Factor out read_firmware_device()

lib/chromeos/load_firmware_fw.c

 /*
  * Copyright (c) 2011 The Chromium OS Authors. All rights reserved.
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  *
  * Alternatively, this software may be distributed under the terms of the
  * GNU General Public License ("GPL") version 2 as published by the Free
  * Software Foundation.
  */
 
@@ skipping 19 matching lines @@
 }
 
 void GetFirmwareBody_dispose(firmware_storage_t *f)
 {
         int i;
         for (i = 0; i < 2; i ++)
                 if (f->firmware_body[i])
                         free(f->firmware_body[i]);
 }
 
+int read_firmware_device(firmware_storage_t *file, off_t offset, void *buf,
+                size_t count)
+{
+        ssize_t size;
+
+        if (file->seek(file->context, offset, SEEK_SET) < 0) {
+                debug(PREFIX "seek to address 0x%08x fail\n", offset);
+                return -1;
+        }
+
+        size = 0;
+        while (count > 0 &&
+                        (size = file->read(file->context, buf, count)) > 0) {
+                count -= size;
+                buf += size;
+        }
+
+        if (size < 0) {
+                debug(PREFIX "an error occur when read firmware: %d\n", size);
+                return -1;
+        }
+
+        if (count > 0) {
+                debug(PREFIX "cannot read all data: %d\n", count);
+                return -1;
+        }
+
+        return 0;
+}
+
 /*
  * See vboot_reference/firmware/include/load_firmware_fw.h for documentation of
  * this function.
  */
 int GetFirmwareBody(LoadFirmwareParams *params, uint64_t index)
 {
         firmware_storage_t *f;
         void *block;
         VbKeyBlockHeader *kbh;
         VbFirmwarePreambleHeader *fph;
@@ skipping 53 matching lines @@
                 /*
                  * See vboot_reference/firmware/include/load_firmware_fw.h for
                  * documentation of this function.
                  */
                 UpdateFirmwareBodyHash(params, firmware_body, n);
                 firmware_body += n;
         }
 
         return 0;
 }