Add a new VOP, VOP_VPTOCNP, which translates a vnode to its component name

on a best-effort basis.  Teach vn_fullpath to use this new VOP if a
regular VFS cache lookup fails.  This VOP is designed to supplement the
VFS cache to provide a better chance that a vnode-to-name lookup will
succeed.

Currently, an implementation for devfs is being committed.  The default
implementation is to return ENOENT.

A big thanks to kib for the mentorship on this, and to pho for running it
through his stress test suite.

Reviewed by:	arch
Approved by:	kib

1 files changed, 10 insertions, 0 deletions

diff --git a/sys/kern/vnode_if.src b/sys/kern/vnode_if.src
index 3733156..36ea434 100644
--- a/sys/kern/vnode_if.src
+++ b/sys/kern/vnode_if.src
@@ -595,3 +595,13 @@ vop_vptofh {
 	IN struct vnode *vp;
 	IN struct fid *fhp;
 };
+
+%% vptocnp		vp	L L L
+%% vptocnp		vpp	- U -
+
+vop_vptocnp {
+	IN struct vnode *vp;
+	OUT struct vnode **vpp;
+	INOUT char *buf;
+	INOUT int *buflen;
+};