Re: [RFC] git-pack-refs --prune

From: Junio C Hamano <junkio@cox.net>
Date: Sep 18, 2006, 18:44 UTC
Message-ID: <7vhcz5ow0a.fsf@assigned-by-dhcp.cox.net>
In-Reply-To: <Pine.LNX.4.64.0609180934360.4388@g5.osdl.org>

Linus Torvalds <torvalds@osdl.org> writes:

Show 11 quoted lines

> The way to fix both these problems at once would be to add a flag to the 
> "for_each_ref()", which says whether it followed a link, or whether it was 
> already packed, so that we wouldn't pack symlinks at all, and we wouldn't 
> add already-packed refs to the "keeprefs" list.
>
> But that requires a sligh semantic extension to "do_for_each_ref()" (and 
> "struct ref_list" needs a flag to say whether it was looked up through a 
> symlink).
>
> I was thinking that the easy way to solve it is to just _pack_ everything 
> (the way we do now - incorrectly for symrefs), but never prune a symref.

I see. Thanks for pointing out the issue with symrefs. I think clone with --use-separate-remote creates remote/$that_repo/HEAD that points at the branch the remote side's HEAD points at (to be precise, the one it guessed the remote side's HEAD points at), so this is a real issue already.

I wanted to update for_each_ref() anyway for other reasons (it really should take callback data -- the way the current users use global variables to work this around is eyesore), so hopefully I'll find time to take a look at it.

Rough outline:

 - for_each_ref() and friends become:

   typedef int each_ref_fn(const char *refname,
			   const unsigned char *sha1,
   #define REF_IS_SYMREF 01
   #define REF_IS_PACKED 02
                           int flags, /* above bits or'ed */ 
                           void *cb_data);
   int for_each_ref(each_ref_fn fn, void *cb_data);

 - handle_one_ref notices a symref and ignores it; it remembers
   refs that are not symref and are still loose for later
   pruning under --prune.

We might want to update the initial handshake of upload-pack protocol so that peek-remote and fetch-pack can tell which one is a symref pointing at what. Do the usual server_capabilities discovery in connect.c::get_remote_heads(), and if an extension "symref" is supported than ask for symref information (typically we would only get "HEAD points at refs/heads/foo" and nothing else). Then git-clone.sh does not have to make a guess. But that is a separate topic.