kernfs: prepare for cgroup's kernfs conversion

index 8c63ae1..bfbfb48 100644
@@ -654,22 +654,36 @@ static int kernfs_iop_mkdir(struct inode *dir, struct dentry *dentry,
 {
 	struct kernfs_node *parent = dir->i_private;
 	struct kernfs_dir_ops *kdops = kernfs_root(parent)->dir_ops;
+	int ret;
 
 	if (!kdops || !kdops->mkdir)
 		return -EPERM;
 
-	return kdops->mkdir(parent, dentry->d_name.name, mode);
+	if (!kernfs_get_active(parent))
+		return -ENODEV;
+
+	ret = kdops->mkdir(parent, dentry->d_name.name, mode);
+
+	kernfs_put_active(parent);
+	return ret;
 }
 
 static int kernfs_iop_rmdir(struct inode *dir, struct dentry *dentry)
 {
 	struct kernfs_node *kn  = dentry->d_fsdata;
 	struct kernfs_dir_ops *kdops = kernfs_root(kn)->dir_ops;
+	int ret;
 
 	if (!kdops || !kdops->rmdir)
 		return -EPERM;
 
-	return kdops->rmdir(kn);
+	if (!kernfs_get_active(kn))
+		return -ENODEV;
+
+	ret = kdops->rmdir(kn);
+
+	kernfs_put_active(kn);
+	return ret;
 }
 
 static int kernfs_iop_rename(struct inode *old_dir, struct dentry *old_dentry,

@@ -678,11 +692,24 @@ static int kernfs_iop_rename(struct inode *old_dir, struct dentry *old_dentry,
 	struct kernfs_node *kn  = old_dentry->d_fsdata;
 	struct kernfs_node *new_parent = new_dir->i_private;
 	struct kernfs_dir_ops *kdops = kernfs_root(kn)->dir_ops;
+	int ret;
 
 	if (!kdops || !kdops->rename)
 		return -EPERM;
 
-	return kdops->rename(kn, new_parent, new_dentry->d_name.name);
+	if (!kernfs_get_active(kn))
+		return -ENODEV;
+
+	if (!kernfs_get_active(new_parent)) {
+		kernfs_put_active(kn);
+		return -ENODEV;
+	}
+
+	ret = kdops->rename(kn, new_parent, new_dentry->d_name.name);
+
+	kernfs_put_active(new_parent);
+	kernfs_put_active(kn);
+	return ret;
 }
 
 const struct inode_operations kernfs_dir_iops = {

index 02ac334..58a131d 100644
@@ -111,7 +111,8 @@ struct kernfs_node {
  * kernfs_dir_ops may be specified on kernfs_create_root() to support
  * directory manipulation syscalls.  These optional callbacks are invoked
  * on the matching syscalls and can perform any kernfs operations which
- * don't necessarily have to be the exact operation requested.
+ * don't necessarily have to be the exact operation requested.  An active
+ * reference is held for each kernfs_node parameter.
  */
 struct kernfs_dir_ops {
 	int (*mkdir)(struct kernfs_node *parent, const char *name,

index bfbfb48..f58d2f1 100644
@@ -527,13 +527,14 @@ EXPORT_SYMBOL_GPL(kernfs_find_and_get_ns);
 
 /**
  * kernfs_create_root - create a new kernfs hierarchy
- * @kdops: optional directory syscall operations for the hierarchy
+ * @scops: optional syscall operations for the hierarchy
  * @priv: opaque data associated with the new directory
  *
  * Returns the root of the new hierarchy on success, ERR_PTR() value on
  * failure.
  */
-struct kernfs_root *kernfs_create_root(struct kernfs_dir_ops *kdops, void *priv)
+struct kernfs_root *kernfs_create_root(struct kernfs_syscall_ops *scops,
+				       void *priv)
 {
 	struct kernfs_root *root;
 	struct kernfs_node *kn;

@@ -556,7 +557,7 @@ struct kernfs_root *kernfs_create_root(struct kernfs_dir_ops *kdops, void *priv)
 	kn->priv = priv;
 	kn->dir.root = root;
 
-	root->dir_ops = kdops;
+	root->syscall_ops = scops;
 	root->kn = kn;
 	init_waitqueue_head(&root->deactivate_waitq);
 

@@ -653,16 +654,16 @@ static int kernfs_iop_mkdir(struct inode *dir, struct dentry *dentry,
 			    umode_t mode)
 {
 	struct kernfs_node *parent = dir->i_private;
-	struct kernfs_dir_ops *kdops = kernfs_root(parent)->dir_ops;
+	struct kernfs_syscall_ops *scops = kernfs_root(parent)->syscall_ops;
 	int ret;
 
-	if (!kdops || !kdops->mkdir)
+	if (!scops || !scops->mkdir)
 		return -EPERM;
 
 	if (!kernfs_get_active(parent))
 		return -ENODEV;
 
-	ret = kdops->mkdir(parent, dentry->d_name.name, mode);
+	ret = scops->mkdir(parent, dentry->d_name.name, mode);
 
 	kernfs_put_active(parent);
 	return ret;

@@ -671,16 +672,16 @@ static int kernfs_iop_mkdir(struct inode *dir, struct dentry *dentry,
 static int kernfs_iop_rmdir(struct inode *dir, struct dentry *dentry)
 {
 	struct kernfs_node *kn  = dentry->d_fsdata;
-	struct kernfs_dir_ops *kdops = kernfs_root(kn)->dir_ops;
+	struct kernfs_syscall_ops *scops = kernfs_root(kn)->syscall_ops;
 	int ret;
 
-	if (!kdops || !kdops->rmdir)
+	if (!scops || !scops->rmdir)
 		return -EPERM;
 
 	if (!kernfs_get_active(kn))
 		return -ENODEV;
 
-	ret = kdops->rmdir(kn);
+	ret = scops->rmdir(kn);
 
 	kernfs_put_active(kn);
 	return ret;

@@ -691,10 +692,10 @@ static int kernfs_iop_rename(struct inode *old_dir, struct dentry *old_dentry,
 {
 	struct kernfs_node *kn  = old_dentry->d_fsdata;
 	struct kernfs_node *new_parent = new_dir->i_private;
-	struct kernfs_dir_ops *kdops = kernfs_root(kn)->dir_ops;
+	struct kernfs_syscall_ops *scops = kernfs_root(kn)->syscall_ops;
 	int ret;
 
-	if (!kdops || !kdops->rename)
+	if (!scops || !scops->rename)
 		return -EPERM;
 
 	if (!kernfs_get_active(kn))

@@ -705,7 +706,7 @@ static int kernfs_iop_rename(struct inode *old_dir, struct dentry *old_dentry,
 		return -ENODEV;
 	}
 
-	ret = kdops->rename(kn, new_parent, new_dentry->d_name.name);
+	ret = scops->rename(kn, new_parent, new_dentry->d_name.name);
 
 	kernfs_put_active(new_parent);
 	kernfs_put_active(kn);

index 58a131d..5ddc474 100644
@@ -108,13 +108,13 @@ struct kernfs_node {
 };
 
 /*
- * kernfs_dir_ops may be specified on kernfs_create_root() to support
- * directory manipulation syscalls.  These optional callbacks are invoked
- * on the matching syscalls and can perform any kernfs operations which
- * don't necessarily have to be the exact operation requested.  An active
- * reference is held for each kernfs_node parameter.
+ * kernfs_syscall_ops may be specified on kernfs_create_root() to support
+ * syscalls.  These optional callbacks are invoked on the matching syscalls
+ * and can perform any kernfs operations which don't necessarily have to be
+ * the exact operation requested.  An active reference is held for each
+ * kernfs_node parameter.
  */
-struct kernfs_dir_ops {
+struct kernfs_syscall_ops {
 	int (*mkdir)(struct kernfs_node *parent, const char *name,
 		     umode_t mode);
 	int (*rmdir)(struct kernfs_node *kn);

@@ -128,7 +128,7 @@ struct kernfs_root {
 
 	/* private fields, do not use outside kernfs proper */
 	struct ida		ino_ida;
-	struct kernfs_dir_ops	*dir_ops;
+	struct kernfs_syscall_ops *syscall_ops;
 	wait_queue_head_t	deactivate_waitq;
 };
 

@@ -219,7 +219,7 @@ struct kernfs_node *kernfs_find_and_get_ns(struct kernfs_node *parent,
 void kernfs_get(struct kernfs_node *kn);
 void kernfs_put(struct kernfs_node *kn);
 
-struct kernfs_root *kernfs_create_root(struct kernfs_dir_ops *kdops,
+struct kernfs_root *kernfs_create_root(struct kernfs_syscall_ops *scops,
 				       void *priv);
 void kernfs_destroy_root(struct kernfs_root *root);
 

@@ -273,7 +273,7 @@ static inline void kernfs_get(struct kernfs_node *kn) { }
 static inline void kernfs_put(struct kernfs_node *kn) { }
 
 static inline struct kernfs_root *
-kernfs_create_root(struct kernfs_dir_ops *kdops, void *priv)
+kernfs_create_root(struct kernfs_syscall_ops *scops, void *priv)
 { return ERR_PTR(-ENOSYS); }
 
 static inline void kernfs_destroy_root(struct kernfs_root *root) { }

index 0d6ce89..70cc698 100644
@@ -19,10 +19,33 @@
 
 struct kmem_cache *kernfs_node_cache;
 
+static int kernfs_sop_remount_fs(struct super_block *sb, int *flags, char *data)
+{
+	struct kernfs_root *root = kernfs_info(sb)->root;
+	struct kernfs_syscall_ops *scops = root->syscall_ops;
+
+	if (scops && scops->remount_fs)
+		return scops->remount_fs(root, flags, data);
+	return 0;
+}
+
+static int kernfs_sop_show_options(struct seq_file *sf, struct dentry *dentry)
+{
+	struct kernfs_root *root = kernfs_root(dentry->d_fsdata);
+	struct kernfs_syscall_ops *scops = root->syscall_ops;
+
+	if (scops && scops->show_options)
+		return scops->show_options(sf, root);
+	return 0;
+}
+
 static const struct super_operations kernfs_sops = {
 	.statfs		= simple_statfs,
 	.drop_inode	= generic_delete_inode,
 	.evict_inode	= kernfs_evict_inode,
+
+	.remount_fs	= kernfs_sop_remount_fs,
+	.show_options	= kernfs_sop_show_options,
 };
 
 static int kernfs_fill_super(struct super_block *sb)

index 5ddc474..5d5b7e9 100644
@@ -115,6 +115,9 @@ struct kernfs_node {
  * kernfs_node parameter.
  */
 struct kernfs_syscall_ops {
+	int (*remount_fs)(struct kernfs_root *root, int *flags, char *data);
+	int (*show_options)(struct seq_file *sf, struct kernfs_root *root);
+
 	int (*mkdir)(struct kernfs_node *parent, const char *name,
 		     umode_t mode);
 	int (*rmdir)(struct kernfs_node *kn);

index f58d2f1..89f8462 100644
@@ -629,7 +629,7 @@ static struct dentry *kernfs_iop_lookup(struct inode *dir,
 	kn = kernfs_find_ns(parent, dentry->d_name.name, ns);
 
 	/* no such entry */
-	if (!kn) {
+	if (!kn || !kernfs_active(kn)) {
 		ret = NULL;
 		goto out_unlock;
 	}

@@ -1112,8 +1112,8 @@ static struct kernfs_node *kernfs_dir_pos(const void *ns,
 				break;
 		}
 	}
-	/* Skip over entries in the wrong namespace */
-	while (pos && pos->ns != ns) {
+	/* Skip over entries which are dying/dead or in the wrong namespace */
+	while (pos && (!kernfs_active(pos) || pos->ns != ns)) {
 		struct rb_node *node = rb_next(&pos->rb);
 		if (!node)
 			pos = NULL;

@@ -1127,14 +1127,15 @@ static struct kernfs_node *kernfs_dir_next_pos(const void *ns,
 	struct kernfs_node *parent, ino_t ino, struct kernfs_node *pos)
 {
 	pos = kernfs_dir_pos(ns, parent, ino, pos);
-	if (pos)
+	if (pos) {
 		do {
 			struct rb_node *node = rb_next(&pos->rb);
 			if (!node)
 				pos = NULL;
 			else
 				pos = rb_to_kn(node);
-		} while (pos && pos->ns != ns);
+		} while (pos && (!kernfs_active(pos) || pos->ns != ns));
+	}
 	return pos;
 }
 

index 89f8462..3cff0a2 100644
@@ -435,7 +435,7 @@ int kernfs_add_one(struct kernfs_node *kn)
 		goto out_unlock;
 
 	ret = -ENOENT;
-	if (!kernfs_active(parent))
+	if ((parent->flags & KERNFS_ACTIVATED) && !kernfs_active(parent))
 		goto out_unlock;
 
 	kn->hash = kernfs_name_hash(kn->name, kn->ns);

@@ -451,9 +451,19 @@ int kernfs_add_one(struct kernfs_node *kn)
 		ps_iattrs->ia_ctime = ps_iattrs->ia_mtime = CURRENT_TIME;
 	}
 
-	/* Mark the entry added into directory tree */
-	atomic_sub(KN_DEACTIVATED_BIAS, &kn->active);
-	ret = 0;
+	mutex_unlock(&kernfs_mutex);
+
+	/*
+	 * Activate the new node unless CREATE_DEACTIVATED is requested.
+	 * If not activated here, the kernfs user is responsible for
+	 * activating the node with kernfs_activate().  A node which hasn't
+	 * been activated is not visible to userland and its removal won't
+	 * trigger deactivation.
+	 */
+	if (!(kernfs_root(kn)->flags & KERNFS_ROOT_CREATE_DEACTIVATED))
+		kernfs_activate(kn);
+	return 0;
+
 out_unlock:
 	mutex_unlock(&kernfs_mutex);
 	return ret;

@@ -528,13 +538,14 @@ EXPORT_SYMBOL_GPL(kernfs_find_and_get_ns);
 /**
  * kernfs_create_root - create a new kernfs hierarchy
  * @scops: optional syscall operations for the hierarchy
+ * @flags: KERNFS_ROOT_* flags
  * @priv: opaque data associated with the new directory
  *
  * Returns the root of the new hierarchy on success, ERR_PTR() value on
  * failure.
  */
 struct kernfs_root *kernfs_create_root(struct kernfs_syscall_ops *scops,
-				       void *priv)
+				       unsigned int flags, void *priv)
 {
 	struct kernfs_root *root;
 	struct kernfs_node *kn;

@@ -553,14 +564,17 @@ struct kernfs_root *kernfs_create_root(struct kernfs_syscall_ops *scops,
 		return ERR_PTR(-ENOMEM);
 	}
 
-	atomic_sub(KN_DEACTIVATED_BIAS, &kn->active);
 	kn->priv = priv;
 	kn->dir.root = root;
 
 	root->syscall_ops = scops;
+	root->flags = flags;
 	root->kn = kn;
 	init_waitqueue_head(&root->deactivate_waitq);
 
+	if (!(root->flags & KERNFS_ROOT_CREATE_DEACTIVATED))
+		kernfs_activate(kn);
+
 	return root;
 }
 

@@ -783,6 +797,40 @@ static struct kernfs_node *kernfs_next_descendant_post(struct kernfs_node *pos,
 	return pos->parent;
 }
 
+/**
+ * kernfs_activate - activate a node which started deactivated
+ * @kn: kernfs_node whose subtree is to be activated
+ *
+ * If the root has KERNFS_ROOT_CREATE_DEACTIVATED set, a newly created node
+ * needs to be explicitly activated.  A node which hasn't been activated
+ * isn't visible to userland and deactivation is skipped during its
+ * removal.  This is useful to construct atomic init sequences where
+ * creation of multiple nodes should either succeed or fail atomically.
+ *
+ * The caller is responsible for ensuring that this function is not called
+ * after kernfs_remove*() is invoked on @kn.
+ */
+void kernfs_activate(struct kernfs_node *kn)
+{
+	struct kernfs_node *pos;
+
+	mutex_lock(&kernfs_mutex);
+
+	pos = NULL;
+	while ((pos = kernfs_next_descendant_post(pos, kn))) {
+		if (!pos || (pos->flags & KERNFS_ACTIVATED))
+			continue;
+
+		WARN_ON_ONCE(pos->parent && RB_EMPTY_NODE(&pos->rb));
+		WARN_ON_ONCE(atomic_read(&pos->active) != KN_DEACTIVATED_BIAS);
+
+		atomic_sub(KN_DEACTIVATED_BIAS, &pos->active);
+		pos->flags |= KERNFS_ACTIVATED;
+	}
+
+	mutex_unlock(&kernfs_mutex);
+}
+
 static void __kernfs_remove(struct kernfs_node *kn)
 {
 	struct kernfs_node *pos;

@@ -817,7 +865,16 @@ static void __kernfs_remove(struct kernfs_node *kn)
 		 */
 		kernfs_get(pos);
 
-		kernfs_drain(pos);
+		/*
+		 * Drain iff @kn was activated.  This avoids draining and
+		 * its lockdep annotations for nodes which have never been
+		 * activated and allows embedding kernfs_remove() in create
+		 * error paths without worrying about draining.
+		 */
+		if (kn->flags & KERNFS_ACTIVATED)
+			kernfs_drain(pos);
+		else
+			WARN_ON_ONCE(atomic_read(&kn->active) != KN_DEACTIVATED_BIAS);
 
 		/*
 		 * kernfs_unlink_sibling() succeeds once per node.  Use it

index 6211230..5c7fdd9 100644
@@ -62,7 +62,7 @@ int __init sysfs_init(void)
 {
 	int err;
 
-	sysfs_root = kernfs_create_root(NULL, NULL);
+	sysfs_root = kernfs_create_root(NULL, 0, NULL);
 	if (IS_ERR(sysfs_root))
 		return PTR_ERR(sysfs_root);
 

index 5d5b7e9..4520c86 100644
@@ -38,6 +38,7 @@ enum kernfs_node_type {
 #define KERNFS_FLAG_MASK	~KERNFS_TYPE_MASK
 
 enum kernfs_node_flag {
+	KERNFS_ACTIVATED	= 0x0010,
 	KERNFS_NS		= 0x0020,
 	KERNFS_HAS_SEQ_SHOW	= 0x0040,
 	KERNFS_HAS_MMAP		= 0x0080,

@@ -47,6 +48,11 @@ enum kernfs_node_flag {
 	KERNFS_SUICIDED		= 0x0800,
 };
 
+/* @flags for kernfs_create_root() */
+enum kernfs_root_flag {
+	KERNFS_ROOT_CREATE_DEACTIVATED = 0x0001,
+};
+
 /* type-specific structures for kernfs_node union members */
 struct kernfs_elem_dir {
 	unsigned long		subdirs;

@@ -128,6 +134,7 @@ struct kernfs_syscall_ops {
 struct kernfs_root {
 	/* published fields */
 	struct kernfs_node	*kn;
+	unsigned int		flags;	/* KERNFS_ROOT_* flags */
 
 	/* private fields, do not use outside kernfs proper */
 	struct ida		ino_ida;

@@ -223,7 +230,7 @@ void kernfs_get(struct kernfs_node *kn);
 void kernfs_put(struct kernfs_node *kn);
 
 struct kernfs_root *kernfs_create_root(struct kernfs_syscall_ops *scops,
-				       void *priv);
+				       unsigned int flags, void *priv);
 void kernfs_destroy_root(struct kernfs_root *root);
 
 struct kernfs_node *kernfs_create_dir_ns(struct kernfs_node *parent,

@@ -239,6 +246,7 @@ struct kernfs_node *__kernfs_create_file(struct kernfs_node *parent,
 struct kernfs_node *kernfs_create_link(struct kernfs_node *parent,
 				       const char *name,
 				       struct kernfs_node *target);
+void kernfs_activate(struct kernfs_node *kn);
 void kernfs_remove(struct kernfs_node *kn);
 void kernfs_break_active_protection(struct kernfs_node *kn);
 void kernfs_unbreak_active_protection(struct kernfs_node *kn);

@@ -276,7 +284,8 @@ static inline void kernfs_get(struct kernfs_node *kn) { }
 static inline void kernfs_put(struct kernfs_node *kn) { }
 
 static inline struct kernfs_root *
-kernfs_create_root(struct kernfs_syscall_ops *scops, void *priv)
+kernfs_create_root(struct kernfs_syscall_ops *scops, unsigned int flags,
+		   void *priv)
 { return ERR_PTR(-ENOSYS); }
 
 static inline void kernfs_destroy_root(struct kernfs_root *root) { }

@@ -298,6 +307,8 @@ kernfs_create_link(struct kernfs_node *parent, const char *name,
 		   struct kernfs_node *target)
 { return ERR_PTR(-ENOSYS); }
 
+static inline void kernfs_activate(struct kernfs_node *kn) { }
+
 static inline void kernfs_remove(struct kernfs_node *kn) { }
 
 static inline bool kernfs_remove_self(struct kernfs_node *kn)

index 10a8c91..ddcb471 100644
@@ -252,19 +252,9 @@ static ssize_t kernfs_fop_write(struct file *file, const char __user *user_buf,
 				size_t count, loff_t *ppos)
 {
 	struct kernfs_open_file *of = kernfs_of(file);
-	ssize_t len = min_t(size_t, count, PAGE_SIZE);
 	const struct kernfs_ops *ops;
-	char *buf;
-
-	buf = kmalloc(len + 1, GFP_KERNEL);
-	if (!buf)
-		return -ENOMEM;
-
-	if (copy_from_user(buf, user_buf, len)) {
-		len = -EFAULT;
-		goto out_free;
-	}
-	buf[len] = '\0';	/* guarantee string termination */
+	char *buf = NULL;
+	ssize_t len;
 
 	/*
 	 * @of->mutex nests outside active ref and is just to ensure that

@@ -273,22 +263,45 @@ static ssize_t kernfs_fop_write(struct file *file, const char __user *user_buf,
 	mutex_lock(&of->mutex);
 	if (!kernfs_get_active(of->kn)) {
 		mutex_unlock(&of->mutex);
-		len = -ENODEV;
-		goto out_free;
+		return -ENODEV;
 	}
 
 	ops = kernfs_ops(of->kn);
-	if (ops->write)
-		len = ops->write(of, buf, len, *ppos);
-	else
+	if (!ops->write) {
 		len = -EINVAL;
+		goto out_unlock;
+	}
+
+	if (ops->atomic_write_len) {
+		len = count;
+		if (len > ops->atomic_write_len) {
+			len = -E2BIG;
+			goto out_unlock;
+		}
+	} else {
+		len = min_t(size_t, count, PAGE_SIZE);
+	}
+
+	buf = kmalloc(len + 1, GFP_KERNEL);
+	if (!buf) {
+		len = -ENOMEM;
+		goto out_unlock;
+	}
 
+	if (copy_from_user(buf, user_buf, len)) {
+		len = -EFAULT;
+		goto out_unlock;
+	}
+	buf[len] = '\0';	/* guarantee string termination */
+
+	len = ops->write(of, buf, len, *ppos);
+out_unlock:
 	kernfs_put_active(of->kn);
 	mutex_unlock(&of->mutex);
 
 	if (len > 0)
 		*ppos += len;
-out_free:
+
 	kfree(buf);
 	return len;
 }

index 4520c86..47f5235 100644
@@ -178,9 +178,13 @@ struct kernfs_ops {
 			loff_t off);
 
 	/*
-	 * write() is bounced through kernel buffer and a write larger than
-	 * PAGE_SIZE results in partial operation of PAGE_SIZE.
+	 * write() is bounced through kernel buffer.  If atomic_write_len
+	 * is not set, a write larger than PAGE_SIZE results in partial
+	 * operations of PAGE_SIZE chunks.  If atomic_write_len is set,
+	 * writes upto the specified size are executed atomically but
+	 * larger ones are rejected with -E2BIG.
 	 */
+	size_t atomic_write_len;
 	ssize_t (*write)(struct kernfs_open_file *of, char *buf, size_t bytes,
 			 loff_t off);
 

index 47f5235..9ca0f09 100644
@@ -146,6 +146,7 @@ struct kernfs_open_file {
 	/* published fields */
 	struct kernfs_node	*kn;
 	struct file		*file;
+	void			*priv;
 
 	/* private fields, do not use outside kernfs proper */
 	struct mutex		mutex;

index 3cff0a2..42a250f 100644
@@ -350,6 +350,24 @@ const struct dentry_operations kernfs_dops = {
 	.d_release	= kernfs_dop_release,
 };
 
+/**
+ * kernfs_node_from_dentry - determine kernfs_node associated with a dentry
+ * @dentry: the dentry in question
+ *
+ * Return the kernfs_node associated with @dentry.  If @dentry is not a
+ * kernfs one, %NULL is returned.
+ *
+ * While the returned kernfs_node will stay accessible as long as @dentry
+ * is accessible, the returned node can be in any state and the caller is
+ * fully responsible for determining what's accessible.
+ */
+struct kernfs_node *kernfs_node_from_dentry(struct dentry *dentry)
+{
+	if (dentry->d_op == &kernfs_dops)
+		return dentry->d_fsdata;
+	return NULL;
+}
+
 static struct kernfs_node *__kernfs_new_node(struct kernfs_root *root,
 					     const char *name, umode_t mode,
 					     unsigned flags)

index 70cc698..e5b28b0 100644
@@ -48,6 +48,20 @@ static const struct super_operations kernfs_sops = {
 	.show_options	= kernfs_sop_show_options,
 };
 
+/**
+ * kernfs_root_from_sb - determine kernfs_root associated with a super_block
+ * @sb: the super_block in question
+ *
+ * Return the kernfs_root associated with @sb.  If @sb is not a kernfs one,
+ * %NULL is returned.
+ */
+struct kernfs_root *kernfs_root_from_sb(struct super_block *sb)
+{
+	if (sb->s_op == &kernfs_sops)
+		return kernfs_info(sb)->root;
+	return NULL;
+}
+
 static int kernfs_fill_super(struct super_block *sb)
 {
 	struct kernfs_super_info *info = kernfs_info(sb);

index 9ca0f09..9c89904 100644
@@ -234,6 +234,9 @@ struct kernfs_node *kernfs_find_and_get_ns(struct kernfs_node *parent,
 void kernfs_get(struct kernfs_node *kn);
 void kernfs_put(struct kernfs_node *kn);
 
+struct kernfs_node *kernfs_node_from_dentry(struct dentry *dentry);
+struct kernfs_root *kernfs_root_from_sb(struct super_block *sb);
+
 struct kernfs_root *kernfs_create_root(struct kernfs_syscall_ops *scops,
 				       unsigned int flags, void *priv);
 void kernfs_destroy_root(struct kernfs_root *root);

@@ -288,6 +291,12 @@ kernfs_find_and_get_ns(struct kernfs_node *parent, const char *name,
 static inline void kernfs_get(struct kernfs_node *kn) { }
 static inline void kernfs_put(struct kernfs_node *kn) { }
 
+static inline struct kernfs_node *kernfs_node_from_dentry(struct dentry *dentry)
+{ return NULL; }
+
+static inline struct kernfs_root *kernfs_root_from_sb(struct super_block *sb)
+{ return NULL; }
+
 static inline struct kernfs_root *
 kernfs_create_root(struct kernfs_syscall_ops *scops, unsigned int flags,
 		   void *priv)

@@ -388,6 +397,13 @@ static inline int kernfs_remove_by_name(struct kernfs_node *parent,
 	return kernfs_remove_by_name_ns(parent, name, NULL);
 }
 
+static inline int kernfs_rename(struct kernfs_node *kn,
+				struct kernfs_node *new_parent,
+				const char *new_name)
+{
+	return kernfs_rename_ns(kn, new_parent, new_name, NULL);
+}
+
 static inline struct dentry *
 kernfs_mount(struct file_system_type *fs_type, int flags,
 	     struct kernfs_root *root)

index 42a250f..a347792 100644
@@ -19,6 +19,8 @@
 #include "kernfs-internal.h"
 
 DEFINE_MUTEX(kernfs_mutex);
+static DEFINE_SPINLOCK(kernfs_rename_lock);	/* kn->parent and ->name */
+static char kernfs_pr_cont_buf[PATH_MAX];	/* protected by rename_lock */
 
 #define rb_to_kn(X) rb_entry((X), struct kernfs_node, rb)
 

@@ -37,6 +39,141 @@ static bool kernfs_lockdep(struct kernfs_node *kn)
 #endif
 }
 
+static int kernfs_name_locked(struct kernfs_node *kn, char *buf, size_t buflen)
+{
+	return strlcpy(buf, kn->parent ? kn->name : "/", buflen);
+}
+
+static char * __must_check kernfs_path_locked(struct kernfs_node *kn, char *buf,
+					      size_t buflen)
+{
+	char *p = buf + buflen;
+	int len;
+
+	*--p = '\0';
+
+	do {
+		len = strlen(kn->name);
+		if (p - buf < len + 1) {
+			buf[0] = '\0';
+			p = NULL;
+			break;
+		}
+		p -= len;
+		memcpy(p, kn->name, len);
+		*--p = '/';
+		kn = kn->parent;
+	} while (kn && kn->parent);
+
+	return p;
+}
+
+/**
+ * kernfs_name - obtain the name of a given node
+ * @kn: kernfs_node of interest
+ * @buf: buffer to copy @kn's name into
+ * @buflen: size of @buf
+ *
+ * Copies the name of @kn into @buf of @buflen bytes.  The behavior is
+ * similar to strlcpy().  It returns the length of @kn's name and if @buf
+ * isn't long enough, it's filled upto @buflen-1 and nul terminated.
+ *
+ * This function can be called from any context.
+ */
+int kernfs_name(struct kernfs_node *kn, char *buf, size_t buflen)
+{
+	unsigned long flags;
+	int ret;
+
+	spin_lock_irqsave(&kernfs_rename_lock, flags);
+	ret = kernfs_name_locked(kn, buf, buflen);
+	spin_unlock_irqrestore(&kernfs_rename_lock, flags);
+	return ret;
+}
+
+/**
+ * kernfs_path - build full path of a given node
+ * @kn: kernfs_node of interest
+ * @buf: buffer to copy @kn's name into
+ * @buflen: size of @buf
+ *
+ * Builds and returns the full path of @kn in @buf of @buflen bytes.  The
+ * path is built from the end of @buf so the returned pointer usually
+ * doesn't match @buf.  If @buf isn't long enough, @buf is nul terminated
+ * and %NULL is returned.
+ */
+char *kernfs_path(struct kernfs_node *kn, char *buf, size_t buflen)
+{
+	unsigned long flags;
+	char *p;
+
+	spin_lock_irqsave(&kernfs_rename_lock, flags);
+	p = kernfs_path_locked(kn, buf, buflen);
+	spin_unlock_irqrestore(&kernfs_rename_lock, flags);
+	return p;
+}
+
+/**
+ * pr_cont_kernfs_name - pr_cont name of a kernfs_node
+ * @kn: kernfs_node of interest
+ *
+ * This function can be called from any context.
+ */
+void pr_cont_kernfs_name(struct kernfs_node *kn)
+{
+	unsigned long flags;
+
+	spin_lock_irqsave(&kernfs_rename_lock, flags);
+
+	kernfs_name_locked(kn, kernfs_pr_cont_buf, sizeof(kernfs_pr_cont_buf));
+	pr_cont("%s", kernfs_pr_cont_buf);
+
+	spin_unlock_irqrestore(&kernfs_rename_lock, flags);
+}
+
+/**
+ * pr_cont_kernfs_path - pr_cont path of a kernfs_node
+ * @kn: kernfs_node of interest
+ *
+ * This function can be called from any context.
+ */
+void pr_cont_kernfs_path(struct kernfs_node *kn)
+{
+	unsigned long flags;
+	char *p;
+
+	spin_lock_irqsave(&kernfs_rename_lock, flags);
+
+	p = kernfs_path_locked(kn, kernfs_pr_cont_buf,
+			       sizeof(kernfs_pr_cont_buf));
+	if (p)
+		pr_cont("%s", p);
+	else
+		pr_cont("<name too long>");
+
+	spin_unlock_irqrestore(&kernfs_rename_lock, flags);
+}
+
+/**
+ * kernfs_get_parent - determine the parent node and pin it
+ * @kn: kernfs_node of interest
+ *
+ * Determines @kn's parent, pins and returns it.  This function can be
+ * called from any context.
+ */
+struct kernfs_node *kernfs_get_parent(struct kernfs_node *kn)
+{
+	struct kernfs_node *parent;
+	unsigned long flags;
+
+	spin_lock_irqsave(&kernfs_rename_lock, flags);
+	parent = kn->parent;
+	kernfs_get(parent);
+	spin_unlock_irqrestore(&kernfs_rename_lock, flags);
+
+	return parent;
+}
+
 /**
  *	kernfs_name_hash
  *	@name: Null terminated string to hash

@@ -1103,8 +1240,14 @@ int kernfs_remove_by_name_ns(struct kernfs_node *parent, const char *name,
 int kernfs_rename_ns(struct kernfs_node *kn, struct kernfs_node *new_parent,
 		     const char *new_name, const void *new_ns)
 {
+	struct kernfs_node *old_parent;
+	const char *old_name = NULL;
 	int error;
 
+	/* can't move or rename root */
+	if (!kn->parent)
+		return -EINVAL;
+
 	mutex_lock(&kernfs_mutex);
 
 	error = -ENOENT;

@@ -1126,13 +1269,8 @@ int kernfs_rename_ns(struct kernfs_node *kn, struct kernfs_node *new_parent,
 		new_name = kstrdup(new_name, GFP_KERNEL);
 		if (!new_name)
 			goto out;
-
-		if (kn->flags & KERNFS_STATIC_NAME)
-			kn->flags &= ~KERNFS_STATIC_NAME;
-		else
-			kfree(kn->name);
-
-		kn->name = new_name;
+	} else {
+		new_name = NULL;
 	}
 
 	/*

@@ -1140,12 +1278,29 @@ int kernfs_rename_ns(struct kernfs_node *kn, struct kernfs_node *new_parent,
 	 */
 	kernfs_unlink_sibling(kn);
 	kernfs_get(new_parent);
-	kernfs_put(kn->parent);
-	kn->ns = new_ns;
-	kn->hash = kernfs_name_hash(kn->name, kn->ns);
+
+	/* rename_lock protects ->parent and ->name accessors */
+	spin_lock_irq(&kernfs_rename_lock);
+
+	old_parent = kn->parent;
 	kn->parent = new_parent;
+
+	kn->ns = new_ns;
+	if (new_name) {
+		if (!(kn->flags & KERNFS_STATIC_NAME))
+			old_name = kn->name;
+		kn->flags &= ~KERNFS_STATIC_NAME;
+		kn->name = new_name;
+	}
+
+	spin_unlock_irq(&kernfs_rename_lock);
+
+	kn->hash = kernfs_name_hash(new_name, new_ns);
 	kernfs_link_sibling(kn);
 
+	kernfs_put(old_parent);
+	kfree(old_name);
+
 	error = 0;
  out:
 	mutex_unlock(&kernfs_mutex);

68 lines not on this page · raw message

index 9c89904..b7cb267 100644
@@ -91,7 +91,12 @@ struct kernfs_node {
 #ifdef CONFIG_DEBUG_LOCK_ALLOC
 	struct lockdep_map	dep_map;
 #endif
-	/* the following two fields are published */
+	/*
+	 * Use kernfs_get_parent() and kernfs_name/path() instead of
+	 * accessing the following two fields directly.  If the node is
+	 * never moved to a different parent, it is safe to access the
+	 * parent directly.
+	 */
 	struct kernfs_node	*parent;
 	const char		*name;
 

@@ -229,6 +234,12 @@ static inline bool kernfs_ns_enabled(struct kernfs_node *kn)
 	return kn->flags & KERNFS_NS;
 }
 
+int kernfs_name(struct kernfs_node *kn, char *buf, size_t buflen);
+char * __must_check kernfs_path(struct kernfs_node *kn, char *buf,
+				size_t buflen);
+void pr_cont_kernfs_name(struct kernfs_node *kn);
+void pr_cont_kernfs_path(struct kernfs_node *kn);
+struct kernfs_node *kernfs_get_parent(struct kernfs_node *kn);
 struct kernfs_node *kernfs_find_and_get_ns(struct kernfs_node *parent,
 					   const char *name, const void *ns);
 void kernfs_get(struct kernfs_node *kn);

@@ -283,6 +294,19 @@ static inline void kernfs_enable_ns(struct kernfs_node *kn) { }
 static inline bool kernfs_ns_enabled(struct kernfs_node *kn)
 { return false; }
 
+static inline int kernfs_name(struct kernfs_node *kn, char *buf, size_t buflen)
+{ return -ENOSYS; }
+
+char * __must_check kernfs_path(struct kernfs_node *kn, char *buf,
+				size_t buflen)
+{ return NULL; }
+
+static inline void pr_cont_kernfs_name(struct kernfs_node *kn) { }
+static inline void pr_cont_kernfs_path(struct kernfs_node *kn) { }
+
+static inline struct kernfs_node *kernfs_get_parent(struct kernfs_node *kn)
+{ return NULL; }
+
 static inline struct kernfs_node *
 kernfs_find_and_get_ns(struct kernfs_node *parent, const char *name,
 		       const void *ns)

index 42a250f..a347792 100644
@@ -19,6 +19,8 @@
 #include "kernfs-internal.h"
 
 DEFINE_MUTEX(kernfs_mutex);
+static DEFINE_SPINLOCK(kernfs_rename_lock);	/* kn->parent and ->name */
+static char kernfs_pr_cont_buf[PATH_MAX];	/* protected by rename_lock */
 
 #define rb_to_kn(X) rb_entry((X), struct kernfs_node, rb)
 

@@ -37,6 +39,141 @@ static bool kernfs_lockdep(struct kernfs_node *kn)
 #endif
 }
 
+static int kernfs_name_locked(struct kernfs_node *kn, char *buf, size_t buflen)
+{
+	return strlcpy(buf, kn->parent ? kn->name : "/", buflen);
+}
+
+static char * __must_check kernfs_path_locked(struct kernfs_node *kn, char *buf,
+					      size_t buflen)
+{
+	char *p = buf + buflen;
+	int len;
+
+	*--p = '\0';
+
+	do {
+		len = strlen(kn->name);
+		if (p - buf < len + 1) {
+			buf[0] = '\0';
+			p = NULL;
+			break;
+		}
+		p -= len;
+		memcpy(p, kn->name, len);
+		*--p = '/';
+		kn = kn->parent;
+	} while (kn && kn->parent);
+
+	return p;
+}
+
+/**
+ * kernfs_name - obtain the name of a given node
+ * @kn: kernfs_node of interest
+ * @buf: buffer to copy @kn's name into
+ * @buflen: size of @buf
+ *
+ * Copies the name of @kn into @buf of @buflen bytes.  The behavior is
+ * similar to strlcpy().  It returns the length of @kn's name and if @buf
+ * isn't long enough, it's filled upto @buflen-1 and nul terminated.
+ *
+ * This function can be called from any context.
+ */
+int kernfs_name(struct kernfs_node *kn, char *buf, size_t buflen)
+{
+	unsigned long flags;
+	int ret;
+
+	spin_lock_irqsave(&kernfs_rename_lock, flags);
+	ret = kernfs_name_locked(kn, buf, buflen);
+	spin_unlock_irqrestore(&kernfs_rename_lock, flags);
+	return ret;
+}
+
+/**
+ * kernfs_path - build full path of a given node
+ * @kn: kernfs_node of interest
+ * @buf: buffer to copy @kn's name into
+ * @buflen: size of @buf
+ *
+ * Builds and returns the full path of @kn in @buf of @buflen bytes.  The
+ * path is built from the end of @buf so the returned pointer usually
+ * doesn't match @buf.  If @buf isn't long enough, @buf is nul terminated
+ * and %NULL is returned.
+ */
+char *kernfs_path(struct kernfs_node *kn, char *buf, size_t buflen)
+{
+	unsigned long flags;
+	char *p;
+
+	spin_lock_irqsave(&kernfs_rename_lock, flags);
+	p = kernfs_path_locked(kn, buf, buflen);
+	spin_unlock_irqrestore(&kernfs_rename_lock, flags);
+	return p;
+}
+
+/**
+ * pr_cont_kernfs_name - pr_cont name of a kernfs_node
+ * @kn: kernfs_node of interest
+ *
+ * This function can be called from any context.
+ */
+void pr_cont_kernfs_name(struct kernfs_node *kn)
+{
+	unsigned long flags;
+
+	spin_lock_irqsave(&kernfs_rename_lock, flags);
+
+	kernfs_name_locked(kn, kernfs_pr_cont_buf, sizeof(kernfs_pr_cont_buf));
+	pr_cont("%s", kernfs_pr_cont_buf);
+
+	spin_unlock_irqrestore(&kernfs_rename_lock, flags);
+}
+
+/**
+ * pr_cont_kernfs_path - pr_cont path of a kernfs_node
+ * @kn: kernfs_node of interest
+ *
+ * This function can be called from any context.
+ */
+void pr_cont_kernfs_path(struct kernfs_node *kn)
+{
+	unsigned long flags;
+	char *p;
+
+	spin_lock_irqsave(&kernfs_rename_lock, flags);
+
+	p = kernfs_path_locked(kn, kernfs_pr_cont_buf,
+			       sizeof(kernfs_pr_cont_buf));
+	if (p)
+		pr_cont("%s", p);
+	else
+		pr_cont("<name too long>");
+
+	spin_unlock_irqrestore(&kernfs_rename_lock, flags);
+}
+
+/**
+ * kernfs_get_parent - determine the parent node and pin it
+ * @kn: kernfs_node of interest
+ *
+ * Determines @kn's parent, pins and returns it.  This function can be
+ * called from any context.
+ */
+struct kernfs_node *kernfs_get_parent(struct kernfs_node *kn)
+{
+	struct kernfs_node *parent;
+	unsigned long flags;
+
+	spin_lock_irqsave(&kernfs_rename_lock, flags);
+	parent = kn->parent;
+	kernfs_get(parent);
+	spin_unlock_irqrestore(&kernfs_rename_lock, flags);
+
+	return parent;
+}
+
 /**
  *	kernfs_name_hash
  *	@name: Null terminated string to hash

@@ -1103,8 +1240,14 @@ int kernfs_remove_by_name_ns(struct kernfs_node *parent, const char *name,
 int kernfs_rename_ns(struct kernfs_node *kn, struct kernfs_node *new_parent,
 		     const char *new_name, const void *new_ns)
 {
+	struct kernfs_node *old_parent;
+	const char *old_name = NULL;
 	int error;
 
+	/* can't move or rename root */
+	if (!kn->parent)
+		return -EINVAL;
+
 	mutex_lock(&kernfs_mutex);
 
 	error = -ENOENT;

@@ -1126,13 +1269,8 @@ int kernfs_rename_ns(struct kernfs_node *kn, struct kernfs_node *new_parent,
 		new_name = kstrdup(new_name, GFP_KERNEL);
 		if (!new_name)
 			goto out;
-
-		if (kn->flags & KERNFS_STATIC_NAME)
-			kn->flags &= ~KERNFS_STATIC_NAME;
-		else
-			kfree(kn->name);
-
-		kn->name = new_name;
+	} else {
+		new_name = NULL;
 	}
 
 	/*

@@ -1140,12 +1278,29 @@ int kernfs_rename_ns(struct kernfs_node *kn, struct kernfs_node *new_parent,
 	 */
 	kernfs_unlink_sibling(kn);
 	kernfs_get(new_parent);
-	kernfs_put(kn->parent);
-	kn->ns = new_ns;
-	kn->hash = kernfs_name_hash(kn->name, kn->ns);
+
+	/* rename_lock protects ->parent and ->name accessors */
+	spin_lock_irq(&kernfs_rename_lock);
+
+	old_parent = kn->parent;
 	kn->parent = new_parent;
+
+	kn->ns = new_ns;
+	if (new_name) {
+		if (!(kn->flags & KERNFS_STATIC_NAME))
+			old_name = kn->name;
+		kn->flags &= ~KERNFS_STATIC_NAME;
+		kn->name = new_name;
+	}
+
+	spin_unlock_irq(&kernfs_rename_lock);
+
+	kn->hash = kernfs_name_hash(new_name, new_ns);
 	kernfs_link_sibling(kn);
 
+	kernfs_put(old_parent);
+	kfree(old_name);
+
 	error = 0;
  out:
 	mutex_unlock(&kernfs_mutex);

68 lines not on this page · raw message

index 9c89904..8736ee8 100644
@@ -91,7 +91,12 @@ struct kernfs_node {
 #ifdef CONFIG_DEBUG_LOCK_ALLOC
 	struct lockdep_map	dep_map;
 #endif
-	/* the following two fields are published */
+	/*
+	 * Use kernfs_get_parent() and kernfs_name/path() instead of
+	 * accessing the following two fields directly.  If the node is
+	 * never moved to a different parent, it is safe to access the
+	 * parent directly.
+	 */
 	struct kernfs_node	*parent;
 	const char		*name;
 

@@ -229,6 +234,12 @@ static inline bool kernfs_ns_enabled(struct kernfs_node *kn)
 	return kn->flags & KERNFS_NS;
 }
 
+int kernfs_name(struct kernfs_node *kn, char *buf, size_t buflen);
+char * __must_check kernfs_path(struct kernfs_node *kn, char *buf,
+				size_t buflen);
+void pr_cont_kernfs_name(struct kernfs_node *kn);
+void pr_cont_kernfs_path(struct kernfs_node *kn);
+struct kernfs_node *kernfs_get_parent(struct kernfs_node *kn);
 struct kernfs_node *kernfs_find_and_get_ns(struct kernfs_node *parent,
 					   const char *name, const void *ns);
 void kernfs_get(struct kernfs_node *kn);

@@ -283,6 +294,19 @@ static inline void kernfs_enable_ns(struct kernfs_node *kn) { }
 static inline bool kernfs_ns_enabled(struct kernfs_node *kn)
 { return false; }
 
+static inline int kernfs_name(struct kernfs_node *kn, char *buf, size_t buflen)
+{ return -ENOSYS; }
+
+static inline char * __must_check kernfs_path(struct kernfs_node *kn, char *buf,
+					      size_t buflen)
+{ return NULL; }
+
+static inline void pr_cont_kernfs_name(struct kernfs_node *kn) { }
+static inline void pr_cont_kernfs_path(struct kernfs_node *kn) { }
+
+static inline struct kernfs_node *kernfs_get_parent(struct kernfs_node *kn)
+{ return NULL; }
+
 static inline struct kernfs_node *
 kernfs_find_and_get_ns(struct kernfs_node *parent, const char *name,
 		       const void *ns)

index b7cb267..32b696f 100644
@@ -201,7 +201,7 @@ struct kernfs_ops {
 #endif
 };
 
-#ifdef CONFIG_SYSFS
+#ifdef CONFIG_KERNFS
 
 static inline enum kernfs_node_type kernfs_type(struct kernfs_node *kn)
 {

@@ -284,7 +284,7 @@ void kernfs_kill_sb(struct super_block *sb);
 
 void kernfs_init(void);
 
-#else	/* CONFIG_SYSFS */
+#else	/* CONFIG_KERNFS */
 
 static inline enum kernfs_node_type kernfs_type(struct kernfs_node *kn)
 { return 0; }	/* whatever */

@@ -379,7 +379,7 @@ static inline void kernfs_kill_sb(struct super_block *sb) { }
 
 static inline void kernfs_init(void) { }
 
-#endif	/* CONFIG_SYSFS */
+#endif	/* CONFIG_KERNFS */
 
 static inline struct kernfs_node *
 kernfs_find_and_get(struct kernfs_node *kn, const char *name)

index 14df054..fdaa0c6 100644
@@ -244,6 +244,11 @@ void sysfs_notify(struct kobject *kobj, const char *dir, const char *attr);
 
 int __must_check sysfs_init(void);
 
+static inline void sysfs_enable_ns(struct kernfs_node *kn)
+{
+	return kernfs_enable_ns(kn);
+}
+
 #else /* CONFIG_SYSFS */
 
 static inline int sysfs_create_dir_ns(struct kobject *kobj, const void *ns)

@@ -416,6 +421,10 @@ static inline int __must_check sysfs_init(void)
 	return 0;
 }
 
+static inline void sysfs_enable_ns(struct kernfs_node *kn)
+{
+}
+
 #endif /* CONFIG_SYSFS */
 
 static inline int __must_check sysfs_create_file(struct kobject *kobj,

index cb14aea..58751bb 100644
@@ -94,7 +94,7 @@ static int create_dir(struct kobject *kobj)
 		BUG_ON(ops->type >= KOBJ_NS_TYPES);
 		BUG_ON(!kobj_ns_type_registered(ops->type));
 
-		kernfs_enable_ns(kobj->sd);
+		sysfs_enable_ns(kobj->sd);
 	}
 
 	return 0;