s390/dasd: add device ping attribute

Add a function to check if a device is accessible.
This makes mostly sense for copy pair secondary devices but it will work
for all devices.

The sysfs attribute ping is a write only attribute and will issue a NOP
CCW to the device.
In case of success it will return zero. If the device is not accessible
it will return an error code.

Signed-off-by: Stefan Haberland <sth@linux.ibm.com>
Reviewed-by: Jan Hoeppner <hoeppner@linux.ibm.com>
Link: https://lore.kernel.org/r/20220920192616.808070-8-sth@linux.ibm.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>

drivers/s390/block/dasd_devmap.c

@@ -2234,6 +2234,40 @@ out:
 }
 static DEVICE_ATTR(copy_role, 0444, dasd_copy_role_show, NULL);
 
+static ssize_t dasd_device_ping(struct device *dev,
+				struct device_attribute *attr,
+				const char *buf, size_t count)
+{
+	struct dasd_device *device;
+	size_t rc;
+
+	device = dasd_device_from_cdev(to_ccwdev(dev));
+	if (IS_ERR(device))
+		return -ENODEV;
+
+	/*
+	 * do not try during offline processing
+	 * early check only
+	 * the sleep_on function itself checks for offline
+	 * processing again
+	 */
+	if (test_bit(DASD_FLAG_OFFLINE, &device->flags)) {
+		rc = -EBUSY;
+		goto out;
+	}
+	if (!device->discipline || !device->discipline->device_ping) {
+		rc = -EOPNOTSUPP;
+		goto out;
+	}
+	rc = device->discipline->device_ping(device);
+	if (!rc)
+		rc = count;
+out:
+	dasd_put_device(device);
+	return rc;
+}
+static DEVICE_ATTR(ping, 0200, NULL, dasd_device_ping);
+
 #define DASD_DEFINE_ATTR(_name, _func)					\
 static ssize_t dasd_##_name##_show(struct device *dev,			\
 				   struct device_attribute *attr,	\
@@ -2292,6 +2326,7 @@ static struct attribute * dasd_attrs[] = {
 	&dev_attr_fc_security.attr,
 	&dev_attr_copy_pair.attr,
 	&dev_attr_copy_role.attr,
+	&dev_attr_ping.attr,
 	NULL,
 };
 

drivers/s390/block/dasd_eckd.c

@@ -6277,6 +6277,49 @@ static int dasd_eckd_query_pprc_status(struct dasd_device *device,
 	return rc;
 }
 
+/*
+ * ECKD NOP - no operation
+ */
+static int dasd_eckd_nop(struct dasd_device *device)
+{
+	struct dasd_ccw_req *cqr;
+	struct ccw1 *ccw;
+	int rc;
+
+	cqr = dasd_smalloc_request(DASD_ECKD_MAGIC, 1, 1, device, NULL);
+	if (IS_ERR(cqr)) {
+		DBF_EVENT_DEVID(DBF_WARNING, device->cdev, "%s",
+				"Could not allocate NOP request");
+		return PTR_ERR(cqr);
+	}
+	cqr->startdev = device;
+	cqr->memdev = device;
+	cqr->block = NULL;
+	cqr->retries = 1;
+	cqr->expires = 10 * HZ;
+
+	ccw = cqr->cpaddr;
+	ccw->cmd_code = DASD_ECKD_CCW_NOP;
+	ccw->flags |= CCW_FLAG_SLI;
+
+	cqr->buildclk = get_tod_clock();
+	cqr->status = DASD_CQR_FILLED;
+
+	rc = dasd_sleep_on_interruptible(cqr);
+	if (rc != 0) {
+		DBF_EVENT_DEVID(DBF_WARNING, device->cdev,
+				"NOP failed with rc=%d\n", rc);
+		rc = -EOPNOTSUPP;
+	}
+	dasd_sfree_request(cqr, cqr->memdev);
+	return rc;
+}
+
+static int dasd_eckd_device_ping(struct dasd_device *device)
+{
+	return dasd_eckd_nop(device);
+}
+
 /*
  * Perform Subsystem Function - CUIR response
  */
@@ -6899,6 +6942,7 @@ static struct dasd_discipline dasd_eckd_discipline = {
 	.pprc_status = dasd_eckd_query_pprc_status,
 	.pprc_enabled = dasd_eckd_pprc_enabled,
 	.copy_pair_swap = dasd_eckd_copy_pair_swap,
+	.device_ping = dasd_eckd_device_ping,
 };
 
 static int __init

drivers/s390/block/dasd_eckd.h

@@ -13,6 +13,7 @@
 /*****************************************************************************
  * SECTION: CCW Definitions
  ****************************************************************************/
+#define DASD_ECKD_CCW_NOP		 0x03
 #define DASD_ECKD_CCW_WRITE		 0x05
 #define DASD_ECKD_CCW_READ		 0x06
 #define DASD_ECKD_CCW_WRITE_HOME_ADDRESS 0x09

drivers/s390/block/dasd_int.h

@@ -439,6 +439,7 @@ struct dasd_discipline {
 	int (*pprc_status)(struct dasd_device *, struct	dasd_pprc_data_sc4 *);
 	bool (*pprc_enabled)(struct dasd_device *);
 	int (*copy_pair_swap)(struct dasd_device *, char *, char *);
+	int (*device_ping)(struct dasd_device *);
 };
 
 extern struct dasd_discipline *dasd_diag_discipline_pointer;