pack-object: tolerate broken packs that have duplicated objects

When --reuse-delta is in effect (which is the default), and an existing
pack in the repository has the same object registered twice (e.g. one copy
in a non-delta format and the other copy in a delta against some other
object), an attempt to repack the repository can result in a cyclic delta
dependency, causing write_one() function to infinitely recurse into
itself.

Detect such a case and break the loopy dependency by writing out an object
that is involved in such a loop in the non-delta format.

Signed-off-by: Junio C Hamano <gitster@pobox.com>

diff --git a/builtin/pack-objects.c b/builtin/pack-objects.c
index c6e2d8766b0ec15fcfe9dc0a60ee81db6750b527..5ae808b8d932f8b70155129297264534c8f4d8c1 100644 (file)
--- a/builtin/pack-objects.c
+++ b/builtin/pack-objects.c
@@ -404,25 +404,56 @@ static unsigned long write_object(struct sha1file *f,
        return hdrlen + datalen;
 }
 
-static int write_one(struct sha1file *f,
-                              struct object_entry *e,
-                              off_t *offset)
+enum write_one_status {
+       WRITE_ONE_SKIP = -1, /* already written */
+       WRITE_ONE_BREAK = 0, /* writing this will bust the limit; not written */
+       WRITE_ONE_WRITTEN = 1, /* normal */
+       WRITE_ONE_RECURSIVE = 2 /* already scheduled to be written */
+};
+
+static enum write_one_status write_one(struct sha1file *f,
+                                      struct object_entry *e,
+                                      off_t *offset)
 {
        unsigned long size;
+       int recursing;
 
-       /* offset is non zero if object is written already. */
-       if (e->idx.offset || e->preferred_base)
-               return -1;
+       /*
+        * we set offset to 1 (which is an impossible value) to mark
+        * the fact that this object is involved in "write its base
+        * first before writing a deltified object" recursion.
+        */
+       recursing = (e->idx.offset == 1);
+       if (recursing) {
+               warning("recursive delta detected for object %s",
+                       sha1_to_hex(e->idx.sha1));
+               return WRITE_ONE_RECURSIVE;
+       } else if (e->idx.offset || e->preferred_base) {
+               /* offset is non zero if object is written already. */
+               return WRITE_ONE_SKIP;
+       }
 
        /* if we are deltified, write out base object first. */
-       if (e->delta && !write_one(f, e->delta, offset))
-               return 0;
+       if (e->delta) {
+               e->idx.offset = 1; /* now recurse */
+               switch (write_one(f, e->delta, offset)) {
+               case WRITE_ONE_RECURSIVE:
+                       /* we cannot depend on this one */
+                       e->delta = NULL;
+                       break;
+               default:
+                       break;
+               case WRITE_ONE_BREAK:
+                       e->idx.offset = recursing;
+                       return WRITE_ONE_BREAK;
+               }
+       }
 
        e->idx.offset = *offset;
        size = write_object(f, e, *offset);
        if (!size) {
-               e->idx.offset = 0;
-               return 0;
+               e->idx.offset = recursing;
+               return WRITE_ONE_BREAK;
        }
        written_list[nr_written++] = &e->idx;
 
@@ -430,7 +461,7 @@ static int write_one(struct sha1file *f,
        if (signed_add_overflows(*offset, size))
                die("pack too large for current definition of off_t");
        *offset += size;
-       return 1;
+       return WRITE_ONE_WRITTEN;
 }
 
 static void write_pack_file(void)
@@ -468,7 +499,7 @@ static void write_pack_file(void)
                offset = sizeof(hdr);
                nr_written = 0;
                for (; i < nr_objects; i++) {
-                       if (!write_one(f, objects + i, &offset))
+                       if (write_one(f, objects + i, &offset) == WRITE_ONE_BREAK)
                                break;
                        display_progress(progress_state, written);
                }