Merge tag 'vfs-7.0-rc1.atomic_open' of git://git.kernel.org/pub/scm/linux/kernel/git/vfs/vfs

Pull vfs atomic_open updates from Christian Brauner:
 "Allow knfsd to use atomic_open()

  While knfsd offers combined exclusive create and open results to
  clients, on some filesystems those results are not atomic. The
  separate vfs_create() + vfs_open() sequence in dentry_create() can
  produce races and unexpected errors. For example, open O_CREAT with
  mode 0 will succeed in creating the file but return -EACCES from
  vfs_open(). Additionally, network filesystems benefit from reducing
  remote round-trip operations by using a single atomic_open() call.

  Teach dentry_create() -- whose sole caller is knfsd -- to use
  atomic_open() for filesystems that support it"

* tag 'vfs-7.0-rc1.atomic_open' of git://git.kernel.org/pub/scm/linux/kernel/git/vfs/vfs:
  fs/namei: fix kernel-doc markup for dentry_create
  VFS/knfsd: Teach dentry_create() to use atomic_open()
  VFS: Prepare atomic_open() for dentry_create()
  VFS: move dentry_create() from fs/open.c to fs/namei.c

1 files changed, 73 insertions, 7 deletions

diff --git a/fs/namei.c b/fs/namei.c
index 3e5884f46faf..76bc569ace8e 100644
--- a/fs/namei.c
+++ b/fs/namei.c
@@ -4290,19 +4290,16 @@ static int may_o_create(struct mnt_idmap *idmap,
  *
  * Returns an error code otherwise.
  */
-static struct dentry *atomic_open(struct nameidata *nd, struct dentry *dentry,
+static struct dentry *atomic_open(const struct path *path, struct dentry *dentry,
 				  struct file *file,
 				  int open_flag, umode_t mode)
 {
 	struct dentry *const DENTRY_NOT_SET = (void *) -1UL;
-	struct inode *dir =  nd->path.dentry->d_inode;
+	struct inode *dir =  path->dentry->d_inode;
 	int error;
 
-	if (nd->flags & LOOKUP_DIRECTORY)
-		open_flag |= O_DIRECTORY;
-
 	file->__f_path.dentry = DENTRY_NOT_SET;
-	file->__f_path.mnt = nd->path.mnt;
+	file->__f_path.mnt = path->mnt;
 	error = dir->i_op->atomic_open(dir, dentry, file,
 				       open_to_namei_flags(open_flag), mode);
 	d_lookup_done(dentry);
@@ -4414,7 +4411,9 @@ static struct dentry *lookup_open(struct nameidata *nd, struct file *file,
 	if (create_error)
 		open_flag &= ~O_CREAT;
 	if (dir_inode->i_op->atomic_open) {
-		dentry = atomic_open(nd, dentry, file, open_flag, mode);
+		if (nd->flags & LOOKUP_DIRECTORY)
+			open_flag |= O_DIRECTORY;
+		dentry = atomic_open(&nd->path, dentry, file, open_flag, mode);
 		if (unlikely(create_error) && dentry == ERR_PTR(-ENOENT))
 			dentry = ERR_PTR(create_error);
 		return dentry;
@@ -4948,6 +4947,73 @@ inline struct dentry *start_creating_user_path(
 }
 EXPORT_SYMBOL(start_creating_user_path);
 
+/**
+ * dentry_create - Create and open a file
+ * @path: path to create
+ * @flags: O\_ flags
+ * @mode: mode bits for new file
+ * @cred: credentials to use
+ *
+ * Caller must hold the parent directory's lock, and have prepared
+ * a negative dentry, placed in @path->dentry, for the new file.
+ *
+ * Caller sets @path->mnt to the vfsmount of the filesystem where
+ * the new file is to be created. The parent directory and the
+ * negative dentry must reside on the same filesystem instance.
+ *
+ * On success, returns a ``struct file *``. Otherwise an ERR_PTR
+ * is returned.
+ */
+struct file *dentry_create(struct path *path, int flags, umode_t mode,
+			   const struct cred *cred)
+{
+	struct file *file __free(fput) = NULL;
+	struct dentry *dentry = path->dentry;
+	struct dentry *dir = dentry->d_parent;
+	struct inode *dir_inode = d_inode(dir);
+	struct mnt_idmap *idmap;
+	int error, create_error;
+
+	file = alloc_empty_file(flags, cred);
+	if (IS_ERR(file))
+		return file;
+
+	idmap = mnt_idmap(path->mnt);
+
+	if (dir_inode->i_op->atomic_open) {
+		path->dentry = dir;
+		mode = vfs_prepare_mode(idmap, dir_inode, mode, S_IALLUGO, S_IFREG);
+
+		create_error = may_o_create(idmap, path, dentry, mode);
+		if (create_error)
+			flags &= ~O_CREAT;
+
+		dentry = atomic_open(path, dentry, file, flags, mode);
+		error = PTR_ERR_OR_ZERO(dentry);
+
+		if (unlikely(create_error) && error == -ENOENT)
+			error = create_error;
+
+		if (!error) {
+			if (file->f_mode & FMODE_CREATED)
+				fsnotify_create(dir->d_inode, dentry);
+			if (file->f_mode & FMODE_OPENED)
+				fsnotify_open(file);
+		}
+
+		path->dentry = dentry;
+
+	} else {
+		error = vfs_create(mnt_idmap(path->mnt), path->dentry, mode, NULL);
+		if (!error)
+			error = vfs_open(path, file);
+	}
+	if (unlikely(error))
+		return ERR_PTR(error);
+
+	return no_free_ptr(file);
+}
+EXPORT_SYMBOL(dentry_create);
 
 /**
  * vfs_mknod - create device node or file