s390/dasd: add copy pair swap capability

In case of errors or misbehaviour of the primary device a controlled
failover to one of the configured secondary devices needs to be
performed.

The swap processing stops I/O on the primary device, all requests are
re-queued to the blocklayer queue, the entries in the copy relation are
swapped and finally the link to the blockdevice is moved from primary to
secondary dasd device.
After this, the secondary becomes the new primary device and I/O is
restarted on that device.

Signed-off-by: Stefan Haberland <sth@linux.ibm.com>
Reviewed-by: Jan Hoeppner <hoeppner@linux.ibm.com>
Link: https://lore.kernel.org/r/20220920192616.808070-5-sth@linux.ibm.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>

1 files changed, 94 insertions, 0 deletions

diff --git a/drivers/s390/block/dasd_eckd.c b/drivers/s390/block/dasd_eckd.c
index c8a226f070fa..d4d3bd33553b 100644
--- a/drivers/s390/block/dasd_eckd.c
+++ b/drivers/s390/block/dasd_eckd.c
@@ -6119,6 +6119,99 @@ static int dasd_hosts_print(struct dasd_device *device, struct seq_file *m)
 	return 0;
 }
 
+static struct dasd_device
+*copy_relation_find_device(struct dasd_copy_relation *copy,
+			   char *busid)
+{
+	int i;
+
+	for (i = 0; i < DASD_CP_ENTRIES; i++) {
+		if (copy->entry[i].configured &&
+		    strncmp(copy->entry[i].busid, busid, DASD_BUS_ID_SIZE) == 0)
+			return copy->entry[i].device;
+	}
+	return NULL;
+}
+
+/*
+ * set the new active/primary device
+ */
+static void copy_pair_set_active(struct dasd_copy_relation *copy, char *new_busid,
+				 char *old_busid)
+{
+	int i;
+
+	for (i = 0; i < DASD_CP_ENTRIES; i++) {
+		if (copy->entry[i].configured &&
+		    strncmp(copy->entry[i].busid, new_busid,
+			    DASD_BUS_ID_SIZE) == 0) {
+			copy->active = &copy->entry[i];
+			copy->entry[i].primary = true;
+		} else if (copy->entry[i].configured &&
+			   strncmp(copy->entry[i].busid, old_busid,
+				   DASD_BUS_ID_SIZE) == 0) {
+			copy->entry[i].primary = false;
+		}
+	}
+}
+
+/*
+ * The function will swap the role of a given copy pair.
+ * During the swap operation the relation of the blockdevice is disconnected
+ * from the old primary and connected to the new.
+ *
+ * IO is paused on the block queue before swap and may be resumed afterwards.
+ */
+static int dasd_eckd_copy_pair_swap(struct dasd_device *device, char *prim_busid,
+				    char *sec_busid)
+{
+	struct dasd_device *primary, *secondary;
+	struct dasd_copy_relation *copy;
+	struct dasd_block *block;
+	struct gendisk *gdp;
+
+	copy = device->copy;
+	if (!copy)
+		return DASD_COPYPAIRSWAP_INVALID;
+	primary = copy->active->device;
+	if (!primary)
+		return DASD_COPYPAIRSWAP_INVALID;
+	/* double check if swap has correct primary */
+	if (strncmp(dev_name(&primary->cdev->dev), prim_busid, DASD_BUS_ID_SIZE) != 0)
+		return DASD_COPYPAIRSWAP_PRIMARY;
+
+	secondary = copy_relation_find_device(copy, sec_busid);
+	if (!secondary)
+		return DASD_COPYPAIRSWAP_SECONDARY;
+
+	/*
+	 * usually the device should be quiesced for swap
+	 * for paranoia stop device and requeue requests again
+	 */
+	dasd_device_set_stop_bits(primary, DASD_STOPPED_PPRC);
+	dasd_device_set_stop_bits(secondary, DASD_STOPPED_PPRC);
+	dasd_generic_requeue_all_requests(primary);
+
+	/* swap DASD internal device <> block assignment */
+	block = primary->block;
+	primary->block = NULL;
+	secondary->block = block;
+	block->base = secondary;
+	/* set new primary device in COPY relation */
+	copy_pair_set_active(copy, sec_busid, prim_busid);
+
+	/* swap blocklayer device link */
+	gdp = block->gdp;
+	dasd_add_link_to_gendisk(gdp, secondary);
+
+	/* re-enable device */
+	dasd_device_remove_stop_bits(primary, DASD_STOPPED_PPRC);
+	dasd_device_remove_stop_bits(secondary, DASD_STOPPED_PPRC);
+	dasd_schedule_device_bh(secondary);
+
+	return DASD_COPYPAIRSWAP_SUCCESS;
+}
+
 /*
  * Perform Subsystem Function - Peer-to-Peer Remote Copy Extended Query
  */
@@ -6805,6 +6898,7 @@ static struct dasd_discipline dasd_eckd_discipline = {
 	.ese_read = dasd_eckd_ese_read,
 	.pprc_status = dasd_eckd_query_pprc_status,
 	.pprc_enabled = dasd_eckd_pprc_enabled,
+	.copy_pair_swap = dasd_eckd_copy_pair_swap,
 };
 
 static int __init