exists is bogus. The goal here is to produce a synthetic link count
which won't confuse fts and similar routines which "know" that
directories with a link count of 2 don't have subdirectories (and
thus, they can avoid having to stat every entry in the directory
looking for subdirectories which aren't there).
We know that non-UNIX filesystem implementations may return a link
count of `1' for directories with an indeterminate number of
subdirectories; if either the upper or lower layer returns a link
count of `1', return a link count of 1. If both layers return a link
count of 2, return a link count of 2; otherwise, return the sum of the
link count of both layers.
Also, fix PR7430: unionfs ignores read-only mounts. Check for
MNT_RDONLY in union_lookup (more-or-less as in layer_lookup) as well
as union_access() and union_setattr().
Note that a read-only union layer may still cause side effects on the
underlying filesystems... Most notably, we'll still attempt to create
shadow directories in the upper layer. Also, of course, we'll
side-effect atimes in the lower layer.
"panic: lockmgr: using decommisioned lock"
(only if DIAGNOSTIC)
The problem turned out to be due to the way LK_DRAIN was (not) handled
in union_lock; it just got passed through to the lock on the upper
vnode (which got marked as decommissioned, instead of that happening
to the union vnode. When the upper vnode was next locked (typically
when it was released), it went kaboom.
deadlock in VOP_FSYNC() if the unreferenced vnode picked for
reclamation happened to be stacked on top of a vnode the process
already had locked. This could happen if the same filesystem was
accessed both through a union mount and directly; it seemed to happen
most frequently when the direct access was through NFS.
Avoid this deadlock by changing vinvalbuf to pass a new FSYNC_RECLAIM
flag bit to VOP_FSYNC() to indicate that a reclaim is in progress and
only a `shallow' fsync is necessary.
Do nothing in *_fsync() in umapfs, nullfs, and unionfs when
FSYNC_RECLAIM is set; the underlying vnodes will shortly be released
in *_reclaim and may be reclaimed (and fsync'ed) later.
(1) Fix a typo that caused a NULL pointer deref.
(2) union_copyup() locks the vnode, so unlock it before calling relookup().
PR #5272, MINOURA, Makoto <minoura@kw.netlaputa.ne.jp>.
vn, with a 0 component. If the upper fs was a unionfs,
union_whiteout() would deref compnent to get a struct proc, and panic.
struct proc was only being passed to FIXUP, which never used it. It
turns out this happened a lot. I ripped most of the unneeded code
out, and left in the few places that really did need the proc handle.
* Change the argument names to vop_link so they actually make sense.
* Implement vop_link and vop_symlink for all file systems, so they do proper
cleanup.
* Require the file system to decide whether or not linking and unlinking of
directories is allowed, and disable it for all current file systems.
