aufs: workqueue

Aufs uses the workqueue both synchronously and asynchronously.
For sync-use-case, aufs uses its own specific wkq since doesn't want to
be disturbed by other tasks on the system. For async-use-case, aufs uses
the system global workqueue.
Aufs has to prevent itself to being unmounted during the async-task is
queued.

See also the document in this commit.
Signed-off-by: J. R. Okajima <hooanon05g@gmail.com>

Documentation/filesystems/aufs/design/02struct.txt

@@ -37,3 +37,31 @@ among multiple writable branches, XIB files, pseudo-links and kobject.
 See below in detail.
 About the policies which supports copy-down a directory, see
 wbr_policy.txt too.
+
+
+Workqueue
+----------------------------------------------------------------------
+Aufs sometimes requires privilege access to a branch. For instance,
+in copy-up/down operation. When a user process is going to make changes
+to a file which exists in the lower readonly branch only, and the mode
+of one of ancestor directories may not be writable by a user
+process. Here aufs copy-up the file with its ancestors and they may
+require privilege to set its owner/group/mode/etc.
+This is a typical case of a application character of aufs (see
+Introduction).
+
+Aufs uses workqueue synchronously for this case. It creates its own
+workqueue. The workqueue is a kernel thread and has privilege. Aufs
+passes the request to call mkdir or write (for example), and wait for
+its completion. This approach solves a problem of a signal handler
+simply.
+If aufs didn't adopt the workqueue and changed the privilege of the
+process, then the process may receive the unexpected SIGXFSZ or other
+signals.
+
+Also aufs uses the system global workqueue ("events" kernel thread) too
+for asynchronous tasks, such like handling inotify/fsnotify, re-creating a
+whiteout base and etc. This is unrelated to a privilege.
+Most of aufs operation tries acquiring a rw_semaphore for aufs
+superblock at the beginning, at the same time waits for the completion
+of all queued asynchronous tasks.

fs/aufs/Makefile

@@ -11,7 +11,7 @@ ccflags-y += -include ${srctree}/include/uapi/linux/aufs_type.h
 
 obj-$(CONFIG_AUFS_FS) += aufs.o
 aufs-y := module.o sbinfo.o super.o branch.o opts.o \
-	vfsub.o dcsub.o \
+	wkq.o vfsub.o dcsub.o \
 	cpup.o \
 	dinfo.o \
 	iinfo.o inode.o

fs/aufs/aufs.h

@@ -34,6 +34,7 @@
 #include "rwsem.h"
 #include "super.h"
 #include "vfsub.h"
+#include "wkq.h"
 
 #endif /* __KERNEL__ */
 #endif /* __AUFS_H__ */

fs/aufs/debug.c

@@ -203,8 +203,8 @@ void au_dpri_sb(struct super_block *sb)
 	sbinfo = au_sbi(sb);
 	if (!sbinfo)
 		return;
-	dpri("gen %u, kobj %d\n",
-	     sbinfo->si_generation,
+	dpri("nw %d, gen %u, kobj %d\n",
+	     atomic_read(&sbinfo->si_nowait.nw_len), sbinfo->si_generation,
 	     kref_read(&sbinfo->si_kobj.kref));
 	for (bindex = 0; bindex <= sbinfo->si_bbot; bindex++)
 		do_pri_br(bindex, sbinfo->si_branch[0 + bindex]);
@@ -265,3 +265,15 @@ void au_dbg_verify_gen(struct dentry *parent, unsigned int sigen)
 	}
 	au_dpages_free(&dpages);
 }
+
+void au_dbg_verify_kthread(void)
+{
+	if (au_wkq_test()) {
+		/* au_dbg_blocked(); re-commit later */
+		/*
+		 * It may be recursive, but udba=notify between two aufs mounts,
+		 * where a single ro branch is shared, is not a problem.
+		 */
+		/* WARN_ON(1); */
+	}
+}

fs/aufs/debug.h

@@ -83,6 +83,7 @@ void au_dpri_sb(struct super_block *sb);
 #define au_dbg_verify_dinode(d) __au_dbg_verify_dinode(d, __func__, __LINE__)
 void __au_dbg_verify_dinode(struct dentry *dentry, const char *func, int line);
 void au_dbg_verify_gen(struct dentry *parent, unsigned int sigen);
+void au_dbg_verify_kthread(void);
 
 #define AuDbgInode(i) do { \
 	mutex_lock(&au_dbg_mtx); \
@@ -114,6 +115,7 @@ void au_dbg_verify_gen(struct dentry *parent, unsigned int sigen);
 #else
 AuStubVoid(au_dbg_verify_dinode, struct dentry *dentry)
 AuStubVoid(au_dbg_verify_gen, struct dentry *parent, unsigned int sigen)
+AuStubVoid(au_dbg_verify_kthread, void)
 
 #define AuDbgInode(i)		do {} while (0)
 #define AuDbgDAlias(i)		do {} while (0)

fs/aufs/module.c

@@ -120,13 +120,19 @@ static int __init aufs_init(void)
 
 	memset(au_cache, 0, sizeof(au_cache));
 
-	err = au_cache_init();
+	err = au_wkq_init();
 	if (unlikely(err))
 		goto out;
+	err = au_cache_init();
+	if (unlikely(err))
+		goto out_wkq;
 
 	/* since we define pr_fmt, call printk directly */
 	printk(KERN_INFO AUFS_NAME " " AUFS_VERSION "\n");
+	goto out; /* success */
 
+out_wkq:
+	au_wkq_fin();
 out:
 	return err;
 }

fs/aufs/sbinfo.c

@@ -18,6 +18,7 @@ void au_si_free(struct kobject *kobj)
 	struct au_sbinfo *sbinfo;
 
 	sbinfo = container_of(kobj, struct au_sbinfo, si_kobj);
+	AuDebugOn(atomic_read(&sbinfo->si_nowait.nw_len));
 
 	au_rw_write_lock(&sbinfo->si_rwsem);
 	au_br_free(sbinfo);
@@ -44,6 +45,7 @@ int au_si_alloc(struct super_block *sb)
 	if (unlikely(!sbinfo->si_branch))
 		goto out_sbinfo;
 
+	au_nwt_init(&sbinfo->si_nowait);
 	au_rw_init_wlock(&sbinfo->si_rwsem);
 
 	sbinfo->si_bbot = -1;
@@ -116,3 +118,26 @@ aufs_bindex_t au_new_br_id(struct super_block *sb)
 
 	return -1;
 }
+
+/* ---------------------------------------------------------------------- */
+
+/* it is ok that new 'nwt' tasks are appended while we are sleeping */
+int si_read_lock(struct super_block *sb, int flags)
+{
+	if (au_ftest_lock(flags, FLUSH))
+		au_nwt_flush(&au_sbi(sb)->si_nowait);
+
+	si_noflush_read_lock(sb);
+
+	return 0; /* re-commit later */
+}
+
+int si_write_lock(struct super_block *sb, int flags)
+{
+	if (au_ftest_lock(flags, FLUSH))
+		au_nwt_flush(&au_sbi(sb)->si_nowait);
+
+	si_noflush_write_lock(sb);
+
+	return 0; /* re-commit later */
+}

fs/aufs/super.h

@@ -15,9 +15,13 @@
 #include <linux/fs.h>
 #include <linux/kobject.h>
 #include "rwsem.h"
+#include "wkq.h"
 
 struct au_branch;
 struct au_sbinfo {
+	/* nowait tasks in the system-wide workqueue */
+	struct au_nowait_tasks	si_nowait;
+
 	/*
 	 * tried sb->s_umount, but failed due to the dependency between i_mutex.
 	 * rwsem for au_sbinfo is necessary.
@@ -49,10 +53,11 @@ struct au_sbinfo {
 
 /* ---------------------------------------------------------------------- */
 
-/* flags for __si_read_lock()/aufs_read_lock()/di_read_lock() */
+/* flags for si_read_lock()/aufs_read_lock()/di_read_lock() */
 #define AuLock_DW		1		/* write-lock dentry */
 #define AuLock_IR		(1 << 1)	/* read-lock inode */
 #define AuLock_IW		(1 << 2)	/* write-lock inode */
+#define AuLock_FLUSH		(1 << 3)	/* wait for 'nowait' tasks */
 #define au_ftest_lock(flags, name)	((flags) & AuLock_##name)
 #define au_fset_lock(flags, name) \
 	do { (flags) |= AuLock_##name; } while (0)
@@ -72,6 +77,9 @@ int au_sbr_realloc(struct au_sbinfo *sbinfo, int nbr, int may_shrink);
 unsigned int au_sigen_inc(struct super_block *sb);
 aufs_bindex_t au_new_br_id(struct super_block *sb);
 
+int si_read_lock(struct super_block *sb, int flags);
+int si_write_lock(struct super_block *sb, int flags);
+
 /* ---------------------------------------------------------------------- */
 
 static inline struct au_sbinfo *au_sbi(struct super_block *sb)
@@ -101,6 +109,65 @@ static inline struct au_sbinfo *au_sbi(struct super_block *sb)
 #define SiMustAnyLock(sb)	AuRwMustAnyLock(&au_sbi(sb)->si_rwsem)
 #define SiMustWriteLock(sb)	AuRwMustWriteLock(&au_sbi(sb)->si_rwsem)
 
+static inline void si_noflush_read_lock(struct super_block *sb)
+{
+	__si_read_lock(sb);
+	/* re-commit later */
+}
+
+static inline int si_noflush_read_trylock(struct super_block *sb)
+{
+	return __si_read_trylock(sb);	/* re-commit later */
+}
+
+static inline void si_noflush_write_lock(struct super_block *sb)
+{
+	__si_write_lock(sb);
+	/* re-commit later */
+}
+
+static inline int si_noflush_write_trylock(struct super_block *sb)
+{
+	return __si_write_trylock(sb);	/* re-commit later */
+}
+
+#if 0 /* reserved */
+static inline int si_read_trylock(struct super_block *sb, int flags)
+{
+	if (au_ftest_lock(flags, FLUSH))
+		au_nwt_flush(&au_sbi(sb)->si_nowait);
+	return si_noflush_read_trylock(sb);
+}
+#endif
+
+static inline void si_read_unlock(struct super_block *sb)
+{
+	/* re-commit later */
+	__si_read_unlock(sb);
+}
+
+#if 0 /* reserved */
+static inline int si_write_trylock(struct super_block *sb, int flags)
+{
+	if (au_ftest_lock(flags, FLUSH))
+		au_nwt_flush(&au_sbi(sb)->si_nowait);
+	return si_noflush_write_trylock(sb);
+}
+#endif
+
+static inline void si_write_unlock(struct super_block *sb)
+{
+	/* re-commit later */
+	__si_write_unlock(sb);
+}
+
+#if 0 /* reserved */
+static inline void si_downgrade_lock(struct super_block *sb)
+{
+	__si_downgrade_lock(sb);
+}
+#endif
+
 /* ---------------------------------------------------------------------- */
 
 static inline aufs_bindex_t au_sbbot(struct super_block *sb)

fs/aufs/wkq.c

+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Copyright (C) 2005-2019 Junjiro R. Okajima
+ */
+
+/*
+ * workqueue for asynchronous/super-io operations
+ * todo: try new credential scheme
+ */
+
+#include <linux/module.h>
+#include <linux/sched/signal.h>
+#include "aufs.h"
+
+/* internal workqueue named AUFS_WKQ_NAME */
+
+static struct workqueue_struct *au_wkq;
+
+struct au_wkinfo {
+	struct work_struct wk;
+	struct kobject *kobj;
+
+	unsigned int flags; /* see wkq.h */
+
+	au_wkq_func_t func;
+	void *args;
+
+#ifdef CONFIG_LOCKDEP
+	int dont_check;
+	struct held_lock **hlock;
+#endif
+
+	struct completion *comp;
+};
+
+/* ---------------------------------------------------------------------- */
+/*
+ * Aufs passes some operations to the workqueue such as the internal copyup.
+ * This scheme looks rather unnatural for LOCKDEP debugging feature, since the
+ * job run by workqueue depends upon the locks acquired in the other task.
+ * Delegating a small operation to the workqueue, aufs passes its lockdep
+ * information too. And the job in the workqueue restores the info in order to
+ * pretend as if it acquired those locks. This is just to make LOCKDEP work
+ * correctly and expectedly.
+ */
+
+#ifndef CONFIG_LOCKDEP
+AuStubInt0(au_wkq_lockdep_alloc, struct au_wkinfo *wkinfo);
+AuStubVoid(au_wkq_lockdep_free, struct au_wkinfo *wkinfo);
+AuStubVoid(au_wkq_lockdep_pre, struct au_wkinfo *wkinfo);
+AuStubVoid(au_wkq_lockdep_post, struct au_wkinfo *wkinfo);
+AuStubVoid(au_wkq_lockdep_init, struct au_wkinfo *wkinfo);
+#else
+static void au_wkq_lockdep_init(struct au_wkinfo *wkinfo)
+{
+	wkinfo->hlock = NULL;
+	wkinfo->dont_check = 0;
+}
+
+/*
+ * 1: matched
+ * 0: unmatched
+ */
+static int au_wkq_lockdep_test(struct lock_class_key *key, const char *name)
+{
+	static DEFINE_SPINLOCK(spin);
+	static struct {
+		char *name;
+		struct lock_class_key *key;
+	} a[] = {
+		{ .name = "&sbinfo->si_rwsem" },
+		{ .name = "&finfo->fi_rwsem" },
+		{ .name = "&dinfo->di_rwsem" },
+		{ .name = "&iinfo->ii_rwsem" }
+	};
+	static int set;
+	int i;
+
+	/* lockless read from 'set.' see below */
+	if (set == ARRAY_SIZE(a)) {
+		for (i = 0; i < ARRAY_SIZE(a); i++)
+			if (a[i].key == key)
+				goto match;
+		goto unmatch;
+	}
+
+	spin_lock(&spin);
+	if (set)
+		for (i = 0; i < ARRAY_SIZE(a); i++)
+			if (a[i].key == key) {
+				spin_unlock(&spin);
+				goto match;
+			}
+	for (i = 0; i < ARRAY_SIZE(a); i++) {
+		if (a[i].key) {
+			if (unlikely(a[i].key == key)) { /* rare but possible */
+				spin_unlock(&spin);
+				goto match;
+			} else
+				continue;
+		}
+		if (strstr(a[i].name, name)) {
+			/*
+			 * the order of these three lines is important for the
+			 * lockless read above.
+			 */
+			a[i].key = key;
+			spin_unlock(&spin);
+			set++;
+			/* AuDbg("%d, %s\n", set, name); */
+			goto match;
+		}
+	}
+	spin_unlock(&spin);
+	goto unmatch;
+
+match:
+	return 1;
+unmatch:
+	return 0;
+}
+
+static int au_wkq_lockdep_alloc(struct au_wkinfo *wkinfo)
+{
+	int err, n;
+	struct task_struct *curr;
+	struct held_lock **hl, *held_locks, *p;
+
+	err = 0;
+	curr = current;
+	wkinfo->dont_check = lockdep_recursing(curr);
+	if (wkinfo->dont_check)
+		goto out;
+	n = curr->lockdep_depth;
+	if (!n)
+		goto out;
+
+	err = -ENOMEM;
+	wkinfo->hlock = kmalloc_array(n + 1, sizeof(*wkinfo->hlock), GFP_NOFS);
+	if (unlikely(!wkinfo->hlock))
+		goto out;
+
+	err = 0;
+#if 0
+	if (0 && au_debug_test()) /* left for debugging */
+		lockdep_print_held_locks(curr);
+#endif
+	held_locks = curr->held_locks;
+	hl = wkinfo->hlock;
+	while (n--) {
+		p = held_locks++;
+		if (au_wkq_lockdep_test(p->instance->key, p->instance->name))
+			*hl++ = p;
+	}
+	*hl = NULL;
+
+out:
+	return err;
+}
+
+static void au_wkq_lockdep_free(struct au_wkinfo *wkinfo)
+{
+	au_kfree_try_rcu(wkinfo->hlock);
+}
+
+static void au_wkq_lockdep_pre(struct au_wkinfo *wkinfo)
+{
+	struct held_lock *p, **hl = wkinfo->hlock;
+	int subclass;
+
+	if (wkinfo->dont_check)
+		lockdep_off();
+	if (!hl)
+		return;
+	while ((p = *hl++)) { /* assignment */
+		subclass = lockdep_hlock_class(p)->subclass;
+		/* AuDbg("%s, %d\n", p->instance->name, subclass); */
+		if (p->read)
+			rwsem_acquire_read(p->instance, subclass, 0,
+					   /*p->acquire_ip*/_RET_IP_);
+		else
+			rwsem_acquire(p->instance, subclass, 0,
+				      /*p->acquire_ip*/_RET_IP_);
+	}
+}
+
+static void au_wkq_lockdep_post(struct au_wkinfo *wkinfo)
+{
+	struct held_lock *p, **hl = wkinfo->hlock;
+
+	if (wkinfo->dont_check)
+		lockdep_on();
+	if (!hl)
+		return;
+	while ((p = *hl++)) /* assignment */
+		rwsem_release(p->instance, 0, /*p->acquire_ip*/_RET_IP_);
+}
+#endif
+
+static void wkq_func(struct work_struct *wk)
+{
+	struct au_wkinfo *wkinfo = container_of(wk, struct au_wkinfo, wk);
+
+	AuDebugOn(!uid_eq(current_fsuid(), GLOBAL_ROOT_UID));
+	AuDebugOn(rlimit(RLIMIT_FSIZE) != RLIM_INFINITY);
+
+	au_wkq_lockdep_pre(wkinfo);
+	wkinfo->func(wkinfo->args);
+	au_wkq_lockdep_post(wkinfo);
+	if (au_ftest_wkq(wkinfo->flags, WAIT))
+		complete(wkinfo->comp);
+	else {
+		kobject_put(wkinfo->kobj);
+		module_put(THIS_MODULE); /* todo: ?? */
+		au_kfree_rcu(wkinfo);
+	}
+}
+
+/*
+ * Since struct completion is large, try allocating it dynamically.
+ */
+#if 1 /* defined(CONFIG_4KSTACKS) || defined(AuTest4KSTACKS) */
+#define AuWkqCompDeclare(name)	struct completion *comp = NULL
+
+static int au_wkq_comp_alloc(struct au_wkinfo *wkinfo, struct completion **comp)
+{
+	*comp = kmalloc(sizeof(**comp), GFP_NOFS);
+	if (*comp) {
+		init_completion(*comp);
+		wkinfo->comp = *comp;
+		return 0;
+	}
+	return -ENOMEM;
+}
+
+static void au_wkq_comp_free(struct completion *comp)
+{
+	au_kfree_rcu(comp);
+}
+
+#else
+
+/* no braces */
+#define AuWkqCompDeclare(name) \
+	DECLARE_COMPLETION_ONSTACK(_ ## name); \
+	struct completion *comp = &_ ## name
+
+static int au_wkq_comp_alloc(struct au_wkinfo *wkinfo, struct completion **comp)
+{
+	wkinfo->comp = *comp;
+	return 0;
+}
+
+static void au_wkq_comp_free(struct completion *comp __maybe_unused)
+{
+	/* empty */
+}
+#endif /* 4KSTACKS */
+
+static void au_wkq_run(struct au_wkinfo *wkinfo)
+{
+	au_dbg_verify_kthread();
+
+	if (au_ftest_wkq(wkinfo->flags, WAIT)) {
+		INIT_WORK_ONSTACK(&wkinfo->wk, wkq_func);
+		queue_work(au_wkq, &wkinfo->wk);
+	} else {
+		INIT_WORK(&wkinfo->wk, wkq_func);
+		schedule_work(&wkinfo->wk);
+	}
+}
+
+/*
+ * Be careful. It is easy to make deadlock happen.
+ * processA: lock, wkq and wait
+ * processB: wkq and wait, lock in wkq
+ * --> deadlock
+ */
+int au_wkq_do_wait(unsigned int flags, au_wkq_func_t func, void *args)
+{
+	int err;
+	AuWkqCompDeclare(comp);
+	struct au_wkinfo wkinfo = {
+		.flags	= flags,
+		.func	= func,
+		.args	= args
+	};
+
+	err = au_wkq_comp_alloc(&wkinfo, &comp);
+	if (unlikely(err))
+		goto out;
+	err = au_wkq_lockdep_alloc(&wkinfo);
+	if (unlikely(err))
+		goto out_comp;
+	if (!err) {
+		au_wkq_run(&wkinfo);
+		/* no timeout, no interrupt */
+		wait_for_completion(wkinfo.comp);
+	}
+	au_wkq_lockdep_free(&wkinfo);
+
+out_comp:
+	au_wkq_comp_free(comp);
+out:
+	destroy_work_on_stack(&wkinfo.wk);
+	return err;
+}
+
+/*
+ * Note: dget/dput() in func for aufs dentries are not supported. It will be a
+ * problem in a concurrent umounting.
+ */
+int au_wkq_nowait(au_wkq_func_t func, void *args, struct super_block *sb,
+		  unsigned int flags)
+{
+	int err;
+	struct au_wkinfo *wkinfo;
+
+	atomic_inc(&au_sbi(sb)->si_nowait.nw_len);
+
+	/*
+	 * wkq_func() must free this wkinfo.
+	 * it highly depends upon the implementation of workqueue.
+	 */
+	err = 0;
+	wkinfo = kmalloc(sizeof(*wkinfo), GFP_NOFS);
+	if (wkinfo) {
+		wkinfo->kobj = &au_sbi(sb)->si_kobj;
+		wkinfo->flags = flags & ~AuWkq_WAIT;
+		wkinfo->func = func;
+		wkinfo->args = args;
+		wkinfo->comp = NULL;
+		au_wkq_lockdep_init(wkinfo);
+		kobject_get(wkinfo->kobj);
+		__module_get(THIS_MODULE); /* todo: ?? */
+
+		au_wkq_run(wkinfo);
+	} else {
+		err = -ENOMEM;
+		au_nwt_done(&au_sbi(sb)->si_nowait);
+	}
+
+	return err;
+}
+
+/* ---------------------------------------------------------------------- */
+
+void au_nwt_init(struct au_nowait_tasks *nwt)
+{
+	atomic_set(&nwt->nw_len, 0);
+	/* smp_mb(); */ /* atomic_set */
+	init_waitqueue_head(&nwt->nw_wq);
+}
+
+void au_wkq_fin(void)
+{
+	destroy_workqueue(au_wkq);
+}
+
+int __init au_wkq_init(void)
+{
+	int err;
+
+	err = 0;
+	au_wkq = alloc_workqueue(AUFS_WKQ_NAME, 0, WQ_DFL_ACTIVE);
+	if (IS_ERR(au_wkq))
+		err = PTR_ERR(au_wkq);
+	else if (!au_wkq)
+		err = -ENOMEM;
+
+	return err;
+}

fs/aufs/wkq.h

+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * Copyright (C) 2005-2019 Junjiro R. Okajima
+ */
+
+/*
+ * workqueue for asynchronous/super-io operations
+ * todo: try new credentials management scheme
+ */
+
+#ifndef __AUFS_WKQ_H__
+#define __AUFS_WKQ_H__
+
+#ifdef __KERNEL__
+
+#include <linux/wait.h>
+
+struct super_block;
+
+/* ---------------------------------------------------------------------- */
+
+/*
+ * in the next operation, wait for the 'nowait' tasks in system-wide workqueue
+ */
+struct au_nowait_tasks {
+	atomic_t		nw_len;
+	wait_queue_head_t	nw_wq;
+};
+
+/* ---------------------------------------------------------------------- */
+
+typedef void (*au_wkq_func_t)(void *args);
+
+/* wkq flags */
+#define AuWkq_WAIT	1
+#define au_ftest_wkq(flags, name)	((flags) & AuWkq_##name)
+#define au_fset_wkq(flags, name) \
+	do { (flags) |= AuWkq_##name; } while (0)
+#define au_fclr_wkq(flags, name) \
+	do { (flags) &= ~AuWkq_##name; } while (0)
+
+/* wkq.c */
+int au_wkq_do_wait(unsigned int flags, au_wkq_func_t func, void *args);
+int au_wkq_nowait(au_wkq_func_t func, void *args, struct super_block *sb,
+		  unsigned int flags);
+void au_nwt_init(struct au_nowait_tasks *nwt);
+int __init au_wkq_init(void);
+void au_wkq_fin(void);
+
+/* ---------------------------------------------------------------------- */
+
+static inline int au_wkq_test(void)
+{
+	return current->flags & PF_WQ_WORKER;
+}
+
+static inline int au_wkq_wait(au_wkq_func_t func, void *args)
+{
+	return au_wkq_do_wait(AuWkq_WAIT, func, args);
+}
+
+static inline void au_nwt_done(struct au_nowait_tasks *nwt)
+{
+	if (atomic_dec_and_test(&nwt->nw_len))
+		wake_up_all(&nwt->nw_wq);
+}
+
+static inline int au_nwt_flush(struct au_nowait_tasks *nwt)
+{
+	wait_event(nwt->nw_wq, !atomic_read(&nwt->nw_len));
+	return 0;
+}
+
+#endif /* __KERNEL__ */
+#endif /* __AUFS_WKQ_H__ */

include/uapi/linux/aufs_type.h

@@ -54,6 +54,12 @@ typedef int16_t aufs_bindex_t;
 #endif
 #endif /* __KERNEL__ */
 
+/* ---------------------------------------------------------------------- */
+
+#define AUFS_FSTYPE		AUFS_NAME
+
+#define AUFS_WKQ_NAME		AUFS_NAME "d"
+
 /* branch permissions and attributes */
 #define AUFS_BRPERM_RO		"ro"