vfs: Add hierarchy support to directory entries

It will be useful to take better and safer VFS decisions in the future.
For example, avoiding code that uses the absolute path to determine something.

Signed-off-by: Raphael S. Carvalho <raphaelsc@cloudius-systems.com>
Signed-off-by: Pekka Enberg <penberg@cloudius-systems.com>

fs/vfs/vfs.h

@@ -137,7 +137,7 @@ int	 vfs_findroot(char *path, struct mount **mp, char **root);
 
 int	 fs_noop(void);
 
-struct dentry *dentry_alloc(struct vnode *vp, const char *path);
+struct dentry *dentry_alloc(struct dentry *parent_dp, struct vnode *vp, const char *path);
 void	dref(struct dentry *dp);
 void	drele(struct dentry *dp);
 

fs/vfs/vfs_lookup.c

@@ -59,7 +59,7 @@ dentry_hash(struct mount *mp, const char *path)
 
 
 struct dentry *
-dentry_alloc(struct vnode *vp, const char *path)
+dentry_alloc(struct dentry *parent_dp, struct vnode *vp, const char *path)
 {
 	struct mount *mp = vp->v_mount;
 	struct dentry *dp = calloc(sizeof(*dp), 1);
@@ -73,6 +73,12 @@ dentry_alloc(struct vnode *vp, const char *path)
 	dp->d_vnode = vp;
 	dp->d_mount = mp;
 	dp->d_path = strdup(path);
+
+	if (parent_dp) {
+		dref(parent_dp);
+	}
+	dp->d_parent = parent_dp;
+
 	vn_add_name(vp, dp);
 
 	mutex_lock(&dentry_hash_lock);
@@ -126,6 +132,10 @@ drele(struct dentry *dp)
 
 	mutex_unlock(&dentry_hash_lock);
 
+	if (dp->d_parent) {
+		drele(dp->d_parent);
+	}
+
 	vrele(dp->d_vnode);
 
 	free(dp->d_path);
@@ -211,7 +221,7 @@ namei(char *path, struct dentry **dpp)
 				return error;
 			}
 
-			dp = dentry_alloc(vp, node);
+			dp = dentry_alloc(ddp, vp, node);
 			vput(vp);
 
 			if (!dp) {

fs/vfs/vfs_mount.cc

@@ -173,7 +173,7 @@ sys_mount(char *dev, char *dir, char *fsname, int flags, void *data)
     vp->v_flags = VROOT;
     vp->v_mode = S_IFDIR | S_IRUSR | S_IWUSR | S_IXUSR;
 
-    mp->m_root = dentry_alloc(vp, "/");
+    mp->m_root = dentry_alloc(NULL, vp, "/");
     if (!mp->m_root) {
         vput(vp);
         goto err3;
@@ -318,6 +318,11 @@ sys_pivot_root(const char *new_root, const char *put_old)
         }
         newmp->m_covered = NULL;
 
+        if (newmp->m_root->d_parent) {
+            drele(newmp->m_root->d_parent);
+        }
+        newmp->m_root->d_parent = NULL;
+
         free(oldmp);
 
         strlcpy(newmp->m_path, "/", sizeof(newmp->m_path));

fs/vfs/vfs_syscalls.cc

@@ -777,7 +777,7 @@ sys_link(char *oldpath, char *newpath)
 		goto out1;
 
 	/* Map newpath into dentry hash with the same vnode as oldpath */
-	if (!(newdp = dentry_alloc(vp, newpath))) {
+	if (!(newdp = dentry_alloc(newdirdp, vp, newpath))) {
 		error = ENOMEM;
 		goto out1;
 	}

include/osv/dentry.h

@@ -19,6 +19,7 @@ struct dentry {
 	char		*d_path;	/* pointer to path in fs */
 	struct vnode	*d_vnode;
 	struct mount	*d_mount;
+	struct dentry   *d_parent; /* pointer to parent */
 	LIST_ENTRY(dentry) d_names_link; /* link fo vnode::d_names */
 };