[PATCH] loop sendfile retval

Buffer I/O error on device loop: its use of sendfile is (trivially)
broken - retval is usually count done, only an error when negative.

This code (like the old one) does not correctly handle partial reads.

Nearby spinlocking clearly bogus, delete instead of remarking on it.

drivers/block/loop.c

@@ -304,21 +304,16 @@ do_lo_receive(struct loop_device *lo,
 {
 	struct lo_read_data cookie;
 	struct file *file;
-	int error;
+	int retval;
 
 	cookie.lo = lo;
 	cookie.data = kmap(bvec->bv_page) + bvec->bv_offset;
 	cookie.bsize = bsize;
-
-	/* umm, what does this lock actually try to protect? */
-	spin_lock_irq(&lo->lo_lock);
 	file = lo->lo_backing_file;
-	spin_unlock_irq(&lo->lo_lock);
-
-	error = file->f_op->sendfile(file, &pos, bvec->bv_len,
+	retval = file->f_op->sendfile(file, &pos, bvec->bv_len,
 			lo_read_actor, &cookie);
 	kunmap(bvec->bv_page);
-	return error;
+	return (retval < 0)? retval: 0;
 }
 
 static int