[LTP] [PATCH] syscalls/statx13: Add basic test for STATX_WRITE_ATOMIC on regular file

[Gaurav Pathak <gpathak@suse.de>]

From: Gaurav Pathak <gaurav.pathak@suse.com>

This patch adds a new test to validate these atomic write limit fields.
The test ensures the filesystem correctly advertises the STATX_ATTR_WRITE_ATOMIC
attribute when queried on a file opened with O_DIRECT. It also verifies that the
reported optimized maximum is logically consistent by falling within the
absolute minimum and maximum boundaries. Furthermore, it checks that all
reported atomic write unit sizes are valid powers of two, adhering to the strict
requirements of the kernel block layer.

If the underlying storage hardware or filesystem lacks atomic write
support, the test gracefully skips with TCONF.

Fixes: #1224

Signed-off-by: Gaurav Pathak <gaurav.pathak@suse.com>
---
 configure.ac                               |   2 +-
 testcases/kernel/syscalls/statx/.gitignore |   1 +
 testcases/kernel/syscalls/statx/statx13.c  | 130 +++++++++++++++++++++
 3 files changed, 132 insertions(+), 1 deletion(-)
 create mode 100644 testcases/kernel/syscalls/statx/statx13.c

diff --git a/configure.ac b/configure.ac
index 18bfdb88c..72f423c56 100644
--- a/configure.ac
+++ b/configure.ac
@@ -181,7 +181,7 @@ AC_CHECK_MEMBERS([struct iocb.aio_rw_flags],,,[#include <linux/aio_abi.h>])
 AC_CHECK_MEMBERS([struct fanotify_event_info_fid.fsid.__val],,,[#include <sys/fanotify.h>])
 AC_CHECK_MEMBERS([struct perf_event_mmap_page.aux_head],,,[#include <linux/perf_event.h>])
 AC_CHECK_MEMBERS([struct sigaction.sa_sigaction],[],[],[#include <signal.h>])
-AC_CHECK_MEMBERS([struct statx.stx_mnt_id, struct statx.stx_dio_mem_align],,,[
+AC_CHECK_MEMBERS([struct statx.stx_mnt_id, struct statx.stx_dio_mem_align, struct statx.stx_atomic_write_unit_max_opt],,,[
 #define _GNU_SOURCE
 #include <sys/stat.h>
 ])
diff --git a/testcases/kernel/syscalls/statx/.gitignore b/testcases/kernel/syscalls/statx/.gitignore
index f6a423eed..e601a46a3 100644
--- a/testcases/kernel/syscalls/statx/.gitignore
+++ b/testcases/kernel/syscalls/statx/.gitignore
@@ -10,3 +10,4 @@
 /statx10
 /statx11
 /statx12
+/statx13
diff --git a/testcases/kernel/syscalls/statx/statx13.c b/testcases/kernel/syscalls/statx/statx13.c
new file mode 100644
index 000000000..5f73807b4
--- /dev/null
+++ b/testcases/kernel/syscalls/statx/statx13.c
@@ -0,0 +1,130 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * Copyright (c) 2026 SUSE LLC <gaurav.pathak@suse.com>
+ */
+
+/*\
+ * This test validates the STATX_WRITE_ATOMIC feature (introduced in Linux 6.13).
+ * It ensures that supported filesystems (xfs as of now) correctly report their
+ * atomic write limits to user space when queried via statx().
+ *
+ * The test performs the following validations:
+ * - Creates a test file using O_DIRECT (a prerequisite for atomic writes).
+ * - Calls statx() with the STATX_WRITE_ATOMIC mask to retrieve the limits.
+ * - Verifies that stx_atomic_write_unit_min, stx_atomic_write_unit_max, and
+ *    stx_atomic_write_unit_max_opt are logically consistent (e.g., max_opt is
+ *    within the min and max bounds).
+ * - Ensures all reported atomic write unit sizes are valid powers of two.
+ */
+
+#define _GNU_SOURCE
+#include <sys/param.h>
+#include "tst_test.h"
+
+#define MNTPOINT "mnt_point"
+#define TESTFILE MNTPOINT"/testfile"
+#define MODE 0644
+
+#define WRITE_SIZE 4096
+#define ALIGNMENT  4096
+
+static int file_fd = -1;
+
+static void verify_statx(void)
+{
+	struct statx buff;
+
+	TST_EXP_PASS_SILENT(statx(AT_FDCWD, TESTFILE, 0, STATX_BASIC_STATS | STATX_WRITE_ATOMIC, &buff),
+			"statx(AT_FDCWD, %s, 0, STATX_WRITE_ATOMIC, &buf)", TESTFILE);
+
+	if (!(buff.stx_attributes & STATX_ATTR_WRITE_ATOMIC)) {
+		tst_res(TCONF, "Filesystem does not support STATX_WRITE_ATOMIC");
+		return;
+	}
+
+	if (buff.stx_atomic_write_unit_min > 0 &&
+			__builtin_popcount(buff.stx_atomic_write_unit_min) == 1)
+		tst_res(TPASS, "stx_atomic_write_unit_min(%u) is power of 2",
+				buff.stx_atomic_write_unit_min);
+	else
+		tst_res(TFAIL, "stx_atomic_write_unit_min(%u) is not a power of 2",
+				buff.stx_atomic_write_unit_min);
+
+	if (buff.stx_atomic_write_unit_max > 0 &&
+			__builtin_popcount(buff.stx_atomic_write_unit_max) == 1)
+		tst_res(TPASS, "stx_atomic_write_unit_max(%u) is power of 2",
+				buff.stx_atomic_write_unit_max);
+	else
+		tst_res(TFAIL, "stx_atomic_write_unit_max(%u) is not a power of 2",
+				buff.stx_atomic_write_unit_max);
+
+#ifdef HAVE_STRUCT_STATX_STX_ATOMIC_WRITE_UNIT_MAX_OPT
+	if (buff.stx_atomic_write_unit_max_opt == 0) {
+		tst_res(TINFO, "stx_atomic_write_unit_max_opt is 0 (no optimized max reported)");
+	} else {
+		if (buff.stx_atomic_write_unit_max_opt > buff.stx_atomic_write_unit_max)
+			tst_res(TFAIL, "stx_atomic_write_unit_max_opt (%u) exceeds max (%u)",
+					buff.stx_atomic_write_unit_max_opt,
+					buff.stx_atomic_write_unit_max);
+
+		else if (buff.stx_atomic_write_unit_max_opt < buff.stx_atomic_write_unit_min)
+			tst_res(TFAIL, "stx_atomic_write_unit_max_opt (%u) is less than min (%u)",
+					buff.stx_atomic_write_unit_max_opt,
+					buff.stx_atomic_write_unit_min);
+		else
+			tst_res(TPASS, "stx_atomic_write_unit_max_opt (%u) is within valid range [%u, %u]",
+					buff.stx_atomic_write_unit_max_opt,
+					buff.stx_atomic_write_unit_min,
+					buff.stx_atomic_write_unit_max);
+
+		if (__builtin_popcount(buff.stx_atomic_write_unit_max_opt) != 1)
+			tst_res(TFAIL, "stx_atomic_write_unit_max_opt (%u) is not a power of 2",
+					buff.stx_atomic_write_unit_max_opt);
+	}
+#else
+    tst_res(TCONF, "stx_atomic_write_unit_max_opt is not defined in struct statx");
+#endif
+}
+
+static void setup(void)
+{
+	char *data_buff = SAFE_MEMALIGN(ALIGNMENT, WRITE_SIZE);
+
+	if (strcmp(tst_device->fs_type, "xfs") && strcmp(tst_device->fs_type, "ext4"))
+		tst_brk(TCONF, "This test only supports ext4 and xfs");
+
+	umask(0);
+	memset(data_buff, '@', WRITE_SIZE);
+
+	file_fd =  SAFE_OPEN(TESTFILE, O_RDWR | O_CREAT | O_DIRECT, MODE);
+	SAFE_WRITE(SAFE_WRITE_ALL, file_fd, data_buff, WRITE_SIZE);
+}
+
+static void cleanup(void)
+{
+	if (file_fd > -1)
+		SAFE_CLOSE(file_fd);
+}
+
+static struct tst_test test = {
+	.test_all = verify_statx,
+	.setup = setup,
+	.cleanup = cleanup,
+	.min_kver = "6.13",
+	.needs_root = 1,
+	.needs_device = 1,
+	.needs_tmpdir = 1,
+	.mntpoint = MNTPOINT,
+	.mount_device = 1,
+	.filesystems = (struct tst_fs[]) {
+		{
+			.type = "xfs",
+			.mkfs_opts = (const char *const []){"-f", "-bsize=16K", NULL},
+		},
+        {
+            .type = "ext4",
+            .mkfs_opts = (const char *const []){"-O", "bigalloc", "-b", "4096", "-C", "65536", NULL},
+        },
+		{}
+	},
+};
-- 
2.51.0


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