linux-kernel - [PATCH v2 12/28] test_printf: Drop requirement that sprintf not write past nul

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Message-Id: <20220519172421.162394-13-kent.overstreet@gmail.com>
Date:   Thu, 19 May 2022 13:24:05 -0400
From:   Kent Overstreet <kent.overstreet@...il.com>
To:     linux-kernel@...r.kernel.org, linux-mm@...r.kernel.org,
        pmladek@...e.com, rostedt@...dmis.org, senozhatsky@...omium.org
Cc:     Kent Overstreet <kent.overstreet@...il.com>,
        andriy.shevchenko@...ux.intel.com, willy@...radead.org
Subject: [PATCH v2 12/28] test_printf: Drop requirement that sprintf not write past nul

The current test code checks that sprintf never writes past the
terminating nul. This is a rather strange requirement, completely
separate from writing past the end of the buffer, which of course we
can't do: writing anywhere to the buffer passed to snprintf, within size
of course, should be perfectly fine.

Since this check has no documentation as to where it comes from or what
depends on it, and it's getting in the way of further refactoring
(printf_spec handling is right now scattered massively throughout the
code, and we'd like to consolidate it) - delete it.

Also, many current pretty-printers building up their output on the
stack, and then copy it to the actual output buffer - by eliminating
this requirement we can kill those extra buffers.

Signed-off-by: Kent Overstreet <kent.overstreet@...il.com>
---
 lib/test_printf.c | 6 ------
 1 file changed, 6 deletions(-)

diff --git a/lib/test_printf.c b/lib/test_printf.c
index 1e1604ef1a..0804ab788d 100644
--- a/lib/test_printf.c
+++ b/lib/test_printf.c
@@ -78,12 +78,6 @@ do_test(int bufsize, const char *expect, int elen,
 		return 1;
 	}

-	if (memchr_inv(test_buffer + written + 1, FILL_CHAR, BUF_SIZE + PAD_SIZE - (written + 1))) {
-		pr_warn("vsnprintf(buf, %d, \"%s\", ...) wrote beyond the nul-terminator\n",
-			bufsize, fmt);
-		return 1;
-	}
-
 	if (memcmp(test_buffer, expect, written)) {
 		pr_warn("vsnprintf(buf, %d, \"%s\", ...) wrote '%s', expected '%.*s'\n",
 			bufsize, fmt, test_buffer, written, expect);
-- 
2.36.0