In Finit issue #196 we were reminded [1] of a missing inotify flag in
Linux older kernels, IN_MASK_CREATE.  Finit makes use of this internally
for monitoring PID conditions, and more.  This is a central mechanism to
synchronize services at boot and reload at runtime.

The following patch for Linux 4.9.0, was provided by Andy Savage for
other people that may want to run Finit on slightly older kernels.

[1]: https://github.com/troglobit/finit/issues/196

Index: fs/notify/inotify/inotify_user.c
===================================================================
--- fs.orig/notify/inotify/inotify_user.c
+++ fs/notify/inotify/inotify_user.c
@@ -522,6 +522,7 @@ static int inotify_update_existing_watch
 	__u32 old_mask, new_mask;
 	__u32 mask;
 	int add = (arg & IN_MASK_ADD);
+	int create = (arg & IN_MASK_CREATE);
 	int ret;

 	mask = inotify_arg_to_mask(arg);
@@ -529,6 +530,8 @@ static int inotify_update_existing_watch
 	fsn_mark = fsnotify_find_inode_mark(group, inode);
 	if (!fsn_mark)
 		return -ENOENT;
+	else if (create)
+		return -EEXIST;

 	i_mark = container_of(fsn_mark, struct inotify_inode_mark, fsn_mark);

@@ -726,6 +729,10 @@ SYSCALL_DEFINE3(inotify_add_watch, int,
 	if (unlikely(!f.file))
 		return -EBADF;

+	/* IN_MASK_ADD and IN_MASK_CREATE don't make sense together */
+	if (unlikely((mask & IN_MASK_ADD) && (mask & IN_MASK_CREATE)))
+		return -EINVAL;
+
 	/* verify that this is indeed an inotify instance */
 	if (unlikely(f.file->f_op != &inotify_fops)) {
 		ret = -EINVAL;
@@ -814,7 +821,7 @@ static int __init inotify_user_setup(voi
 	BUILD_BUG_ON(IN_ISDIR != FS_ISDIR);
 	BUILD_BUG_ON(IN_ONESHOT != FS_IN_ONESHOT);

-	BUG_ON(hweight32(ALL_INOTIFY_BITS) != 21);
+	BUG_ON(hweight32(ALL_INOTIFY_BITS) != 22);

 	inotify_inode_mark_cachep = KMEM_CACHE(inotify_inode_mark, SLAB_PANIC);

Index: include/linux/inotify.h
===================================================================
--- include.orig/linux/inotify.h
+++ include/linux/inotify.h
@@ -17,6 +17,6 @@ extern struct ctl_table inotify_table[];
 			  IN_DELETE_SELF | IN_MOVE_SELF | IN_UNMOUNT | \
 			  IN_Q_OVERFLOW | IN_IGNORED | IN_ONLYDIR | \
 			  IN_DONT_FOLLOW | IN_EXCL_UNLINK | IN_MASK_ADD | \
-			  IN_ISDIR | IN_ONESHOT)
+			  IN_MASK_CREATE | IN_ISDIR | IN_ONESHOT)

 #endif	/* _LINUX_INOTIFY_H */
Index: include/uapi/linux/inotify.h
===================================================================
--- include.orig/uapi/linux/inotify.h
+++ include/uapi/linux/inotify.h
@@ -52,6 +52,7 @@ struct inotify_event {
 #define IN_ONLYDIR		0x01000000	/* only watch the path if it is a directory */
 #define IN_DONT_FOLLOW		0x02000000	/* don't follow a sym link */
 #define IN_EXCL_UNLINK		0x04000000	/* exclude events on unlinked objects */
+#define IN_MASK_CREATE		0x10000000	/* only create watches */
 #define IN_MASK_ADD		0x20000000	/* add to the mask of an already existing watch */
 #define IN_ISDIR		0x40000000	/* event occurred against dir */
 #define IN_ONESHOT		0x80000000	/* only send event once */