[PATCH v3 4/4] pack-refs: add fully-peeled trait
- From
Jeff King <peff@peff.net>
- Date
- Mar 18, 2013, 11:37 UTC
- Message-ID
- <20130318113732.GA14789@sigill.intra.peff.net>
- In-Reply-To
- <7vli9lre1j.fsf@alter.siamese.dyndns.org>
On Sun, Mar 17, 2013 at 01:01:44PM -0700, Junio C Hamano wrote:
Show 6 quoted lines
> > + * All references in the file that can be peeled are peeled. > > + * Inversely (and this is more important, any references in the > > A missing closing paren after "more important". Also the e-mail > quote reveals there is some inconsistent indentation (HTs vs runs of > SPs) here.
Thanks, will fix (the whitespace damage is due to me cutting and pasting from Michael's commit).
Show 5 quoted lines
> > > + * file for which no peeled value is recorded is not peelable. This > > + * trait should typically be written alongside "fully-peeled" for > > Alongside "peeled", no?
Urgh, yes. Will fix.
> [...] > I am not sure why you find this any more readable.
I was trying to avoid the "set PEELED globally, but sometimes unset it for specific refs" pattern which I think is confusing to the reader. But I think what you wrote is even better. I used an enum rather than two variables to make it clear that only ones takes effect. I had wanted to use a switch, also, but you end up either repeating yourself, or doing this gross fall-through:
switch (peeled) {
case PEELED_TAGS:
if (prefixcmp(refname, "refs/tags/"))
break;
/* fall-through */
case PEELED_FULLY:
last->ref |= REF_KNOWS_PEELED;
break;
default:
/* we know nothing */
}So I just stuck with the conditional.
Here's the re-roll.
-- >8 -- From: Michael Haggerty <mhagger@alum.mit.edu> Subject: [PATCH] pack-refs: add fully-peeled trait
Older versions of pack-refs did not write peel lines for refs outside of refs/tags. This meant that on reading the pack-refs file, we might set the REF_KNOWS_PEELED flag for such a ref, even though we do not know anything about its peeled value.
The previous commit updated the writer to always peel, no matter what the ref is. That means that packed-refs files written by newer versions of git are fine to be read by both old and new versions of git. However, we still have the problem of reading packed-refs files written by older versions of git, or by other implementations which have not yet learned the same trick.
The simplest fix would be to always unset the REF_KNOWS_PEELED flag for refs outside of refs/tags that do not have a peel line (if it has a peel line, we know it is valid, but we cannot assume a missing peel line means anything). But that loses an important optimization, as upload-pack should not need to load the object pointed to by refs/heads/foo to determine that it is not a tag.
Instead, we add a "fully-peeled" trait to the packed-refs file. If it is set, we know that we can trust a missing peel line to mean that a ref cannot be peeled. Otherwise, we fall back to assuming nothing.
[commit message and tests by Jeff King <peff@peff.net>]
Signed-off-by: Michael Haggerty <mhagger@alum.mit.edu> Signed-off-by: Jeff King <peff@peff.net> --- pack-refs.c | 2 +- refs.c | 49 ++++++++++++++++++++++++++++++++++++++++++++----- t/t3211-peel-ref.sh | 22 ++++++++++++++++++++++ 3 files changed, 67 insertions(+), 6 deletions(-)
diff --git a/pack-refs.c b/pack-refs.c index ebde785..4461f71 100644 --- a/pack-refs.c +++ b/pack-refs.c @@ -128,7 +128,7 @@ int pack_refs(unsigned int flags) die_errno("unable to create ref-pack file structure"); /* perhaps other traits later as well */ - fprintf(cbdata.refs_file, "# pack-refs with: peeled \n"); + fprintf(cbdata.refs_file, "# pack-refs with: peeled fully-peeled \n"); for_each_ref(handle_one_ref, &cbdata); if (ferror(cbdata.refs_file)) diff --git a/refs.c b/refs.c index 175b9fc..e2b760d 100644 --- a/refs.c +++ b/refs.c @@ -803,11 +803,38 @@ static void read_packed_refs(FILE *f, struct ref_dir *dir) return line; } +/* + * Read f, which is a packed-refs file, into dir. + * + * A comment line of the form "# pack-refs with: " may contain zero or + * more traits. We interpret the traits as follows: + * + * No traits: + * + * Probably no references are peeled. But if the file contains a + * peeled value for a reference, we will use it. + * + * peeled: + * + * References under "refs/tags/", if they *can* be peeled, *are* + * peeled in this file. References outside of "refs/tags/" are + * probably not peeled even if they could have been, but if we find + * a peeled value for such a reference we will use it. + * + * fully-peeled: + * + * All references in the file that can be peeled are peeled. + * Inversely (and this is more important), any references in the + * file for which no peeled value is recorded is not peelable. This + * trait should typically be written alongside "peeled" for + * compatibility with older clients, but we do not require it + * (i.e., "peeled" is a no-op if "fully-peeled" is set). + */ static void read_packed_refs(FILE *f, struct ref_dir *dir) { struct ref_entry *last = NULL; char refline[PATH_MAX]; - int flag = REF_ISPACKED; + enum { PEELED_NONE, PEELED_TAGS, PEELED_FULLY } peeled = PEELED_NONE; while (fgets(refline, sizeof(refline), f)) { unsigned char sha1[20]; @@ -816,15 +843,20 @@ static void read_packed_refs(FILE *f, struct ref_dir *dir) if (!strncmp(refline, header, sizeof(header)-1)) { const char *traits = refline + sizeof(header) - 1; - if (strstr(traits, " peeled ")) - flag |= REF_KNOWS_PEELED; + if (strstr(traits, " fully-peeled ")) + peeled = PEELED_FULLY; + else if (strstr(traits, " peeled ")) + peeled = PEELED_TAGS; /* perhaps other traits later as well */ continue; } refname = parse_ref_line(refline, sha1); if (refname) { - last = create_ref_entry(refname, sha1, flag, 1); + last = create_ref_entry(refname, sha1, REF_ISPACKED, 1); + if (peeled == PEELED_FULLY || + (peeled == PEELED_TAGS && !prefixcmp(refname, "refs/tags/"))) + last->flag |= REF_KNOWS_PEELED; add_ref(dir, last); continue; } @@ -832,8 +864,15 @@ static void read_packed_refs(FILE *f, struct ref_dir *dir) refline[0] == '^' && strlen(refline) == 42 && refline[41] == '\n' && - !get_sha1_hex(refline + 1, sha1)) + !get_sha1_hex(refline + 1, sha1)) { hashcpy(last->u.value.peeled, sha1); + /* + * Regardless of what the file header said, + * we definitely know the value of *this* + * reference: + */ + last->flag |= REF_KNOWS_PEELED; + } } } diff --git a/t/t3211-peel-ref.sh b/t/t3211-peel-ref.sh index 85f09be..d4d7792 100755 --- a/t/t3211-peel-ref.sh +++ b/t/t3211-peel-ref.sh @@ -39,4 +39,26 @@ test_expect_success 'refs are peeled outside of refs/tags (packed)' ' test_cmp expect actual ' +test_expect_success 'create old-style pack-refs without fully-peeled' ' + # Git no longer writes without fully-peeled, so we just write our own + # from scratch; we could also munge the existing file to remove the + # fully-peeled bits, but that seems even more prone to failure, + # especially if the format ever changes again. At least this way we + # know we are emulating exactly what an older git would have written. + { + echo "# pack-refs with: peeled " && + print_ref "refs/heads/master" && + print_ref "refs/outside/foo" && + print_ref "refs/tags/base" && + print_ref "refs/tags/foo" && + echo "^$(git rev-parse "refs/tags/foo^{}")" + } >tmp && + mv tmp .git/packed-refs +' + +test_expect_success 'refs are peeled outside of refs/tags (old packed)' ' + git show-ref -d >actual && + test_cmp expect actual +' + test_done
-- 1.8.2.rc2.7.gef06216