[PATCH net-next v4 2/8] selftests/net: Provide test_snprintf() helper

Dmitry Safonov via B4 Relay
2024-08-23T22:05:18Z

Instead of pre-allocating a fixed-sized buffer of TEST_MSG_BUFFER_SIZE
and printing into it, call vsnprintf() with str = NULL, which will
return the needed size of the buffer. This hack is documented in
man 3 vsnprintf.

Essentially, in C++ terms, it re-invents std::stringstream, which is
going to be used to print different tracing paths and formatted strings.
Use it straight away in __test_print() - which is thread-safe version of
printing in selftests.

Signed-off-by: Dmitry Safonov <0x7f454c46@gmail.com>
---
tools/testing/selftests/net/tcp_ao/lib/aolib.h | 59 ++++++++++++++++++++++----
1 file changed, 50 insertions(+), 9 deletions(-)

diff --git a/tools/testing/selftests/net/tcp_ao/lib/aolib.h b/tools/testing/selftests/net/tcp_ao/lib/aolib.h
index fbc7f6111815..78466863435f 100644
--- a/tools/testing/selftests/net/tcp_ao/lib/aolib.h
+++ b/tools/testing/selftests/net/tcp_ao/lib/aolib.h
@@ -37,17 +37,58 @@ extern void __test_xfail(const char *buf);
extern void __test_error(const char *buf);
extern void __test_skip(const char *buf);

-__attribute__((__format__(__printf__, 2, 3)))
-static inline void __test_print(void (*fn)(const char *), const char *fmt, ...)
+static inline char *test_snprintf(const char *fmt, va_list vargs)
{
-#define TEST_MSG_BUFFER_SIZE 4096
- char buf[TEST_MSG_BUFFER_SIZE];
- va_list arg;
+ char *ret = NULL;
+ size_t size = 0;
+ va_list tmp;
+ int n = 0;

- va_start(arg, fmt);
- vsnprintf(buf, sizeof(buf), fmt, arg);
- va_end(arg);
- fn(buf);
+ va_copy(tmp, vargs);
+ n = vsnprintf(ret, size, fmt, tmp);
+ if (n < 0)
+ return NULL;
+
+ size = n + 1;
+ ret = malloc(size);
+ if (!ret)
+ return NULL;
+
+ n = vsnprintf(ret, size, fmt, vargs);
+ if (n < 0 || n > size - 1) {
+ free(ret);
+ return NULL;
+ }
+ return ret;
+}
+
+static __printf(1, 2) inline char *test_sprintf(const char *fmt, ...)
+{
+ va_list vargs;
+ char *ret;
+
+ va_start(vargs, fmt);
+ ret = test_snprintf(fmt, vargs);
+ va_end(vargs);
+
+ return ret;
+}
+
+static __printf(2, 3) inline void __test_print(void (*fn)(const char *),
+ const char *fmt, ...)
+{
+ va_list vargs;
+ char *msg;
+
+ va_start(vargs, fmt);
+ msg = test_snprintf(fmt, vargs);
+ va_end(vargs);
+
+ if (!msg)
+ return;
+
+ fn(msg);
+ free(msg);
}

#define test_print(fmt, ...) \

--
2.42.2