vfs: introduce d_mark_tmpfile_name()

CIFS requires O_TMPFILE dentries to have names of newly created
delete-on-close files in the server so it can build full pathnames
from the root of the share when performing operations on them.

Suggested-by: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Paulo Alcantara (Red Hat) <pc@manguebit.org>
Cc: Christian Brauner <brauner@kernel.org>
Cc: Jan Kara <jack@suse.cz>
Cc: David Howells <dhowells@redhat.com>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: linux-fsdevel@vger.kernel.org
Cc: linux-cifs@vger.kernel.org
Signed-off-by: Steve French <stfrench@microsoft.com>

Author: pcacjr

fs/dcache.c

@@ -3196,6 +3196,25 @@ void d_mark_tmpfile(struct file *file, struct inode *inode)
 }
 EXPORT_SYMBOL(d_mark_tmpfile);
 
+void d_mark_tmpfile_name(struct file *file, const struct qstr *name)
+{
+	struct dentry *dentry = file->f_path.dentry;
+	char *dname = dentry->d_shortname.string;
+
+	BUG_ON(dname_external(dentry));
+	BUG_ON(d_really_is_positive(dentry));
+	BUG_ON(!d_unlinked(dentry));
+	BUG_ON(name->len > DNAME_INLINE_LEN - 1);
+	spin_lock(&dentry->d_parent->d_lock);
+	spin_lock_nested(&dentry->d_lock, DENTRY_D_LOCK_NESTED);
+	dentry->__d_name.len = name->len;
+	memcpy(dname, name->name, name->len);
+	dname[name->len] = '\0';
+	spin_unlock(&dentry->d_lock);
+	spin_unlock(&dentry->d_parent->d_lock);
+}
+EXPORT_SYMBOL(d_mark_tmpfile_name);
+
 void d_tmpfile(struct file *file, struct inode *inode)
 {
 	struct dentry *dentry = file->f_path.dentry;

include/linux/dcache.h

@@ -264,6 +264,7 @@ extern void d_invalidate(struct dentry *);
 extern struct dentry * d_make_root(struct inode *);
 
 extern void d_mark_tmpfile(struct file *, struct inode *);
+void d_mark_tmpfile_name(struct file *file, const struct qstr *name);
 extern void d_tmpfile(struct file *, struct inode *);
 
 extern struct dentry *d_find_alias(struct inode *);