From df805ed6cfdc3345ce238101104c51bef5ec09e7 Mon Sep 17 00:00:00 2001 From: Jeff King Date: Mon, 4 Mar 2019 23:46:38 -0500 Subject: doc/fsck: clarify --connectivity-only behavior On reading this again, there are two things that were not immediately clear to me: - we do still check links to blobs, even though we don't open the blobs themselves - we do not do the normal fsck checks, even for non-blob objects we do open Let's reword it to make these points a little more clear. Signed-off-by: Jeff King Signed-off-by: Junio C Hamano diff --git a/Documentation/git-fsck.txt b/Documentation/git-fsck.txt index ab9a93f..b2a32d5 100644 --- a/Documentation/git-fsck.txt +++ b/Documentation/git-fsck.txt @@ -62,9 +62,13 @@ index file, all SHA-1 references in `refs` namespace, and all reflogs with --no-full. --connectivity-only:: - Check only the connectivity of tags, commits and tree objects. By - avoiding to unpack blobs, this speeds up the operation, at the - expense of missing corrupt objects or other problematic issues. + Check only the connectivity of reachable objects, making sure + that any objects referenced by a reachable tag, commit, or tree + is present. This speeds up the operation by avoiding reading + blobs entirely (though it does still check that referenced blobs + exist). This will detect corruption in commits and trees, but + not do any semantic checks (e.g., for format errors). Corruption + in blob objects will not be detected at all. --strict:: Enable more strict checking, namely to catch a file mode -- cgit v0.10.2-6-g49f6 From 8d8c2a5aef0fd20a68271697e50412791c06d9b7 Mon Sep 17 00:00:00 2001 From: Jeff King Date: Mon, 4 Mar 2019 23:47:39 -0500 Subject: fsck: always compute USED flags for unreachable objects The --connectivity-only option avoids opening every object, and instead just marks reachable objects with a flag and compares this to the set of all objects. This strategy is discussed in more detail in 3e3f8bd608 (fsck: prepare dummy objects for --connectivity-check, 2017-01-17). This means that we report _every_ unreachable object as dangling. Whereas in a full fsck, we'd have actually opened and parsed each of those unreachable objects, marking their child objects with the USED flag, to mean "this was mentioned by another object". And thus we can report only the tip of an unreachable segment of the object graph as dangling. You can see this difference with a trivial example: tree=$(git hash-object -t tree -w /dev/null) one=$(echo one | git commit-tree $tree) two=$(echo two | git commit-tree -p $one $tree) Running `git fsck` will report only $two as dangling, but with --connectivity-only, both commits (and the tree) are reported. Likewise, using --lost-found would write all three objects. We can make --connectivity-only work like the normal case by taking a separate pass over the unreachable objects, parsing them and marking objects they refer to as USED. That still avoids parsing any blobs, though we do pay the cost to access any unreachable commits and trees (which may or may not be noticeable, depending on how many you have). If neither --dangling nor --lost-found is in effect, then we can skip this step entirely, just like we do now. That makes "--connectivity-only --no-dangling" just as fast as the current "--connectivity-only". I.e., we do the correct thing always, but you can still tweak the options to make it faster if you don't care about dangling objects. Signed-off-by: Jeff King Signed-off-by: Junio C Hamano diff --git a/Documentation/git-fsck.txt b/Documentation/git-fsck.txt index b2a32d5..f467119 100644 --- a/Documentation/git-fsck.txt +++ b/Documentation/git-fsck.txt @@ -69,6 +69,10 @@ index file, all SHA-1 references in `refs` namespace, and all reflogs exist). This will detect corruption in commits and trees, but not do any semantic checks (e.g., for format errors). Corruption in blob objects will not be detected at all. ++ +Unreachable tags, commits, and trees will also be accessed to find the +tips of dangling segments of history. Use `--no-dangling` if you don't +care about this output and want to speed it up further. --strict:: Enable more strict checking, namely to catch a file mode diff --git a/builtin/fsck.c b/builtin/fsck.c index 3c3e0f0..1d98248 100644 --- a/builtin/fsck.c +++ b/builtin/fsck.c @@ -216,6 +216,48 @@ static int mark_used(struct object *obj, int type, void *data, struct fsck_optio return 0; } +static void mark_unreachable_referents(const struct object_id *oid) +{ + struct fsck_options options = FSCK_OPTIONS_DEFAULT; + struct object *obj = lookup_object(the_repository, oid->hash); + + if (!obj || !(obj->flags & HAS_OBJ)) + return; /* not part of our original set */ + if (obj->flags & REACHABLE) + return; /* reachable objects already traversed */ + + /* + * Avoid passing OBJ_NONE to fsck_walk, which will parse the object + * (and we want to avoid parsing blobs). + */ + if (obj->type == OBJ_NONE) { + enum object_type type = oid_object_info(the_repository, + &obj->oid, NULL); + if (type > 0) + object_as_type(the_repository, obj, type, 0); + } + + options.walk = mark_used; + fsck_walk(obj, NULL, &options); +} + +static int mark_loose_unreachable_referents(const struct object_id *oid, + const char *path, + void *data) +{ + mark_unreachable_referents(oid); + return 0; +} + +static int mark_packed_unreachable_referents(const struct object_id *oid, + struct packed_git *pack, + uint32_t pos, + void *data) +{ + mark_unreachable_referents(oid); + return 0; +} + /* * Check a single reachable object */ @@ -328,6 +370,26 @@ static void check_connectivity(void) /* Traverse the pending reachable objects */ traverse_reachable(); + /* + * With --connectivity-only, we won't have actually opened and marked + * unreachable objects with USED. Do that now to make --dangling, etc + * accurate. + */ + if (connectivity_only && (show_dangling || write_lost_and_found)) { + /* + * Even though we already have a "struct object" for each of + * these in memory, we must not iterate over the internal + * object hash as we do below. Our loop would potentially + * resize the hash, making our iteration invalid. + * + * Instead, we'll just go back to the source list of objects, + * and ignore any that weren't present in our earlier + * traversal. + */ + for_each_loose_object(mark_loose_unreachable_referents, NULL, 0); + for_each_packed_object(mark_packed_unreachable_referents, NULL, 0); + } + /* Look up all the requirements, warn about missing objects.. */ max = get_max_object_index(); if (verbose) diff --git a/t/t1450-fsck.sh b/t/t1450-fsck.sh index e20e8fa..b203f40 100755 --- a/t/t1450-fsck.sh +++ b/t/t1450-fsck.sh @@ -740,7 +740,7 @@ test_expect_success 'fsck detects truncated loose object' ' # for each of type, we have one version which is referenced by another object # (and so while unreachable, not dangling), and another variant which really is # dangling. -test_expect_success 'fsck notices dangling objects' ' +test_expect_success 'create dangling-object repository' ' git init dangling && ( cd dangling && @@ -751,12 +751,17 @@ test_expect_success 'fsck notices dangling objects' ' commit=$(git commit-tree $tree) && dcommit=$(git commit-tree -p $commit $tree) && - cat >expect <<-EOF && + cat >expect <<-EOF dangling blob $dblob dangling commit $dcommit dangling tree $dtree EOF + ) +' +test_expect_success 'fsck notices dangling objects' ' + ( + cd dangling && git fsck >actual && # the output order is non-deterministic, as it comes from a hash sort actual.sorted && @@ -764,6 +769,16 @@ test_expect_success 'fsck notices dangling objects' ' ) ' +test_expect_success 'fsck --connectivity-only notices dangling objects' ' + ( + cd dangling && + git fsck --connectivity-only >actual && + # the output order is non-deterministic, as it comes from a hash + sort actual.sorted && + test_i18ncmp expect actual.sorted + ) +' + test_expect_success 'fsck $name notices bogus $name' ' test_must_fail git fsck bogus && test_must_fail git fsck $ZERO_OID -- cgit v0.10.2-6-g49f6