[PATCH] inotify (1/5): split kernel API from userspace support

The following series of patches introduces a kernel API for inotify,
making it possible for kernel modules to benefit from inotify's
mechanism for watching inodes.  With these patches, inotify will
maintain for each caller a list of watches (via an embedded struct
inotify_watch), where each inotify_watch is associated with a
corresponding struct inode.  The caller registers an event handler and
specifies for which filesystem events their event handler should be
called per inotify_watch.
Signed-off-by: Amy Griffis <amy.griffis@hp.com>
Acked-by: Robert Love <rml@novell.com>
Acked-by: John McCutchan <john@johnmccutchan.com>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

fs/Kconfig

@@ -393,18 +393,30 @@ config INOTIFY
 	bool "Inotify file change notification support"
 	default y
 	---help---
-	  Say Y here to enable inotify support and the associated system
-	  calls.  Inotify is a file change notification system and a
-	  replacement for dnotify.  Inotify fixes numerous shortcomings in
-	  dnotify and introduces several new features.  It allows monitoring
-	  of both files and directories via a single open fd.  Other features
-	  include multiple file events, one-shot support, and unmount
+	  Say Y here to enable inotify support.  Inotify is a file change
+	  notification system and a replacement for dnotify.  Inotify fixes
+	  numerous shortcomings in dnotify and introduces several new features
+	  including multiple file events, one-shot support, and unmount
 	  notification.
 
 	  For more information, see Documentation/filesystems/inotify.txt
 
 	  If unsure, say Y.
 
+config INOTIFY_USER
+	bool "Inotify support for userspace"
+	depends on INOTIFY
+	default y
+	---help---
+	  Say Y here to enable inotify support for userspace, including the
+	  associated system calls.  Inotify allows monitoring of both files and
+	  directories via a single open fd.  Events are read from the file
+	  descriptor, which is also select()- and poll()-able.
+
+	  For more information, see Documentation/filesystems/inotify.txt
+
+	  If unsure, say Y.
+
 config QUOTA
 	bool "Quota support"
 	help

fs/Makefile

@@ -13,6 +13,7 @@ obj-y :=	open.o read_write.o file_table.o buffer.o  bio.o super.o \
 		ioprio.o pnode.o drop_caches.o splice.o sync.o
 
 obj-$(CONFIG_INOTIFY)		+= inotify.o
+obj-$(CONFIG_INOTIFY_USER)	+= inotify_user.o
 obj-$(CONFIG_EPOLL)		+= eventpoll.o
 obj-$(CONFIG_COMPAT)		+= compat.o compat_ioctl.o
 

include/linux/inotify.h

@@ -68,8 +68,37 @@ struct inotify_event {
 #include <linux/dcache.h>
 #include <linux/fs.h>
 
+/*
+ * struct inotify_watch - represents a watch request on a specific inode
+ *
+ * h_list is protected by ih->mutex of the associated inotify_handle.
+ * i_list, mask are protected by inode->inotify_mutex of the associated inode.
+ * ih, inode, and wd are never written to once the watch is created.
+ *
+ * Callers must use the established inotify interfaces to access inotify_watch
+ * contents.  The content of this structure is private to the inotify
+ * implementation.
+ */
+struct inotify_watch {
+	struct list_head	h_list;	/* entry in inotify_handle's list */
+	struct list_head	i_list;	/* entry in inode's list */
+	atomic_t		count;	/* reference count */
+	struct inotify_handle	*ih;	/* associated inotify handle */
+	struct inode		*inode;	/* associated inode */
+	__s32			wd;	/* watch descriptor */
+	__u32			mask;	/* event mask for this watch */
+};
+
+struct inotify_operations {
+	void (*handle_event)(struct inotify_watch *, u32, u32, u32,
+			     const char *);
+	void (*destroy_watch)(struct inotify_watch *);
+};
+
 #ifdef CONFIG_INOTIFY
 
+/* Kernel API for producing events */
+
 extern void inotify_d_instantiate(struct dentry *, struct inode *);
 extern void inotify_d_move(struct dentry *);
 extern void inotify_inode_queue_event(struct inode *, __u32, __u32,
@@ -80,6 +109,18 @@ extern void inotify_unmount_inodes(struct list_head *);
 extern void inotify_inode_is_dead(struct inode *);
 extern u32 inotify_get_cookie(void);
 
+/* Kernel Consumer API */
+
+extern struct inotify_handle *inotify_init(const struct inotify_operations *);
+extern void inotify_destroy(struct inotify_handle *);
+extern __s32 inotify_find_update_watch(struct inotify_handle *, struct inode *,
+				       u32);
+extern __s32 inotify_add_watch(struct inotify_handle *, struct inotify_watch *,
+			       struct inode *, __u32);
+extern int inotify_rm_wd(struct inotify_handle *, __u32);
+extern void get_inotify_watch(struct inotify_watch *);
+extern void put_inotify_watch(struct inotify_watch *);
+
 #else
 
 static inline void inotify_d_instantiate(struct dentry *dentry,
@@ -116,6 +157,41 @@ static inline u32 inotify_get_cookie(void)
 	return 0;
 }
 
+static inline struct inotify_handle *inotify_init(const struct inotify_operations *ops)
+{
+	return ERR_PTR(-EOPNOTSUPP);
+}
+
+static inline void inotify_destroy(struct inotify_handle *ih)
+{
+}
+
+static inline __s32 inotify_find_update_watch(struct inotify_handle *ih,
+					      struct inode *inode, u32 mask)
+{
+	return -EOPNOTSUPP;
+}
+
+static inline __s32 inotify_add_watch(struct inotify_handle *ih,
+				      struct inotify_watch *watch,
+				      struct inode *inode, __u32 mask)
+{
+	return -EOPNOTSUPP;
+}
+
+static inline int inotify_rm_wd(struct inotify_handle *ih, __u32 wd)
+{
+	return -EOPNOTSUPP;
+}
+
+static inline void get_inotify_watch(struct inotify_watch *watch)
+{
+}
+
+static inline void put_inotify_watch(struct inotify_watch *watch)
+{
+}
+
 #endif	/* CONFIG_INOTIFY */
 
 #endif	/* __KERNEL __ */

include/linux/sched.h

@@ -494,7 +494,7 @@ struct user_struct {
 	atomic_t processes;	/* How many processes does this user have? */
 	atomic_t files;		/* How many open files does this user have? */
 	atomic_t sigpending;	/* How many pending signals does this user have? */
-#ifdef CONFIG_INOTIFY
+#ifdef CONFIG_INOTIFY_USER
 	atomic_t inotify_watches; /* How many inotify watches does this user have? */
 	atomic_t inotify_devs;	/* How many inotify devs does this user have opened? */
 #endif

kernel/sysctl.c

@@ -150,7 +150,7 @@ extern ctl_table random_table[];
 #ifdef CONFIG_UNIX98_PTYS
 extern ctl_table pty_table[];
 #endif
-#ifdef CONFIG_INOTIFY
+#ifdef CONFIG_INOTIFY_USER
 extern ctl_table inotify_table[];
 #endif
 
@@ -1028,7 +1028,7 @@ static ctl_table fs_table[] = {
 		.mode		= 0644,
 		.proc_handler	= &proc_doulongvec_minmax,
 	},
-#ifdef CONFIG_INOTIFY
+#ifdef CONFIG_INOTIFY_USER
 	{
 		.ctl_name	= FS_INOTIFY,
 		.procname	= "inotify",

kernel/user.c

@@ -140,7 +140,7 @@ struct user_struct * alloc_uid(uid_t uid)
 		atomic_set(&new->processes, 0);
 		atomic_set(&new->files, 0);
 		atomic_set(&new->sigpending, 0);
-#ifdef CONFIG_INOTIFY
+#ifdef CONFIG_INOTIFY_USER
 		atomic_set(&new->inotify_watches, 0);
 		atomic_set(&new->inotify_devs, 0);
 #endif