[parted-devel] reproducible output

[Steffen Dettmer]

On Wed, Jun 19, 2019 at 8:16 PM Brian C. Lane <bcl at redhat.com> wrote:

> According to comments in misc.c zeros could be mis-interpreted so it
> would have to be something else, like the failure value for
> generate_random_uint32 of 0xffffffff

I think SOURCE_DATE_EPOCH (which is a uint32_t AFAIK) maybe
could directly be used as long as it isn't a problem having the same
rnd everywhere?

> It looks like we're using uuid_generate everywhere so setting a seed
> isn't possible as far as I know. It tries really hard to actually be
> random :)

Isn't uuid_generate using the seeded generator and shouldn't the values
be the same if the same seed is used? For example, SOURCE_DATE_EPOCH?

> Are partitions really part of the problem? When I've read about
> reproducible builds it has been the binaries that have been the focus.

In my case (proprietary) I have to deliver a disk image including a partition
table (but apparently the filesystem contains a lot of unstable values anyway).

> It may make sense to use an environmental variable instead of a switch,
> that way it could be overridden without needing to change the tooling
> that uses parted/libparted. Is there a standard for forcing a UUID value
> like there is with SOURCE_DATE_EPOCH for time? FORCE_UUID or something
> like that?

If the UUID values should differ (to avoid that two file systems get
the same one),
couldn't seeding the RND to SOURCE_DATE_EPOCH be a way?
The every UUID would be different within one run but each the same in the next.
(I think there are details to consider, such as XOR some control
vector / constant
to avoid that two tools generate the same "rnd" values etc)

Steffen