[bitbake-devel] [PATCH] data/siggen: Switch md5 -> sha256

[Mike Crowe]

On Monday 17 December 2018 at 17:16:45 +0000, Richard Purdie wrote:
> Similarly to the codeparser change, change to sha256 hashes due to worries
> over collisions. The main impact of this change is slightly slower parsing
> time as well as longer sstate file names.
> 
> Signed-off-by: Richard Purdie <richard.purdie at linuxfoundation.org>

This change has given us several sstate cache filenames that exceed the 255
character limit of ext4. :(

We have a recipe that constructs a source tree from three separate Git
repositories, so we end up with a PV that is 93 characters long, which
doesn't help.

I've found that using urlsafe_b64encode to shorten the SHA-256 hashes
reduces the filename lengths by 21 characters, which is more than the 14
characters we need to save. However, there's a risk of collisions if the
cache is stored on a case-insensitive filesystem.

Would you be amenable to a patch to use urlsafe_b64encode?

If not, would you be amenable to a patch that consolidated the algorithm
into a single function called from the places you changed so that we can
patch it locally more easily? Or perhaps there's another way to make it
configurable?

Thanks.

Mike.