...instead of hardwired 0x314 (which is rather wrong
for modern kernels and hardware, just ran into that
with yet another Matrox G200eW WPCM450).

This keyword was misused due to the lack of understanding
of its meaning; thanks zerg@ for the hint, let's hide the
kernel boot parameters not expected to be modified by user
under the hood (and vice versa in some cases).

Note that this is just a keyword shift in all cases
but mediacheck where "showopts" is now added.

NB: this keyword is only relevant for gfxboot.

The former approach to handling "LiveCD with sessions"
has been to mangle "automatic=method:cdrom" into
"automatic=method:disk,label:ALT*" within gfxboot
so that propagator and make-initrd-propagator would
try and discover/create a filesystem labelled
"alt-live-storage" on a LiveFlash's free space.

Then "live_rw" handling has been unified in
make-initrd-propagator (as of 0.18-alt1) to accept
any of "label" subparameter or "live_rw" argument
to go and create_disk_slice().

Then propagator's cdrom.c has been fixed to actually
try sdX1 before sdX (as of 20150306-alt1).

And now it's all been tested to verify that:
- flash "ro" and "rw" boot is OK
- CD-ROM "ro" boot is OK
- CD-ROM "rw" boot is fine given that there's
  a partition labeled "alt-live-storage" elsewhere

This is a can of worms indeed :-/

References
~~~~~~~~~~
* http://altlinux.org/initrd-propagator
* http://altlinux.org/make-initrd-propagator
* http://bugzilla.altlinux.org/28289

The initial revision was brilliantly buggy: it is *so* apparent
that cdrom will never be actually used for rw slice that this
has evaded my attention rather completely.

There's a need for a separate boot target since
persistent storage is way slower than tmpfs indeed;
usbflash has a tendency for huge performance drops
given simultaneous writes in addition to reads which
are the bottleneck already.

make-initrd-propagator 0.18 introduced ext4 rw slice,
so the corresponding kernel module needs to be included
into stage1; see also #28289.

NB: not available on x86_64-efi (or hybrid GPT to be strict)
due to fragility of the hack being made: parted(8) panics
upon seeing that, and good ol' fdisk is unable to treat it.

NB: use/live/rw use/rescue/rx use/syslinux/ui/gfxboot
are unlikely to play very nice together due to the latter's
magic l10n: "session" label is taken by live_rw config snippet
and *is* translated in design-bootloader-source;
OTOH "rescue_session" is *not*.