[S390] dasd: add hyper PAV support to DASD device driver, part 1

Parallel access volumes (PAV) is a storage server feature, that allows
to start multiple channel programs on the same DASD in parallel. It
defines alias devices which can be used as alternative paths to the
same disk. With the old base PAV support we only needed rudimentary
functionality in the DASD device driver. As the mapping between base
and alias devices was static, we just had to export an identifier
(uid) and could leave the combining of devices to external layers
like a device mapper multipath.
Now hyper PAV removes the requirement to dedicate alias devices to
specific base devices. Instead each alias devices can be combined with
multiple base device on a per request basis. This requires full
support by the DASD device driver as now each channel program itself
has to identify the target base device.
The changes to the dasd device driver and the ECKD discipline are:
- Separate subchannel device representation (dasd_device) from block
  device representation (dasd_block). Only base devices are block
  devices.
- Gather information about base and alias devices and possible
  combinations.
- For each request decide which dasd_device should be used (base or
  alias) and build specific channel program.
- Support summary unit checks, which allow the storage server to
  upgrade / downgrade between base and hyper PAV at runtime (support
  is mandatory).

Signed-off-by: Stefan Weinhuber <wein@de.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>

1 files changed, 903 insertions, 0 deletions

diff --git a/drivers/s390/block/dasd_alias.c b/drivers/s390/block/dasd_alias.c
new file mode 100644
index 000000000000..3a40bee9d358
--- /dev/null
+++ b/drivers/s390/block/dasd_alias.c
@@ -0,0 +1,903 @@
+/*
+ * PAV alias management for the DASD ECKD discipline
+ *
+ * Copyright IBM Corporation, 2007
+ * Author(s): Stefan Weinhuber <wein@de.ibm.com>
+ */
+
+#include <linux/list.h>
+#include <asm/ebcdic.h>
+#include "dasd_int.h"
+#include "dasd_eckd.h"
+
+#ifdef PRINTK_HEADER
+#undef PRINTK_HEADER
+#endif                          /* PRINTK_HEADER */
+#define PRINTK_HEADER "dasd(eckd):"
+
+
+/*
+ * General concept of alias management:
+ * - PAV and DASD alias management is specific to the eckd discipline.
+ * - A device is connected to an lcu as long as the device exists.
+ *   dasd_alias_make_device_known_to_lcu will be called wenn the
+ *   device is checked by the eckd discipline and
+ *   dasd_alias_disconnect_device_from_lcu will be called
+ *   before the device is deleted.
+ * - The dasd_alias_add_device / dasd_alias_remove_device
+ *   functions mark the point when a device is 'ready for service'.
+ * - A summary unit check is a rare occasion, but it is mandatory to
+ *   support it. It requires some complex recovery actions before the
+ *   devices can be used again (see dasd_alias_handle_summary_unit_check).
+ * - dasd_alias_get_start_dev will find an alias device that can be used
+ *   instead of the base device and does some (very simple) load balancing.
+ *   This is the function that gets called for each I/O, so when improving
+ *   something, this function should get faster or better, the rest has just
+ *   to be correct.
+ */
+
+
+static void summary_unit_check_handling_work(struct work_struct *);
+static void lcu_update_work(struct work_struct *);
+static int _schedule_lcu_update(struct alias_lcu *, struct dasd_device *);
+
+static struct alias_root aliastree = {
+        .serverlist = LIST_HEAD_INIT(aliastree.serverlist),
+        .lock = __SPIN_LOCK_UNLOCKED(aliastree.lock),
+};
+
+static struct alias_server *_find_server(struct dasd_uid *uid)
+{
+        struct alias_server *pos;
+        list_for_each_entry(pos, &aliastree.serverlist, server) {
+                if (!strncmp(pos->uid.vendor, uid->vendor,
+                             sizeof(uid->vendor))
+                    && !strncmp(pos->uid.serial, uid->serial,
+                                sizeof(uid->serial)))
+                        return pos;
+        };
+        return NULL;
+}
+
+static struct alias_lcu *_find_lcu(struct alias_server *server,
+                                   struct dasd_uid *uid)
+{
+        struct alias_lcu *pos;
+        list_for_each_entry(pos, &server->lculist, lcu) {
+                if (pos->uid.ssid == uid->ssid)
+                        return pos;
+        };
+        return NULL;
+}
+
+static struct alias_pav_group *_find_group(struct alias_lcu *lcu,
+                                           struct dasd_uid *uid)
+{
+        struct alias_pav_group *pos;
+        __u8 search_unit_addr;
+
+        /* for hyper pav there is only one group */
+        if (lcu->pav == HYPER_PAV) {
+                if (list_empty(&lcu->grouplist))
+                        return NULL;
+                else
+                        return list_first_entry(&lcu->grouplist,
+                                                struct alias_pav_group, group);
+        }
+
+        /* for base pav we have to find the group that matches the base */
+        if (uid->type == UA_BASE_DEVICE)
+                search_unit_addr = uid->real_unit_addr;
+        else
+                search_unit_addr = uid->base_unit_addr;
+        list_for_each_entry(pos, &lcu->grouplist, group) {
+                if (pos->uid.base_unit_addr == search_unit_addr)
+                        return pos;
+        };
+        return NULL;
+}
+
+static struct alias_server *_allocate_server(struct dasd_uid *uid)
+{
+        struct alias_server *server;
+
+        server = kzalloc(sizeof(*server), GFP_KERNEL);
+        if (!server)
+                return ERR_PTR(-ENOMEM);
+        memcpy(server->uid.vendor, uid->vendor, sizeof(uid->vendor));
+        memcpy(server->uid.serial, uid->serial, sizeof(uid->serial));
+        INIT_LIST_HEAD(&server->server);
+        INIT_LIST_HEAD(&server->lculist);
+        return server;
+}
+
+static void _free_server(struct alias_server *server)
+{
+        kfree(server);
+}
+
+static struct alias_lcu *_allocate_lcu(struct dasd_uid *uid)
+{
+        struct alias_lcu *lcu;
+
+        lcu = kzalloc(sizeof(*lcu), GFP_KERNEL);
+        if (!lcu)
+                return ERR_PTR(-ENOMEM);
+        lcu->uac = kzalloc(sizeof(*(lcu->uac)), GFP_KERNEL | GFP_DMA);
+        if (!lcu->uac)
+                goto out_err1;
+        lcu->rsu_cqr = kzalloc(sizeof(*lcu->rsu_cqr), GFP_KERNEL | GFP_DMA);
+        if (!lcu->rsu_cqr)
+                goto out_err2;
+        lcu->rsu_cqr->cpaddr = kzalloc(sizeof(struct ccw1),
+                                       GFP_KERNEL | GFP_DMA);
+        if (!lcu->rsu_cqr->cpaddr)
+                goto out_err3;
+        lcu->rsu_cqr->data = kzalloc(16, GFP_KERNEL | GFP_DMA);
+        if (!lcu->rsu_cqr->data)
+                goto out_err4;
+
+        memcpy(lcu->uid.vendor, uid->vendor, sizeof(uid->vendor));
+        memcpy(lcu->uid.serial, uid->serial, sizeof(uid->serial));
+        lcu->uid.ssid = uid->ssid;
+        lcu->pav = NO_PAV;
+        lcu->flags = NEED_UAC_UPDATE | UPDATE_PENDING;
+        INIT_LIST_HEAD(&lcu->lcu);
+        INIT_LIST_HEAD(&lcu->inactive_devices);
+        INIT_LIST_HEAD(&lcu->active_devices);
+        INIT_LIST_HEAD(&lcu->grouplist);
+        INIT_WORK(&lcu->suc_data.worker, summary_unit_check_handling_work);
+        INIT_DELAYED_WORK(&lcu->ruac_data.dwork, lcu_update_work);
+        spin_lock_init(&lcu->lock);
+        return lcu;
+
+out_err4:
+        kfree(lcu->rsu_cqr->cpaddr);
+out_err3:
+        kfree(lcu->rsu_cqr);
+out_err2:
+        kfree(lcu->uac);
+out_err1:
+        kfree(lcu);
+        return ERR_PTR(-ENOMEM);
+}
+
+static void _free_lcu(struct alias_lcu *lcu)
+{
+        kfree(lcu->rsu_cqr->data);
+        kfree(lcu->rsu_cqr->cpaddr);
+        kfree(lcu->rsu_cqr);
+        kfree(lcu->uac);
+        kfree(lcu);
+}
+
+/*
+ * This is the function that will allocate all the server and lcu data,
+ * so this function must be called first for a new device.
+ * If the return value is 1, the lcu was already known before, if it
+ * is 0, this is a new lcu.
+ * Negative return code indicates that something went wrong (e.g. -ENOMEM)
+ */
+int dasd_alias_make_device_known_to_lcu(struct dasd_device *device)
+{
+        struct dasd_eckd_private *private;
+        unsigned long flags;
+        struct alias_server *server, *newserver;
+        struct alias_lcu *lcu, *newlcu;
+        int is_lcu_known;
+        struct dasd_uid *uid;
+
+        private = (struct dasd_eckd_private *) device->private;
+        uid = &private->uid;
+        spin_lock_irqsave(&aliastree.lock, flags);
+        is_lcu_known = 1;
+        server = _find_server(uid);
+        if (!server) {
+                spin_unlock_irqrestore(&aliastree.lock, flags);
+                newserver = _allocate_server(uid);
+                if (IS_ERR(newserver))
+                        return PTR_ERR(newserver);
+                spin_lock_irqsave(&aliastree.lock, flags);
+                server = _find_server(uid);
+                if (!server) {
+                        list_add(&newserver->server, &aliastree.serverlist);
+                        server = newserver;
+                        is_lcu_known = 0;
+                } else {
+                        /* someone was faster */
+                        _free_server(newserver);
+                }
+        }
+
+        lcu = _find_lcu(server, uid);
+        if (!lcu) {
+                spin_unlock_irqrestore(&aliastree.lock, flags);
+                newlcu = _allocate_lcu(uid);
+                if (IS_ERR(newlcu))
+                        return PTR_ERR(lcu);
+                spin_lock_irqsave(&aliastree.lock, flags);
+                lcu = _find_lcu(server, uid);
+                if (!lcu) {
+                        list_add(&newlcu->lcu, &server->lculist);
+                        lcu = newlcu;
+                        is_lcu_known = 0;
+                } else {
+                        /* someone was faster */
+                        _free_lcu(newlcu);
+                }
+                is_lcu_known = 0;
+        }
+        spin_lock(&lcu->lock);
+        list_add(&device->alias_list, &lcu->inactive_devices);
+        private->lcu = lcu;
+        spin_unlock(&lcu->lock);
+        spin_unlock_irqrestore(&aliastree.lock, flags);
+
+        return is_lcu_known;
+}
+
+/*
+ * This function removes a device from the scope of alias management.
+ * The complicated part is to make sure that it is not in use by
+ * any of the workers. If necessary cancel the work.
+ */
+void dasd_alias_disconnect_device_from_lcu(struct dasd_device *device)
+{
+        struct dasd_eckd_private *private;
+        unsigned long flags;
+        struct alias_lcu *lcu;
+        struct alias_server *server;
+        int was_pending;
+
+        private = (struct dasd_eckd_private *) device->private;
+        lcu = private->lcu;
+        spin_lock_irqsave(&lcu->lock, flags);
+        list_del_init(&device->alias_list);
+        /* make sure that the workers don't use this device */
+        if (device == lcu->suc_data.device) {
+                spin_unlock_irqrestore(&lcu->lock, flags);
+                cancel_work_sync(&lcu->suc_data.worker);
+                spin_lock_irqsave(&lcu->lock, flags);
+                if (device == lcu->suc_data.device)
+                        lcu->suc_data.device = NULL;
+        }
+        was_pending = 0;
+        if (device == lcu->ruac_data.device) {
+                spin_unlock_irqrestore(&lcu->lock, flags);
+                was_pending = 1;
+                cancel_delayed_work_sync(&lcu->ruac_data.dwork);
+                spin_lock_irqsave(&lcu->lock, flags);
+                if (device == lcu->ruac_data.device)
+                        lcu->ruac_data.device = NULL;
+        }
+        private->lcu = NULL;
+        spin_unlock_irqrestore(&lcu->lock, flags);
+
+        spin_lock_irqsave(&aliastree.lock, flags);
+        spin_lock(&lcu->lock);
+        if (list_empty(&lcu->grouplist) &&
+            list_empty(&lcu->active_devices) &&
+            list_empty(&lcu->inactive_devices)) {
+                list_del(&lcu->lcu);
+                spin_unlock(&lcu->lock);
+                _free_lcu(lcu);
+                lcu = NULL;
+        } else {
+                if (was_pending)
+                        _schedule_lcu_update(lcu, NULL);
+                spin_unlock(&lcu->lock);
+        }
+        server = _find_server(&private->uid);
+        if (server && list_empty(&server->lculist)) {
+                list_del(&server->server);
+                _free_server(server);
+        }
+        spin_unlock_irqrestore(&aliastree.lock, flags);
+}
+
+/*
+ * This function assumes that the unit address configuration stored
+ * in the lcu is up to date and will update the device uid before
+ * adding it to a pav group.
+ */
+static int _add_device_to_lcu(struct alias_lcu *lcu,
+                              struct dasd_device *device)
+{
+
+        struct dasd_eckd_private *private;
+        struct alias_pav_group *group;
+        struct dasd_uid *uid;
+
+        private = (struct dasd_eckd_private *) device->private;
+        uid = &private->uid;
+        uid->type = lcu->uac->unit[uid->real_unit_addr].ua_type;
+        uid->base_unit_addr = lcu->uac->unit[uid->real_unit_addr].base_ua;
+        dasd_set_uid(device->cdev, &private->uid);
+
+        /* if we have no PAV anyway, we don't need to bother with PAV groups */
+        if (lcu->pav == NO_PAV) {
+                list_move(&device->alias_list, &lcu->active_devices);
+                return 0;
+        }
+
+        group = _find_group(lcu, uid);
+        if (!group) {
+                group = kzalloc(sizeof(*group), GFP_ATOMIC);
+                if (!group)
+                        return -ENOMEM;
+                memcpy(group->uid.vendor, uid->vendor, sizeof(uid->vendor));
+                memcpy(group->uid.serial, uid->serial, sizeof(uid->serial));
+                group->uid.ssid = uid->ssid;
+                if (uid->type == UA_BASE_DEVICE)
+                        group->uid.base_unit_addr = uid->real_unit_addr;
+                else
+                        group->uid.base_unit_addr = uid->base_unit_addr;
+                INIT_LIST_HEAD(&group->group);
+                INIT_LIST_HEAD(&group->baselist);
+                INIT_LIST_HEAD(&group->aliaslist);
+                list_add(&group->group, &lcu->grouplist);
+        }
+        if (uid->type == UA_BASE_DEVICE)
+                list_move(&device->alias_list, &group->baselist);
+        else
+                list_move(&device->alias_list, &group->aliaslist);
+        private->pavgroup = group;
+        return 0;
+};
+
+static void _remove_device_from_lcu(struct alias_lcu *lcu,
+                                    struct dasd_device *device)
+{
+        struct dasd_eckd_private *private;
+        struct alias_pav_group *group;
+
+        private = (struct dasd_eckd_private *) device->private;
+        list_move(&device->alias_list, &lcu->inactive_devices);
+        group = private->pavgroup;
+        if (!group)
+                return;
+        private->pavgroup = NULL;
+        if (list_empty(&group->baselist) && list_empty(&group->aliaslist)) {
+                list_del(&group->group);
+                kfree(group);
+                return;
+        }
+        if (group->next == device)
+                group->next = NULL;
+};
+
+static int read_unit_address_configuration(struct dasd_device *device,
+                                           struct alias_lcu *lcu)
+{
+        struct dasd_psf_prssd_data *prssdp;
+        struct dasd_ccw_req *cqr;
+        struct ccw1 *ccw;
+        int rc;
+        unsigned long flags;
+
+        cqr = dasd_kmalloc_request("ECKD",
+                                   1 /* PSF */  + 1 /* RSSD */ ,
+                                   (sizeof(struct dasd_psf_prssd_data)),
+                                   device);
+        if (IS_ERR(cqr))
+                return PTR_ERR(cqr);
+        cqr->startdev = device;
+        cqr->memdev = device;
+        clear_bit(DASD_CQR_FLAGS_USE_ERP, &cqr->flags);
+        cqr->retries = 10;
+        cqr->expires = 20 * HZ;
+
+        /* Prepare for Read Subsystem Data */
+        prssdp = (struct dasd_psf_prssd_data *) cqr->data;
+        memset(prssdp, 0, sizeof(struct dasd_psf_prssd_data));
+        prssdp->order = PSF_ORDER_PRSSD;
+        prssdp->suborder = 0x0e;        /* Read unit address configuration */
+        /* all other bytes of prssdp must be zero */
+
+        ccw = cqr->cpaddr;
+        ccw->cmd_code = DASD_ECKD_CCW_PSF;
+        ccw->count = sizeof(struct dasd_psf_prssd_data);
+        ccw->flags |= CCW_FLAG_CC;
+        ccw->cda = (__u32)(addr_t) prssdp;
+
+        /* Read Subsystem Data - feature codes */
+        memset(lcu->uac, 0, sizeof(*(lcu->uac)));
+
+        ccw++;
+        ccw->cmd_code = DASD_ECKD_CCW_RSSD;
+        ccw->count = sizeof(*(lcu->uac));
+        ccw->cda = (__u32)(addr_t) lcu->uac;
+
+        cqr->buildclk = get_clock();
+        cqr->status = DASD_CQR_FILLED;
+
+        /* need to unset flag here to detect race with summary unit check */
+        spin_lock_irqsave(&lcu->lock, flags);
+        lcu->flags &= ~NEED_UAC_UPDATE;
+        spin_unlock_irqrestore(&lcu->lock, flags);
+
+        do {
+                rc = dasd_sleep_on(cqr);
+        } while (rc && (cqr->retries > 0));
+        if (rc) {
+                spin_lock_irqsave(&lcu->lock, flags);
+                lcu->flags |= NEED_UAC_UPDATE;
+                spin_unlock_irqrestore(&lcu->lock, flags);
+        }
+        dasd_kfree_request(cqr, cqr->memdev);
+        return rc;
+}
+
+static int _lcu_update(struct dasd_device *refdev, struct alias_lcu *lcu)
+{
+        unsigned long flags;
+        struct alias_pav_group *pavgroup, *tempgroup;
+        struct dasd_device *device, *tempdev;
+        int i, rc;
+        struct dasd_eckd_private *private;
+
+        spin_lock_irqsave(&lcu->lock, flags);
+        list_for_each_entry_safe(pavgroup, tempgroup, &lcu->grouplist, group) {
+                list_for_each_entry_safe(device, tempdev, &pavgroup->baselist,
+                                         alias_list) {
+                        list_move(&device->alias_list, &lcu->active_devices);
+                        private = (struct dasd_eckd_private *) device->private;
+                        private->pavgroup = NULL;
+                }
+                list_for_each_entry_safe(device, tempdev, &pavgroup->aliaslist,
+                                         alias_list) {
+                        list_move(&device->alias_list, &lcu->active_devices);
+                        private = (struct dasd_eckd_private *) device->private;
+                        private->pavgroup = NULL;
+                }
+                list_del(&pavgroup->group);
+                kfree(pavgroup);
+        }
+        spin_unlock_irqrestore(&lcu->lock, flags);
+
+        rc = read_unit_address_configuration(refdev, lcu);
+        if (rc)
+                return rc;
+
+        spin_lock_irqsave(&lcu->lock, flags);
+        lcu->pav = NO_PAV;
+        for (i = 0; i < MAX_DEVICES_PER_LCU; ++i) {
+                switch (lcu->uac->unit[i].ua_type) {
+                case UA_BASE_PAV_ALIAS:
+                        lcu->pav = BASE_PAV;
+                        break;
+                case UA_HYPER_PAV_ALIAS:
+                        lcu->pav = HYPER_PAV;
+                        break;
+                }
+                if (lcu->pav != NO_PAV)
+                        break;
+        }
+
+        list_for_each_entry_safe(device, tempdev, &lcu->active_devices,
+                                 alias_list) {
+                _add_device_to_lcu(lcu, device);
+        }
+        spin_unlock_irqrestore(&lcu->lock, flags);
+        return 0;
+}
+
+static void lcu_update_work(struct work_struct *work)
+{
+        struct alias_lcu *lcu;
+        struct read_uac_work_data *ruac_data;
+        struct dasd_device *device;
+        unsigned long flags;
+        int rc;
+
+        ruac_data = container_of(work, struct read_uac_work_data, dwork.work);
+        lcu = container_of(ruac_data, struct alias_lcu, ruac_data);
+        device = ruac_data->device;
+        rc = _lcu_update(device, lcu);
+        /*
+         * Need to check flags again, as there could have been another
+         * prepare_update or a new device a new device while we were still
+         * processing the data
+         */
+        spin_lock_irqsave(&lcu->lock, flags);
+        if (rc || (lcu->flags & NEED_UAC_UPDATE)) {
+                DEV_MESSAGE(KERN_WARNING, device, "could not update"
+                            " alias data in lcu (rc = %d), retry later", rc);
+                schedule_delayed_work(&lcu->ruac_data.dwork, 30*HZ);
+        } else {
+                lcu->ruac_data.device = NULL;
+                lcu->flags &= ~UPDATE_PENDING;
+        }
+        spin_unlock_irqrestore(&lcu->lock, flags);
+}
+
+static int _schedule_lcu_update(struct alias_lcu *lcu,
+                                struct dasd_device *device)
+{
+        struct dasd_device *usedev = NULL;
+        struct alias_pav_group *group;
+
+        lcu->flags |= NEED_UAC_UPDATE;
+        if (lcu->ruac_data.device) {
+                /* already scheduled or running */
+                return 0;
+        }
+        if (device && !list_empty(&device->alias_list))
+                usedev = device;
+
+        if (!usedev && !list_empty(&lcu->grouplist)) {
+                group = list_first_entry(&lcu->grouplist,
+                                         struct alias_pav_group, group);
+                if (!list_empty(&group->baselist))
+                        usedev = list_first_entry(&group->baselist,
+                                                  struct dasd_device,
+                                                  alias_list);
+                else if (!list_empty(&group->aliaslist))
+                        usedev = list_first_entry(&group->aliaslist,
+                                                  struct dasd_device,
+                                                  alias_list);
+        }
+        if (!usedev && !list_empty(&lcu->active_devices)) {
+                usedev = list_first_entry(&lcu->active_devices,
+                                          struct dasd_device, alias_list);
+        }
+        /*
+         * if we haven't found a proper device yet, give up for now, the next
+         * device that will be set active will trigger an lcu update
+         */
+        if (!usedev)
+                return -EINVAL;
+        lcu->ruac_data.device = usedev;
+        schedule_delayed_work(&lcu->ruac_data.dwork, 0);
+        return 0;
+}
+
+int dasd_alias_add_device(struct dasd_device *device)
+{
+        struct dasd_eckd_private *private;
+        struct alias_lcu *lcu;
+        unsigned long flags;
+        int rc;
+
+        private = (struct dasd_eckd_private *) device->private;
+        lcu = private->lcu;
+        rc = 0;
+        spin_lock_irqsave(&lcu->lock, flags);
+        if (!(lcu->flags & UPDATE_PENDING)) {
+                rc = _add_device_to_lcu(lcu, device);
+                if (rc)
+                        lcu->flags |= UPDATE_PENDING;
+        }
+        if (lcu->flags & UPDATE_PENDING) {
+                list_move(&device->alias_list, &lcu->active_devices);
+                _schedule_lcu_update(lcu, device);
+        }
+        spin_unlock_irqrestore(&lcu->lock, flags);
+        return rc;
+}
+
+int dasd_alias_remove_device(struct dasd_device *device)
+{
+        struct dasd_eckd_private *private;
+        struct alias_lcu *lcu;
+        unsigned long flags;
+
+        private = (struct dasd_eckd_private *) device->private;
+        lcu = private->lcu;
+        spin_lock_irqsave(&lcu->lock, flags);
+        _remove_device_from_lcu(lcu, device);
+        spin_unlock_irqrestore(&lcu->lock, flags);
+        return 0;
+}
+
+struct dasd_device *dasd_alias_get_start_dev(struct dasd_device *base_device)
+{
+
+        struct dasd_device *alias_device;
+        struct alias_pav_group *group;
+        struct alias_lcu *lcu;
+        struct dasd_eckd_private *private, *alias_priv;
+        unsigned long flags;
+
+        private = (struct dasd_eckd_private *) base_device->private;
+        group = private->pavgroup;
+        lcu = private->lcu;
+        if (!group || !lcu)
+                return NULL;
+        if (lcu->pav == NO_PAV ||
+            lcu->flags & (NEED_UAC_UPDATE | UPDATE_PENDING))
+                return NULL;
+
+        spin_lock_irqsave(&lcu->lock, flags);
+        alias_device = group->next;
+        if (!alias_device) {
+                if (list_empty(&group->aliaslist)) {
+                        spin_unlock_irqrestore(&lcu->lock, flags);
+                        return NULL;
+                } else {
+                        alias_device = list_first_entry(&group->aliaslist,
+                                                        struct dasd_device,
+                                                        alias_list);
+                }
+        }
+        if (list_is_last(&alias_device->alias_list, &group->aliaslist))
+                group->next = list_first_entry(&group->aliaslist,
+                                               struct dasd_device, alias_list);
+        else
+                group->next = list_first_entry(&alias_device->alias_list,
+                                               struct dasd_device, alias_list);
+        spin_unlock_irqrestore(&lcu->lock, flags);
+        alias_priv = (struct dasd_eckd_private *) alias_device->private;
+        if ((alias_priv->count < private->count) && !alias_device->stopped)
+                return alias_device;
+        else
+                return NULL;
+}
+
+/*
+ * Summary unit check handling depends on the way alias devices
+ * are handled so it is done here rather then in dasd_eckd.c
+ */
+static int reset_summary_unit_check(struct alias_lcu *lcu,
+                                    struct dasd_device *device,
+                                    char reason)
+{
+        struct dasd_ccw_req *cqr;
+        int rc = 0;
+
+        cqr = lcu->rsu_cqr;
+        strncpy((char *) &cqr->magic, "ECKD", 4);
+        ASCEBC((char *) &cqr->magic, 4);
+        cqr->cpaddr->cmd_code = DASD_ECKD_CCW_RSCK;
+        cqr->cpaddr->flags = 0 ;
+        cqr->cpaddr->count = 16;
+        cqr->cpaddr->cda = (__u32)(addr_t) cqr->data;
+        ((char *)cqr->data)[0] = reason;
+
+        clear_bit(DASD_CQR_FLAGS_USE_ERP, &cqr->flags);
+        cqr->retries = 255;     /* set retry counter to enable basic ERP */
+        cqr->startdev = device;
+        cqr->memdev = device;
+        cqr->block = NULL;
+        cqr->expires = 5 * HZ;
+        cqr->buildclk = get_clock();
+        cqr->status = DASD_CQR_FILLED;
+
+        rc = dasd_sleep_on_immediatly(cqr);
+        return rc;
+}
+
+static void _restart_all_base_devices_on_lcu(struct alias_lcu *lcu)
+{
+        struct alias_pav_group *pavgroup;
+        struct dasd_device *device;
+        struct dasd_eckd_private *private;
+
+        /* active and inactive list can contain alias as well as base devices */
+        list_for_each_entry(device, &lcu->active_devices, alias_list) {
+                private = (struct dasd_eckd_private *) device->private;
+                if (private->uid.type != UA_BASE_DEVICE)
+                        continue;
+                dasd_schedule_block_bh(device->block);
+                dasd_schedule_device_bh(device);
+        }
+        list_for_each_entry(device, &lcu->inactive_devices, alias_list) {
+                private = (struct dasd_eckd_private *) device->private;
+                if (private->uid.type != UA_BASE_DEVICE)
+                        continue;
+                dasd_schedule_block_bh(device->block);
+                dasd_schedule_device_bh(device);
+        }
+        list_for_each_entry(pavgroup, &lcu->grouplist, group) {
+                list_for_each_entry(device, &pavgroup->baselist, alias_list) {
+                        dasd_schedule_block_bh(device->block);
+                        dasd_schedule_device_bh(device);
+                }
+        }
+}
+
+static void flush_all_alias_devices_on_lcu(struct alias_lcu *lcu)
+{
+        struct alias_pav_group *pavgroup;
+        struct dasd_device *device, *temp;
+        struct dasd_eckd_private *private;
+        int rc;
+        unsigned long flags;
+        LIST_HEAD(active);
+
+        /*
+         * Problem here ist that dasd_flush_device_queue may wait
+         * for termination of a request to complete. We can't keep
+         * the lcu lock during that time, so we must assume that
+         * the lists may have changed.
+         * Idea: first gather all active alias devices in a separate list,
+         * then flush the first element of this list unlocked, and afterwards
+         * check if it is still on the list before moving it to the
+         * active_devices list.
+         */
+
+        spin_lock_irqsave(&lcu->lock, flags);
+        list_for_each_entry_safe(device, temp, &lcu->active_devices,
+                                 alias_list) {
+                private = (struct dasd_eckd_private *) device->private;
+                if (private->uid.type == UA_BASE_DEVICE)
+                        continue;
+                list_move(&device->alias_list, &active);
+        }
+
+        list_for_each_entry(pavgroup, &lcu->grouplist, group) {
+                list_splice_init(&pavgroup->aliaslist, &active);
+        }
+        while (!list_empty(&active)) {
+                device = list_first_entry(&active, struct dasd_device,
+                                          alias_list);
+                spin_unlock_irqrestore(&lcu->lock, flags);
+                rc = dasd_flush_device_queue(device);
+                spin_lock_irqsave(&lcu->lock, flags);
+                /*
+                 * only move device around if it wasn't moved away while we
+                 * were waiting for the flush
+                 */
+                if (device == list_first_entry(&active,
+                                               struct dasd_device, alias_list))
+                        list_move(&device->alias_list, &lcu->active_devices);
+        }
+        spin_unlock_irqrestore(&lcu->lock, flags);
+}
+
+/*
+ * This function is called in interrupt context, so the
+ * cdev lock for device is already locked!
+ */
+static void _stop_all_devices_on_lcu(struct alias_lcu *lcu,
+                                     struct dasd_device *device)
+{
+        struct alias_pav_group *pavgroup;
+        struct dasd_device *pos;
+
+        list_for_each_entry(pos, &lcu->active_devices, alias_list) {
+                if (pos != device)
+                        spin_lock(get_ccwdev_lock(pos->cdev));
+                pos->stopped |= DASD_STOPPED_SU;
+                if (pos != device)
+                        spin_unlock(get_ccwdev_lock(pos->cdev));
+        }
+        list_for_each_entry(pos, &lcu->inactive_devices, alias_list) {
+                if (pos != device)
+                        spin_lock(get_ccwdev_lock(pos->cdev));
+                pos->stopped |= DASD_STOPPED_SU;
+                if (pos != device)
+                        spin_unlock(get_ccwdev_lock(pos->cdev));
+        }
+        list_for_each_entry(pavgroup, &lcu->grouplist, group) {
+                list_for_each_entry(pos, &pavgroup->baselist, alias_list) {
+                        if (pos != device)
+                                spin_lock(get_ccwdev_lock(pos->cdev));
+                        pos->stopped |= DASD_STOPPED_SU;
+                        if (pos != device)
+                                spin_unlock(get_ccwdev_lock(pos->cdev));
+                }
+                list_for_each_entry(pos, &pavgroup->aliaslist, alias_list) {
+                        if (pos != device)
+                                spin_lock(get_ccwdev_lock(pos->cdev));
+                        pos->stopped |= DASD_STOPPED_SU;
+                        if (pos != device)
+                                spin_unlock(get_ccwdev_lock(pos->cdev));
+                }
+        }
+}
+
+static void _unstop_all_devices_on_lcu(struct alias_lcu *lcu)
+{
+        struct alias_pav_group *pavgroup;
+        struct dasd_device *device;
+        unsigned long flags;
+
+        list_for_each_entry(device, &lcu->active_devices, alias_list) {
+                spin_lock_irqsave(get_ccwdev_lock(device->cdev), flags);
+                device->stopped &= ~DASD_STOPPED_SU;
+                spin_unlock_irqrestore(get_ccwdev_lock(device->cdev), flags);
+        }
+
+        list_for_each_entry(device, &lcu->inactive_devices, alias_list) {
+                spin_lock_irqsave(get_ccwdev_lock(device->cdev), flags);
+                device->stopped &= ~DASD_STOPPED_SU;
+                spin_unlock_irqrestore(get_ccwdev_lock(device->cdev), flags);
+        }
+
+        list_for_each_entry(pavgroup, &lcu->grouplist, group) {
+                list_for_each_entry(device, &pavgroup->baselist, alias_list) {
+                        spin_lock_irqsave(get_ccwdev_lock(device->cdev), flags);
+                        device->stopped &= ~DASD_STOPPED_SU;
+                        spin_unlock_irqrestore(get_ccwdev_lock(device->cdev),
+                                               flags);
+                }
+                list_for_each_entry(device, &pavgroup->aliaslist, alias_list) {
+                        spin_lock_irqsave(get_ccwdev_lock(device->cdev), flags);
+                        device->stopped &= ~DASD_STOPPED_SU;
+                        spin_unlock_irqrestore(get_ccwdev_lock(device->cdev),
+                                               flags);
+                }
+        }
+}
+
+static void summary_unit_check_handling_work(struct work_struct *work)
+{
+        struct alias_lcu *lcu;
+        struct summary_unit_check_work_data *suc_data;
+        unsigned long flags;
+        struct dasd_device *device;
+
+        suc_data = container_of(work, struct summary_unit_check_work_data,
+                                worker);
+        lcu = container_of(suc_data, struct alias_lcu, suc_data);
+        device = suc_data->device;
+
+        /* 1. flush alias devices */
+        flush_all_alias_devices_on_lcu(lcu);
+
+        /* 2. reset summary unit check */
+        spin_lock_irqsave(get_ccwdev_lock(device->cdev), flags);
+        device->stopped &= ~(DASD_STOPPED_SU | DASD_STOPPED_PENDING);
+        spin_unlock_irqrestore(get_ccwdev_lock(device->cdev), flags);
+        reset_summary_unit_check(lcu, device, suc_data->reason);
+
+        spin_lock_irqsave(&lcu->lock, flags);
+        _unstop_all_devices_on_lcu(lcu);
+        _restart_all_base_devices_on_lcu(lcu);
+        /* 3. read new alias configuration */
+        _schedule_lcu_update(lcu, device);
+        lcu->suc_data.device = NULL;
+        spin_unlock_irqrestore(&lcu->lock, flags);
+}
+
+/*
+ * note: this will be called from int handler context (cdev locked)
+ */
+void dasd_alias_handle_summary_unit_check(struct dasd_device *device,
+                                          struct irb *irb)
+{
+        struct alias_lcu *lcu;
+        char reason;
+        struct dasd_eckd_private *private;
+
+        private = (struct dasd_eckd_private *) device->private;
+
+        reason = irb->ecw[8];
+        DEV_MESSAGE(KERN_WARNING, device, "%s %x",
+                    "eckd handle summary unit check: reason", reason);
+
+        lcu = private->lcu;
+        if (!lcu) {
+                DEV_MESSAGE(KERN_WARNING, device, "%s",
+                            "device not ready to handle summary"
+                            " unit check (no lcu structure)");
+                return;
+        }
+        spin_lock(&lcu->lock);
+        _stop_all_devices_on_lcu(lcu, device);
+        /* prepare for lcu_update */
+        private->lcu->flags |= NEED_UAC_UPDATE | UPDATE_PENDING;
+        /* If this device is about to be removed just return and wait for
+         * the next interrupt on a different device
+         */
+        if (list_empty(&device->alias_list)) {
+                DEV_MESSAGE(KERN_WARNING, device, "%s",
+                            "device is in offline processing,"
+                            " don't do summary unit check handling");
+                spin_unlock(&lcu->lock);
+                return;
+        }
+        if (lcu->suc_data.device) {
+                /* already scheduled or running */
+                DEV_MESSAGE(KERN_WARNING, device, "%s",
+                            "previous instance of summary unit check worker"
+                            " still pending");
+                spin_unlock(&lcu->lock);
+                return ;
+        }
+        lcu->suc_data.reason = reason;
+        lcu->suc_data.device = device;
+        spin_unlock(&lcu->lock);
+        schedule_work(&lcu->suc_data.worker);
+};