selftests/nolibc: correctly report errors from printf() and friends

When an error is encountered by printf() it needs to be reported.
errno() is already set by the callback.

sprintf() is different, but that keeps working and is already tested.

Also add a new test.

Fixes: 7e4346f4a3a6 ("tools/nolibc/stdio: add a minimal [vf]printf() implementation")
Signed-off-by: Thomas Weißschuh <thomas.weissschuh@linutronix.de>
Acked-by: Willy Tarreau <w@1wt.eu>
Link: https://lore.kernel.org/r/20250704-nolibc-printf-error-v1-2-74b7a092433b@linutronix.de
Signed-off-by: Thomas Weißschuh <linux@weissschuh.net>

diff --git a/tools/include/nolibc/stdio.h b/tools/include/nolibc/stdio.h
index c470d334ef3f410d0584e01045d380347d61ad95..7630234408c584a560b059f0a7e30d407d186f17 100644 (file)
--- a/tools/include/nolibc/stdio.h
+++ b/tools/include/nolibc/stdio.h
@@ -358,11 +358,11 @@ int __nolibc_printf(__nolibc_printf_cb cb, intptr_t state, size_t n, const char
                                n -= w;
                                while (width-- > w) {
                                        if (cb(state, " ", 1) != 0)
-                                               break;
+                                               return -1;
                                        written += 1;
                                }
                                if (cb(state, outstr, w) != 0)
-                                       break;
+                                       return -1;
                        }
 
                        written += len;

diff --git a/tools/testing/selftests/nolibc/nolibc-test.c b/tools/testing/selftests/nolibc/nolibc-test.c
index ef80861105f5672874502901ec8d1c2bfb8a74d1..a297ee0d6d0754dfcd9f9e5609d42c7442dabc4e 100644 (file)
--- a/tools/testing/selftests/nolibc/nolibc-test.c
+++ b/tools/testing/selftests/nolibc/nolibc-test.c
@@ -1662,6 +1662,28 @@ int test_strerror(void)
        return 0;
 }
 
+static int test_printf_error(void)
+{
+       int fd, ret, saved_errno;
+
+       fd = open("/dev/full", O_RDWR);
+       if (fd == -1)
+               return 1;
+
+       errno = 0;
+       ret = dprintf(fd, "foo");
+       saved_errno = errno;
+       close(fd);
+
+       if (ret != -1)
+               return 2;
+
+       if (saved_errno != ENOSPC)
+               return 3;
+
+       return 0;
+}
+
 static int run_printf(int min, int max)
 {
        int test;
@@ -1691,6 +1713,7 @@ static int run_printf(int min, int max)
                CASE_TEST(width_trunc);  EXPECT_VFPRINTF(25, "                    ", "%25d", 1); break;
                CASE_TEST(scanf);        EXPECT_ZR(1, test_scanf()); break;
                CASE_TEST(strerror);     EXPECT_ZR(1, test_strerror()); break;
+               CASE_TEST(printf_error); EXPECT_ZR(1, test_printf_error()); break;
                case __LINE__:
                        return ret; /* must be last */
                /* note: do not set any defaults so as to permit holes above */