Re: [PATCH v3 00/30] pack-bitmap: pseudo-merge reachability bitmaps

From: Jeff King <peff@peff.net>
Date: May 25, 2024, 03:15 UTC
Message-ID: <20240525031516.GB1889620@coredump.intra.peff.net>
In-Reply-To: <Zk+hP++s/Pz+yym4@nand.local>

On Thu, May 23, 2024 at 04:04:15PM -0400, Taylor Blau wrote:

Show 19 quoted lines

> On Thu, May 23, 2024 at 07:05:32AM -0400, Jeff King wrote:
> > I wonder if the start of the pseudo-merge section should have a 4-byte
> > version/flags field itself? I don't think that's something we've done
> > before, and maybe it's overkill. I dunno. It's just a lot easier to do
> > now than later.
> 
> I think the tricky thing here would be that the extension itself is a
> variable size, so every version would have to put the "extension size"
> field in the same place.
> 
> Otherwise, an older Git client which doesn't understand a future version
> of the pseudo-merge extension wouldn't know how large the extension is,
> and wouldn't be able to adjust the index_end field appropriately to skip
> over it.
> 
> Of course, we could make it a convention that says "all versions have to
> place the extension size field at the same relative offset", but it
> feels weird to read some of the extension while not understanding the
> whole thing.

Ah, yeah, I didn't think of that. That definitely complicates things.

It certainly would be possible to have a version+size header at the start. Which is...basically reinventing the chunk format. Let's not worry about it for now, and as a long-term thing we might consider moving the bitmap format over to the chunk style.

-Peff