On 09/19/2012 08:30 PM, Junio C Hamano wrote:
Torsten Bögershausen <tbo...@web.de> writes:

"is a blob, not a commit" is likely to come from validating of the
tag 66f6581d that presumably point at 63499e4; it reads the tag,
learns the name of the object that is tagged and the type of it,
remembers that the object pointed at (which it hasn't and is going
to validate next) _must_ be a commit (because tag says so) and then
realizes when it reads 63499e4 it is a blob and barfs.

And that is what _should_ happen in that test.  It crafts a
malformed tag that points at a blob and claims that it is a commit.
The test makes sure fsck catches that, and it does.

On the other hand, "is a commit, not a blob", unless you have a tag
that directly points at a blob, is more likely to come from
validating some tree object.  It reads the tree, learns the name of
the object contained in the tree and infers the type of that object
from the mode bits in the tree (100644 or 100755 would mean the
object must be a blob), goes on to validate that object and realizes
it is a commit and barfs.

The good news:
With help of Junio's comments I probably found the reason why the test behaves differently:

The objects are checked in a certain order, based on the inode number.

Which seems to be the same on most machines: when files are created
in a certain order, then the inode numbers are in the same order.

When the inode numbering changes for reasons known to the file system, the order changes and fsck takes a different code path.

To provoke the error, the following helped at my Linux box:

diff --git a/builtin/fsck.c b/builtin/fsck.c
index a710227..bba8082 100644
--- a/builtin/fsck.c
+++ b/builtin/fsck.c
@@ -373,7 +373,7 @@ static struct {

 static int ino_compare(const void *_a, const void *_b)
-       const struct sha1_entry *a = _a, *b = _b;
+       const struct sha1_entry *a = _b, *b = _a;
        unsigned long ino1 = a->ino, ino2 = b->ino;
        return ino1 < ino2 ? -1 : ino1 > ino2 ? 1 : 0;

The bad news: I haven't found the time to prepare a fix.


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