Re: [PATCH 07/11] vfs: add cross-rename

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On Mon, Jan 13, 2014 at 08:52:27AM +0100, Jan Kara wrote:
> On Wed 08-01-14 23:10:11, Miklos Szeredi wrote:

> > +	if (max_links && new_dir != old_dir) {
> >  		error = -EMLINK;
> > -		if (max_links && !target && new_dir != old_dir &&
> > -		    new_dir->i_nlink >= max_links)
> > +		if (is_dir && !new_is_dir && new_dir->i_nlink >= max_links)
> > +			goto out;
> > +		if ((flags & RENAME_EXCHANGE) && !is_dir && new_is_dir &&
> > +		    old_dir->i_nlink > max_links)
>   This should be >=, shouldn't it?

Yes, good catch, thanks.


> > @@ -4181,12 +4212,23 @@ retry_deleg:
> >  	error = -EEXIST;
> >  	if ((flags & RENAME_NOREPLACE) && d_is_positive(new_dentry))
> >  		goto exit5;
> > +	if (flags & RENAME_EXCHANGE) {
> > +		error = -ENOENT;
> > +		if (!new_dentry->d_inode)
> > +			goto exit5;
>   Should this be d_is_positive()?

Yes, well, actually d_is_negative().

Thanks a lot for the review.  Updated patch below.

Miklos
----

Subject: vfs: add cross-rename
From: Miklos Szeredi <mszeredi@xxxxxxx>

If flags contain RENAME_EXCHANGE then exchange source and destination files.
There's no restriction on the type of the files; e.g. a directory can be
exchanged with a symlink.

Signed-off-by: Miklos Szeredi <mszeredi@xxxxxxx>
---
 fs/dcache.c             |   46 +++++++++++++++++---
 fs/namei.c              |  107 +++++++++++++++++++++++++++++++++---------------
 include/linux/dcache.h  |    1 
 include/uapi/linux/fs.h |    1 
 security/security.c     |   16 +++++++
 5 files changed, 131 insertions(+), 40 deletions(-)

--- a/include/uapi/linux/fs.h
+++ b/include/uapi/linux/fs.h
@@ -36,6 +36,7 @@
 #define SEEK_MAX	SEEK_HOLE
 
 #define RENAME_NOREPLACE	(1 << 0)	/* Don't overwrite target */
+#define RENAME_EXCHANGE		(1 << 1)	/* Exchange source and dest */
 
 struct fstrim_range {
 	__u64 start;
--- a/fs/namei.c
+++ b/fs/namei.c
@@ -4020,6 +4020,8 @@ int vfs_rename(struct inode *old_dir, st
 	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;
 
 	if (source == target)
 		return 0;
@@ -4028,10 +4030,16 @@ int vfs_rename(struct inode *old_dir, st
 	if (error)
 		return error;
 
-	if (!target)
+	if (!target) {
 		error = may_create(new_dir, new_dentry);
-	else
-		error = may_delete(new_dir, new_dentry, is_dir);
+	} else {
+		new_is_dir = d_is_dir(new_dentry);
+
+		if (!(flags & RENAME_EXCHANGE))
+			error = may_delete(new_dir, new_dentry, is_dir);
+		else
+			error = may_delete(new_dir, new_dentry, new_is_dir);
+	}
 	if (error)
 		return error;
 
@@ -4042,10 +4050,17 @@ int vfs_rename(struct inode *old_dir, st
 	 * If we are going to change the parent - check write permissions,
 	 * we'll need to flip '..'.
 	 */
-	if (is_dir && new_dir != old_dir) {
-		error = inode_permission(source, MAY_WRITE);
-		if (error)
-			return error;
+	if (new_dir != old_dir) {
+		if (is_dir) {
+			error = inode_permission(source, MAY_WRITE);
+			if (error)
+				return error;
+		}
+		if ((flags & RENAME_EXCHANGE) && new_is_dir) {
+			error = inode_permission(target, MAY_WRITE);
+			if (error)
+				return error;
+		}
 	}
 
 	error = security_inode_rename(old_dir, old_dentry, new_dir, new_dentry,
@@ -4055,25 +4070,24 @@ int vfs_rename(struct inode *old_dir, st
 
 	old_name = fsnotify_oldname_init(old_dentry->d_name.name);
 	dget(new_dentry);
-	if (!is_dir)
-		lock_two_nondirectories(source, target);
-	else if (target)
-		mutex_lock(&target->i_mutex);
+	if (!(flags & RENAME_EXCHANGE)) {
+		if (!is_dir)
+			lock_two_nondirectories(source, target);
+		else if (target)
+			mutex_lock(&target->i_mutex);
+	}
 
 	error = -EBUSY;
 	if (d_mountpoint(old_dentry) || d_mountpoint(new_dentry))
 		goto out;
 
-	if (is_dir) {
-		unsigned max_links = new_dir->i_sb->s_max_links;
-
+	if (max_links && new_dir != old_dir) {
 		error = -EMLINK;
-		if (max_links && !target && new_dir != old_dir &&
-		    new_dir->i_nlink >= max_links)
+		if (is_dir && !new_is_dir && new_dir->i_nlink >= max_links)
+			goto out;
+		if ((flags & RENAME_EXCHANGE) && !is_dir && new_is_dir &&
+		    old_dir->i_nlink >= max_links)
 			goto out;
-
-		if (target)
-			shrink_dcache_parent(new_dentry);
 	} else {
 		error = try_break_deleg(source, delegated_inode);
 		if (error)
@@ -4084,27 +4098,40 @@ int vfs_rename(struct inode *old_dir, st
 				goto out;
 		}
 	}
+	if (is_dir && !(flags & RENAME_EXCHANGE) && target)
+		shrink_dcache_parent(new_dentry);
 	error = old_dir->i_op->rename(old_dir, old_dentry, new_dir, new_dentry,
 				      flags);
 	if (error)
 		goto out;
 
-	if (target) {
+	if (!(flags & RENAME_EXCHANGE) && target) {
 		if (is_dir)
 			target->i_flags |= S_DEAD;
 		dont_mount(new_dentry);
 	}
-	if (!(old_dir->i_sb->s_type->fs_flags & FS_RENAME_DOES_D_MOVE))
-		d_move(old_dentry, new_dentry);
+	if (!(old_dir->i_sb->s_type->fs_flags & FS_RENAME_DOES_D_MOVE)) {
+		if (!(flags & RENAME_EXCHANGE))
+			d_move(old_dentry, new_dentry);
+		else
+			d_exchange(old_dentry, new_dentry);
+	}
 out:
-	if (!is_dir)
-		unlock_two_nondirectories(source, target);
-	else if (target)
-		mutex_unlock(&target->i_mutex);
+	if (!(flags & RENAME_EXCHANGE)) {
+		if (!is_dir)
+			unlock_two_nondirectories(source, target);
+		else if (target)
+			mutex_unlock(&target->i_mutex);
+	}
 	dput(new_dentry);
-	if (!error)
+	if (!error) {
 		fsnotify_move(old_dir, new_dir, old_name, is_dir,
-			      target, old_dentry);
+			      !(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);
 
 	return error;
@@ -4124,9 +4151,12 @@ SYSCALL_DEFINE5(renameat2, int, olddfd,
 	bool should_retry = false;
 	int error;
 
-	if (flags & ~RENAME_NOREPLACE)
+	if (flags & ~(RENAME_NOREPLACE | RENAME_EXCHANGE))
 		return -EOPNOTSUPP;
 
+	if ((flags & RENAME_NOREPLACE) && (flags & RENAME_EXCHANGE))
+		return -EINVAL;
+
 retry:
 	from = user_path_parent(olddfd, oldname, &oldnd, lookup_flags);
 	if (IS_ERR(from)) {
@@ -4161,7 +4191,8 @@ SYSCALL_DEFINE5(renameat2, int, olddfd,
 
 	oldnd.flags &= ~LOOKUP_PARENT;
 	newnd.flags &= ~LOOKUP_PARENT;
-	newnd.flags |= LOOKUP_RENAME_TARGET;
+	if (!(flags & RENAME_EXCHANGE))
+		newnd.flags |= LOOKUP_RENAME_TARGET;
 
 retry_deleg:
 	trap = lock_rename(new_dir, old_dir);
@@ -4181,12 +4212,23 @@ SYSCALL_DEFINE5(renameat2, int, olddfd,
 	error = -EEXIST;
 	if ((flags & RENAME_NOREPLACE) && d_is_positive(new_dentry))
 		goto exit5;
+	if (flags & RENAME_EXCHANGE) {
+		error = -ENOENT;
+		if (d_is_negative(new_dentry))
+			goto exit5;
+
+		if (!d_is_dir(new_dentry)) {
+			error = -ENOTDIR;
+			if (newnd.last.name[newnd.last.len])
+				goto exit5;
+		}
+	}
 	/* unless the source is a directory trailing slashes give -ENOTDIR */
 	if (!d_is_dir(old_dentry)) {
 		error = -ENOTDIR;
 		if (oldnd.last.name[oldnd.last.len])
 			goto exit5;
-		if (newnd.last.name[newnd.last.len])
+		if (!(flags & RENAME_EXCHANGE) && newnd.last.name[newnd.last.len])
 			goto exit5;
 	}
 	/* source should not be ancestor of target */
@@ -4194,7 +4236,8 @@ SYSCALL_DEFINE5(renameat2, int, olddfd,
 	if (old_dentry == trap)
 		goto exit5;
 	/* target should not be an ancestor of source */
-	error = -ENOTEMPTY;
+	if (!(flags & RENAME_EXCHANGE))
+		error = -ENOTEMPTY;
 	if (new_dentry == trap)
 		goto exit5;
 
--- a/fs/dcache.c
+++ b/fs/dcache.c
@@ -2483,12 +2483,14 @@ static void switch_names(struct dentry *
 			dentry->d_name.name = dentry->d_iname;
 		} else {
 			/*
-			 * Both are internal.  Just copy target to dentry
+			 * Both are internal.
 			 */
-			memcpy(dentry->d_iname, target->d_name.name,
-					target->d_name.len + 1);
-			dentry->d_name.len = target->d_name.len;
-			return;
+			unsigned int i;
+			BUILD_BUG_ON(!IS_ALIGNED(DNAME_INLINE_LEN, sizeof(long)));
+			for (i = 0; i < DNAME_INLINE_LEN / sizeof(long); i++) {
+				swap(((long *) &dentry->d_iname)[i],
+				     ((long *) &target->d_iname)[i]);
+			}
 		}
 	}
 	swap(dentry->d_name.len, target->d_name.len);
@@ -2545,13 +2547,15 @@ static void dentry_unlock_parents_for_mo
  * __d_move - move a dentry
  * @dentry: entry to move
  * @target: new dentry
+ * @exchange: exchange the two dentries
  *
  * Update the dcache to reflect the move of a file name. Negative
  * dcache entries should not be moved in this way. Caller must hold
  * rename_lock, the i_mutex of the source and target directories,
  * and the sb->s_vfs_rename_mutex if they differ. See lock_rename().
  */
-static void __d_move(struct dentry * dentry, struct dentry * target)
+static void __d_move(struct dentry *dentry, struct dentry *target,
+		     bool exchange)
 {
 	if (!dentry->d_inode)
 		printk(KERN_WARNING "VFS: moving negative dcache entry\n");
@@ -2575,6 +2579,10 @@ static void __d_move(struct dentry * den
 
 	/* Unhash the target: dput() will then get rid of it */
 	__d_drop(target);
+	if (exchange) {
+		__d_rehash(target,
+			   d_hash(dentry->d_parent, dentry->d_name.hash));
+	}
 
 	list_del(&dentry->d_u.d_child);
 	list_del(&target->d_u.d_child);
@@ -2601,6 +2609,8 @@ static void __d_move(struct dentry * den
 	write_seqcount_end(&dentry->d_seq);
 
 	dentry_unlock_parents_for_move(dentry, target);
+	if (exchange)
+		fsnotify_d_move(target);
 	spin_unlock(&target->d_lock);
 	fsnotify_d_move(dentry);
 	spin_unlock(&dentry->d_lock);
@@ -2618,11 +2628,31 @@ static void __d_move(struct dentry * den
 void d_move(struct dentry *dentry, struct dentry *target)
 {
 	write_seqlock(&rename_lock);
-	__d_move(dentry, target);
+	__d_move(dentry, target, false);
 	write_sequnlock(&rename_lock);
 }
 EXPORT_SYMBOL(d_move);
 
+/*
+ * d_exchange - exchange two dentries
+ * @dentry1: first dentry
+ * @dentry2: second dentry
+ */
+void d_exchange(struct dentry *dentry1, struct dentry *dentry2)
+{
+	write_seqlock(&rename_lock);
+
+	WARN_ON(!dentry1->d_inode);
+	WARN_ON(!dentry2->d_inode);
+	WARN_ON(IS_ROOT(dentry1));
+	WARN_ON(IS_ROOT(dentry2));
+
+	__d_move(dentry1, dentry2, true);
+
+	write_sequnlock(&rename_lock);
+}
+
+
 /**
  * d_ancestor - search for an ancestor
  * @p1: ancestor dentry
@@ -2670,7 +2700,7 @@ static struct dentry *__d_unalias(struct
 	m2 = &alias->d_parent->d_inode->i_mutex;
 out_unalias:
 	if (likely(!d_mountpoint(alias))) {
-		__d_move(alias, dentry);
+		__d_move(alias, dentry, false);
 		ret = alias;
 	}
 out_err:
--- a/include/linux/dcache.h
+++ b/include/linux/dcache.h
@@ -308,6 +308,7 @@ extern void dentry_update_name_case(stru
 
 /* used for rename() and baskets */
 extern void d_move(struct dentry *, struct dentry *);
+extern void d_exchange(struct dentry *, struct dentry *);
 extern struct dentry *d_ancestor(struct dentry *, struct dentry *);
 
 /* appendix may either be NULL or be used for transname suffixes */
--- a/security/security.c
+++ b/security/security.c
@@ -439,6 +439,14 @@ int security_path_rename(struct path *ol
 	if (unlikely(IS_PRIVATE(old_dentry->d_inode) ||
 		     (new_dentry->d_inode && IS_PRIVATE(new_dentry->d_inode))))
 		return 0;
+
+	if (flags & RENAME_EXCHANGE) {
+		int err = security_ops->path_rename(new_dir, new_dentry,
+						    old_dir, old_dentry);
+		if (err)
+			return err;
+	}
+
 	return security_ops->path_rename(old_dir, old_dentry, new_dir,
 					 new_dentry);
 }
@@ -531,6 +539,14 @@ int security_inode_rename(struct inode *
         if (unlikely(IS_PRIVATE(old_dentry->d_inode) ||
             (new_dentry->d_inode && IS_PRIVATE(new_dentry->d_inode))))
 		return 0;
+
+	if (flags & RENAME_EXCHANGE) {
+		int err = security_ops->inode_rename(new_dir, new_dentry,
+						     old_dir, old_dentry);
+		if (err)
+			return err;
+	}
+
 	return security_ops->inode_rename(old_dir, old_dentry,
 					   new_dir, new_dentry);
 }
--
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