Re: Oddity in libufs.

From: John-Mark Gurney (gurney_j_at_resnet.uoregon.edu)
Date: 09/27/05

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    Date: Mon, 26 Sep 2005 20:08:03 -0700
To: Frank Mayhar <frank@exit.com>

    Frank Mayhar wrote this message on Mon, Sep 26, 2005 at 16:11 -0700:
    > On Sun, 2005-09-25 at 21:23 -0700, John-Mark Gurney wrote:
    > > Frank Mayhar wrote this message on Sat, Sep 24, 2005 at 20:26 -0700:
    > > > I've been using libufs as the I/O mechanism for my (heavy) modification
    > > > of sysutils/ffsrecov. It's working to my needs and now I'm poking at
    > >
    > > Well, I've recently rewrote ffsrecov in python, and have put up a
    > > preliminary copy up at:
    > > http://people.freebsd.org/~jmg/ffsrecov/
    >
    > Sigh. Of _course_ you have. Where were you in June when I was begging
    > for this?

    busy doing other stuff... (and not having a HD failure, and then a
    failure of the backup disk, which somehow managed to shift the blocks
    containing the root inode and a few inodes after it 8 bytes, yes bytes,
    later in the disk)... which got/made me rewrite ffsrecov...

    > (Er, and, why python, of all things?)

    Well, partly because python makes it easier to be an interactive
    recovery utility... Like my backup disk, I don't know how it happened
    but inodes 2 through 16 (the only ones allocated in the first cg) for
    some reason were shifted 8 bytes later on the disk... w/ C, that'd of
    been very difficult to fix, but using interactive python it made it
    easy:
    import block
    import ffsrecov
    b = block.Block(open('/dev/da0'))
    f = ffsrecov.FFS(b)
    print repr(f['/']) # hmmm, root inode is messed up
    inodeblk = f.getblock(f.ino_to_fsba(2))
    print repr(inodeblk[:512]) # print out the first sector
    inodeblk = inodeblk[8:] # drop the first 8 bytes
    tmpinodes = [ ffsrecov.FFSInode(fs, i, inodeblk[i * 256: (i + 1) * 256]) for i in range(2, 17) ] # generate inodes
    filter(lambda x: f.inodes.__setitem__(x.ino, x), tmpinodes) # put them in the cache (f.inodes is a WeakValueDictionary)
    print f['/'] # wow, things are much better!
    print map(None, f['/']) # now I can see the other file entries

    It lets me do things like make use of the WeakValueDictionary for inodes
    (cache the inode as long as the program keeps a reference to it), along
    with garbage collection... plus, I don't ever have to worry about
    messing up pointers and getting a crash (which I had in my earlier version
    of ffsrecov)... also, it only took me a weekend to write...

    The real big thing is that I don't have to worry about the differences
    between ufs1_daddr_t and ufs2_daddr_t, and w/ the classes, lets me
    treat inodes from both UFS1 and UFS2 exactly the same... 

    -- 
  John-Mark Gurney				Voice: +1 415 225 5579
     "All that I will do, has been done, All that I have, has not."
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