[parted-devel] reproducible output

[Brian C. Lane]

On Wed, Jun 19, 2019 at 09:36:15PM +0200, Steffen Dettmer wrote:
> 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?

We can't, it isn't enough bits for GPT UUIDs. We need 128 bits.

> 
> > 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?

No, uuid_generate uses /dev/urandom

> > 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)

I don't see why you would want to do that -- it's better to just pass in
a value to use and let the tools decide if they want to use a constant
or whatever.

If we're going to take changes like these, they need to be as simple as
possible to prevent interfering with normal parted usage.

-- 
Brian C. Lane (PST8PDT) - weldr.io - lorax - parted