[Buildroot] [PATCH] support: Allow compression of sdcard.img

[Alexey Brodkin <Alexey.Brodkin@synopsys.com>]

Hi Yann,

On Mon, 2018-01-08 at 00:00 +0100, Yann E. MORIN wrote:
> Evgeniy, All,
> 
> On 2017-12-18 16:51 +0300, Evgeniy Didin spake thusly:
> > In image files, generated by genimage.sh, there
> > are tens of megabytes most of which might be filled
> > with zeros as partitions are made a bit larger than
> > needed for minimalictic rootfs (which allows users to
> > add more libs and aps later on without messign with
> > partition sizes).
> > 
> > So adding an option for genimage.sh script, setting which
> > we gzip image file and greatly reduce it size.
> 
> Sorry, I am not in favour if this.
> 
> Today you're adding gzip compression (and by the way, -g is really
> unusual for a compresion option, it usually is called -z), but tomorrow
> someone will want xz compression, then another one will want lzo or lzip
> or whatever...

Well I'm not sure if the idea behind that move was clearly explained.
The point was to generate larger first partition so users may squeeze more
stuff there (like splashscreens/logos for U-Boot, larger uImage/zImage or
a couple of them even) while keeping smaller footprint of the resulting artifact
(sdcard.img.xxx). We were inspired by OpenWrt guys who compress images,
see https://downloads.lede-project.org/releases/17.01.4/targets/brcm2708/bcm2710/lede-17.01.4-brcm2708-bcm2710-rpi-3-ext4-sdcard.img.gz
as an example.

> And then someone will want to add gpg signature and encryption or
> whatnot...

That's for sure :)

> So, in such situation, I would argue that one should provide their
> post-image script, that does whatever last-minute tweaks on the
> generated image(s).

Ok it's OK by me as well.

> And by the way, this patch compreses the image, but does not remove the
> original, so this is actually a loss of space.

Sure, that should be addressed.

> So I am not in favour of this patch, sorry.

Anyways, thanks for the review!

-Alexey