drivers/s390/block/dcssblk.c

// SPDX-License-Identifier: GPL-2.0
/*
 * dcssblk.c -- the S/390 block driver for dcss memory
 *
 * Authors: Carsten Otte, Stefan Weinhuber, Gerald Schaefer
 */

#define pr_fmt(fmt) "dcssblk: " 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/uio.h>
#include <linux/dax.h>
#include <linux/io.h>
#include <asm/extmem.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 gendisk *disk, blk_mode_t mode);
static void dcssblk_release(struct gendisk *disk);
static void dcssblk_submit_bio(struct bio *bio);
static long dcssblk_dax_direct_access(struct dax_device *dax_dev, pgoff_t pgoff,
		long nr_pages, enum dax_access_mode mode, 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,
	.submit_bio	= dcssblk_submit_bio,
	.open    	= dcssblk_open,
	.release 	= dcssblk_release,
};

static int dcssblk_dax_zero_page_range(struct dax_device *dax_dev,
				       pgoff_t pgoff, size_t nr_pages)
{
	long rc;
	void *kaddr;

	rc = dax_direct_access(dax_dev, pgoff, nr_pages, DAX_ACCESS,
			&kaddr, NULL);
	if (rc < 0)
		return dax_mem2blk_err(rc);

	memset(kaddr, 0, nr_pages << PAGE_SHIFT);
	dax_flush(dax_dev, kaddr, nr_pages << PAGE_SHIFT);
	return 0;
}

static const struct dax_operations dcssblk_dax_ops = {
	.direct_access = dcssblk_dax_direct_access,
	.zero_page_range = dcssblk_dax_zero_page_range,
};

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;
	int num_of_segments;
	struct list_head seg_list;
	struct dax_device *dax_dev;
	struct dev_pagemap pgmap;
	void *pgmap_addr;
};

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_objs(struct segment_info, dev_info->num_of_segments);
	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_obj(struct segment_info);
	if (*seg_info == NULL)
		return -ENOMEM;

	strscpy((*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;
}

/*
 * 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 sysfs_emit(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);
	up_write(&dcssblk_devices_sem);

	dax_remove_host(dev_info->gd);
	kill_dax(dev_info->dax_dev);
	put_dax(dev_info->dax_dev);
	if (dev_info->pgmap_addr)
		devm_memunmap_pages(&dev_info->dev, &dev_info->pgmap);
	del_gendisk(dev_info->gd);
	put_disk(dev_info->gd);

	if (device_remove_file_self(dev, attr)) {
		device_unregister(dev);
		put_device(dev);
	}
	return rc;
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 sysfs_emit(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) {
				if (entry->segment_type == SEG_TYPE_EN ||
				    entry->segment_type == SEG_TYPE_SN)
					pr_warn("DCSS %s is of type SN or EN"
						" and cannot be saved\n",
						entry->segment_name);
				else
					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)
{
	struct dcssblk_dev_info *dev_info;
	struct segment_info *entry;
	int i;

	i = 0;
	down_read(&dcssblk_devices_sem);
	dev_info = container_of(dev, struct dcssblk_dev_info, dev);
	list_for_each_entry(entry, &dev_info->seg_list, lh)
		i += sysfs_emit_at(buf, i, "%s\n", entry->segment_name);
	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,
};

static int dcssblk_setup_dax(struct dcssblk_dev_info *dev_info)
{
	struct dax_device *dax_dev;

	dax_dev = alloc_dax(dev_info, &dcssblk_dax_ops);
	if (IS_ERR(dax_dev))
		return PTR_ERR(dax_dev);
	set_dax_synchronous(dax_dev);
	dev_info->dax_dev = dax_dev;
	return dax_add_host(dev_info->dax_dev, dev_info->gd);
}

/*
 * device attribute for adding devices
 */
static ssize_t
dcssblk_add_store(struct device *dev, struct device_attribute *attr, const char *buf, size_t count)
{
	struct queue_limits lim = {
		.logical_block_size	= 4096,
		.features		= BLK_FEAT_DAX,
	};
	int rc, i, j, num_of_segments;
	struct dcssblk_dev_info *dev_info;
	struct segment_info *seg_info, *temp;
	char *local_buf;
	void *addr;
	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; (i < count && (buf[i] != '\0') && (buf[i] != '\n')); i++) {
		for (j = i; j < count &&
			(buf[j] != ':') &&
			(buf[j] != '\0') &&
			(buf[j] != '\n'); 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_obj(struct dcssblk_dev_info);
			if (dev_info == NULL) {
				rc = -ENOMEM;
				goto out;
			}
			strscpy(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;
	}
	strscpy(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, "%s", 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 = blk_alloc_disk(&lim, NUMA_NO_NODE);
	if (IS_ERR(dev_info->gd)) {
		rc = PTR_ERR(dev_info->gd);
		goto seg_list_del;
	}
	dev_info->gd->major = dcssblk_major;
	dev_info->gd->minors = DCSSBLK_MINORS_PER_DISK;
	dev_info->gd->fops = &dcssblk_devops;
	dev_info->gd->private_data = dev_info;
	dev_info->gd->flags |= GENHD_FL_NO_PART;

	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;
	scnprintf(dev_info->gd->disk_name, sizeof(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;

	if (!IS_ALIGNED(dev_info->start, SUBSECTION_SIZE) ||
	    !IS_ALIGNED(dev_info->end + 1, SUBSECTION_SIZE)) {
		pr_info("DCSS %s is not aligned to %lu bytes, DAX support disabled\n",
			local_buf, SUBSECTION_SIZE);
	} else {
		dev_info->pgmap.type		= MEMORY_DEVICE_FS_DAX;
		dev_info->pgmap.range.start	= dev_info->start;
		dev_info->pgmap.range.end	= dev_info->end;
		dev_info->pgmap.nr_range	= 1;
		addr = devm_memremap_pages(&dev_info->dev, &dev_info->pgmap);
		if (IS_ERR(addr)) {
			rc = PTR_ERR(addr);
			goto put_dev;
		}
		dev_info->pgmap_addr = addr;
		rc = dcssblk_setup_dax(dev_info);
		if (rc)
			goto out_dax;
		pr_info("DAX support enabled for DCSS %s\n", local_buf);
	}

	get_device(&dev_info->dev);
	rc = device_add_disk(&dev_info->dev, dev_info->gd, NULL);
	if (rc)
		goto out_dax_host;

	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;

out_dax_host:
	put_device(&dev_info->dev);
	dax_remove_host(dev_info->gd);
out_dax:
	kill_dax(dev_info->dax_dev);
	put_dax(dev_info->dax_dev);
	if (dev_info->pgmap_addr)
		devm_memunmap_pages(&dev_info->dev, &dev_info->pgmap);
put_dev:
	list_del(&dev_info->lh);
	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:
	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; (i < count && (*(buf+i)!='\0') && (*(buf+i)!='\n')); 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_warn("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_warn("Device %s cannot be removed while it is in use\n",
			local_buf);
		rc = -EBUSY;
		goto out_buf;
	}

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

	dax_remove_host(dev_info->gd);
	kill_dax(dev_info->dax_dev);
	put_dax(dev_info->dax_dev);
	if (dev_info->pgmap_addr)
		devm_memunmap_pages(&dev_info->dev, &dev_info->pgmap);
	del_gendisk(dev_info->gd);
	put_disk(dev_info->gd);

	device_unregister(&dev_info->dev);
	put_device(&dev_info->dev);

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

static int
dcssblk_open(struct gendisk *disk, blk_mode_t mode)
{
	struct dcssblk_dev_info *dev_info = disk->private_data;
	int rc;

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

static void
dcssblk_release(struct gendisk *disk)
{
	struct dcssblk_dev_info *dev_info = disk->private_data;
	struct segment_info *entry;

	if (!dev_info) {
		WARN_ON(1);
		return;
	}
	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) {
			if (entry->segment_type == SEG_TYPE_EN ||
			    entry->segment_type == SEG_TYPE_SN)
				pr_warn("DCSS %s is of type SN or EN and cannot"
					" be saved\n", entry->segment_name);
			else
				segment_save(entry->segment_name);
		}
		dev_info->save_pending = 0;
	}
	up_write(&dcssblk_devices_sem);
}

static void
dcssblk_submit_bio(struct bio *bio)
{
	struct dcssblk_dev_info *dev_info;
	struct bio_vec bvec;
	struct bvec_iter iter;
	unsigned long index;
	void *page_addr;
	unsigned long source_addr;
	unsigned long bytes_done;

	bytes_done = 0;
	dev_info = bio->bi_bdev->bd_disk->private_data;
	if (dev_info == NULL)
		goto fail;
	if (!IS_ALIGNED(bio->bi_iter.bi_sector, 8) ||
	    !IS_ALIGNED(bio->bi_iter.bi_size, PAGE_SIZE))
		/* Request is not page-aligned. */
		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_warn("Writing to %s failed because it is a read-only device\n",
					dev_name(&dev_info->dev));
				goto fail;
			}
		}
	}

	index = (bio->bi_iter.bi_sector >> 3);
	bio_for_each_segment(bvec, bio, iter) {
		page_addr = bvec_virt(&bvec);
		source_addr = dev_info->start + (index<<12) + bytes_done;
		if (unlikely(!IS_ALIGNED((unsigned long)page_addr, PAGE_SIZE) ||
			     !IS_ALIGNED(bvec.bv_len, PAGE_SIZE)))
			// More paranoia.
			goto fail;
		if (bio_data_dir(bio) == READ)
			memcpy(page_addr, __va(source_addr), bvec.bv_len);
		else
			memcpy(__va(source_addr), page_addr, bvec.bv_len);
		bytes_done += bvec.bv_len;
	}
	bio_endio(bio);
	return;
fail:
	bio_io_error(bio);
}

static long
__dcssblk_direct_access(struct dcssblk_dev_info *dev_info, pgoff_t pgoff,
		long nr_pages, void **kaddr, unsigned long *pfn)
{
	resource_size_t offset = pgoff * PAGE_SIZE;
	unsigned long dev_sz;

	dev_sz = dev_info->end - dev_info->start + 1;
	if (kaddr)
		*kaddr = __va(dev_info->start + offset);
	if (pfn)
		*pfn = PFN_DOWN(dev_info->start + offset);

	return (dev_sz - offset) / PAGE_SIZE;
}

static long
dcssblk_dax_direct_access(struct dax_device *dax_dev, pgoff_t pgoff,
		long nr_pages, enum dax_access_mode mode, void **kaddr,
		unsigned long *pfn)
{
	struct dcssblk_dev_info *dev_info = dax_get_private(dax_dev);

	return __dcssblk_direct_access(dev_info, pgoff, nr_pages, kaddr, pfn);
}

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; (j < DCSSBLK_PARM_LEN) &&
			    (dcssblk_segments[j] != ',')  &&
			    (dcssblk_segments[j] != '\0') &&
			    (dcssblk_segments[j] != '('); 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;
	}
}

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

static int __init
dcssblk_init(void)
{
	int rc;

	dcssblk_root_dev = root_device_register("dcssblk");
	if (IS_ERR(dcssblk_root_dev))
		return PTR_ERR(dcssblk_root_dev);
	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);

	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_DESCRIPTION("S/390 block driver for DCSS memory");
MODULE_LICENSE("GPL");