Detect DAX devices and and warn in LUKS format.

DAX / persistent memory devices do not provide atomic sector updates,
any single modification can corrupt the whole encryption block.

lib/internal.h

@@ -113,6 +113,7 @@ void device_release_excl(struct crypt_device *cd, struct device *device);
 void device_disable_direct_io(struct device *device);
 int device_is_identical(struct device *device1, struct device *device2);
 int device_is_rotational(struct device *device);
+int device_is_dax(struct device *device);
 size_t device_alignment(struct device *device);
 int device_direct_io(const struct device *device);
 int device_fallocate(struct device *device, uint64_t size);
@@ -157,6 +158,7 @@ int crypt_confirm(struct crypt_device *cd, const char *msg);
 
 char *crypt_lookup_dev(const char *dev_id);
 int crypt_dev_is_rotational(int major, int minor);
+int crypt_dev_is_dax(int major, int minor);
 int crypt_dev_is_partition(const char *dev_path);
 char *crypt_get_partition_device(const char *dev_path, uint64_t offset, uint64_t size);
 char *crypt_get_base_device(const char *dev_path);

lib/setup.c

@@ -1733,6 +1733,9 @@ static int _crypt_format_luks1(struct crypt_device *cd,
 			return -ENOMEM;
 	}
 
+	if (device_is_dax(crypt_data_device(cd)) > 0)
+		log_std(cd, _("WARNING: DAX device can corrupt data as it does not guarantee atomic sector updates.\n"));
+
 	if (params && cd->metadata_device) {
 		/* For detached header the alignment is used directly as data offset */
 		if (!cd->data_offset)
@@ -1835,6 +1838,9 @@ static int _crypt_format_luks2(struct crypt_device *cd,
 			return -ENOMEM;
 	}
 
+	if (device_is_dax(crypt_data_device(cd)) > 0)
+		log_std(cd, _("WARNING: DAX device can corrupt data as it does not guarantee atomic sector updates.\n"));
+
 	if (sector_size_autodetect) {
 		sector_size = device_optimal_encryption_sector_size(cd, crypt_data_device(cd));
 		log_dbg(cd, "Auto-detected optimal encryption sector size for device %s is %d bytes.",

lib/utils_device.c

@@ -985,6 +985,22 @@ int device_is_rotational(struct device *device)
 	return crypt_dev_is_rotational(major(st.st_rdev), minor(st.st_rdev));
 }
 
+int device_is_dax(struct device *device)
+{
+	struct stat st;
+
+	if (!device)
+		return -EINVAL;
+
+	if (stat(device_path(device), &st) < 0)
+		return -EINVAL;
+
+	if (!S_ISBLK(st.st_mode))
+		return 0;
+
+	return crypt_dev_is_dax(major(st.st_rdev), minor(st.st_rdev));
+}
+
 size_t device_alignment(struct device *device)
 {
 	int devfd;

lib/utils_devpath.c

@@ -220,6 +220,16 @@ int crypt_dev_is_rotational(int major, int minor)
 	return val ? 1 : 0;
 }
 
+int crypt_dev_is_dax(int major, int minor)
+{
+	uint64_t val;
+
+	if (!_sysfs_get_uint64(major, minor, &val, "queue/dax"))
+		return 0; /* if failed, expect non-DAX device */
+
+	return val ? 1 : 0;
+}
+
 int crypt_dev_is_partition(const char *dev_path)
 {
 	uint64_t val;