posix: fs: implement fdatasync()

`fdatasync()` is basically equivalent to `fsync()` according
to the standards.

Added test for it.

Signed-off-by: Yong Cong Sin <[email protected]>

Author: ycsin

doc/services/portability/posix/option_groups/index.rst

@@ -803,7 +803,7 @@ _POSIX_SYNCHRONIZED_IO
    :header: API, Supported
    :widths: 50,10
 
-    fdatasync(),
+    fdatasync(),yes
     fsync(),yes
     msync(),yes
 

include/zephyr/posix/unistd.h

@@ -35,6 +35,10 @@ off_t lseek(int file, off_t offset, int whence);
 int fsync(int fd);
 int ftruncate(int fd, off_t length);
 
+#ifdef CONFIG_POSIX_SYNCHRONIZED_IO
+int fdatasync(int fd);
+#endif /* CONFIG_POSIX_SYNCHRONIZED_IO */
+
 /* File System related operations */
 int rename(const char *old, const char *newp);
 int unlink(const char *path);

lib/posix/options/fsync.c

@@ -16,3 +16,10 @@ int fsync(int fd)
 #ifdef CONFIG_POSIX_FILE_SYSTEM_ALIAS_FSYNC
 FUNC_ALIAS(fsync, _fsync, int);
 #endif
+
+#ifdef CONFIG_POSIX_SYNCHRONIZED_IO
+int fdatasync(int fd)
+{
+	return fsync(fd);
+}
+#endif /* CONFIG_POSIX_SYNCHRONIZED_IO */

tests/posix/fs/src/test_fs_file.c

@@ -159,6 +159,26 @@ static int test_file_fsync(void)
 	return res;
 }
 
+#ifdef CONFIG_POSIX_SYNCHRONIZED_IO
+static int test_file_fdatasync(void)
+{
+	int res = 0;
+
+	if (file < 0)
+		return res;
+
+	res = fdatasync(file);
+	if (res < 0) {
+		TC_ERROR("Failed to sync file: %d, errno = %d\n", res, errno);
+		res = TC_FAIL;
+	}
+
+	close(file);
+	file = -1;
+	return res;
+}
+#endif /* CONFIG_POSIX_SYNCHRONIZED_IO */
+
 static int test_file_truncate(void)
 {
 	int res = 0;
@@ -251,6 +271,23 @@ ZTEST(posix_fs_file_test, test_fs_sync)
 	zassert_true(test_file_fsync() == TC_PASS);
 }
 
+/**
+ * @brief Test for POSIX fdatasync API
+ *
+ * @details Test sync the file through POSIX fdatasync API.
+ */
+ZTEST(posix_fs_file_test, test_fs_datasync)
+{
+#ifdef CONFIG_POSIX_SYNCHRONIZED_IO
+	/* FIXME: restructure tests as per #46897 */
+	zassert_true(test_file_open() == TC_PASS);
+	zassert_true(test_file_write() == TC_PASS);
+	zassert_true(test_file_fdatasync() == TC_PASS);
+#else
+	ztest_test_skip();
+#endif
+}
+
 /**
  * @brief Test for POSIX ftruncate API
  *

tests/posix/headers/src/unistd_h.c

@@ -230,7 +230,7 @@ ZTEST(posix_headers, test_unistd_h)
 	/* zassert_not_null(fchdir); */ /* not implemented */
 	/* zassert_not_null(fchown); */ /* not implemented */
 	/* zassert_not_null(fchownat); */ /* not implemented */
-	/* zassert_not_null(fdatasync); */ /* not implemented */
+	zassert_not_null(fdatasync);
 	/* zassert_not_null(fexecve); */ /* not implemented */
 	/* zassert_not_null(fork); */ /* not implemented */
 	/* zassert_not_null(fpathconf); */ /* not implemented */