM (see
http://paste.debian.net/110203/ ).
Same kernel boots with compression set to -7.

Some figures can be obtained here:
http://www.gsp.com/cgi-bin/man.cgi?section=1&topic=lzcat

It was suggested we should introduce something like
LZMA_COMPRESSION_LEVEL or use internal tables to find better level
from targets memory amount.
In the meanwhile I think we should change the defaults in bitbake.conf.

Opinions?

Andrea