From 27be76b230b07360b64aec06d6b0b9bc9e993603 Mon Sep 17 00:00:00 2001 From: Taylor Blau Date: Thu, 6 Mar 2025 10:34:48 -0500 Subject: [PATCH 1/2] refs.c: remove empty '--exclude' patterns In 59c35fac54 (refs/packed-backend.c: implement jump lists to avoid excluded pattern(s), 2023-07-10), the packed-refs backend learned how to construct "jump lists" to avoid enumerating sections of the packed-refs file that we know the caller is going to throw out anyway. This process works by finding the start- and end-points (that is, where in the packed-refs file corresponds to the range we're going to ignore) for each exclude pattern, then constructing a jump list based on that. At enumeration time we'll consult the jump list to skip past everything in the range(s) found in the previous step, saving time when excluding a large portion of references. But when there is a --exclude pattern which is just the empty string, the behavior is a little funky. When we try and exclude the empty string, the matched range covers the entire packed-refs file, meaning that we won't output any packed references. But the empty pattern doesn't actually match any references to begin with! For example, on my copy of git.git I can do: $ git for-each-ref '' | wc -l 0 So "git for-each-ref --exclude=''" shouldn't actually remove anything from the output, and ought to be equivalent to "git for-each-ref". But it's not, and in fact: $ git for-each-ref | wc -l 2229 $ git for-each-ref --exclude='' | wc -l 480 But why does the '--exclude' version output only some of the references in the repository? Here's a hint: $ find .git/refs -type f | wc -l 480 Indeed, because the files backend doesn't implement[^1] the same jump list concept as the packed backend we get the correct result for the loose references, but none of the packed references. Since the empty string exclude pattern doesn't match anything, we can discard them before the packed-refs backend has a chance to even see it (and likewise for reftable, which also implements a similar concept since 1869525066 (refs/reftable: wire up support for exclude patterns, 2024-09-16)). This approach (copying only some of the patterns into a strvec at the refs.c layer) may seem heavy-handed, but it's setting us up to fix another bug in the following commit where the fix will involve modifying the incoming patterns. [^1]: As noted in 59c35fac54. We technically could avoid opening and enumerating the contents of, for e.g., "$GIT_DIR/refs/heads/foo/" if we knew that we were excluding anything under the 'refs/heads/foo' hierarchy. But the --exclude stuff is all best-effort anyway, since the caller is expected to cull out any results that they don't want. Noticed-by: Jeff King Signed-off-by: Taylor Blau Signed-off-by: Junio C Hamano --- refs.c | 16 ++++++++++++++++ t/t1419-exclude-refs.sh | 10 ++++++++++ 2 files changed, 26 insertions(+) diff --git a/refs.c b/refs.c index 915aeb4d1d..fa943d7d64 100644 --- a/refs.c +++ b/refs.c @@ -1560,6 +1560,20 @@ struct ref_iterator *refs_ref_iterator_begin( enum do_for_each_ref_flags flags) { struct ref_iterator *iter; + struct strvec normalized_exclude_patterns = STRVEC_INIT; + + if (exclude_patterns) { + for (size_t i = 0; exclude_patterns[i]; i++) { + const char *pattern = exclude_patterns[i]; + size_t len = strlen(pattern); + if (!len) + continue; + + strvec_push(&normalized_exclude_patterns, pattern); + } + + exclude_patterns = normalized_exclude_patterns.v; + } if (!(flags & DO_FOR_EACH_INCLUDE_BROKEN)) { static int ref_paranoia = -1; @@ -1580,6 +1594,8 @@ struct ref_iterator *refs_ref_iterator_begin( if (trim) iter = prefix_ref_iterator_begin(iter, "", trim); + strvec_clear(&normalized_exclude_patterns); + return iter; } diff --git a/t/t1419-exclude-refs.sh b/t/t1419-exclude-refs.sh index 1359574419..b5e01e9f45 100755 --- a/t/t1419-exclude-refs.sh +++ b/t/t1419-exclude-refs.sh @@ -125,4 +125,14 @@ test_expect_success 'meta-characters are discarded' ' assert_no_jumps perf ' +test_expect_success 'empty string exclude pattern is ignored' ' + git update-ref refs/heads/loose $(git rev-parse refs/heads/foo/1) && + + for_each_ref__exclude refs/heads "" >actual 2>perf && + for_each_ref >expect && + + test_cmp expect actual && + assert_no_jumps perf +' + test_done From 10e8a9352bcc7b21a64e0b321f302cf900ac8c77 Mon Sep 17 00:00:00 2001 From: Taylor Blau Date: Thu, 6 Mar 2025 10:34:53 -0500 Subject: [PATCH 2/2] refs.c: stop matching non-directory prefixes in exclude patterns In the packed-refs backend, our implementation of '--exclude' (dating back to 59c35fac54 (refs/packed-backend.c: implement jump lists to avoid excluded pattern(s), 2023-07-10)) considers, for example: $ git for-each-ref --exclude=refs/heads/ba to exclude "refs/heads/bar", "refs/heads/baz", and so on. The files backend, which does not implement '--exclude' (and relies on the caller to cull out results that don't match) naturally will enumerate "refs/heads/bar" and so on. So in the above example, 'for-each-ref' will try and see if "refs/heads/ba" matches "refs/heads/bar" (since the files backend simply enumerated every loose reference), and, realizing that it does not match, output the reference as expected. (A caller that did want to exclude "refs/heads/bar" and "refs/heads/baz" might instead run "git for-each-ref --exclude='refs/heads/ba*'"). This can lead to strange behavior, like seeing a different set of references advertised via 'upload-pack' depending on what set of references were loose versus packed. So there is a subtle bug with '--exclude' which is that in the packed-refs backend we will consider "refs/heads/bar" to be a pattern match against "refs/heads/ba" when we shouldn't. Likewise, the reftable backend (which in this case is bug-compatible with the packed backend) exhibits the same broken behavior. There are a few ways to fix this. One is to tighten the rules in cmp_record_to_refname(), which is used to determine the start/end-points of the jump list used by the packed backend. In this new "strict" mode, the comparison function would handle the case where we've reached the end of the pattern by introducing a new check like so: while (1) { if (*r1 == '\n') return *r2 ? -1 : 0; if (!*r2) if (strict && *r1 != '/') /* <- here */ return 1; return start ? 1 : -1; if (*r1 != *r2) return (unsigned char)*r1 < (unsigned char)*r2 ? -1 : +1; r1++; r2++; } (eliding out the rest of cmp_record_to_refname()). Equivalently, we could teach refs/packed-backend::populate_excluded_jump_list() to append a trailing '/' if one does not already exist, forcing an exclude pattern like "refs/heads/ba" to only match "refs/heads/ba/abc" and so forth. But since the same problem exists in reftable, we can fix both at once by performing this pre-processing step one layer up in refs.c at the common entrypoint for the two, which is 'refs_ref_iterator_begin()'. Since that solution is both the simplest and only requires modification in one spot, let's normalize exclude patterns so that they end with a trailing slash. This causes us to unify the behavior between all three backends. There is some minor test fallout in the "overlapping excluded regions" test, which happens to use 'refs/ba' as an exclude pattern, and expects references under the "refs/heads/bar/*" and "refs/heads/baz/*" hierarchies to be excluded from the results. But that test fallout is expected, because the test was codifying the buggy behavior to begin with, and should have never been written that way. Split that into its own test (since the range is no longer overlapping under the stricter interpretation of --exclude patterns presented here). Create a new test which does have overlapping regions by using a refs/heads/bar/4/... hierarchy and excluding both "refs/heads/bar" and "refs/heads/bar/4". Reported-by: SURA Helped-by: Jeff King Signed-off-by: Taylor Blau Signed-off-by: Junio C Hamano --- refs.c | 6 +++++- t/t1419-exclude-refs.sh | 16 ++++++++++++++-- 2 files changed, 19 insertions(+), 3 deletions(-) diff --git a/refs.c b/refs.c index fa943d7d64..e4fda6b4bb 100644 --- a/refs.c +++ b/refs.c @@ -1569,7 +1569,11 @@ struct ref_iterator *refs_ref_iterator_begin( if (!len) continue; - strvec_push(&normalized_exclude_patterns, pattern); + if (pattern[len - 1] == '/') + strvec_push(&normalized_exclude_patterns, pattern); + else + strvec_pushf(&normalized_exclude_patterns, "%s/", + pattern); } exclude_patterns = normalized_exclude_patterns.v; diff --git a/t/t1419-exclude-refs.sh b/t/t1419-exclude-refs.sh index b5e01e9f45..11d6dfdb25 100755 --- a/t/t1419-exclude-refs.sh +++ b/t/t1419-exclude-refs.sh @@ -46,6 +46,10 @@ test_expect_success 'setup' ' echo "create refs/heads/$name/$i $base" || return 1 done || return 1 done >in && + for i in 5 6 7 + do + echo "create refs/heads/bar/4/$i $base" || return 1 + done >>in && echo "delete refs/heads/main" >>in && git update-ref --stdin actual 2>perf && - for_each_ref refs/heads/foo refs/heads/quux >expect && + for_each_ref refs/heads/bar refs/heads/foo refs/heads/quux >expect && + + test_cmp expect actual && + assert_jumps 1 perf +' + +test_expect_success 'overlapping excluded regions' ' + for_each_ref__exclude refs/heads refs/heads/bar refs/heads/bar/4 >actual 2>perf && + for_each_ref refs/heads/baz refs/heads/foo refs/heads/quux >expect && test_cmp expect actual && assert_jumps 1 perf