s390/dasd: add ioctl to perform a swap of the drivers copy pair

The newly defined ioctl BIODASDCOPYPAIRSWAP takes a structure that
specifies a copy pair that should be swapped. It will call the device
discipline function to perform the swap operation.

The structure looks as followed:

struct dasd_copypair_swap_data_t {
       char primary[20];
       char secondary[20];
       __u8 reserved[64];
};

where primary is the old primary device that will be replaced by the
secondary device. The old primary will become a secondary device
afterwards.

Signed-off-by: Stefan Haberland <sth@linux.ibm.com>
Reviewed-by: Jan Hoeppner <hoeppner@linux.ibm.com>
Link: https://lore.kernel.org/r/20220920192616.808070-6-sth@linux.ibm.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>

arch/s390/include/uapi/asm/dasd.h

@@ -182,6 +182,18 @@ typedef struct format_data_t {
 	unsigned int intensity;
 } format_data_t;
 
+/*
+ * struct dasd_copypair_swap_data_t
+ * represents all data necessary to issue a swap of the copy pair relation
+ */
+struct dasd_copypair_swap_data_t {
+	char primary[20]; /* BUSID of primary */
+	char secondary[20]; /* BUSID of secondary */
+
+	/* Reserved for future updates. */
+	__u8 reserved[64];
+};
+
 /*
  * values to be used for format_data_t.intensity
  * 0/8: normal format
@@ -326,6 +338,8 @@ struct dasd_snid_ioctl_data {
 #define BIODASDSATTR   _IOW(DASD_IOCTL_LETTER,2,attrib_data_t)
 /* Release Allocated Space */
 #define BIODASDRAS     _IOW(DASD_IOCTL_LETTER, 3, format_data_t)
+/* Swap copy pair relation */
+#define BIODASDCOPYPAIRSWAP _IOW(DASD_IOCTL_LETTER, 4, struct dasd_copypair_swap_data_t)
 
 /* Get Sense Path Group ID (SNID) data */
 #define BIODASDSNID    _IOWR(DASD_IOCTL_LETTER, 1, struct dasd_snid_ioctl_data)

drivers/s390/block/dasd_ioctl.c

@@ -379,6 +379,56 @@ out_err:
 	return rc;
 }
 
+/*
+ * Swap driver iternal copy relation.
+ */
+static int
+dasd_ioctl_copy_pair_swap(struct block_device *bdev, void __user *argp)
+{
+	struct dasd_copypair_swap_data_t data;
+	struct dasd_device *device;
+	int rc;
+
+	if (!capable(CAP_SYS_ADMIN))
+		return -EACCES;
+
+	device = dasd_device_from_gendisk(bdev->bd_disk);
+	if (!device)
+		return -ENODEV;
+
+	if (copy_from_user(&data, argp, sizeof(struct dasd_copypair_swap_data_t))) {
+		dasd_put_device(device);
+		return -EFAULT;
+	}
+	if (memchr_inv(data.reserved, 0, sizeof(data.reserved))) {
+		pr_warn("%s: Ivalid swap data specified.\n",
+			dev_name(&device->cdev->dev));
+		dasd_put_device(device);
+		return DASD_COPYPAIRSWAP_INVALID;
+	}
+	if (bdev_is_partition(bdev)) {
+		pr_warn("%s: The specified DASD is a partition and cannot be swapped\n",
+			dev_name(&device->cdev->dev));
+		dasd_put_device(device);
+		return DASD_COPYPAIRSWAP_INVALID;
+	}
+	if (!device->copy) {
+		pr_warn("%s: The specified DASD has no copy pair set up\n",
+			dev_name(&device->cdev->dev));
+		dasd_put_device(device);
+		return -ENODEV;
+	}
+	if (!device->discipline->copy_pair_swap) {
+		dasd_put_device(device);
+		return -EOPNOTSUPP;
+	}
+	rc = device->discipline->copy_pair_swap(device, data.primary,
+						data.secondary);
+	dasd_put_device(device);
+
+	return rc;
+}
+
 #ifdef CONFIG_DASD_PROFILE
 /*
  * Reset device profile information
@@ -637,6 +687,9 @@ int dasd_ioctl(struct block_device *bdev, fmode_t mode,
 	case BIODASDRAS:
 		rc = dasd_ioctl_release_space(bdev, argp);
 		break;
+	case BIODASDCOPYPAIRSWAP:
+		rc = dasd_ioctl_copy_pair_swap(bdev, argp);
+		break;
 	default:
 		/* if the discipline has an ioctl method try it. */
 		rc = -ENOTTY;