devcoredump: use memory_read_from_buffer

Use memory_read_from_buffer() to simplify devcd_readv().

Reviewed-by: Chaitanya Kulkarni <chaitanya.kulkarni@wdc.com>
Reviewed-by: Johannes Berg <johannes@sipsolutions.net>
Signed-off-by: Akinobu Mita <akinobu.mita@gmail.com>
Link: https://lore.kernel.org/r/1564243146-5681-2-git-send-email-akinobu.mita@gmail.com
Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Link: https://lore.kernel.org/r/20190731100007.32684-1-johannes@sipsolutions.net
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Author: mita

drivers/base/devcoredump.c

@@ -164,16 +164,7 @@ static struct class devcd_class = {
 static ssize_t devcd_readv(char *buffer, loff_t offset, size_t count,
 			   void *data, size_t datalen)
 {
-	if (offset > datalen)
-		return -EINVAL;
-
-	if (offset + count > datalen)
-		count = datalen - offset;
-
-	if (count)
-		memcpy(buffer, ((u8 *)data) + offset, count);
-
-	return count;
+	return memory_read_from_buffer(buffer, count, &offset, data, datalen);
 }
 
 static void devcd_freev(void *data)