Commit 49d31c2f authored by Al Viro's avatar Al Viro
Browse files

dentry name snapshots 



take_dentry_name_snapshot() takes a safe snapshot of dentry name;
if the name is a short one, it gets copied into caller-supplied
structure, otherwise an extra reference to external name is grabbed
(those are never modified).  In either case the pointer to stable
string is stored into the same structure.

dentry must be held by the caller of take_dentry_name_snapshot(),
but may be freely dropped afterwards - the snapshot will stay
until destroyed by release_dentry_name_snapshot().

Intended use:
	struct name_snapshot s;

	take_dentry_name_snapshot(&s, dentry);
	...
	access s.name
	...
	release_dentry_name_snapshot(&s);

Replaces fsnotify_oldname_...(), gets used in fsnotify to obtain the name
to pass down with event.

Signed-off-by: default avatarAl Viro <viro@zeniv.linux.org.uk>
parent a8e2b636

fs/dcache.c

+27 −0
Original line number Diff line number Diff line
@@ -277,6 +277,33 @@ static inline int dname_external(const struct dentry *dentry) 
	return dentry->d_name.name != dentry->d_iname;

}



void take_dentry_name_snapshot(struct name_snapshot *name, struct dentry *dentry)

{

	spin_lock(&dentry->d_lock);

	if (unlikely(dname_external(dentry))) {

		struct external_name *p = external_name(dentry);

		atomic_inc(&p->u.count);

		spin_unlock(&dentry->d_lock);

		name->name = p->name;

	} else {

		memcpy(name->inline_name, dentry->d_iname, DNAME_INLINE_LEN);

		spin_unlock(&dentry->d_lock);

		name->name = name->inline_name;

	}

}

EXPORT_SYMBOL(take_dentry_name_snapshot);



void release_dentry_name_snapshot(struct name_snapshot *name)

{

	if (unlikely(name->name != name->inline_name)) {

		struct external_name *p;

		p = container_of(name->name, struct external_name, name[0]);

		if (unlikely(atomic_dec_and_test(&p->u.count)))

			kfree_rcu(p, u.head);

	}

}

EXPORT_SYMBOL(release_dentry_name_snapshot);



static inline void __d_set_inode_and_type(struct dentry *dentry,

					  struct inode *inode,

					  unsigned type_flags)

fs/debugfs/inode.c

+5 −5
Original line number Diff line number Diff line
@@ -766,7 +766,7 @@ struct dentry *debugfs_rename(struct dentry *old_dir, struct dentry *old_dentry, 
{

	int error;

	struct dentry *dentry = NULL, *trap;

	const char *old_name;

	struct name_snapshot old_name;



	trap = lock_rename(new_dir, old_dir);

	/* Source or destination directories don't exist? */
@@ -781,19 +781,19 @@ struct dentry *debugfs_rename(struct dentry *old_dir, struct dentry *old_dentry, 
	if (IS_ERR(dentry) || dentry == trap || d_really_is_positive(dentry))

		goto exit;



	old_name = fsnotify_oldname_init(old_dentry->d_name.name);

	take_dentry_name_snapshot(&old_name, old_dentry);



	error = simple_rename(d_inode(old_dir), old_dentry, d_inode(new_dir),

			      dentry, 0);

	if (error) {

		fsnotify_oldname_free(old_name);

		release_dentry_name_snapshot(&old_name);

		goto exit;

	}

	d_move(old_dentry, dentry);

	fsnotify_move(d_inode(old_dir), d_inode(new_dir), old_name,

	fsnotify_move(d_inode(old_dir), d_inode(new_dir), old_name.name,

		d_is_dir(old_dentry),

		NULL, old_dentry);

	fsnotify_oldname_free(old_name);

	release_dentry_name_snapshot(&old_name);

	unlock_rename(new_dir, old_dir);

	dput(dentry);

	return old_dentry;

fs/namei.c

+4 −4
Original line number Diff line number Diff line
@@ -4362,11 +4362,11 @@ int vfs_rename(struct inode *old_dir, struct dentry *old_dentry, 
{

	int error;

	bool is_dir = d_is_dir(old_dentry);

	const unsigned char *old_name;

	struct inode *source = old_dentry->d_inode;

	struct inode *target = new_dentry->d_inode;

	bool new_is_dir = false;

	unsigned max_links = new_dir->i_sb->s_max_links;

	struct name_snapshot old_name;



	if (source == target)

		return 0;
@@ -4413,7 +4413,7 @@ int vfs_rename(struct inode *old_dir, struct dentry *old_dentry, 
	if (error)

		return error;



	old_name = fsnotify_oldname_init(old_dentry->d_name.name);

	take_dentry_name_snapshot(&old_name, old_dentry);

	dget(new_dentry);

	if (!is_dir || (flags & RENAME_EXCHANGE))

		lock_two_nondirectories(source, target);
@@ -4468,14 +4468,14 @@ out: 
		inode_unlock(target);

	dput(new_dentry);

	if (!error) {

		fsnotify_move(old_dir, new_dir, old_name, is_dir,

		fsnotify_move(old_dir, new_dir, old_name.name, is_dir,

			      !(flags & RENAME_EXCHANGE) ? target : NULL, old_dentry);

		if (flags & RENAME_EXCHANGE) {

			fsnotify_move(new_dir, old_dir, old_dentry->d_name.name,

				      new_is_dir, NULL, new_dentry);

		}

	}

	fsnotify_oldname_free(old_name);

	release_dentry_name_snapshot(&old_name);



	return error;

}

fs/notify/fsnotify.c

+6 −2
Original line number Diff line number Diff line
@@ -161,16 +161,20 @@ int __fsnotify_parent(const struct path *path, struct dentry *dentry, __u32 mask 
	if (unlikely(!fsnotify_inode_watches_children(p_inode)))

		__fsnotify_update_child_dentry_flags(p_inode);

	else if (p_inode->i_fsnotify_mask & mask) {

		struct name_snapshot name;



		/* we are notifying a parent so come up with the new mask which

		 * specifies these are events which came from a child. */

		mask |= FS_EVENT_ON_CHILD;



		take_dentry_name_snapshot(&name, dentry);

		if (path)

			ret = fsnotify(p_inode, mask, path, FSNOTIFY_EVENT_PATH,

				       dentry->d_name.name, 0);

				       name.name, 0);

		else

			ret = fsnotify(p_inode, mask, dentry->d_inode, FSNOTIFY_EVENT_INODE,

				       dentry->d_name.name, 0);

				       name.name, 0);

		release_dentry_name_snapshot(&name);

	}



	dput(parent);

include/linux/dcache.h

+6 −0
Original line number Diff line number Diff line
@@ -591,5 +591,11 @@ static inline struct inode *d_real_inode(const struct dentry *dentry) 
	return d_backing_inode(d_real((struct dentry *) dentry, NULL, 0));

}



struct name_snapshot {

	const char *name;

	char inline_name[DNAME_INLINE_LEN];

};

void take_dentry_name_snapshot(struct name_snapshot *, struct dentry *);

void release_dentry_name_snapshot(struct name_snapshot *);



#endif	/* __LINUX_DCACHE_H */

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