fsnotify(): switch to passing const struct qstr * for file_name

Note that in fnsotify_move() and fsnotify_link() we are guaranteed
that dentry->d_name won't change during the fsnotify() evaluation
(by having the parent directory locked exclusive), so we don't
need to fetch dentry->d_name.name in the callers.  In fsnotify_dirent()
the same stability of dentry->d_name is also true, but it's a bit
more convoluted - there is one callchain (devpts_pty_new() ->
fsnotify_create() -> fsnotify_dirent()) where the parent is _not_
locked, but on devpts ->d_name of everything is unchanging; it
has neither explicit nor implicit renames.
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

fs/kernfs/file.c

@@ -885,6 +885,7 @@ static void kernfs_notify_workfn(struct work_struct *work)
 	list_for_each_entry(info, &kernfs_root(kn)->supers, node) {
 		struct kernfs_node *parent;
 		struct inode *inode;
+		struct qstr name;
 
 		/*
 		 * We want fsnotify_modify() on @kn but as the
@@ -896,6 +897,7 @@ static void kernfs_notify_workfn(struct work_struct *work)
 		if (!inode)
 			continue;
 
+		name = (struct qstr)QSTR_INIT(kn->name, strlen(kn->name));
 		parent = kernfs_get_parent(kn);
 		if (parent) {
 			struct inode *p_inode;
@@ -903,7 +905,7 @@ static void kernfs_notify_workfn(struct work_struct *work)
 			p_inode = ilookup(info->sb, parent->id.ino);
 			if (p_inode) {
 				fsnotify(p_inode, FS_MODIFY | FS_EVENT_ON_CHILD,
-					 inode, FSNOTIFY_EVENT_INODE, kn->name, 0);
+					 inode, FSNOTIFY_EVENT_INODE, &name, 0);
 				iput(p_inode);
 			}
 
@@ -911,7 +913,7 @@ static void kernfs_notify_workfn(struct work_struct *work)
 		}
 
 		fsnotify(inode, FS_MODIFY, inode, FSNOTIFY_EVENT_INODE,
-			 kn->name, 0);
+			 &name, 0);
 		iput(inode);
 	}
 

fs/notify/fsnotify.c

@@ -179,10 +179,10 @@ int __fsnotify_parent(const struct path *path, struct dentry *dentry, __u32 mask
 		take_dentry_name_snapshot(&name, dentry);
 		if (path)
 			ret = fsnotify(p_inode, mask, path, FSNOTIFY_EVENT_PATH,
-				       name.name.name, 0);
+				       &name.name, 0);
 		else
 			ret = fsnotify(p_inode, mask, dentry->d_inode, FSNOTIFY_EVENT_INODE,
-				       name.name.name, 0);
+				       &name.name, 0);
 		release_dentry_name_snapshot(&name);
 	}
 
@@ -325,7 +325,7 @@ static void fsnotify_iter_next(struct fsnotify_iter_info *iter_info)
  * notification event in whatever means they feel necessary.
  */
 int fsnotify(struct inode *to_tell, __u32 mask, const void *data, int data_is,
-	     const unsigned char *file_name, u32 cookie)
+	     const struct qstr *file_name, u32 cookie)
 {
 	struct fsnotify_iter_info iter_info = {};
 	struct super_block *sb = to_tell->i_sb;
@@ -379,7 +379,7 @@ int fsnotify(struct inode *to_tell, __u32 mask, const void *data, int data_is,
 	 */
 	while (fsnotify_iter_select_report_types(&iter_info)) {
 		ret = send_to_group(to_tell, mask, data, data_is, cookie,
-				    file_name, &iter_info);
+				    file_name->name, &iter_info);
 
 		if (ret && (mask & ALL_FSNOTIFY_PERM_EVENTS))
 			goto out;

include/linux/fsnotify.h

@@ -27,7 +27,7 @@ static inline int fsnotify_dirent(struct inode *dir, struct dentry *dentry,
 				  __u32 mask)
 {
 	return fsnotify(dir, mask, d_inode(dentry), FSNOTIFY_EVENT_INODE,
-			dentry->d_name.name, 0);
+			&dentry->d_name, 0);
 }
 
 /* Notify this dentry's parent about a child's events. */
@@ -111,7 +111,7 @@ static inline void fsnotify_move(struct inode *old_dir, struct inode *new_dir,
 	__u32 old_dir_mask = FS_MOVED_FROM;
 	__u32 new_dir_mask = FS_MOVED_TO;
 	__u32 mask = FS_MOVE_SELF;
-	const unsigned char *new_name = moved->d_name.name;
+	const struct qstr *new_name = &moved->d_name;
 
 	if (old_dir == new_dir)
 		old_dir_mask |= FS_DN_RENAME;
@@ -122,7 +122,7 @@ static inline void fsnotify_move(struct inode *old_dir, struct inode *new_dir,
 		mask |= FS_ISDIR;
 	}
 
-	fsnotify(old_dir, old_dir_mask, source, FSNOTIFY_EVENT_INODE, old_name->name,
+	fsnotify(old_dir, old_dir_mask, source, FSNOTIFY_EVENT_INODE, old_name,
 		 fs_cookie);
 	fsnotify(new_dir, new_dir_mask, source, FSNOTIFY_EVENT_INODE, new_name,
 		 fs_cookie);
@@ -178,7 +178,7 @@ static inline void fsnotify_nameremove(struct dentry *dentry, int isdir)
 	take_dentry_name_snapshot(&name, dentry);
 
 	fsnotify(d_inode(parent), mask, d_inode(dentry), FSNOTIFY_EVENT_INODE,
-		 name.name.name, 0);
+		 &name.name, 0);
 
 	release_dentry_name_snapshot(&name);
 	dput(parent);
@@ -218,7 +218,7 @@ static inline void fsnotify_link(struct inode *dir, struct inode *inode, struct
 	fsnotify_link_count(inode);
 	audit_inode_child(dir, new_dentry, AUDIT_TYPE_CHILD_CREATE);
 
-	fsnotify(dir, FS_CREATE, inode, FSNOTIFY_EVENT_INODE, new_dentry->d_name.name, 0);
+	fsnotify(dir, FS_CREATE, inode, FSNOTIFY_EVENT_INODE, &new_dentry->d_name, 0);
 }
 
 /*

include/linux/fsnotify_backend.h

@@ -350,7 +350,7 @@ struct fsnotify_mark {
 
 /* main fsnotify call to send events */
 extern int fsnotify(struct inode *to_tell, __u32 mask, const void *data, int data_is,
-		    const unsigned char *name, u32 cookie);
+		    const struct qstr *name, u32 cookie);
 extern int __fsnotify_parent(const struct path *path, struct dentry *dentry, __u32 mask);
 extern void __fsnotify_inode_delete(struct inode *inode);
 extern void __fsnotify_vfsmount_delete(struct vfsmount *mnt);
@@ -505,7 +505,7 @@ static inline void fsnotify_init_event(struct fsnotify_event *event,
 #else
 
 static inline int fsnotify(struct inode *to_tell, __u32 mask, const void *data, int data_is,
-			   const unsigned char *name, u32 cookie)
+			   const struct qstr *name, u32 cookie)
 {
 	return 0;
 }