[PATCH] inotify

inotify is intended to correct the deficiencies of dnotify, particularly
its inability to scale and its terrible user interface:

        * dnotify requires the opening of one fd per each directory
          that you intend to watch. This quickly results in too many
          open files and pins removable media, preventing unmount.
        * dnotify is directory-based. You only learn about changes to
          directories. Sure, a change to a file in a directory affects
          the directory, but you are then forced to keep a cache of
          stat structures.
        * dnotify's interface to user-space is awful.  Signals?

inotify provides a more usable, simple, powerful solution to file change
notification:

        * inotify's interface is a system call that returns a fd, not SIGIO.
	  You get a single fd, which is select()-able.
        * inotify has an event that says "the filesystem that the item
          you were watching is on was unmounted."
        * inotify can watch directories or files.

Inotify is currently used by Beagle (a desktop search infrastructure),
Gamin (a FAM replacement), and other projects.

See Documentation/filesystems/inotify.txt.
Signed-off-by: Robert Love <rml@novell.com>
Cc: John McCutchan <ttb@tentacle.dhs.org>
Cc: Christoph Hellwig <hch@lst.de>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

Documentation/filesystems/inotify.txt

+				    inotify
+	     a powerful yet simple file change notification system
+
+
+
+Document started 15 Mar 2005 by Robert Love <rml@novell.com>
+
+(i) User Interface
+
+Inotify is controlled by a set of three sys calls 
+
+First step in using inotify is to initialise an inotify instance
+
+	int fd = inotify_init ();
+
+Change events are managed by "watches".  A watch is an (object,mask) pair where
+the object is a file or directory and the mask is a bit mask of one or more
+inotify events that the application wishes to receive.  See <linux/inotify.h>
+for valid events.  A watch is referenced by a watch descriptor, or wd.
+
+Watches are added via a path to the file.
+
+Watches on a directory will return events on any files inside of the directory.
+
+Adding a watch is simple,
+
+	int wd = inotify_add_watch (fd, path, mask);
+
+You can add a large number of files via something like
+
+	for each file to watch {
+		int wd = inotify_add_watch (fd, file, mask);
+	}
+
+You can update an existing watch in the same manner, by passing in a new mask.
+
+An existing watch is removed via the INOTIFY_IGNORE ioctl, for example
+
+	inotify_rm_watch (fd, wd);
+
+Events are provided in the form of an inotify_event structure that is read(2)
+from a inotify instance fd.  The filename is of dynamic length and follows the 
+struct. It is of size len.  The filename is padded with null bytes to ensure 
+proper alignment.  This padding is reflected in len.
+
+You can slurp multiple events by passing a large buffer, for example
+
+	size_t len = read (fd, buf, BUF_LEN);
+
+Will return as many events as are available and fit in BUF_LEN.
+
+each inotify instance fd is also select()- and poll()-able.
+
+You can find the size of the current event queue via the FIONREAD ioctl.
+
+All watches are destroyed and cleaned up on close.
+
+
+(ii) Internal Kernel Implementation
+
+Each open inotify instance is associated with an inotify_device structure.
+
+Each watch is associated with an inotify_watch structure.  Watches are chained
+off of each associated device and each associated inode.
+
+See fs/inotify.c for the locking and lifetime rules.
+
+
+(iii) Rationale
+
+Q: What is the design decision behind not tying the watch to the open fd of
+   the watched object?
+
+A: Watches are associated with an open inotify device, not an open file.
+   This solves the primary problem with dnotify: keeping the file open pins
+   the file and thus, worse, pins the mount.  Dnotify is therefore infeasible
+   for use on a desktop system with removable media as the media cannot be
+   unmounted.
+
+Q: What is the design decision behind using an-fd-per-device as opposed to
+   an fd-per-watch?
+
+A: An fd-per-watch quickly consumes more file descriptors than are allowed,
+   more fd's than are feasible to manage, and more fd's than are optimally
+   select()-able.  Yes, root can bump the per-process fd limit and yes, users
+   can use epoll, but requiring both is a silly and extraneous requirement.
+   A watch consumes less memory than an open file, separating the number
+   spaces is thus sensible.  The current design is what user-space developers
+   want: Users initialize inotify, once, and add n watches, requiring but one fd
+   and no twiddling with fd limits.  Initializing an inotify instance two
+   thousand times is silly.  If we can implement user-space's preferences 
+   cleanly--and we can, the idr layer makes stuff like this trivial--then we 
+   should.
+
+   There are other good arguments.  With a single fd, there is a single
+   item to block on, which is mapped to a single queue of events.  The single
+   fd returns all watch events and also any potential out-of-band data.  If
+   every fd was a separate watch,
+
+   - There would be no way to get event ordering.  Events on file foo and
+     file bar would pop poll() on both fd's, but there would be no way to tell
+     which happened first.  A single queue trivially gives you ordering.  Such
+     ordering is crucial to existing applications such as Beagle.  Imagine
+     "mv a b ; mv b a" events without ordering.
+
+   - We'd have to maintain n fd's and n internal queues with state,
+     versus just one.  It is a lot messier in the kernel.  A single, linear
+     queue is the data structure that makes sense.
+
+   - User-space developers prefer the current API.  The Beagle guys, for
+     example, love it.  Trust me, I asked.  It is not a surprise: Who'd want
+     to manage and block on 1000 fd's via select?
+
+   - You'd have to manage the fd's, as an example: Call close() when you
+     received a delete event.
+
+   - No way to get out of band data.
+
+   - 1024 is still too low.  ;-)
+
+   When you talk about designing a file change notification system that
+   scales to 1000s of directories, juggling 1000s of fd's just does not seem
+   the right interface.  It is too heavy.
+
+Q: Why the system call approach?
+
+A: The poor user-space interface is the second biggest problem with dnotify.
+   Signals are a terrible, terrible interface for file notification.  Or for
+   anything, for that matter.  The ideal solution, from all perspectives, is a
+   file descriptor-based one that allows basic file I/O and poll/select.
+   Obtaining the fd and managing the watches could have been done either via a
+   device file or a family of new system calls.  We decided to implement a
+   family of system calls because that is the preffered approach for new kernel
+   features and it means our user interface requirements.
+
+   Additionally, it _is_ possible to  more than one instance  and
+   juggle more than one queue and thus more than one associated fd.
+

arch/i386/kernel/syscall_table.S

@@ -291,3 +291,6 @@ ENTRY(sys_call_table)
 	.long sys_keyctl
 	.long sys_ioprio_set
 	.long sys_ioprio_get		/* 290 */
+	.long sys_inotify_init
+	.long sys_inotify_add_watch
+	.long sys_inotify_rm_watch

fs/Kconfig

@@ -359,6 +359,19 @@ config ROMFS_FS
 	  If you don't know whether you need it, then you don't need it:
 	  answer N.
 
+config INOTIFY
+	bool "Inotify file change notification support"
+	default y
+	---help---
+	  Say Y here to enable inotify support and the /dev/inotify character
+	  device.  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.  Multiple file
+	  events are supported.
+
+	  If unsure, say Y.
+
 config QUOTA
 	bool "Quota support"
 	help

fs/Makefile

@@ -12,6 +12,7 @@ obj-y :=	open.o read_write.o file_table.o buffer.o  bio.o super.o \
 		seq_file.o xattr.o libfs.o fs-writeback.o mpage.o direct-io.o \
 		ioprio.o
 
+obj-$(CONFIG_INOTIFY)		+= inotify.o
 obj-$(CONFIG_EPOLL)		+= eventpoll.o
 obj-$(CONFIG_COMPAT)		+= compat.o
 

fs/attr.c

@@ -10,7 +10,7 @@
 #include <linux/mm.h>
 #include <linux/string.h>
 #include <linux/smp_lock.h>
-#include <linux/dnotify.h>
+#include <linux/fsnotify.h>
 #include <linux/fcntl.h>
 #include <linux/quotaops.h>
 #include <linux/security.h>
@@ -107,31 +107,8 @@ int inode_setattr(struct inode * inode, struct iattr * attr)
 out:
 	return error;
 }
-
 EXPORT_SYMBOL(inode_setattr);
 
-int setattr_mask(unsigned int ia_valid)
-{
-	unsigned long dn_mask = 0;
-
-	if (ia_valid & ATTR_UID)
-		dn_mask |= DN_ATTRIB;
-	if (ia_valid & ATTR_GID)
-		dn_mask |= DN_ATTRIB;
-	if (ia_valid & ATTR_SIZE)
-		dn_mask |= DN_MODIFY;
-	/* both times implies a utime(s) call */
-	if ((ia_valid & (ATTR_ATIME|ATTR_MTIME)) == (ATTR_ATIME|ATTR_MTIME))
-		dn_mask |= DN_ATTRIB;
-	else if (ia_valid & ATTR_ATIME)
-		dn_mask |= DN_ACCESS;
-	else if (ia_valid & ATTR_MTIME)
-		dn_mask |= DN_MODIFY;
-	if (ia_valid & ATTR_MODE)
-		dn_mask |= DN_ATTRIB;
-	return dn_mask;
-}
-
 int notify_change(struct dentry * dentry, struct iattr * attr)
 {
 	struct inode *inode = dentry->d_inode;
@@ -197,11 +174,9 @@ int notify_change(struct dentry * dentry, struct iattr * attr)
 	if (ia_valid & ATTR_SIZE)
 		up_write(&dentry->d_inode->i_alloc_sem);
 
-	if (!error) {
-		unsigned long dn_mask = setattr_mask(ia_valid);
-		if (dn_mask)
-			dnotify_parent(dentry, dn_mask);
-	}
+	if (!error)
+		fsnotify_change(dentry, ia_valid);
+
 	return error;
 }
 

fs/compat.c

@@ -37,7 +37,7 @@
 #include <linux/ctype.h>
 #include <linux/module.h>
 #include <linux/dirent.h>
-#include <linux/dnotify.h>
+#include <linux/fsnotify.h>
 #include <linux/highuid.h>
 #include <linux/sunrpc/svc.h>
 #include <linux/nfsd/nfsd.h>
@@ -1307,9 +1307,13 @@ static ssize_t compat_do_readv_writev(int type, struct file *file,
 out:
 	if (iov != iovstack)
 		kfree(iov);
-	if ((ret + (type == READ)) > 0)
-		dnotify_parent(file->f_dentry,
-				(type == READ) ? DN_ACCESS : DN_MODIFY);
+	if ((ret + (type == READ)) > 0) {
+		struct dentry *dentry = file->f_dentry;
+		if (type == READ)
+			fsnotify_access(dentry);
+		else
+			fsnotify_modify(dentry);
+	}
 	return ret;
 }
 

fs/file_table.c

@@ -16,6 +16,7 @@
 #include <linux/eventpoll.h>
 #include <linux/mount.h>
 #include <linux/cdev.h>
+#include <linux/fsnotify.h>
 
 /* sysctl tunables... */
 struct files_stat_struct files_stat = {
@@ -126,6 +127,8 @@ void fastcall __fput(struct file *file)
 	struct inode *inode = dentry->d_inode;
 
 	might_sleep();
+
+	fsnotify_close(file);
 	/*
 	 * The function eventpoll_release() should be the first called
 	 * in the file cleanup chain.

fs/inode.c

@@ -21,6 +21,7 @@
 #include <linux/pagemap.h>
 #include <linux/cdev.h>
 #include <linux/bootmem.h>
+#include <linux/inotify.h>
 
 /*
  * This is needed for the following functions:
@@ -202,6 +203,10 @@ void inode_init_once(struct inode *inode)
 	INIT_LIST_HEAD(&inode->i_data.i_mmap_nonlinear);
 	spin_lock_init(&inode->i_lock);
 	i_size_ordered_init(inode);
+#ifdef CONFIG_INOTIFY
+	INIT_LIST_HEAD(&inode->inotify_watches);
+	sema_init(&inode->inotify_sem, 1);
+#endif
 }
 
 EXPORT_SYMBOL(inode_init_once);
@@ -351,6 +356,7 @@ int invalidate_inodes(struct super_block * sb)
 
 	down(&iprune_sem);
 	spin_lock(&inode_lock);
+	inotify_unmount_inodes(&sb->s_inodes);
 	busy = invalidate_list(&sb->s_inodes, &throw_away);
 	spin_unlock(&inode_lock);
 

fs/namei.c

@@ -21,7 +21,7 @@
 #include <linux/namei.h>
 #include <linux/quotaops.h>
 #include <linux/pagemap.h>
-#include <linux/dnotify.h>
+#include <linux/fsnotify.h>
 #include <linux/smp_lock.h>
 #include <linux/personality.h>
 #include <linux/security.h>
@@ -1312,7 +1312,7 @@ int vfs_create(struct inode *dir, struct dentry *dentry, int mode,
 	DQUOT_INIT(dir);
 	error = dir->i_op->create(dir, dentry, mode, nd);
 	if (!error) {
-		inode_dir_notify(dir, DN_CREATE);
+		fsnotify_create(dir, dentry->d_name.name);
 		security_inode_post_create(dir, dentry, mode);
 	}
 	return error;
@@ -1637,7 +1637,7 @@ int vfs_mknod(struct inode *dir, struct dentry *dentry, int mode, dev_t dev)
 	DQUOT_INIT(dir);
 	error = dir->i_op->mknod(dir, dentry, mode, dev);
 	if (!error) {
-		inode_dir_notify(dir, DN_CREATE);
+		fsnotify_create(dir, dentry->d_name.name);
 		security_inode_post_mknod(dir, dentry, mode, dev);
 	}
 	return error;
@@ -1710,7 +1710,7 @@ int vfs_mkdir(struct inode *dir, struct dentry *dentry, int mode)
 	DQUOT_INIT(dir);
 	error = dir->i_op->mkdir(dir, dentry, mode);
 	if (!error) {
-		inode_dir_notify(dir, DN_CREATE);
+		fsnotify_mkdir(dir, dentry->d_name.name);
 		security_inode_post_mkdir(dir,dentry, mode);
 	}
 	return error;
@@ -1801,7 +1801,7 @@ int vfs_rmdir(struct inode *dir, struct dentry *dentry)
 	}
 	up(&dentry->d_inode->i_sem);
 	if (!error) {
-		inode_dir_notify(dir, DN_DELETE);
+		fsnotify_rmdir(dentry, dentry->d_inode, dir);
 		d_delete(dentry);
 	}
 	dput(dentry);
@@ -1874,9 +1874,10 @@ int vfs_unlink(struct inode *dir, struct dentry *dentry)
 
 	/* We don't d_delete() NFS sillyrenamed files--they still exist. */
 	if (!error && !(dentry->d_flags & DCACHE_NFSFS_RENAMED)) {
+		fsnotify_unlink(dentry, dir);
 		d_delete(dentry);
-		inode_dir_notify(dir, DN_DELETE);
 	}
+
 	return error;
 }
 
@@ -1950,7 +1951,7 @@ int vfs_symlink(struct inode *dir, struct dentry *dentry, const char *oldname, i
 	DQUOT_INIT(dir);
 	error = dir->i_op->symlink(dir, dentry, oldname);
 	if (!error) {
-		inode_dir_notify(dir, DN_CREATE);
+		fsnotify_create(dir, dentry->d_name.name);
 		security_inode_post_symlink(dir, dentry, oldname);
 	}
 	return error;
@@ -2023,7 +2024,7 @@ int vfs_link(struct dentry *old_dentry, struct inode *dir, struct dentry *new_de
 	error = dir->i_op->link(old_dentry, dir, new_dentry);
 	up(&old_dentry->d_inode->i_sem);
 	if (!error) {
-		inode_dir_notify(dir, DN_CREATE);
+		fsnotify_create(dir, new_dentry->d_name.name);
 		security_inode_post_link(old_dentry, dir, new_dentry);
 	}
 	return error;
@@ -2187,6 +2188,7 @@ int vfs_rename(struct inode *old_dir, struct dentry *old_dentry,
 {
 	int error;
 	int is_dir = S_ISDIR(old_dentry->d_inode->i_mode);
+	const char *old_name;
 
 	if (old_dentry->d_inode == new_dentry->d_inode)
  		return 0;
@@ -2208,18 +2210,18 @@ int vfs_rename(struct inode *old_dir, struct dentry *old_dentry,
 	DQUOT_INIT(old_dir);
 	DQUOT_INIT(new_dir);
 
+	old_name = fsnotify_oldname_init(old_dentry->d_name.name);
+
 	if (is_dir)
 		error = vfs_rename_dir(old_dir,old_dentry,new_dir,new_dentry);
 	else
 		error = vfs_rename_other(old_dir,old_dentry,new_dir,new_dentry);
 	if (!error) {
-		if (old_dir == new_dir)
-			inode_dir_notify(old_dir, DN_RENAME);
-		else {
-			inode_dir_notify(old_dir, DN_DELETE);
-			inode_dir_notify(new_dir, DN_CREATE);
-		}
+		const char *new_name = old_dentry->d_name.name;
+		fsnotify_move(old_dir, new_dir, old_name, new_name, is_dir);
 	}
+	fsnotify_oldname_free(old_name);
+
 	return error;
 }
 

fs/nfsd/vfs.c

@@ -45,7 +45,7 @@
 #endif /* CONFIG_NFSD_V3 */
 #include <linux/nfsd/nfsfh.h>
 #include <linux/quotaops.h>
-#include <linux/dnotify.h>
+#include <linux/fsnotify.h>
 #include <linux/posix_acl.h>
 #include <linux/posix_acl_xattr.h>
 #ifdef CONFIG_NFSD_V4
@@ -860,7 +860,7 @@ nfsd_vfs_read(struct svc_rqst *rqstp, struct svc_fh *fhp, struct file *file,
 		nfsdstats.io_read += err;
 		*count = err;
 		err = 0;
-		dnotify_parent(file->f_dentry, DN_ACCESS);
+		fsnotify_access(file->f_dentry);
 	} else 
 		err = nfserrno(err);
 out:
@@ -916,7 +916,7 @@ nfsd_vfs_write(struct svc_rqst *rqstp, struct svc_fh *fhp, struct file *file,
 	set_fs(oldfs);
 	if (err >= 0) {
 		nfsdstats.io_write += cnt;
-		dnotify_parent(file->f_dentry, DN_MODIFY);
+		fsnotify_modify(file->f_dentry);
 	}
 
 	/* clear setuid/setgid flag after write */

fs/open.c

@@ -10,7 +10,7 @@
 #include <linux/file.h>
 #include <linux/smp_lock.h>
 #include <linux/quotaops.h>
-#include <linux/dnotify.h>
+#include <linux/fsnotify.h>
 #include <linux/module.h>
 #include <linux/slab.h>
 #include <linux/tty.h>
@@ -951,6 +951,7 @@ asmlinkage long sys_open(const char __user * filename, int flags, int mode)
 				put_unused_fd(fd);
 				fd = PTR_ERR(f);
 			} else {
+				fsnotify_open(f->f_dentry);
 				fd_install(fd, f);
 			}
 		}

fs/read_write.c

@@ -10,7 +10,7 @@
 #include <linux/file.h>
 #include <linux/uio.h>
 #include <linux/smp_lock.h>
-#include <linux/dnotify.h>
+#include <linux/fsnotify.h>
 #include <linux/security.h>
 #include <linux/module.h>
 #include <linux/syscalls.h>
@@ -252,7 +252,7 @@ ssize_t vfs_read(struct file *file, char __user *buf, size_t count, loff_t *pos)
 			else
 				ret = do_sync_read(file, buf, count, pos);
 			if (ret > 0) {
-				dnotify_parent(file->f_dentry, DN_ACCESS);
+				fsnotify_access(file->f_dentry);
 				current->rchar += ret;
 			}
 			current->syscr++;
@@ -303,7 +303,7 @@ ssize_t vfs_write(struct file *file, const char __user *buf, size_t count, loff_
 			else
 				ret = do_sync_write(file, buf, count, pos);
 			if (ret > 0) {
-				dnotify_parent(file->f_dentry, DN_MODIFY);
+				fsnotify_modify(file->f_dentry);
 				current->wchar += ret;
 			}
 			current->syscw++;
@@ -539,9 +539,12 @@ static ssize_t do_readv_writev(int type, struct file *file,
 out:
 	if (iov != iovstack)
 		kfree(iov);
-	if ((ret + (type == READ)) > 0)
-		dnotify_parent(file->f_dentry,
-				(type == READ) ? DN_ACCESS : DN_MODIFY);
+	if ((ret + (type == READ)) > 0) {
+		if (type == READ)
+			fsnotify_access(file->f_dentry);
+		else
+			fsnotify_modify(file->f_dentry);
+	}
 	return ret;
 Efault:
 	ret = -EFAULT;

fs/sysfs/file.c

@@ -3,7 +3,7 @@
  */
 
 #include <linux/module.h>
-#include <linux/dnotify.h>
+#include <linux/fsnotify.h>
 #include <linux/kobject.h>
 #include <linux/namei.h>
 #include <asm/uaccess.h>
@@ -391,9 +391,6 @@ int sysfs_create_file(struct kobject * kobj, const struct attribute * attr)
  * sysfs_update_file - update the modified timestamp on an object attribute.
  * @kobj: object we're acting for.
  * @attr: attribute descriptor.
- *
- * Also call dnotify for the dentry, which lots of userspace programs
- * use.
  */
 int sysfs_update_file(struct kobject * kobj, const struct attribute * attr)
 {
@@ -408,7 +405,7 @@ int sysfs_update_file(struct kobject * kobj, const struct attribute * attr)
 		if (victim->d_inode && 
 		    (victim->d_parent->d_inode == dir->d_inode)) {
 			victim->d_inode->i_mtime = CURRENT_TIME;
-			dnotify_parent(victim, DN_MODIFY);
+			fsnotify_modify(victim);
 
 			/**
 			 * Drop reference from initial sysfs_get_dentry().

fs/xattr.c

@@ -16,6 +16,7 @@
 #include <linux/security.h>
 #include <linux/syscalls.h>
 #include <linux/module.h>
+#include <linux/fsnotify.h>
 #include <asm/uaccess.h>
 
 /*
@@ -57,8 +58,10 @@ setxattr(struct dentry *d, char __user *name, void __user *value,
 		if (error)
 			goto out;
 		error = d->d_inode->i_op->setxattr(d, kname, kvalue, size, flags);
-		if (!error)
+		if (!error) {
+			fsnotify_xattr(d);
 			security_inode_post_setxattr(d, kname, kvalue, size, flags);
+		}
 out:
 		up(&d->d_inode->i_sem);
 	}

include/asm-i386/unistd.h

@@ -296,8 +296,11 @@
 #define __NR_keyctl		288
 #define __NR_ioprio_set		289
 #define __NR_ioprio_get		290
+#define __NR_inotify_init	291
+#define __NR_inotify_add_watch	292
+#define __NR_inotify_rm_watch	293
 
-#define NR_syscalls 291
+#define NR_syscalls 294
 
 /*
  * user-visible error numbers are in the range -1 - -128: see

include/linux/fs.h

@@ -474,6 +474,11 @@ struct inode {
 	struct dnotify_struct	*i_dnotify; /* for directory notifications */
 #endif
 
+#ifdef CONFIG_INOTIFY
+	struct list_head	inotify_watches; /* watches on this inode */
+	struct semaphore	inotify_sem;	/* protects the watches list */
+#endif
+
 	unsigned long		i_state;
 	unsigned long		dirtied_when;	/* jiffies of first dirtying */
 
@@ -1393,7 +1398,6 @@ extern void emergency_remount(void);
 extern int do_remount_sb(struct super_block *sb, int flags,
 			 void *data, int force);
 extern sector_t bmap(struct inode *, sector_t);
-extern int setattr_mask(unsigned int);
 extern int notify_change(struct dentry *, struct iattr *);
 extern int permission(struct inode *, int, struct nameidata *);
 extern int generic_permission(struct inode *, int,

include/linux/fsnotify.h

+#ifndef _LINUX_FS_NOTIFY_H
+#define _LINUX_FS_NOTIFY_H
+
+/*
+ * include/linux/fsnotify.h - generic hooks for filesystem notification, to
+ * reduce in-source duplication from both dnotify and inotify.
+ *
+ * We don't compile any of this away in some complicated menagerie of ifdefs.
+ * Instead, we rely on the code inside to optimize away as needed.
+ *
+ * (C) Copyright 2005 Robert Love
+ */
+
+#ifdef __KERNEL__
+
+#include <linux/dnotify.h>
+#include <linux/inotify.h>
+
+/*
+ * fsnotify_move - file old_name at old_dir was moved to new_name at new_dir
+ */
+static inline void fsnotify_move(struct inode *old_dir, struct inode *new_dir,
+				 const char *old_name, const char *new_name,
+				 int isdir)
+{
+	u32 cookie = inotify_get_cookie();
+
+	if (old_dir == new_dir)
+		inode_dir_notify(old_dir, DN_RENAME);
+	else {
+		inode_dir_notify(old_dir, DN_DELETE);
+		inode_dir_notify(new_dir, DN_CREATE);
+	}
+
+	if (isdir)
+		isdir = IN_ISDIR;
+	inotify_inode_queue_event(old_dir, IN_MOVED_FROM|isdir,cookie,old_name);
+	inotify_inode_queue_event(new_dir, IN_MOVED_TO|isdir, cookie, new_name);
+}
+
+/*
+ * fsnotify_unlink - file was unlinked
+ */
+static inline void fsnotify_unlink(struct dentry *dentry, struct inode *dir)
+{
+	struct inode *inode = dentry->d_inode;
+
+	inode_dir_notify(dir, DN_DELETE);
+	inotify_inode_queue_event(dir, IN_DELETE, 0, dentry->d_name.name);
+	inotify_inode_queue_event(inode, IN_DELETE_SELF, 0, NULL);
+
+	inotify_inode_is_dead(inode);
+}
+
+/*
+ * fsnotify_rmdir - directory was removed
+ */
+static inline void fsnotify_rmdir(struct dentry *dentry, struct inode *inode,
+				  struct inode *dir)
+{
+	inode_dir_notify(dir, DN_DELETE);
+	inotify_inode_queue_event(dir,IN_DELETE|IN_ISDIR,0,dentry->d_name.name);
+	inotify_inode_queue_event(inode, IN_DELETE_SELF | IN_ISDIR, 0, NULL);
+	inotify_inode_is_dead(inode);
+}
+
+/*
+ * fsnotify_create - 'name' was linked in
+ */
+static inline void fsnotify_create(struct inode *inode, const char *name)
+{
+	inode_dir_notify(inode, DN_CREATE);
+	inotify_inode_queue_event(inode, IN_CREATE, 0, name);
+}
+
+/*
+ * fsnotify_mkdir - directory 'name' was created
+ */
+static inline void fsnotify_mkdir(struct inode *inode, const char *name)
+{
+	inode_dir_notify(inode, DN_CREATE);
+	inotify_inode_queue_event(inode, IN_CREATE | IN_ISDIR, 0, name);
+}
+
+/*
+ * fsnotify_access - file was read
+ */
+static inline void fsnotify_access(struct dentry *dentry)
+{
+	struct inode *inode = dentry->d_inode;
+	u32 mask = IN_ACCESS;
+
+	if (S_ISDIR(inode->i_mode))
+		mask |= IN_ISDIR;
+
+	dnotify_parent(dentry, DN_ACCESS);
+	inotify_dentry_parent_queue_event(dentry, mask, 0, dentry->d_name.name);
+	inotify_inode_queue_event(inode, mask, 0, NULL);
+}
+
+/*
+ * fsnotify_modify - file was modified
+ */
+static inline void fsnotify_modify(struct dentry *dentry)
+{
+	struct inode *inode = dentry->d_inode;
+	u32 mask = IN_MODIFY;
+
+	if (S_ISDIR(inode->i_mode))
+		mask |= IN_ISDIR;
+
+	dnotify_parent(dentry, DN_MODIFY);
+	inotify_dentry_parent_queue_event(dentry, mask, 0, dentry->d_name.name);
+	inotify_inode_queue_event(inode, mask, 0, NULL);
+}
+
+/*
+ * fsnotify_open - file was opened
+ */
+static inline void fsnotify_open(struct dentry *dentry)
+{
+	struct inode *inode = dentry->d_inode;
+	u32 mask = IN_OPEN;
+
+	if (S_ISDIR(inode->i_mode))
+		mask |= IN_ISDIR;
+
+	inotify_inode_queue_event(inode, mask, 0, NULL);
+	inotify_dentry_parent_queue_event(dentry, mask, 0, dentry->d_name.name);
+}
+
+/*
+ * fsnotify_close - file was closed
+ */
+static inline void fsnotify_close(struct file *file)
+{
+	struct dentry *dentry = file->f_dentry;
+	struct inode *inode = dentry->d_inode;
+	const char *name = dentry->d_name.name;
+	mode_t mode = file->f_mode;
+	u32 mask = (mode & FMODE_WRITE) ? IN_CLOSE_WRITE : IN_CLOSE_NOWRITE;
+
+	if (S_ISDIR(inode->i_mode))
+		mask |= IN_ISDIR;
+
+	inotify_dentry_parent_queue_event(dentry, mask, 0, name);
+	inotify_inode_queue_event(inode, mask, 0, NULL);
+}
+
+/*
+ * fsnotify_xattr - extended attributes were changed
+ */
+static inline void fsnotify_xattr(struct dentry *dentry)
+{
+	struct inode *inode = dentry->d_inode;
+	u32 mask = IN_ATTRIB;
+
+	if (S_ISDIR(inode->i_mode))
+		mask |= IN_ISDIR;
+
+	inotify_dentry_parent_queue_event(dentry, mask, 0, dentry->d_name.name);
+	inotify_inode_queue_event(inode, mask, 0, NULL);
+}
+
+/*
+ * fsnotify_change - notify_change event.  file was modified and/or metadata
+ * was changed.
+ */
+static inline void fsnotify_change(struct dentry *dentry, unsigned int ia_valid)
+{
+	struct inode *inode = dentry->d_inode;
+	int dn_mask = 0;
+	u32 in_mask = 0;
+
+	if (ia_valid & ATTR_UID) {
+		in_mask |= IN_ATTRIB;
+		dn_mask |= DN_ATTRIB;
+	}
+	if (ia_valid & ATTR_GID) {
+		in_mask |= IN_ATTRIB;
+		dn_mask |= DN_ATTRIB;
+	}
+	if (ia_valid & ATTR_SIZE) {
+		in_mask |= IN_MODIFY;
+		dn_mask |= DN_MODIFY;
+	}
+	/* both times implies a utime(s) call */
+	if ((ia_valid & (ATTR_ATIME | ATTR_MTIME)) == (ATTR_ATIME | ATTR_MTIME))
+	{
+		in_mask |= IN_ATTRIB;
+		dn_mask |= DN_ATTRIB;
+	} else if (ia_valid & ATTR_ATIME) {
+		in_mask |= IN_ACCESS;
+		dn_mask |= DN_ACCESS;
+	} else if (ia_valid & ATTR_MTIME) {
+		in_mask |= IN_MODIFY;
+		dn_mask |= DN_MODIFY;
+	}
+	if (ia_valid & ATTR_MODE) {
+		in_mask |= IN_ATTRIB;
+		dn_mask |= DN_ATTRIB;
+	}
+
+	if (dn_mask)
+		dnotify_parent(dentry, dn_mask);
+	if (in_mask) {
+		if (S_ISDIR(inode->i_mode))
+			in_mask |= IN_ISDIR;
+		inotify_inode_queue_event(inode, in_mask, 0, NULL);
+		inotify_dentry_parent_queue_event(dentry, in_mask, 0,
+						  dentry->d_name.name);
+	}
+}
+
+#ifdef CONFIG_INOTIFY	/* inotify helpers */
+
+/*
+ * fsnotify_oldname_init - save off the old filename before we change it
+ */
+static inline const char *fsnotify_oldname_init(const char *name)
+{
+	return kstrdup(name, GFP_KERNEL);
+}
+
+/*
+ * fsnotify_oldname_free - free the name we got from fsnotify_oldname_init
+ */
+static inline void fsnotify_oldname_free(const char *old_name)
+{
+	kfree(old_name);
+}
+
+#else	/* CONFIG_INOTIFY */
+
+static inline const char *fsnotify_oldname_init(const char *name)
+{
+	return NULL;
+}
+
+static inline void fsnotify_oldname_free(const char *old_name)
+{
+}
+
+#endif	/* ! CONFIG_INOTIFY */
+
+#endif	/* __KERNEL__ */
+
+#endif	/* _LINUX_FS_NOTIFY_H */

include/linux/inotify.h

+/*
+ * Inode based directory notification for Linux
+ *
+ * Copyright (C) 2005 John McCutchan
+ */
+
+#ifndef _LINUX_INOTIFY_H
+#define _LINUX_INOTIFY_H
+
+#include <linux/types.h>
+
+/*
+ * struct inotify_event - structure read from the inotify device for each event
+ *
+ * When you are watching a directory, you will receive the filename for events
+ * such as IN_CREATE, IN_DELETE, IN_OPEN, IN_CLOSE, ..., relative to the wd.
+ */
+struct inotify_event {
+	__s32		wd;		/* watch descriptor */
+	__u32		mask;		/* watch mask */
+	__u32		cookie;		/* cookie to synchronize two events */
+	__u32		len;		/* length (including nulls) of name */
+	char		name[0];	/* stub for possible name */
+};
+
+/* the following are legal, implemented events that user-space can watch for */
+#define IN_ACCESS		0x00000001	/* File was accessed */
+#define IN_MODIFY		0x00000002	/* File was modified */
+#define IN_ATTRIB		0x00000004	/* Metadata changed */
+#define IN_CLOSE_WRITE		0x00000008	/* Writtable file was closed */
+#define IN_CLOSE_NOWRITE	0x00000010	/* Unwrittable file closed */
+#define IN_OPEN			0x00000020	/* File was opened */
+#define IN_MOVED_FROM		0x00000040	/* File was moved from X */
+#define IN_MOVED_TO		0x00000080	/* File was moved to Y */
+#define IN_CREATE		0x00000100	/* Subfile was created */
+#define IN_DELETE		0x00000200	/* Subfile was deleted */
+#define IN_DELETE_SELF		0x00000400	/* Self was deleted */
+
+/* the following are legal events.  they are sent as needed to any watch */
+#define IN_UNMOUNT		0x00002000	/* Backing fs was unmounted */
+#define IN_Q_OVERFLOW		0x00004000	/* Event queued overflowed */
+#define IN_IGNORED		0x00008000	/* File was ignored */
+
+/* helper events */
+#define IN_CLOSE		(IN_CLOSE_WRITE | IN_CLOSE_NOWRITE) /* close */
+#define IN_MOVE			(IN_MOVED_FROM | IN_MOVED_TO) /* moves */
+
+/* special flags */
+#define IN_ISDIR		0x40000000	/* event occurred against dir */
+#define IN_ONESHOT		0x80000000	/* only send event once */
+
+/*
+ * All of the events - we build the list by hand so that we can add flags in
+ * the future and not break backward compatibility.  Apps will get only the
+ * events that they originally wanted.  Be sure to add new events here!
+ */
+#define IN_ALL_EVENTS	(IN_ACCESS | IN_MODIFY | IN_ATTRIB | IN_CLOSE_WRITE | \
+			 IN_CLOSE_NOWRITE | IN_OPEN | IN_MOVED_FROM | \
+			 IN_MOVED_TO | IN_DELETE | IN_CREATE | IN_DELETE_SELF)
+
+#ifdef __KERNEL__
+
+#include <linux/dcache.h>
+#include <linux/fs.h>
+#include <linux/config.h>
+
+#ifdef CONFIG_INOTIFY
+
+extern void inotify_inode_queue_event(struct inode *, __u32, __u32,
+				      const char *);
+extern void inotify_dentry_parent_queue_event(struct dentry *, __u32, __u32,
+					      const char *);
+extern void inotify_unmount_inodes(struct list_head *);
+extern void inotify_inode_is_dead(struct inode *);
+extern u32 inotify_get_cookie(void);
+
+#else
+
+static inline void inotify_inode_queue_event(struct inode *inode,
+					     __u32 mask, __u32 cookie,
+					     const char *filename)
+{
+}
+
+static inline void inotify_dentry_parent_queue_event(struct dentry *dentry,
+						     __u32 mask, __u32 cookie,
+						     const char *filename)
+{
+}
+
+static inline void inotify_unmount_inodes(struct list_head *list)
+{
+}
+
+static inline void inotify_inode_is_dead(struct inode *inode)
+{
+}
+
+static inline u32 inotify_get_cookie(void)
+{
+	return 0;
+}
+
+#endif	/* CONFIG_INOTIFY */
+
+#endif	/* __KERNEL __ */
+
+#endif	/* _LINUX_INOTIFY_H */

include/linux/sched.h

@@ -410,6 +410,10 @@ 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
+	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
 	/* protected by mq_lock	*/
 	unsigned long mq_bytes;	/* How many bytes can be allocated to mqueue? */
 	unsigned long locked_shm; /* How many pages of mlocked shm ? */

include/linux/sysctl.h

@@ -61,7 +61,8 @@ enum
 	CTL_DEV=7,		/* Devices */
 	CTL_BUS=8,		/* Busses */
 	CTL_ABI=9,		/* Binary emulation */
-	CTL_CPU=10		/* CPU stuff (speed scaling, etc) */
+	CTL_CPU=10,		/* CPU stuff (speed scaling, etc) */
+	CTL_INOTIFY=11		/* Inotify */
 };
 
 /* CTL_BUS names: */
@@ -70,6 +71,14 @@ enum
 	CTL_BUS_ISA=1		/* ISA */
 };
 
+/* CTL_INOTIFY names: */
+enum
+{
+	INOTIFY_MAX_USER_DEVICES=1,	/* max number of inotify device instances per user */
+	INOTIFY_MAX_USER_WATCHES=2,	/* max number of inotify watches per user */
+	INOTIFY_MAX_QUEUED_EVENTS=3	/* Max number of queued events per inotify device instance */
+};
+
 /* CTL_KERN names: */
 enum
 {

kernel/sys_ni.c

@@ -80,6 +80,9 @@ cond_syscall(sys_keyctl);
 cond_syscall(compat_sys_keyctl);
 cond_syscall(compat_sys_socketcall);
 cond_syscall(sys_set_zone_reclaim);
+cond_syscall(sys_inotify_init);
+cond_syscall(sys_inotify_add_watch);
+cond_syscall(sys_inotify_rm_watch);
 
 /* arch-specific weak syscall entries */
 cond_syscall(sys_pciconfig_read);

kernel/sysctl.c

@@ -67,6 +67,12 @@ extern int printk_ratelimit_jiffies;
 extern int printk_ratelimit_burst;
 extern int pid_max_min, pid_max_max;
 
+#ifdef CONFIG_INOTIFY
+extern int inotify_max_user_devices;
+extern int inotify_max_user_watches;
+extern int inotify_max_queued_events;
+#endif
+
 #if defined(CONFIG_X86_LOCAL_APIC) && defined(CONFIG_X86)
 int unknown_nmi_panic;
 extern int proc_unknown_nmi_panic(ctl_table *, int, struct file *,
@@ -218,6 +224,7 @@ static ctl_table root_table[] = {
 		.mode		= 0555,
 		.child		= dev_table,
 	},
+
 	{ .ctl_name = 0 }
 };
 
@@ -959,6 +966,40 @@ static ctl_table fs_table[] = {
 		.mode		= 0644,
 		.proc_handler	= &proc_dointvec,
 	},
+#ifdef CONFIG_INOTIFY
+	{
+		.ctl_name	= INOTIFY_MAX_USER_DEVICES,
+		.procname	= "max_user_devices",
+		.data		= &inotify_max_user_devices,
+		.maxlen		= sizeof(int),
+		.mode		= 0644,
+		.proc_handler	= &proc_dointvec_minmax,
+		.strategy	= &sysctl_intvec,
+		.extra1		= &zero,
+	},
+
+	{
+		.ctl_name	= INOTIFY_MAX_USER_WATCHES,
+		.procname	= "max_user_watches",
+		.data		= &inotify_max_user_watches,
+		.maxlen		= sizeof(int),
+		.mode		= 0644,
+		.proc_handler	= &proc_dointvec_minmax,
+		.strategy	= &sysctl_intvec,
+		.extra1		= &zero, 
+	},
+
+	{
+		.ctl_name	= INOTIFY_MAX_QUEUED_EVENTS,
+		.procname	= "max_queued_events",
+		.data		= &inotify_max_queued_events,
+		.maxlen		= sizeof(int),
+		.mode		= 0644, 
+		.proc_handler	= &proc_dointvec_minmax,
+		.strategy	= &sysctl_intvec, 
+		.extra1		= &zero
+	},
+#endif
 	{ .ctl_name = 0 }
 };
 

kernel/user.c

@@ -120,6 +120,10 @@ 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
+		atomic_set(&new->inotify_watches, 0);
+		atomic_set(&new->inotify_devs, 0);
+#endif
 
 		new->mq_bytes = 0;
 		new->locked_shm = 0;