[hfs-user] (no subject)

Mark Day mday@apple.com
Fri, 11 Jun 2004 15:38:59 -0700


On Jun 11, 2004, at 8:33 AM, Pierre Duhem wrote:

> I build a HFS image with about 41000 little files.
>
> The catalog mapping bitmap in the B-tree header overflows at about 
> 6,500
> files. The first independent node overflows at about 18,300 and the 
> second at
> about 30,400 files.
>
> Therefore, I have following linkage:
> 0 (header) points to 0x0800
> 0x0800 points to 0x1770
> 0x1770 points to 0x26E0
>
> However, when I run fsck_hfs on the CD-ROM I burned from this image, I
> get an error message:
>
> Invalid map node linkage
> 4, 9952

That error is E_MapLk in the code.  What it's doing is following the 
chain of forward pointers starting with the header node (i.e. following 
the chain of nodes containing map records).  It is adding up the sizes 
of each of the map records, in bytes, in order to compare with the 
number of bytes needed to map all of the nodes (based on the total node 
count in the B-tree header; don't forget to round *up* to whole 
bytes!).  The error is reported when one of the following happens:

1. A forward link of 0 is found, but the sizes of the map records 
aren't large enough to map all of the nodes.  That is, it was expecting 
to find additional map records.

2. A non-zero forward link is found, but the map records found so far 
have enough space to represent the total number of nodes.  Note that it 
is OK for the very last map record to be larger than strictly necessary 
(based on the total number of nodes).

Either case could happen if the total node count is wrong, or if the 
record offsets in the header node or map nodes are wrong.

> Btw, 9952 is 0x26E0 in decimal, which means that the program is not
> happy with my solution, in particular with the last node in the linked
> list.

My first guess is that you didn't set the forward pointer in node 
0x26e0 to zero.

> When looking at several volumes formatted and filled on a Macintosh
> (Mac OS X 1O.2, if it matters), I see that there is always a totally
> empty node (with nothing in it, even in the node header) pointed to by
> the last node where the bitmap was used.
>
> Should I also implement this?

That shouldn't be happening.  Any node pointed to by any other node in 
the tree should have a valid header.  And any node not in the tree 
should be filled with zeroes.

-Mark