Date: Sat, 5 Aug 2006 17:17:51 +0200 From: "Michiel Pelt" <pelt22@gmail.com> To: freebsd-fs@freebsd.org Subject: VOP_LOOKUP of .. in msdosfs Message-ID: <cee5e2ee0608050817u67f0c08cw73ec68f54400375b@mail.gmail.com>
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Hi,
I am developing a filesystem which doesn't have a . and .. in the root. So I
emulate them, just like msdosfs does. I looked at the msdosfs code. Correct
me if I am wrong, but I think there is something wrong with it.
The msdosfs_lookup function in msdosfs_lookup.c has code dealing with the
rootdirectory at the label foundroot:. At line 523 (release 6.1 code) of the
release code is this piece of code:
pdp = vdp;
if (flags & ISDOTDOT) {
VOP_UNLOCK(pdp, 0, td);
error = deget(pmp, cluster, blkoff, &tdp);
vn_lock(pdp, LK_EXCLUSIVE | LK_RETRY, td);
if (error)
return (error);
*vpp = DETOV(tdp);
}
This code has been copied from ffs code, but fails for msdosfs.
For starters the introduction of the 'pdp' pointer has no function
whatsoever.
Consider a lookup for .. in the root. In msdosfs the /. and /.. directories
are represented by one and the same vnode (see deget() in msdosfs_denode.c).
The deget gets and locks the vnode that was unlocked by VOP_UNLOCK. The
vn_lock that follows fails with a panic because the vnode is already locked.
So why does this not happen in practice? Because the ISDOTDOT case is
handled by vfs_lookup and never reaches VOP_LOOKUP.
I did get the error because I forgot to set the VV_ROOT flag in the vnode
returned by VFS_ROOT ;-(.
Best Regards
Michiel
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