add `ignore_missing_links` mode to revwalk

When pack-objects is computing the reachability bitmap to
serve a fetch request, it can erroneously die() if some of
the UNINTERESTING objects are not present. Upload-pack
throws away HAVE lines from the client for objects we do not
have, but we may have a tip object without all of its
ancestors (e.g., if the tip is no longer reachable and was
new enough to survive a `git prune`, but some of its
reachable objects did get pruned).

In the non-bitmap case, we do a revision walk with the HAVE
objects marked as UNINTERESTING. The revision walker
explicitly ignores errors in accessing UNINTERESTING commits
to handle this case (and we do not bother looking at
UNINTERESTING trees or blobs at all).

When we have bitmaps, however, the process is quite
different.  The bitmap index for a pack-objects run is
calculated in two separate steps:

First, we perform an extensive walk from all the HAVEs to
find the full set of objects reachable from them. This walk
is usually optimized away because we are expected to hit an
object with a bitmap during the traversal, which allows us
to terminate early.

Secondly, we perform an extensive walk from all the WANTs,
which usually also terminates early because we hit a commit
with an existing bitmap.

Once we have the resulting bitmaps from the two walks, we
AND-NOT them together to obtain the resulting set of objects
we need to pack.

When we are walking the HAVE objects, the revision walker
does not know that we are walking it only to mark the
results as uninteresting. We strip out the UNINTERESTING flag,
because those objects _are_ interesting to us during the
first walk. We want to keep going to get a complete set of
reachable objects if we can.

We need some way to tell the revision walker that it's OK to
silently truncate the HAVE walk, just like it does for the
UNINTERESTING case. This patch introduces a new
`ignore_missing_links` flag to the `rev_info` struct, which
we set only for the HAVE walk.

It also adds tests to cover UNINTERESTING objects missing
from several positions: a missing blob, a missing tree, and
a missing parent commit. The missing blob already worked (as
we do not care about its contents at all), but the other two
cases caused us to die().

Note that there are a few cases we do not need to test:

1. We do not need to test a missing tree, with the blob
still present. Without the tree that refers to it, we
would not know that the blob is relevant to our walk.

2. We do not need to test a tip commit that is missing.
Upload-pack omits these for us (and in fact, we
complain even in the non-bitmap case if it fails to do
so).

Reported-by: Siddharth Agarwal <sid0@fb.com>
Signed-off-by: Vicent Marti <tanoku@gmail.com>
Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

diff --git a/list-objects.c b/list-objects.c
index 6cbedf0280076d8fe6e49241d89938955ecddead..b2db6ba0d3dcae4af3e738600de3275d4c03a079 100644 (file)
--- a/list-objects.c
+++ b/list-objects.c
@@ -81,8 +81,11 @@ static void process_tree(struct rev_info *revs,
                die("bad tree object");
        if (obj->flags & (UNINTERESTING | SEEN))
                return;
-       if (parse_tree(tree) < 0)
+       if (parse_tree(tree) < 0) {
+               if (revs->ignore_missing_links)
+                       return;
                die("bad tree object %s", sha1_to_hex(obj->sha1));
+       }
        obj->flags |= SEEN;
        show(obj, path, name, cb_data);
        me.up = path;

diff --git a/pack-bitmap.c b/pack-bitmap.c
index ae0b57b95011af835d3b47f253572e8c44f6482e..91e41015316e8d5c166cdee92c453ec23a483dab 100644 (file)
--- a/pack-bitmap.c
+++ b/pack-bitmap.c
@@ -727,8 +727,10 @@ int prepare_bitmap_walk(struct rev_info *revs)
        revs->pending.objects = NULL;
 
        if (haves) {
+               revs->ignore_missing_links = 1;
                haves_bitmap = find_objects(revs, haves, NULL);
                reset_revision_walk();
+               revs->ignore_missing_links = 0;
 
                if (haves_bitmap == NULL)
                        die("BUG: failed to perform bitmap walk");

diff --git a/revision.c b/revision.c
index cddd6051e307cf5455e41cdd404008d5a1967f84..520b3e7df6cc195e369059b3ad134780580c3e60 100644 (file)
--- a/revision.c
+++ b/revision.c
@@ -2866,9 +2866,11 @@ static struct commit *get_revision_1(struct rev_info *revs)
                        if (revs->max_age != -1 &&
                            (commit->date < revs->max_age))
                                continue;
-                       if (add_parents_to_list(revs, commit, &revs->commits, NULL) < 0)
-                               die("Failed to traverse parents of commit %s",
-                                   sha1_to_hex(commit->object.sha1));
+                       if (add_parents_to_list(revs, commit, &revs->commits, NULL) < 0) {
+                               if (!revs->ignore_missing_links)
+                                       die("Failed to traverse parents of commit %s",
+                                               sha1_to_hex(commit->object.sha1));
+                       }
                }
 
                switch (simplify_commit(revs, commit)) {

diff --git a/revision.h b/revision.h
index 9957f3c6e5b123480d2276e7de5206c3a5b697db..4f051d2ea2568509065e3080d23f8932c8516b21 100644 (file)
--- a/revision.h
+++ b/revision.h
@@ -69,7 +69,8 @@ struct rev_info {
        enum rev_sort_order sort_order;
 
        unsigned int    early_output:1,
-                       ignore_missing:1;
+                       ignore_missing:1,
+                       ignore_missing_links:1;
 
        /* Traversal flags */
        unsigned int    dense:1,

diff --git a/t/t5310-pack-bitmaps.sh b/t/t5310-pack-bitmaps.sh
index f13525caa309e48ab32f89066a3e9661dfc25e09..f4f02ba918535d5c40a30585a54469bc12ab96d3 100755 (executable)
--- a/t/t5310-pack-bitmaps.sh
+++ b/t/t5310-pack-bitmaps.sh
@@ -3,6 +3,10 @@
 test_description='exercise basic bitmap functionality'
 . ./test-lib.sh
 
+objpath () {
+       echo ".git/objects/$(echo "$1" | sed -e 's|\(..\)|\1/|')"
+}
+
 test_expect_success 'setup repo with moderate-sized history' '
        for i in $(test_seq 1 10); do
                test_commit $i
@@ -115,6 +119,33 @@ test_expect_success 'fetch (full bitmap)' '
        test_cmp expect actual
 '
 
+test_expect_success 'create objects for missing-HAVE tests' '
+       blob=$(echo "missing have" | git hash-object -w --stdin) &&
+       tree=$(printf "100644 blob $blob\tfile\n" | git mktree) &&
+       parent=$(echo parent | git commit-tree $tree) &&
+       commit=$(echo commit | git commit-tree $tree -p $parent) &&
+       cat >revs <<-EOF
+       HEAD
+       ^HEAD^
+       ^$commit
+       EOF
+'
+
+test_expect_success 'pack with missing blob' '
+       rm $(objpath $blob) &&
+       git pack-objects --stdout --revs <revs >/dev/null
+'
+
+test_expect_success 'pack with missing tree' '
+       rm $(objpath $tree) &&
+       git pack-objects --stdout --revs <revs >/dev/null
+'
+
+test_expect_success 'pack with missing parent' '
+       rm $(objpath $parent) &&
+       git pack-objects --stdout --revs <revs >/dev/null
+'
+
 test_lazy_prereq JGIT '
        type jgit
 '