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, 8 insertions, 0 deletions

diff --git a/sys/kern/vfs_default.c b/sys/kern/vfs_default.c
index d46bf81..a3f3725 100644
--- a/sys/kern/vfs_default.c
+++ b/sys/kern/vfs_default.c
@@ -98,6 +98,7 @@ struct vop_vector default_vnodeops = {
 	.vop_revoke =		VOP_PANIC,
 	.vop_strategy =		vop_nostrategy,
 	.vop_unlock =		vop_stdunlock,
+	.vop_vptocnp =		VOP_ENOENT,
 	.vop_vptofh =		vop_stdvptofh,
 };
 
@@ -138,6 +139,13 @@ vop_einval(struct vop_generic_args *ap)
 }
 
 int
+vop_enoent(struct vop_generic_args *ap)
+{
+
+	return (ENOENT);
+}
+
+int
 vop_null(struct vop_generic_args *ap)
 {