This change tries to force loading the storage driver
for cases when SecureBoot is "helping" the chainloader
to fail, see #29705 for details collected so far.

Of course ahci.ko only does AHCI but that's every storage
controller I've seen on UEFI/SecureBoot systems so far.

It would be better to put it into stage2 in the first place
but this somehow went over my head; rescue made a reminder.

It was removing autodetection setting completely
thus implicitly setting it to the default "all"
with make-initrd-0.8.1+; just set it to be empty.

Thanks legion@ and boyarsh@; see also #28578.

The previous part was fixed and discussed in commit
c30490e2;
so much for a deduplication effort...

This would result in almost immediate

  make[1]: *** [profile/populate] Error 2

as well.

propagator-20121109-alt1 obsoleted initfs (and dropped
mkinitfs script altogether); that was taken into account
in both make-initrd-propagator and mkimage-profiles-desktop
but not in mkimage proper, see also discussion in #27976.

*Of course* the "weird" [ ... ] || ... construct meant to avoid
the non-zero exit status of the whole thing wasn't employed
where it actually does make the difference!

Thanks ildar@ for hitting and reporting this, as in

  + verbose '/usr/lib64/propagator exists'
  + '[' -n '' ']'
  mki-scripts: .../stage1/scripts.d/80-make-initfs: unable to run script.
  make[3]: *** [run-scripts] Error 1

The issue that appeared pretty hard to diagnose occured
to be the enhancement made in make-initrd-propagator=0.8.1-alt1.2
(that didn't hit Sisyphus until merged into 0.10-alt1) which
drops propagator dependency.

And that was optimized out in m-p, of course.

The added pdir check was a hillarious(tm) overlooked bug indeed:
I tried to put .../initfs/initfs instead of .../initfs as the result.

Duly spotted by torabora@, thanks a lot.

Still the kmod+propagator+kernel-image combo needed some tweaking too,
see #27640

A tiny bit less cut-n-paste. :)

Thanks mithraen@ for spotting, boyarsh@ for explaining,
and legion@ for hearty support :)

The problem would manifest itself like this:

  /.host/script.sh: line 20: /usr/lib64/propagator/initfs: \
  No such file or directory
  mki-scripts: .../stage1/scripts.d/80-make-initfs: unable to run script.

An initial draft of it was done half a year ago but several tricky
thingies had kept the code from showing up as it was rather brittle
and incomplete.

This implementation involves quite a few changes all over the place
but finally works good enough for live and installer images.

Please pay attention to the versions of these packages:
- installer-feature-setup-plymouth (0.3.2-alt1+)
- branding-altlinux-sisyphus (20110706-alt2+ if used)
- plymouth (0.8.3-alt20.git20110406+)

See also:
- http://www.altlinux.org/Branding
- http://www.altlinux.org/Plymouth

legion@ implemented skipping depmod call, and that's several more
seconds for most of the images; let's shave these off if possible.

Looks like the 128k default block size is pretty well chosen:
it saves ~6% of image size compared to 64k, and subsequent
differences are ~3% per doubling the block size up to 1M
(thanks led@ for carrying out the tests).

So we'll stick with 256k for "normal" xz compression (inodes
uncompressed) and get 512k back for "tight" one (compressed).
The runtime performance issues are to be examined yet when
bootchart or the like is deployed, nothing drastic though.

With "fast" (gzip/lzo) squash compression inodes go unmolested.

For the record, tight live-webkiosk builds as 95M image in 3:40,
and tight live-flightgear.iso builds as 669M image in 6:34.  Nice.

There's no much sense going for 1M block size: e.g. live-webkiosk
would drop to 93M (3:46) but its load time would increase up to
2:07 as compared to 1:48 for -b 524288 and 1:42 for -b 262144 -noI
on a Duron 500/512M system given the very same DVD+RW media.

The existing implementation would handle kernel differences
just fine but a bit too automatically: if it sees xz support,
that's what will end up being used (and if there's -Xbcj binary
compression filter available for the target platform, it will
be applied unequivocally either).

It's perfectly suitabe for getting fine-tuned release images
but is also a bit too resource-consuming while developing the
image configuration which has no business with its compression.

The one and only knob is SQUASHFS (see doc/variables.txt);
to give an idea of the differences, here are some numbers
for a mostly-binary (43% as per 99-elf-stats) webkiosk livecd
and a rather less so (18%) flightgear one on a dual quad-core
X5570 node (each mksquashfs run used up all the cores):

SQUASHFS | live-webkiosk.iso | live-flightgear.iso
---------+-------------------+---------------------
fast     | 3:30 / 130M       | 5:11 / 852M
normal * | 3:37 / 100M       | 5:35 / 688M
tight    | 3:50 / 98M        | 6:47 / 683M

Thus if the knob isn't fiddled with, the defaults will allow
for a reasonably fast build of a pretty slim image; if one is
building a release or if a particular image is very sensitive
being close to the media capacity then just add SQUASHFS=tight
and see it a percent or two down on size.

Please note that lzo/gzip-compressed images are also quicker
to uncompress thus further helping with test iterations.

Thanks to led@ and glebfm@ for helpful hints and questions.

gns@ has 512k, led@ suggests that it's too much a bit;
let's try 256k.

A larger block size was recommended by led@;
gns@ seems to concur as the 512k value was borrowed
from liveflash.eeepc profile (along with -noI).

The other issue is with binary specific compressors:
x86 was clearly assumed while the data for an educated
guess are pretty handy.  Please note that using filters
incurs additional compression attempts for the utility
to choose the best result.

Initial openSUSE package base taming effort has shown that
relatively few things should be fixed; subst has been generalized
as -i option to sed(1) since its introduction, so let's just fix it.

The features might get copy-pasted (or even copied-and-pruned)
when initialized; there's an unneccessary duplication of the
function name in the line adding it to FEATURES list, thus
prone to being forgotten and causing some havoc later on.

It was wrong in the first place but tackling this with some
double-colon rules ran into terminality issues, and further
tortures were considered unneccessary.

The current solution isn't perfect (no completely transparent
function name registration upon corresponding target being called)
but at least it is an improvement...

- introduced generic stage2 subprofile (non-standalone)
- ported installer and rescue over to stage2/{install2,rescue}
- initial stage2/live (needs more work for sure)
- use make-initrd-propagator
- updated and somewhat extended doc/

NB: mind #26133, #26134