cifs: add cifs_revalidate_file

...to allow updating inode attributes on an existing inode by
filehandle. Change mmap and llseek codepaths to use that
instead of cifs_revalidate_dentry since they have a filehandle
readily available.

Signed-off-by: Jeff Layton <jlayton@redhat.com>
Signed-off-by: Steve French <sfrench@us.ibm.com>

fs/cifs/file.c

@@ -1890,11 +1890,10 @@ static ssize_t cifs_read(struct file *file, char *read_data, size_t read_size,
 
 int cifs_file_mmap(struct file *file, struct vm_area_struct *vma)
 {
-	struct dentry *dentry = file->f_path.dentry;
 	int rc, xid;
 
 	xid = GetXid();
-	rc = cifs_revalidate_dentry(dentry);
+	rc = cifs_revalidate_file(file);
 	if (rc) {
 		cFYI(1, ("Validation prior to mmap failed, error=%d", rc));
 		FreeXid(xid);