safe_macros: Fix confusing safe_read() failure output

In the case that we read() less bytes than expected in the strict mode
we used the same tst_brk() as for the case when read() fails. However
for short reads the errno is in an udefined state and we possibly end up
with confusing TBROK message. Andrea reported EACESS ernno in the TBROK
message on a short read() while developing tests.

Reported-by: Andrea Cervesato <[email protected]>
Signed-off-by: Cyril Hrubis <[email protected]>
Reviewed-by: Petr Vorel <[email protected]>

lib/safe_macros.c

@@ -293,14 +293,18 @@ ssize_t safe_read(const char *file, const int lineno, void (*cleanup_fn) (void),
 
 	rval = read(fildes, buf, nbyte);
 
-	if (rval == -1 || (len_strict && (size_t)rval != nbyte)) {
+	if (rval == -1) {
 		tst_brkm_(file, lineno, TBROK | TERRNO, cleanup_fn,
 			"read(%d,%p,%zu) failed, returned %zd", fildes, buf,
 			nbyte, rval);
 	} else if (rval < 0) {
 		tst_brkm_(file, lineno, TBROK | TERRNO, cleanup_fn,
 			"Invalid read(%d,%p,%zu) return value %zd", fildes,
 			buf, nbyte, rval);
+	} else if (len_strict && (size_t)rval != nbyte) {
+		tst_brkm_(file, lineno, TBROK, cleanup_fn,
+			  "Short read(%d,%p,%zu) returned only %zd",
+			  fildes, buf, nbyte, rval);
 	}
 
 	return rval;