ml_iterator_api

Add an iterator over the currently mounted file systems.

diff -r 7eb89c9de7ec -r 48be60e6e615 sys/kern/vfs_mount.c
--- sys/kern/vfs_mount.c
+++ sys/kern/vfs_mount.c
@@ -94,6 +94,14 @@
 #include <miscfs/genfs/genfs.h>
 #include <miscfs/specfs/specdev.h>
 
+struct mountlist_entry {
+	TAILQ_ENTRY(mountlist_entry) me_list;	/* Mount list. */
+	struct mount *me_mount;			/* Actual mount or
+						   NULL for marker. */
+};
+
+static TAILQ_HEAD(mountlist, mountlist_entry) mount_list;
+
 static struct vnode *vfs_vnode_iterator_next1(struct vnode_iterator *,
     bool (*)(void *, struct vnode *), void *, bool);
 
@@ -119,6 +127,7 @@ void
 vfs_mount_sysinit(void)
 {
 
+	TAILQ_INIT(&mount_list);
 	TAILQ_INIT(&mountlist);
 	mutex_init(&mountlist_lock, MUTEX_DEFAULT, IPL_NONE);
 	mutex_init(&mntvnode_lock, MUTEX_DEFAULT, IPL_NONE);
@@ -769,9 +778,7 @@ mount_domount(struct lwp *l, vnode_t **v
 	cache_purge(vp);
 	mp->mnt_iflag &= ~IMNT_WANTRDWR;
 
-	mutex_enter(&mountlist_lock);
-	TAILQ_INSERT_TAIL(&mountlist, mp, mnt_list);
-	mutex_exit(&mountlist_lock);
+	mountlist_append(mp);
 	if ((mp->mnt_flag & (MNT_RDONLY | MNT_ASYNC)) == 0)
 		vfs_syncer_add_to_worklist(mp);
 	vp->v_mountedhere = mp;
@@ -931,9 +938,7 @@ dounmount(struct mount *mp, int flags, s
 		coveredvp->v_mountedhere = NULL;
 		VOP_UNLOCK(coveredvp);
 	}
-	mutex_enter(&mountlist_lock);
-	TAILQ_REMOVE(&mountlist, mp, mnt_list);
-	mutex_exit(&mountlist_lock);
+	mountlist_remove(mp);
 	if (TAILQ_FIRST(&mp->mnt_vnodelist) != NULL)
 		panic("unmount: dangling vnode");
 	if (used_syncer)
@@ -1439,10 +1444,126 @@ makefstype(const char *type)
 	return rv;
 }
 
+static struct mountlist_entry *
+mountlist_alloc(struct mount *mp)
+{
+	struct mountlist_entry *me;
+
+	me = kmem_zalloc(sizeof(*me), KM_SLEEP);
+	me->me_mount = mp;
+
+	return me;
+}
+
+static void
+mountlist_free(struct mountlist_entry *me)
+{
+
+	kmem_free(me, sizeof(*me));
+}
+
+int
+mountlist_iterate(int (*cb)(struct mount *, void *), void *arg)
+{
+	int error;
+	struct mount *mp;
+	struct mountlist_entry marker, *me;
+
+	error = 0;
+	marker.me_mount = NULL;
+
+	mutex_enter(&mountlist_lock);
+
+	TAILQ_INSERT_HEAD(&mount_list, &marker, me_list);
+
+	while (error == 0) {
+		me = TAILQ_NEXT(&marker, me_list);
+		if (me == NULL) {
+			/* End of list: keep marker and break. */
+			break;
+		}
+		TAILQ_REMOVE(&mount_list, &marker, me_list);
+		TAILQ_INSERT_AFTER(&mount_list, me, &marker, me_list);
+
+		/* Skip other markers. */
+		if (me->me_mount == NULL)
+			continue;
+
+		/* Take an initial reference for vfs_busy() below. */
+		mp = me->me_mount;
+		KASSERT(mp != NULL);
+		atomic_inc_uint(&mp->mnt_refcnt);
+		mutex_exit(&mountlist_lock);
+
+		/* Try to mark this mount busy and call back on success. */
+		if (vfs_busy(mp, NULL) == 0) {
+			error = cb(mp, arg);
+			vfs_unbusy(mp, false, NULL);
+		}
+		vfs_destroy(mp);
+		mutex_enter(&mountlist_lock);
+	}
+
+	TAILQ_REMOVE(&mount_list, &marker, me_list);
+	mutex_exit(&mountlist_lock);
+
+	return error;
+}
+
+/*
+ * Attach new mount to the end of the mount list.
+ */
 void
 mountlist_append(struct mount *mp)
 {
+	struct mountlist_entry *me;
+
+	me = mountlist_alloc(mp);
 	mutex_enter(&mountlist_lock);
+	TAILQ_INSERT_TAIL(&mount_list, me, me_list);
 	TAILQ_INSERT_TAIL(&mountlist, mp, mnt_list);
 	mutex_exit(&mountlist_lock);
 }
+
+/*
+ * Remove mount from mount list.
+ */void
+mountlist_remove(struct mount *mp)
+{
+	struct mountlist_entry *me;
+
+	mutex_enter(&mountlist_lock);
+	TAILQ_FOREACH(me, &mount_list, me_list)
+		if (me->me_mount == mp)
+			break;
+	KASSERT(me != NULL);
+	TAILQ_REMOVE(&mount_list, me, me_list);
+	TAILQ_REMOVE(&mountlist, mp, mnt_list);
+	mutex_exit(&mountlist_lock);
+	mountlist_free(me);
+}
+
+/*
+ * Unlocked variant to traverse the mountlist.
+ * To be used from DDB only.
+ */
+struct mount *
+_mountlist_next(struct mount *mp)
+{
+	struct mountlist_entry *me;
+
+	if (mp == NULL) {
+		me = TAILQ_FIRST(&mount_list);
+	} else {
+		TAILQ_FOREACH(me, &mount_list, me_list)
+			if (me->me_mount == mp)
+				break;
+		if (me != NULL)
+			me = TAILQ_NEXT(me, me_list);
+	}
+
+	while (me != NULL && me->me_mount == NULL)
+		me = TAILQ_NEXT(me, me_list);
+
+	return (me ? me->me_mount : NULL);
+}
diff -r 7eb89c9de7ec -r 48be60e6e615 sys/sys/mount.h
--- sys/sys/mount.h
+++ sys/sys/mount.h
@@ -494,7 +494,11 @@ void *	mount_getspecific(struct mount *,
 void	mount_setspecific(struct mount *, specificdata_key_t, void *);
 
 int	usermount_common_policy(struct mount *, u_long);
+
+int	mountlist_iterate(int (*)(struct mount *, void *), void *);
+struct mount *_mountlist_next(struct mount *);
 void	mountlist_append(struct mount *);
+void	mountlist_remove(struct mount *);
 
 LIST_HEAD(vfs_list_head, vfsops);
 extern struct vfs_list_head vfs_list;