Add exported vfs_hash_index() function, which calculates the canonical

pre-masked hash for the given vnode.  The function assumes that
vp->v_hash is initialized by the filesystem vnode instantiation
function.  At the moment, it is only done if filesystem uses
vfs_hash_insert().

Reviewed by:	peter
Tested by:	peter, pho (previous version)
Sponsored by:	The FreeBSD Foundation
MFC after:	5 days

2 files changed, 8 insertions, 0 deletions

diff --git a/sys/kern/vfs_hash.c b/sys/kern/vfs_hash.c
index f1d4a91..0271e49 100644
--- a/sys/kern/vfs_hash.c
+++ b/sys/kern/vfs_hash.c
@@ -54,6 +54,13 @@ vfs_hashinit(void *dummy __unused)
 /* Must be SI_ORDER_SECOND so desiredvnodes is available */
 SYSINIT(vfs_hash, SI_SUB_VFS, SI_ORDER_SECOND, vfs_hashinit, NULL);
 
+u_int
+vfs_hash_index(struct vnode *vp)
+{
+
+	return (vp->v_hash + vp->v_mount->mnt_hashseed);
+}
+
 static struct vfs_hash_head *
 vfs_hash_bucket(const struct mount *mp, u_int hash)
 {
diff --git a/sys/sys/vnode.h b/sys/sys/vnode.h
index f841f82..ff00eac 100644
--- a/sys/sys/vnode.h
+++ b/sys/sys/vnode.h
@@ -812,6 +812,7 @@ int	fifo_printinfo(struct vnode *);
 typedef int vfs_hash_cmp_t(struct vnode *vp, void *arg);
 
 int vfs_hash_get(const struct mount *mp, u_int hash, int flags, struct thread *td, struct vnode **vpp, vfs_hash_cmp_t *fn, void *arg);
+u_int vfs_hash_index(struct vnode *vp);
 int vfs_hash_insert(struct vnode *vp, u_int hash, int flags, struct thread *td, struct vnode **vpp, vfs_hash_cmp_t *fn, void *arg);
 void vfs_hash_rehash(struct vnode *vp, u_int hash);
 void vfs_hash_remove(struct vnode *vp);