fsnotify: unified filesystem notification backend

fsnotify is a backend for filesystem notification.  fsnotify does
not provide any userspace interface but does provide the basis
needed for other notification schemes such as dnotify.  fsnotify
can be extended to be the backend for inotify or the upcoming
fanotify.  fsnotify provides a mechanism for "groups" to register for
some set of filesystem events and to then deliver those events to
those groups for processing.

fsnotify has a number of benefits, the first being actually shrinking the size
of an inode.  Before fsnotify to support both dnotify and inotify an inode had

        unsigned long           i_dnotify_mask; /* Directory notify events */
        struct dnotify_struct   *i_dnotify; /* for directory notifications */
        struct list_head        inotify_watches; /* watches on this inode */
        struct mutex            inotify_mutex;  /* protects the watches list

But with fsnotify this same functionallity (and more) is done with just

        __u32                   i_fsnotify_mask; /* all events for this inode */
        struct hlist_head       i_fsnotify_mark_entries; /* marks on this inode */

That's right, inotify, dnotify, and fanotify all in 64 bits.  We used that
much space just in inotify_watches alone, before this patch set.

fsnotify object lifetime and locking is MUCH better than what we have today.
inotify locking is incredibly complex.  See 8f7b0ba1c8539 as an example of
what's been busted since inception.  inotify needs to know internal semantics
of superblock destruction and unmounting to function.  The inode pinning and
vfs contortions are horrible.

no fsnotify implementers do allocation under locks.  This means things like
f04b30de3 which (due to an overabundance of caution) changes GFP_KERNEL to
GFP_NOFS can be reverted.  There are no longer any allocation rules when using
or implementing your own fsnotify listener.

fsnotify paves the way for fanotify.  In brief fanotify is a notification
mechanism that delivers the lisener both an 'event' and an open file descriptor
to the object in question.  This means that fanotify is pathname agnostic.
Some on lkml may not care for the original companies or users that pushed for
TALPA, but fanotify was designed with flexibility and input for other users in
mind.  The readahead group expressed interest in fanotify as it could be used
to profile disk access on boot without breaking the audit system.  The desktop
search groups have also expressed interest in fanotify as it solves a number
of the race conditions and problems present with managing inotify when more
than a limited number of specific files are of interest.  fanotify can provide
for a userspace access control system which makes it a clean interface for AV
vendors to hook without trying to do binary patching on the syscall table,
LSM, and everywhere else they do their things today.  With this patch series
fanotify can be implemented in less than 1200 lines of easy to review code.
Almost all of which is the socket based user interface.

This patch series builds fsnotify to the point that it can implement
dnotify and inotify_user.  Patches exist and will be sent soon after
acceptance to finish the in kernel inotify conversion (audit) and implement
fanotify.

Signed-off-by: Eric Paris <eparis@redhat.com>
Acked-by: Al Viro <viro@zeniv.linux.org.uk>
Cc: Christoph Hellwig <hch@lst.de>

1 files changed, 80 insertions, 35 deletions

diff --git a/include/linux/fsnotify.h b/include/linux/fsnotify.h
index 00fbd5b245c9..6c9ebefdac8e 100644
--- a/include/linux/fsnotify.h
+++ b/include/linux/fsnotify.h
@@ -13,6 +13,7 @@
 
 #include <linux/dnotify.h>
 #include <linux/inotify.h>
+#include <linux/fsnotify_backend.h>
 #include <linux/audit.h>
 
 /*
@@ -35,6 +36,16 @@ static inline void fsnotify_d_move(struct dentry *entry)
 }
 
 /*
+ * fsnotify_link_count - inode's link count changed
+ */
+static inline void fsnotify_link_count(struct inode *inode)
+{
+        inotify_inode_queue_event(inode, IN_ATTRIB, 0, NULL, NULL);
+
+        fsnotify(inode, FS_ATTRIB, inode, FSNOTIFY_EVENT_INODE);
+}
+
+/*
  * 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,
@@ -43,28 +54,47 @@ static inline void fsnotify_move(struct inode *old_dir, struct inode *new_dir,
 {
         struct inode *source = moved->d_inode;
         u32 cookie = inotify_get_cookie();
+        __u32 old_dir_mask = 0;
+        __u32 new_dir_mask = 0;
 
-        if (old_dir == new_dir)
+        if (old_dir == new_dir) {
                 inode_dir_notify(old_dir, DN_RENAME);
-        else {
+                old_dir_mask = FS_DN_RENAME;
+        } else {
                 inode_dir_notify(old_dir, DN_DELETE);
+                old_dir_mask = FS_DELETE;
                 inode_dir_notify(new_dir, DN_CREATE);
+                new_dir_mask = FS_CREATE;
         }
 
-        if (isdir)
+        if (isdir) {
                 isdir = IN_ISDIR;
+                old_dir_mask |= FS_IN_ISDIR;
+                new_dir_mask |= FS_IN_ISDIR;
+        }
+
+        old_dir_mask |= FS_MOVED_FROM;
+        new_dir_mask |= FS_MOVED_TO;
+
         inotify_inode_queue_event(old_dir, IN_MOVED_FROM|isdir,cookie,old_name,
                                   source);
         inotify_inode_queue_event(new_dir, IN_MOVED_TO|isdir, cookie, new_name,
                                   source);
 
+        fsnotify(old_dir, old_dir_mask, old_dir, FSNOTIFY_EVENT_INODE);
+        fsnotify(new_dir, new_dir_mask, new_dir, FSNOTIFY_EVENT_INODE);
+
         if (target) {
                 inotify_inode_queue_event(target, IN_DELETE_SELF, 0, NULL, NULL);
                 inotify_inode_is_dead(target);
+
+                /* this is really a link_count change not a removal */
+                fsnotify_link_count(target);
         }
 
         if (source) {
                 inotify_inode_queue_event(source, IN_MOVE_SELF, 0, NULL, NULL);
+                fsnotify(source, FS_MOVE_SELF, moved->d_inode, FSNOTIFY_EVENT_INODE);
         }
         audit_inode_child(new_name, moved, new_dir);
 }
@@ -74,10 +104,12 @@ static inline void fsnotify_move(struct inode *old_dir, struct inode *new_dir,
  */
 static inline void fsnotify_nameremove(struct dentry *dentry, int isdir)
 {
+        __u32 mask = FS_DELETE;
+
         if (isdir)
-                isdir = IN_ISDIR;
+                mask |= FS_IN_ISDIR;
         dnotify_parent(dentry, DN_DELETE);
-        inotify_dentry_parent_queue_event(dentry, IN_DELETE|isdir, 0, dentry->d_name.name);
+        inotify_dentry_parent_queue_event(dentry, mask, 0, dentry->d_name.name);
 }
 
 /*
@@ -87,14 +119,8 @@ static inline void fsnotify_inoderemove(struct inode *inode)
 {
         inotify_inode_queue_event(inode, IN_DELETE_SELF, 0, NULL, NULL);
         inotify_inode_is_dead(inode);
-}
 
-/*
- * fsnotify_link_count - inode's link count changed
- */
-static inline void fsnotify_link_count(struct inode *inode)
-{
-        inotify_inode_queue_event(inode, IN_ATTRIB, 0, NULL, NULL);
+        fsnotify(inode, FS_DELETE_SELF, inode, FSNOTIFY_EVENT_INODE);
 }
 
 /*
@@ -106,6 +132,8 @@ static inline void fsnotify_create(struct inode *inode, struct dentry *dentry)
         inotify_inode_queue_event(inode, IN_CREATE, 0, dentry->d_name.name,
                                   dentry->d_inode);
         audit_inode_child(dentry->d_name.name, dentry, inode);
+
+        fsnotify(inode, FS_CREATE, dentry->d_inode, FSNOTIFY_EVENT_INODE);
 }
 
 /*
@@ -120,6 +148,8 @@ static inline void fsnotify_link(struct inode *dir, struct inode *inode, struct
                                   inode);
         fsnotify_link_count(inode);
         audit_inode_child(new_dentry->d_name.name, new_dentry, dir);
+
+        fsnotify(dir, FS_CREATE, inode, FSNOTIFY_EVENT_INODE);
 }
 
 /*
@@ -127,10 +157,14 @@ static inline void fsnotify_link(struct inode *dir, struct inode *inode, struct
  */
 static inline void fsnotify_mkdir(struct inode *inode, struct dentry *dentry)
 {
+        __u32 mask = (FS_CREATE | FS_IN_ISDIR);
+        struct inode *d_inode = dentry->d_inode;
+
         inode_dir_notify(inode, DN_CREATE);
-        inotify_inode_queue_event(inode, IN_CREATE | IN_ISDIR, 0, 
-                                  dentry->d_name.name, dentry->d_inode);
+        inotify_inode_queue_event(inode, mask, 0, dentry->d_name.name, d_inode);
         audit_inode_child(dentry->d_name.name, dentry, inode);
+
+        fsnotify(inode, mask, d_inode, FSNOTIFY_EVENT_INODE);
 }
 
 /*
@@ -139,14 +173,16 @@ static inline void fsnotify_mkdir(struct inode *inode, struct dentry *dentry)
 static inline void fsnotify_access(struct dentry *dentry)
 {
         struct inode *inode = dentry->d_inode;
-        u32 mask = IN_ACCESS;
+        __u32 mask = FS_ACCESS;
 
         if (S_ISDIR(inode->i_mode))
-                mask |= IN_ISDIR;
+                mask |= FS_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, NULL);
+
+        fsnotify(inode, mask, inode, FSNOTIFY_EVENT_INODE);
 }
 
 /*
@@ -155,14 +191,16 @@ static inline void fsnotify_access(struct dentry *dentry)
 static inline void fsnotify_modify(struct dentry *dentry)
 {
         struct inode *inode = dentry->d_inode;
-        u32 mask = IN_MODIFY;
+        __u32 mask = FS_MODIFY;
 
         if (S_ISDIR(inode->i_mode))
-                mask |= IN_ISDIR;
+                mask |= FS_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, NULL);
+
+        fsnotify(inode, mask, inode, FSNOTIFY_EVENT_INODE);
 }
 
 /*
@@ -171,13 +209,15 @@ static inline void fsnotify_modify(struct dentry *dentry)
 static inline void fsnotify_open(struct dentry *dentry)
 {
         struct inode *inode = dentry->d_inode;
-        u32 mask = IN_OPEN;
+        __u32 mask = FS_OPEN;
 
         if (S_ISDIR(inode->i_mode))
-                mask |= IN_ISDIR;
+                mask |= FS_IN_ISDIR;
 
         inotify_dentry_parent_queue_event(dentry, mask, 0, dentry->d_name.name);
         inotify_inode_queue_event(inode, mask, 0, NULL, NULL);
+
+        fsnotify(inode, mask, inode, FSNOTIFY_EVENT_INODE);
 }
 
 /*
@@ -189,13 +229,15 @@ static inline void fsnotify_close(struct file *file)
         struct inode *inode = dentry->d_inode;
         const char *name = dentry->d_name.name;
         fmode_t mode = file->f_mode;
-        u32 mask = (mode & FMODE_WRITE) ? IN_CLOSE_WRITE : IN_CLOSE_NOWRITE;
+        __u32 mask = (mode & FMODE_WRITE) ? FS_CLOSE_WRITE : FS_CLOSE_NOWRITE;
 
         if (S_ISDIR(inode->i_mode))
-                mask |= IN_ISDIR;
+                mask |= FS_IN_ISDIR;
 
         inotify_dentry_parent_queue_event(dentry, mask, 0, name);
         inotify_inode_queue_event(inode, mask, 0, NULL, NULL);
+
+        fsnotify(inode, mask, file, FSNOTIFY_EVENT_FILE);
 }
 
 /*
@@ -204,13 +246,15 @@ static inline void fsnotify_close(struct file *file)
 static inline void fsnotify_xattr(struct dentry *dentry)
 {
         struct inode *inode = dentry->d_inode;
-        u32 mask = IN_ATTRIB;
+        __u32 mask = FS_ATTRIB;
 
         if (S_ISDIR(inode->i_mode))
-                mask |= IN_ISDIR;
+                mask |= FS_IN_ISDIR;
 
         inotify_dentry_parent_queue_event(dentry, mask, 0, dentry->d_name.name);
         inotify_inode_queue_event(inode, mask, 0, NULL, NULL);
+
+        fsnotify(inode, mask, inode, FSNOTIFY_EVENT_INODE);
 }
 
 /*
@@ -221,34 +265,34 @@ 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;
+        __u32 in_mask = 0;
 
         if (ia_valid & ATTR_UID) {
-                in_mask |= IN_ATTRIB;
+                in_mask |= FS_ATTRIB;
                 dn_mask |= DN_ATTRIB;
         }
         if (ia_valid & ATTR_GID) {
-                in_mask |= IN_ATTRIB;
+                in_mask |= FS_ATTRIB;
                 dn_mask |= DN_ATTRIB;
         }
         if (ia_valid & ATTR_SIZE) {
-                in_mask |= IN_MODIFY;
+                in_mask |= FS_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;
+                in_mask |= FS_ATTRIB;
                 dn_mask |= DN_ATTRIB;
         } else if (ia_valid & ATTR_ATIME) {
-                in_mask |= IN_ACCESS;
+                in_mask |= FS_ACCESS;
                 dn_mask |= DN_ACCESS;
         } else if (ia_valid & ATTR_MTIME) {
-                in_mask |= IN_MODIFY;
+                in_mask |= FS_MODIFY;
                 dn_mask |= DN_MODIFY;
         }
         if (ia_valid & ATTR_MODE) {
-                in_mask |= IN_ATTRIB;
+                in_mask |= FS_ATTRIB;
                 dn_mask |= DN_ATTRIB;
         }
 
@@ -256,14 +300,15 @@ static inline void fsnotify_change(struct dentry *dentry, unsigned int ia_valid)
                 dnotify_parent(dentry, dn_mask);
         if (in_mask) {
                 if (S_ISDIR(inode->i_mode))
-                        in_mask |= IN_ISDIR;
+                        in_mask |= FS_IN_ISDIR;
                 inotify_inode_queue_event(inode, in_mask, 0, NULL, NULL);
                 inotify_dentry_parent_queue_event(dentry, in_mask, 0,
                                                   dentry->d_name.name);
+                fsnotify(inode, in_mask, inode, FSNOTIFY_EVENT_INODE);
         }
 }
 
-#ifdef CONFIG_INOTIFY   /* inotify helpers */
+#if defined(CONFIG_INOTIFY) || defined(CONFIG_FSNOTIFY) /* notify helpers */
 
 /*
  * fsnotify_oldname_init - save off the old filename before we change it
@@ -281,7 +326,7 @@ static inline void fsnotify_oldname_free(const char *old_name)
         kfree(old_name);
 }
 
-#else   /* CONFIG_INOTIFY */
+#else   /* CONFIG_INOTIFY || CONFIG_FSNOTIFY */
 
 static inline const char *fsnotify_oldname_init(const char *name)
 {