[OpenWrt-Devel] [PATCH 2/5] build: image: Add pad-to and pad-rootfs-squashfs helpers

Jo-Philipp Wich jo at mein.io
Mon Apr 1 01:33:40 EDT 2019


>>> I would like to avoid adding generating padded images by default. 
>> To just save some space? We're gzipping the images by default, which makes
>> image padded to 256M just 2.7M big. I find 256M overkill for testing, so
>> that's why I've suggested 32M by default for QEMU padded images.
> Not building padded images saves build time, because the system doesn't
> have to waste so many cycles compressing empty data.

There's so many inefficiencies in the overall build process that gzip
compressing a 256MB file is neglectible.

>>> I just came up with this simple script, which takes an existing image and
>>> pads it to full size: http://nbd.name/pad-image.pl With this, shipping
>>> padded images should be unnecessary.
>> Ok, if that is preferred, it's fine with me. But we should probably add some
>> note somewhere, that in order to test this images in QEMU (x86, armvirt,
>> malta), the images should be padded with this script in order to provide
>> usable images.

Most other targets ship image artifacts which are usable ootb, requiring
one extra step to pad the combined images is a waste of user resources
every single time. It also causes recurring confusion among users
wanting to use x86 builds since the need for padding is neither
documented, nor obvious while a combined.img.gz makes it obvious that it
is an image file which requires decompression.

I really don't see the huge problem with conservatively padding the
combined image artifacts to something like 32 or 48MB, it must not even
be 256M or more.

~ Jo

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