dcssblk.c

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/*
 * dcssblk.c -- the S/390 block driver for dcss memory
 *
 * Authors: Carsten Otte, Stefan Weinhuber, Gerald Schaefer
 */

#define KMSG_COMPONENT "dcssblk"
#define pr_fmt(fmt) KMSG_COMPONENT ": " fmt

#include <linux/module.h>
#include <linux/moduleparam.h>
#include <linux/ctype.h>
#include <linux/errno.h>
#include <linux/init.h>
#include <linux/slab.h>
#include <linux/blkdev.h>
#include <linux/completion.h>
#include <linux/interrupt.h>
#include <linux/platform_device.h>
#include <asm/extmem.h>
#include <asm/io.h>

#define DCSSBLK_NAME "dcssblk"
#define DCSSBLK_MINORS_PER_DISK 1
#define DCSSBLK_PARM_LEN 400
#define DCSS_BUS_ID_SIZE 20

static int dcssblk_open(struct block_device *bdev, fmode_t mode);
static int dcssblk_release(struct gendisk *disk, fmode_t mode);
static void dcssblk_make_request(struct request_queue *q, struct bio *bio);
static int dcssblk_direct_access(struct block_device *bdev, sector_t secnum,
                 void **kaddr, unsigned long *pfn);

static char dcssblk_segments[DCSSBLK_PARM_LEN] = "\0";

static int dcssblk_major;
static const struct block_device_operations dcssblk_devops = {
    .owner      = THIS_MODULE,
    .open       = dcssblk_open,
    .release    = dcssblk_release,
    .direct_access  = dcssblk_direct_access,
};

struct dcssblk_dev_info {
    struct list_head lh;
    struct device dev;
    char segment_name[DCSS_BUS_ID_SIZE];
    atomic_t use_count;
    struct gendisk *gd;
    unsigned long start;
    unsigned long end;
    int segment_type;
    unsigned char save_pending;
    unsigned char is_shared;
    struct request_queue *dcssblk_queue;
    int num_of_segments;
    struct list_head seg_list;
};

struct segment_info {
    struct list_head lh;
    char segment_name[DCSS_BUS_ID_SIZE];
    unsigned long start;
    unsigned long end;
    int segment_type;
};

static ssize_t dcssblk_add_store(struct device * dev, struct device_attribute *attr, const char * buf,
                  size_t count);
static ssize_t dcssblk_remove_store(struct device * dev, struct device_attribute *attr, const char * buf,
                  size_t count);

static DEVICE_ATTR(add, S_IWUSR, NULL, dcssblk_add_store);
static DEVICE_ATTR(remove, S_IWUSR, NULL, dcssblk_remove_store);

static struct device *dcssblk_root_dev;

static LIST_HEAD(dcssblk_devices);
static struct rw_semaphore dcssblk_devices_sem;

/*
 * release function for segment device.
 */
static void
dcssblk_release_segment(struct device *dev)
{
    struct dcssblk_dev_info *dev_info;
    struct segment_info *entry, *temp;

    dev_info = container_of(dev, struct dcssblk_dev_info, dev);
    list_for_each_entry_safe(entry, temp, &dev_info->seg_list, lh) {
        list_del(&entry->lh);
        kfree(entry);
    }
    kfree(dev_info);
    module_put(THIS_MODULE);
}

/*
 * get a minor number. needs to be called with
 * down_write(&dcssblk_devices_sem) and the
 * device needs to be enqueued before the semaphore is
 * freed.
 */
static int
dcssblk_assign_free_minor(struct dcssblk_dev_info *dev_info)
{
    int minor, found;
    struct dcssblk_dev_info *entry;

    if (dev_info == NULL)
        return -EINVAL;
    for (minor = 0; minor < (1<<MINORBITS); minor++) {
        found = 0;
        // test if minor available
        list_for_each_entry(entry, &dcssblk_devices, lh)
            if (minor == entry->gd->first_minor)
                found++;
        if (!found) break; // got unused minor
    }
    if (found)
        return -EBUSY;
    dev_info->gd->first_minor = minor;
    return 0;
}

/*
 * get the struct dcssblk_dev_info from dcssblk_devices
 * for the given name.
 * down_read(&dcssblk_devices_sem) must be held.
 */
static struct dcssblk_dev_info *
dcssblk_get_device_by_name(char *name)
{
    struct dcssblk_dev_info *entry;

    list_for_each_entry(entry, &dcssblk_devices, lh) {
        if (!strcmp(name, entry->segment_name)) {
            return entry;
        }
    }
    return NULL;
}

/*
 * get the struct segment_info from seg_list
 * for the given name.
 * down_read(&dcssblk_devices_sem) must be held.
 */
static struct segment_info *
dcssblk_get_segment_by_name(char *name)
{
    struct dcssblk_dev_info *dev_info;
    struct segment_info *entry;

    list_for_each_entry(dev_info, &dcssblk_devices, lh) {
        list_for_each_entry(entry, &dev_info->seg_list, lh) {
            if (!strcmp(name, entry->segment_name))
                return entry;
        }
    }
    return NULL;
}

/*
 * get the highest address of the multi-segment block.
 */
static unsigned long
dcssblk_find_highest_addr(struct dcssblk_dev_info *dev_info)
{
    unsigned long highest_addr;
    struct segment_info *entry;

    highest_addr = 0;
    list_for_each_entry(entry, &dev_info->seg_list, lh) {
        if (highest_addr < entry->end)
            highest_addr = entry->end;
    }
    return highest_addr;
}

/*
 * get the lowest address of the multi-segment block.
 */
static unsigned long
dcssblk_find_lowest_addr(struct dcssblk_dev_info *dev_info)
{
    int set_first;
    unsigned long lowest_addr;
    struct segment_info *entry;

    set_first = 0;
    lowest_addr = 0;
    list_for_each_entry(entry, &dev_info->seg_list, lh) {
        if (set_first == 0) {
            lowest_addr = entry->start;
            set_first = 1;
        } else {
            if (lowest_addr > entry->start)
                lowest_addr = entry->start;
        }
    }
    return lowest_addr;
}

/*
 * Check continuity of segments.
 */
static int
dcssblk_is_continuous(struct dcssblk_dev_info *dev_info)
{
    int i, j, rc;
    struct segment_info *sort_list, *entry, temp;

    if (dev_info->num_of_segments <= 1)
        return 0;

    sort_list = kzalloc(
            sizeof(struct segment_info) * dev_info->num_of_segments,
            GFP_KERNEL);
    if (sort_list == NULL)
        return -ENOMEM;
    i = 0;
    list_for_each_entry(entry, &dev_info->seg_list, lh) {
        memcpy(&sort_list[i], entry, sizeof(struct segment_info));
        i++;
    }

    /* sort segments */
    for (i = 0; i < dev_info->num_of_segments; i++)
        for (j = 0; j < dev_info->num_of_segments; j++)
            if (sort_list[j].start > sort_list[i].start) {
                memcpy(&temp, &sort_list[i],
                    sizeof(struct segment_info));
                memcpy(&sort_list[i], &sort_list[j],
                    sizeof(struct segment_info));
                memcpy(&sort_list[j], &temp,
                    sizeof(struct segment_info));
            }

    /* check continuity */
    for (i = 0; i < dev_info->num_of_segments - 1; i++) {
        if ((sort_list[i].end + 1) != sort_list[i+1].start) {
            pr_err("Adjacent DCSSs %s and %s are not "
                   "contiguous\n", sort_list[i].segment_name,
                   sort_list[i+1].segment_name);
            rc = -EINVAL;
            goto out;
        }
        /* EN and EW are allowed in a block device */
        if (sort_list[i].segment_type != sort_list[i+1].segment_type) {
            if (!(sort_list[i].segment_type & SEGMENT_EXCLUSIVE) ||
                (sort_list[i].segment_type == SEG_TYPE_ER) ||
                !(sort_list[i+1].segment_type &
                SEGMENT_EXCLUSIVE) ||
                (sort_list[i+1].segment_type == SEG_TYPE_ER)) {
                pr_err("DCSS %s and DCSS %s have "
                       "incompatible types\n",
                       sort_list[i].segment_name,
                       sort_list[i+1].segment_name);
                rc = -EINVAL;
                goto out;
            }
        }
    }
    rc = 0;
out:
    kfree(sort_list);
    return rc;
}

/*
 * Load a segment
 */
static int
dcssblk_load_segment(char *name, struct segment_info **seg_info)
{
    int rc;

    /* already loaded? */
    down_read(&dcssblk_devices_sem);
    *seg_info = dcssblk_get_segment_by_name(name);
    up_read(&dcssblk_devices_sem);
    if (*seg_info != NULL)
        return -EEXIST;

    /* get a struct segment_info */
    *seg_info = kzalloc(sizeof(struct segment_info), GFP_KERNEL);
    if (*seg_info == NULL)
        return -ENOMEM;

    strcpy((*seg_info)->segment_name, name);

    /* load the segment */
    rc = segment_load(name, SEGMENT_SHARED,
            &(*seg_info)->start, &(*seg_info)->end);
    if (rc < 0) {
        segment_warning(rc, (*seg_info)->segment_name);
        kfree(*seg_info);
    } else {
        INIT_LIST_HEAD(&(*seg_info)->lh);
        (*seg_info)->segment_type = rc;
    }
    return rc;
}

static void dcssblk_unregister_callback(struct device *dev)
{
    device_unregister(dev);
    put_device(dev);
}

/*
 * device attribute for switching shared/nonshared (exclusive)
 * operation (show + store)
 */
static ssize_t
dcssblk_shared_show(struct device *dev, struct device_attribute *attr, char *buf)
{
    struct dcssblk_dev_info *dev_info;

    dev_info = container_of(dev, struct dcssblk_dev_info, dev);
    return sprintf(buf, dev_info->is_shared ? "1\n" : "0\n");
}

static ssize_t
dcssblk_shared_store(struct device *dev, struct device_attribute *attr, const char *inbuf, size_t count)
{
    struct dcssblk_dev_info *dev_info;
    struct segment_info *entry, *temp;
    int rc;

    if ((count > 1) && (inbuf[1] != '\n') && (inbuf[1] != '\0'))
        return -EINVAL;
    down_write(&dcssblk_devices_sem);
    dev_info = container_of(dev, struct dcssblk_dev_info, dev);
    if (atomic_read(&dev_info->use_count)) {
        rc = -EBUSY;
        goto out;
    }
    if (inbuf[0] == '1') {
        /* reload segments in shared mode */
        list_for_each_entry(entry, &dev_info->seg_list, lh) {
            rc = segment_modify_shared(entry->segment_name,
                        SEGMENT_SHARED);
            if (rc < 0) {
                BUG_ON(rc == -EINVAL);
                if (rc != -EAGAIN)
                    goto removeseg;
            }
        }
        dev_info->is_shared = 1;
        switch (dev_info->segment_type) {
        case SEG_TYPE_SR:
        case SEG_TYPE_ER:
        case SEG_TYPE_SC:
            set_disk_ro(dev_info->gd, 1);
        }
    } else if (inbuf[0] == '0') {
        /* reload segments in exclusive mode */
        if (dev_info->segment_type == SEG_TYPE_SC) {
            pr_err("DCSS %s is of type SC and cannot be "
                   "loaded as exclusive-writable\n",
                   dev_info->segment_name);
            rc = -EINVAL;
            goto out;
        }
        list_for_each_entry(entry, &dev_info->seg_list, lh) {
            rc = segment_modify_shared(entry->segment_name,
                           SEGMENT_EXCLUSIVE);
            if (rc < 0) {
                BUG_ON(rc == -EINVAL);
                if (rc != -EAGAIN)
                    goto removeseg;
            }
        }
        dev_info->is_shared = 0;
        set_disk_ro(dev_info->gd, 0);
    } else {
        rc = -EINVAL;
        goto out;
    }
    rc = count;
    goto out;

removeseg:
    pr_err("DCSS device %s is removed after a failed access mode "
           "change\n", dev_info->segment_name);
    temp = entry;
    list_for_each_entry(entry, &dev_info->seg_list, lh) {
        if (entry != temp)
            segment_unload(entry->segment_name);
    }
    list_del(&dev_info->lh);

    del_gendisk(dev_info->gd);
    blk_cleanup_queue(dev_info->dcssblk_queue);
    dev_info->gd->queue = NULL;
    put_disk(dev_info->gd);
    rc = device_schedule_callback(dev, dcssblk_unregister_callback);
out:
    up_write(&dcssblk_devices_sem);
    return rc;
}
static DEVICE_ATTR(shared, S_IWUSR | S_IRUSR, dcssblk_shared_show,
           dcssblk_shared_store);

/*
 * device attribute for save operation on current copy
 * of the segment. If the segment is busy, saving will
 * become pending until it gets released, which can be
 * undone by storing a non-true value to this entry.
 * (show + store)
 */
static ssize_t
dcssblk_save_show(struct device *dev, struct device_attribute *attr, char *buf)
{
    struct dcssblk_dev_info *dev_info;

    dev_info = container_of(dev, struct dcssblk_dev_info, dev);
    return sprintf(buf, dev_info->save_pending ? "1\n" : "0\n");
}

static ssize_t
dcssblk_save_store(struct device *dev, struct device_attribute *attr, const char *inbuf, size_t count)
{
    struct dcssblk_dev_info *dev_info;
    struct segment_info *entry;

    if ((count > 1) && (inbuf[1] != '\n') && (inbuf[1] != '\0'))
        return -EINVAL;
    dev_info = container_of(dev, struct dcssblk_dev_info, dev);

    down_write(&dcssblk_devices_sem);
    if (inbuf[0] == '1') {
        if (atomic_read(&dev_info->use_count) == 0) {
            // device is idle => we save immediately
            pr_info("All DCSSs that map to device %s are "
                "saved\n", dev_info->segment_name);
            list_for_each_entry(entry, &dev_info->seg_list, lh) {
                segment_save(entry->segment_name);
            }
        }  else {
            // device is busy => we save it when it becomes
            // idle in dcssblk_release
            pr_info("Device %s is in use, its DCSSs will be "
                "saved when it becomes idle\n",
                dev_info->segment_name);
            dev_info->save_pending = 1;
        }
    } else if (inbuf[0] == '0') {
        if (dev_info->save_pending) {
            // device is busy & the user wants to undo his save
            // request
            dev_info->save_pending = 0;
            pr_info("A pending save request for device %s "
                "has been canceled\n",
                dev_info->segment_name);
        }
    } else {
        up_write(&dcssblk_devices_sem);
        return -EINVAL;
    }
    up_write(&dcssblk_devices_sem);
    return count;
}
static DEVICE_ATTR(save, S_IWUSR | S_IRUSR, dcssblk_save_show,
           dcssblk_save_store);

/*
 * device attribute for showing all segments in a device
 */
static ssize_t
dcssblk_seglist_show(struct device *dev, struct device_attribute *attr,
        char *buf)
{
    int i;

    struct dcssblk_dev_info *dev_info;
    struct segment_info *entry;

    down_read(&dcssblk_devices_sem);
    dev_info = container_of(dev, struct dcssblk_dev_info, dev);
    i = 0;
    buf[0] = '\0';
    list_for_each_entry(entry, &dev_info->seg_list, lh) {
        strcpy(&buf[i], entry->segment_name);
        i += strlen(entry->segment_name);
        buf[i] = '\n';
        i++;
    }
    up_read(&dcssblk_devices_sem);
    return i;
}
static DEVICE_ATTR(seglist, S_IRUSR, dcssblk_seglist_show, NULL);

static struct attribute *dcssblk_dev_attrs[] = {
    &dev_attr_shared.attr,
    &dev_attr_save.attr,
    &dev_attr_seglist.attr,
    NULL,
};
static struct attribute_group dcssblk_dev_attr_group = {
    .attrs = dcssblk_dev_attrs,
};
static const struct attribute_group *dcssblk_dev_attr_groups[] = {
    &dcssblk_dev_attr_group,
    NULL,
};

/*
 * device attribute for adding devices
 */
static ssize_t
dcssblk_add_store(struct device *dev, struct device_attribute *attr, const char *buf, size_t count)
{
    int rc, i, j, num_of_segments;
    struct dcssblk_dev_info *dev_info;
    struct segment_info *seg_info, *temp;
    char *local_buf;
    unsigned long seg_byte_size;

    dev_info = NULL;
    seg_info = NULL;
    if (dev != dcssblk_root_dev) {
        rc = -EINVAL;
        goto out_nobuf;
    }
    if ((count < 1) || (buf[0] == '\0') || (buf[0] == '\n')) {
        rc = -ENAMETOOLONG;
        goto out_nobuf;
    }

    local_buf = kmalloc(count + 1, GFP_KERNEL);
    if (local_buf == NULL) {
        rc = -ENOMEM;
        goto out_nobuf;
    }

    /*
     * parse input
     */
    num_of_segments = 0;
    for (i = 0; ((buf[i] != '\0') && (buf[i] != '\n') && i < count); i++) {
        for (j = i; (buf[j] != ':') &&
            (buf[j] != '\0') &&
            (buf[j] != '\n') &&
            j < count; j++) {
            local_buf[j-i] = toupper(buf[j]);
        }
        local_buf[j-i] = '\0';
        if (((j - i) == 0) || ((j - i) > 8)) {
            rc = -ENAMETOOLONG;
            goto seg_list_del;
        }

        rc = dcssblk_load_segment(local_buf, &seg_info);
        if (rc < 0)
            goto seg_list_del;
        /*
         * get a struct dcssblk_dev_info
         */
        if (num_of_segments == 0) {
            dev_info = kzalloc(sizeof(struct dcssblk_dev_info),
                    GFP_KERNEL);
            if (dev_info == NULL) {
                rc = -ENOMEM;
                goto out;
            }
            strcpy(dev_info->segment_name, local_buf);
            dev_info->segment_type = seg_info->segment_type;
            INIT_LIST_HEAD(&dev_info->seg_list);
        }
        list_add_tail(&seg_info->lh, &dev_info->seg_list);
        num_of_segments++;
        i = j;

        if ((buf[j] == '\0') || (buf[j] == '\n'))
            break;
    }

    /* no trailing colon at the end of the input */
    if ((i > 0) && (buf[i-1] == ':')) {
        rc = -ENAMETOOLONG;
        goto seg_list_del;
    }
    strlcpy(local_buf, buf, i + 1);
    dev_info->num_of_segments = num_of_segments;
    rc = dcssblk_is_continuous(dev_info);
    if (rc < 0)
        goto seg_list_del;

    dev_info->start = dcssblk_find_lowest_addr(dev_info);
    dev_info->end = dcssblk_find_highest_addr(dev_info);

    dev_set_name(&dev_info->dev, dev_info->segment_name);
    dev_info->dev.release = dcssblk_release_segment;
    dev_info->dev.groups = dcssblk_dev_attr_groups;
    INIT_LIST_HEAD(&dev_info->lh);
    dev_info->gd = alloc_disk(DCSSBLK_MINORS_PER_DISK);
    if (dev_info->gd == NULL) {
        rc = -ENOMEM;
        goto seg_list_del;
    }
    dev_info->gd->major = dcssblk_major;
    dev_info->gd->fops = &dcssblk_devops;
    dev_info->dcssblk_queue = blk_alloc_queue(GFP_KERNEL);
    dev_info->gd->queue = dev_info->dcssblk_queue;
    dev_info->gd->private_data = dev_info;
    dev_info->gd->driverfs_dev = &dev_info->dev;
    blk_queue_make_request(dev_info->dcssblk_queue, dcssblk_make_request);
    blk_queue_logical_block_size(dev_info->dcssblk_queue, 4096);

    seg_byte_size = (dev_info->end - dev_info->start + 1);
    set_capacity(dev_info->gd, seg_byte_size >> 9); // size in sectors
    pr_info("Loaded %s with total size %lu bytes and capacity %lu "
        "sectors\n", local_buf, seg_byte_size, seg_byte_size >> 9);

    dev_info->save_pending = 0;
    dev_info->is_shared = 1;
    dev_info->dev.parent = dcssblk_root_dev;

    /*
     *get minor, add to list
     */
    down_write(&dcssblk_devices_sem);
    if (dcssblk_get_segment_by_name(local_buf)) {
        rc = -EEXIST;
        goto release_gd;
    }
    rc = dcssblk_assign_free_minor(dev_info);
    if (rc)
        goto release_gd;
    sprintf(dev_info->gd->disk_name, "dcssblk%d",
        dev_info->gd->first_minor);
    list_add_tail(&dev_info->lh, &dcssblk_devices);

    if (!try_module_get(THIS_MODULE)) {
        rc = -ENODEV;
        goto dev_list_del;
    }
    /*
     * register the device
     */
    rc = device_register(&dev_info->dev);
    if (rc)
        goto put_dev;

    get_device(&dev_info->dev);
    add_disk(dev_info->gd);

    switch (dev_info->segment_type) {
        case SEG_TYPE_SR:
        case SEG_TYPE_ER:
        case SEG_TYPE_SC:
            set_disk_ro(dev_info->gd,1);
            break;
        default:
            set_disk_ro(dev_info->gd,0);
            break;
    }
    up_write(&dcssblk_devices_sem);
    rc = count;
    goto out;

put_dev:
    list_del(&dev_info->lh);
    blk_cleanup_queue(dev_info->dcssblk_queue);
    dev_info->gd->queue = NULL;
    put_disk(dev_info->gd);
    list_for_each_entry(seg_info, &dev_info->seg_list, lh) {
        segment_unload(seg_info->segment_name);
    }
    put_device(&dev_info->dev);
    up_write(&dcssblk_devices_sem);
    goto out;
dev_list_del:
    list_del(&dev_info->lh);
release_gd:
    blk_cleanup_queue(dev_info->dcssblk_queue);
    dev_info->gd->queue = NULL;
    put_disk(dev_info->gd);
    up_write(&dcssblk_devices_sem);
seg_list_del:
    if (dev_info == NULL)
        goto out;
    list_for_each_entry_safe(seg_info, temp, &dev_info->seg_list, lh) {
        list_del(&seg_info->lh);
        segment_unload(seg_info->segment_name);
        kfree(seg_info);
    }
    kfree(dev_info);
out:
    kfree(local_buf);
out_nobuf:
    return rc;
}

/*
 * device attribute for removing devices
 */
static ssize_t
dcssblk_remove_store(struct device *dev, struct device_attribute *attr, const char *buf, size_t count)
{
    struct dcssblk_dev_info *dev_info;
    struct segment_info *entry;
    int rc, i;
    char *local_buf;

    if (dev != dcssblk_root_dev) {
        return -EINVAL;
    }
    local_buf = kmalloc(count + 1, GFP_KERNEL);
    if (local_buf == NULL) {
        return -ENOMEM;
    }
    /*
     * parse input
     */
    for (i = 0; ((*(buf+i)!='\0') && (*(buf+i)!='\n') && i < count); i++) {
        local_buf[i] = toupper(buf[i]);
    }
    local_buf[i] = '\0';
    if ((i == 0) || (i > 8)) {
        rc = -ENAMETOOLONG;
        goto out_buf;
    }

    down_write(&dcssblk_devices_sem);
    dev_info = dcssblk_get_device_by_name(local_buf);
    if (dev_info == NULL) {
        up_write(&dcssblk_devices_sem);
        pr_warning("Device %s cannot be removed because it is not a "
               "known device\n", local_buf);
        rc = -ENODEV;
        goto out_buf;
    }
    if (atomic_read(&dev_info->use_count) != 0) {
        up_write(&dcssblk_devices_sem);
        pr_warning("Device %s cannot be removed while it is in "
               "use\n", local_buf);
        rc = -EBUSY;
        goto out_buf;
    }

    list_del(&dev_info->lh);
    del_gendisk(dev_info->gd);
    blk_cleanup_queue(dev_info->dcssblk_queue);
    dev_info->gd->queue = NULL;
    put_disk(dev_info->gd);
    device_unregister(&dev_info->dev);

    /* unload all related segments */
    list_for_each_entry(entry, &dev_info->seg_list, lh)
        segment_unload(entry->segment_name);

    put_device(&dev_info->dev);
    up_write(&dcssblk_devices_sem);

    rc = count;
out_buf:
    kfree(local_buf);
    return rc;
}

static int
dcssblk_open(struct block_device *bdev, fmode_t mode)
{
    struct dcssblk_dev_info *dev_info;
    int rc;

    dev_info = bdev->bd_disk->private_data;
    if (NULL == dev_info) {
        rc = -ENODEV;
        goto out;
    }
    atomic_inc(&dev_info->use_count);
    bdev->bd_block_size = 4096;
    rc = 0;
out:
    return rc;
}

static int
dcssblk_release(struct gendisk *disk, fmode_t mode)
{
    struct dcssblk_dev_info *dev_info = disk->private_data;
    struct segment_info *entry;
    int rc;

    if (!dev_info) {
        rc = -ENODEV;
        goto out;
    }
    down_write(&dcssblk_devices_sem);
    if (atomic_dec_and_test(&dev_info->use_count)
        && (dev_info->save_pending)) {
        pr_info("Device %s has become idle and is being saved "
            "now\n", dev_info->segment_name);
        list_for_each_entry(entry, &dev_info->seg_list, lh) {
            segment_save(entry->segment_name);
        }
        dev_info->save_pending = 0;
    }
    up_write(&dcssblk_devices_sem);
    rc = 0;
out:
    return rc;
}

static void
dcssblk_make_request(struct request_queue *q, struct bio *bio)
{
    struct dcssblk_dev_info *dev_info;
    struct bio_vec *bvec;
    unsigned long index;
    unsigned long page_addr;
    unsigned long source_addr;
    unsigned long bytes_done;
    int i;

    bytes_done = 0;
    dev_info = bio->bi_bdev->bd_disk->private_data;
    if (dev_info == NULL)
        goto fail;
    if ((bio->bi_sector & 7) != 0 || (bio->bi_size & 4095) != 0)
        /* Request is not page-aligned. */
        goto fail;
    if (((bio->bi_size >> 9) + bio->bi_sector)
            > get_capacity(bio->bi_bdev->bd_disk)) {
        /* Request beyond end of DCSS segment. */
        goto fail;
    }
    /* verify data transfer direction */
    if (dev_info->is_shared) {
        switch (dev_info->segment_type) {
        case SEG_TYPE_SR:
        case SEG_TYPE_ER:
        case SEG_TYPE_SC:
            /* cannot write to these segments */
            if (bio_data_dir(bio) == WRITE) {
                pr_warning("Writing to %s failed because it "
                       "is a read-only device\n",
                       dev_name(&dev_info->dev));
                goto fail;
            }
        }
    }

    index = (bio->bi_sector >> 3);
    bio_for_each_segment(bvec, bio, i) {
        page_addr = (unsigned long)
            page_address(bvec->bv_page) + bvec->bv_offset;
        source_addr = dev_info->start + (index<<12) + bytes_done;
        if (unlikely((page_addr & 4095) != 0) || (bvec->bv_len & 4095) != 0)
            // More paranoia.
            goto fail;
        if (bio_data_dir(bio) == READ) {
            memcpy((void*)page_addr, (void*)source_addr,
                bvec->bv_len);
        } else {
            memcpy((void*)source_addr, (void*)page_addr,
                bvec->bv_len);
        }
        bytes_done += bvec->bv_len;
    }
    bio_endio(bio, 0);
    return;
fail:
    bio_io_error(bio);
}

static int
dcssblk_direct_access (struct block_device *bdev, sector_t secnum,
            void **kaddr, unsigned long *pfn)
{
    struct dcssblk_dev_info *dev_info;
    unsigned long pgoff;

    dev_info = bdev->bd_disk->private_data;
    if (!dev_info)
        return -ENODEV;
    if (secnum % (PAGE_SIZE/512))
        return -EINVAL;
    pgoff = secnum / (PAGE_SIZE / 512);
    if ((pgoff+1)*PAGE_SIZE-1 > dev_info->end - dev_info->start)
        return -ERANGE;
    *kaddr = (void *) (dev_info->start+pgoff*PAGE_SIZE);
    *pfn = virt_to_phys(*kaddr) >> PAGE_SHIFT;

    return 0;
}

static void
dcssblk_check_params(void)
{
    int rc, i, j, k;
    char buf[DCSSBLK_PARM_LEN + 1];
    struct dcssblk_dev_info *dev_info;

    for (i = 0; (i < DCSSBLK_PARM_LEN) && (dcssblk_segments[i] != '\0');
         i++) {
        for (j = i; (dcssblk_segments[j] != ',')  &&
                (dcssblk_segments[j] != '\0') &&
                (dcssblk_segments[j] != '(')  &&
                (j < DCSSBLK_PARM_LEN); j++)
        {
            buf[j-i] = dcssblk_segments[j];
        }
        buf[j-i] = '\0';
        rc = dcssblk_add_store(dcssblk_root_dev, NULL, buf, j-i);
        if ((rc >= 0) && (dcssblk_segments[j] == '(')) {
            for (k = 0; (buf[k] != ':') && (buf[k] != '\0'); k++)
                buf[k] = toupper(buf[k]);
            buf[k] = '\0';
            if (!strncmp(&dcssblk_segments[j], "(local)", 7)) {
                down_read(&dcssblk_devices_sem);
                dev_info = dcssblk_get_device_by_name(buf);
                up_read(&dcssblk_devices_sem);
                if (dev_info)
                    dcssblk_shared_store(&dev_info->dev,
                                 NULL, "0\n", 2);
            }
        }
        while ((dcssblk_segments[j] != ',') &&
               (dcssblk_segments[j] != '\0'))
        {
            j++;
        }
        if (dcssblk_segments[j] == '\0')
            break;
        i = j;
    }
}

/*
 * Suspend / Resume
 */
static int dcssblk_freeze(struct device *dev)
{
    struct dcssblk_dev_info *dev_info;
    int rc = 0;

    list_for_each_entry(dev_info, &dcssblk_devices, lh) {
        switch (dev_info->segment_type) {
            case SEG_TYPE_SR:
            case SEG_TYPE_ER:
            case SEG_TYPE_SC:
                if (!dev_info->is_shared)
                    rc = -EINVAL;
                break;
            default:
                rc = -EINVAL;
                break;
        }
        if (rc)
            break;
    }
    if (rc)
        pr_err("Suspending the system failed because DCSS device %s "
               "is writable\n",
               dev_info->segment_name);
    return rc;
}

static int dcssblk_restore(struct device *dev)
{
    struct dcssblk_dev_info *dev_info;
    struct segment_info *entry;
    unsigned long start, end;
    int rc = 0;

    list_for_each_entry(dev_info, &dcssblk_devices, lh) {
        list_for_each_entry(entry, &dev_info->seg_list, lh) {
            segment_unload(entry->segment_name);
            rc = segment_load(entry->segment_name, SEGMENT_SHARED,
                      &start, &end);
            if (rc < 0) {
// TODO in_use check ?
                segment_warning(rc, entry->segment_name);
                goto out_panic;
            }
            if (start != entry->start || end != entry->end) {
                pr_err("The address range of DCSS %s changed "
                       "while the system was suspended\n",
                       entry->segment_name);
                goto out_panic;
            }
        }
    }
    return 0;
out_panic:
    panic("fatal dcssblk resume error\n");
}

static int dcssblk_thaw(struct device *dev)
{
    return 0;
}

static const struct dev_pm_ops dcssblk_pm_ops = {
    .freeze     = dcssblk_freeze,
    .thaw       = dcssblk_thaw,
    .restore    = dcssblk_restore,
};

static struct platform_driver dcssblk_pdrv = {
    .driver = {
        .name   = "dcssblk",
        .owner  = THIS_MODULE,
        .pm = &dcssblk_pm_ops,
    },
};

static struct platform_device *dcssblk_pdev;


/*
 * The init/exit functions.
 */
static void __exit
dcssblk_exit(void)
{
    platform_device_unregister(dcssblk_pdev);
    platform_driver_unregister(&dcssblk_pdrv);
    root_device_unregister(dcssblk_root_dev);
    unregister_blkdev(dcssblk_major, DCSSBLK_NAME);
}

static int __init
dcssblk_init(void)
{
    int rc;

    rc = platform_driver_register(&dcssblk_pdrv);
    if (rc)
        return rc;

    dcssblk_pdev = platform_device_register_simple("dcssblk", -1, NULL,
                            0);
    if (IS_ERR(dcssblk_pdev)) {
        rc = PTR_ERR(dcssblk_pdev);
        goto out_pdrv;
    }

    dcssblk_root_dev = root_device_register("dcssblk");
    if (IS_ERR(dcssblk_root_dev)) {
        rc = PTR_ERR(dcssblk_root_dev);
        goto out_pdev;
    }
    rc = device_create_file(dcssblk_root_dev, &dev_attr_add);
    if (rc)
        goto out_root;
    rc = device_create_file(dcssblk_root_dev, &dev_attr_remove);
    if (rc)
        goto out_root;
    rc = register_blkdev(0, DCSSBLK_NAME);
    if (rc < 0)
        goto out_root;
    dcssblk_major = rc;
    init_rwsem(&dcssblk_devices_sem);

    dcssblk_check_params();
    return 0;

out_root:
    root_device_unregister(dcssblk_root_dev);
out_pdev:
    platform_device_unregister(dcssblk_pdev);
out_pdrv:
    platform_driver_unregister(&dcssblk_pdrv);
    return rc;
}

module_init(dcssblk_init);
module_exit(dcssblk_exit);

module_param_string(segments, dcssblk_segments, DCSSBLK_PARM_LEN, 0444);
MODULE_PARM_DESC(segments, "Name of DCSS segment(s) to be loaded, "
         "comma-separated list, names in each set separated "
         "by commas are separated by colons, each set contains "
         "names of contiguous segments and each name max. 8 chars.\n"
         "Adding \"(local)\" to the end of each set equals echoing 0 "
         "to /sys/devices/dcssblk/<device name>/shared after loading "
         "the contiguous segments - \n"
         "e.g. segments=\"mydcss1,mydcss2:mydcss3,mydcss4(local)\"");

MODULE_LICENSE("GPL");