fs/kernel_read_file: Add file_size output argument

In preparation for adding partial read support, add an optional output
argument to kernel_read_file*() that reports the file size so callers
can reason more easily about their reading progress.

Signed-off-by: Kees Cook <keescook@chromium.org>
Reviewed-by: Mimi Zohar <zohar@linux.ibm.com>
Reviewed-by: Luis Chamberlain <mcgrof@kernel.org>
Reviewed-by: James Morris <jamorris@linux.microsoft.com>
Acked-by: Scott Branden <scott.branden@broadcom.com>
Link: https://lore.kernel.org/r/20201002173828.2099543-8-keescook@chromium.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/base/firmware_loader/main.c

@@ -500,6 +500,7 @@ fw_get_filesystem_firmware(struct device *device, struct fw_priv *fw_priv,
 
 		/* load firmware files from the mount namespace of init */
 		rc = kernel_read_file_from_path_initns(path, &buffer, msize,
+						       NULL,
 						       READING_FIRMWARE);
 		if (rc < 0) {
 			if (rc != -ENOENT)