Re: [PATCH v2 04/17] odb/source-packed: store pointer to "files" instead of generic source

[Patrick Steinhardt <ps@pks.im>]

On Tue, Jun 16, 2026 at 04:14:02PM -0500, Justin Tobler wrote:
> On 26/06/09 10:50AM, Patrick Steinhardt wrote:
[snip]
> > Detangling this mess is somewhat intricate though, and is made even more
> > intricate because it's not always clear which kind of source one is
> > holding at a specific point in time -- either the parent "files" source,
> > or the child "packed" source.
> > 
> > Make this relationship more explicit by storing a pointer to the "files"
> > source instead of storing a pointer to a generic `struct odb_source`.
> > This will help make subsequent steps a bit clearer.
> > 
> > Note that this is a temporary step, only. At the end of this series
> > we will have dropped the parent pointer completely.
> 
> Ok, so IIUC the eventual goal is to get rid of the pointer entirely, but
> for now we are just making its concrete type explicit without having to
> downcast. It's not immediately obvious to me how this step gets us
> closer to that goal, but that may become more obvious in the next
> patches. :)

The reason this helps is that during the intermediate steps, it's at
times very hard to see which source you're holding if we have both the
generic `base` and the generic `parent` pointer. That makes it quite
easy to confuse those two. So by turning the latter into the `files`
source, some of the intermediate steps become easier to reason about.

Patrick