xref: /openbmc/linux/drivers/block/rnbd/rnbd-srv.c (revision c81cba85)

// SPDX-License-Identifier: GPL-2.0-or-later
/*
 * RDMA Network Block Driver
 *
 * Copyright (c) 2014 - 2018 ProfitBricks GmbH. All rights reserved.
 * Copyright (c) 2018 - 2019 1&1 IONOS Cloud GmbH. All rights reserved.
 * Copyright (c) 2019 - 2020 1&1 IONOS SE. All rights reserved.
 */
#undef pr_fmt
#define pr_fmt(fmt) KBUILD_MODNAME " L" __stringify(__LINE__) ": " fmt

#include <linux/module.h>
#include <linux/blkdev.h>

#include "rnbd-srv.h"
#include "rnbd-srv-dev.h"

MODULE_DESCRIPTION("RDMA Network Block Device Server");
MODULE_LICENSE("GPL");

static u16 port_nr = RTRS_PORT;

module_param_named(port_nr, port_nr, ushort, 0444);
MODULE_PARM_DESC(port_nr,
		 "The port number the server is listening on (default: "
		 __stringify(RTRS_PORT)")");

#define DEFAULT_DEV_SEARCH_PATH "/"

static char dev_search_path[PATH_MAX] = DEFAULT_DEV_SEARCH_PATH;

static int dev_search_path_set(const char *val, const struct kernel_param *kp)
{
	const char *p = strrchr(val, '\n') ? : val + strlen(val);

	if (strlen(val) >= sizeof(dev_search_path))
		return -EINVAL;

	snprintf(dev_search_path, sizeof(dev_search_path), "%.*s",
		 (int)(p - val), val);

	pr_info("dev_search_path changed to '%s'\n", dev_search_path);

	return 0;
}

static struct kparam_string dev_search_path_kparam_str = {
	.maxlen	= sizeof(dev_search_path),
	.string	= dev_search_path
};

static const struct kernel_param_ops dev_search_path_ops = {
	.set	= dev_search_path_set,
	.get	= param_get_string,
};

module_param_cb(dev_search_path, &dev_search_path_ops,
		&dev_search_path_kparam_str, 0444);
MODULE_PARM_DESC(dev_search_path,
		 "Sets the dev_search_path. When a device is mapped this path is prepended to the device path from the map device operation.  If %SESSNAME% is specified in a path, then device will be searched in a session namespace. (default: "
		 DEFAULT_DEV_SEARCH_PATH ")");

static DEFINE_MUTEX(sess_lock);
static DEFINE_SPINLOCK(dev_lock);

static LIST_HEAD(sess_list);
static LIST_HEAD(dev_list);

struct rnbd_io_private {
	struct rtrs_srv_op		*id;
	struct rnbd_srv_sess_dev	*sess_dev;
};

static void rnbd_sess_dev_release(struct kref *kref)
{
	struct rnbd_srv_sess_dev *sess_dev;

	sess_dev = container_of(kref, struct rnbd_srv_sess_dev, kref);
	complete(sess_dev->destroy_comp);
}

static inline void rnbd_put_sess_dev(struct rnbd_srv_sess_dev *sess_dev)
{
	kref_put(&sess_dev->kref, rnbd_sess_dev_release);
}

void rnbd_endio(void *priv, int error)
{
	struct rnbd_io_private *rnbd_priv = priv;
	struct rnbd_srv_sess_dev *sess_dev = rnbd_priv->sess_dev;

	rnbd_put_sess_dev(sess_dev);

	rtrs_srv_resp_rdma(rnbd_priv->id, error);

	kfree(priv);
}

static struct rnbd_srv_sess_dev *
rnbd_get_sess_dev(int dev_id, struct rnbd_srv_session *srv_sess)
{
	struct rnbd_srv_sess_dev *sess_dev;
	int ret = 0;

	rcu_read_lock();
	sess_dev = xa_load(&srv_sess->index_idr, dev_id);
	if (likely(sess_dev))
		ret = kref_get_unless_zero(&sess_dev->kref);
	rcu_read_unlock();

	if (!sess_dev || !ret)
		return ERR_PTR(-ENXIO);

	return sess_dev;
}

static int process_rdma(struct rnbd_srv_session *srv_sess,
			struct rtrs_srv_op *id, void *data, u32 datalen,
			const void *usr, size_t usrlen)
{
	const struct rnbd_msg_io *msg = usr;
	struct rnbd_io_private *priv;
	struct rnbd_srv_sess_dev *sess_dev;
	u32 dev_id;
	int err;
	struct rnbd_dev_blk_io *io;
	struct bio *bio;
	short prio;

	priv = kmalloc(sizeof(*priv), GFP_KERNEL);
	if (!priv)
		return -ENOMEM;

	dev_id = le32_to_cpu(msg->device_id);

	sess_dev = rnbd_get_sess_dev(dev_id, srv_sess);
	if (IS_ERR(sess_dev)) {
		pr_err_ratelimited("Got I/O request on session %s for unknown device id %d\n",
				   srv_sess->sessname, dev_id);
		err = -ENOTCONN;
		goto err;
	}

	priv->sess_dev = sess_dev;
	priv->id = id;

	/* Generate bio with pages pointing to the rdma buffer */
	bio = rnbd_bio_map_kern(data, sess_dev->rnbd_dev->ibd_bio_set, datalen, GFP_KERNEL);
	if (IS_ERR(bio)) {
		err = PTR_ERR(bio);
		rnbd_srv_err(sess_dev, "Failed to generate bio, err: %d\n", err);
		goto sess_dev_put;
	}

	io = container_of(bio, struct rnbd_dev_blk_io, bio);
	io->dev = sess_dev->rnbd_dev;
	io->priv = priv;

	bio->bi_end_io = rnbd_dev_bi_end_io;
	bio->bi_private = io;
	bio->bi_opf = rnbd_to_bio_flags(le32_to_cpu(msg->rw));
	bio->bi_iter.bi_sector = le64_to_cpu(msg->sector);
	bio->bi_iter.bi_size = le32_to_cpu(msg->bi_size);
	prio = srv_sess->ver < RNBD_PROTO_VER_MAJOR ||
	       usrlen < sizeof(*msg) ? 0 : le16_to_cpu(msg->prio);
	bio_set_prio(bio, prio);
	bio_set_dev(bio, sess_dev->rnbd_dev->bdev);

	submit_bio(bio);

	return 0;

sess_dev_put:
	rnbd_put_sess_dev(sess_dev);
err:
	kfree(priv);
	return err;
}

static void destroy_device(struct kref *kref)
{
	struct rnbd_srv_dev *dev = container_of(kref, struct rnbd_srv_dev, kref);

	WARN_ONCE(!list_empty(&dev->sess_dev_list),
		  "Device %s is being destroyed but still in use!\n",
		  dev->id);

	spin_lock(&dev_lock);
	list_del(&dev->list);
	spin_unlock(&dev_lock);

	mutex_destroy(&dev->lock);
	if (dev->dev_kobj.state_in_sysfs)
		/*
		 * Destroy kobj only if it was really created.
		 */
		rnbd_srv_destroy_dev_sysfs(dev);
	else
		kfree(dev);
}

static void rnbd_put_srv_dev(struct rnbd_srv_dev *dev)
{
	kref_put(&dev->kref, destroy_device);
}

void rnbd_destroy_sess_dev(struct rnbd_srv_sess_dev *sess_dev, bool keep_id)
{
	DECLARE_COMPLETION_ONSTACK(dc);

	if (keep_id)
		/* free the resources for the id but don't  */
		/* allow to re-use the id itself because it */
		/* is still used by the client              */
		xa_cmpxchg(&sess_dev->sess->index_idr, sess_dev->device_id,
			   sess_dev, NULL, 0);
	else
		xa_erase(&sess_dev->sess->index_idr, sess_dev->device_id);
	synchronize_rcu();

	sess_dev->destroy_comp = &dc;
	rnbd_put_sess_dev(sess_dev);
	wait_for_completion(&dc); /* wait for inflights to drop to zero */

	rnbd_dev_close(sess_dev->rnbd_dev);
	list_del(&sess_dev->sess_list);
	mutex_lock(&sess_dev->dev->lock);
	list_del(&sess_dev->dev_list);
	if (sess_dev->open_flags & FMODE_WRITE)
		sess_dev->dev->open_write_cnt--;
	mutex_unlock(&sess_dev->dev->lock);

	rnbd_put_srv_dev(sess_dev->dev);

	rnbd_srv_info(sess_dev, "Device closed\n");
	kfree(sess_dev);
}

static void destroy_sess(struct rnbd_srv_session *srv_sess)
{
	struct rnbd_srv_sess_dev *sess_dev, *tmp;

	if (list_empty(&srv_sess->sess_dev_list))
		goto out;

	mutex_lock(&srv_sess->lock);
	list_for_each_entry_safe(sess_dev, tmp, &srv_sess->sess_dev_list,
				 sess_list)
		rnbd_srv_destroy_dev_session_sysfs(sess_dev);
	mutex_unlock(&srv_sess->lock);

out:
	xa_destroy(&srv_sess->index_idr);
	bioset_exit(&srv_sess->sess_bio_set);

	pr_info("RTRS Session %s disconnected\n", srv_sess->sessname);

	mutex_lock(&sess_lock);
	list_del(&srv_sess->list);
	mutex_unlock(&sess_lock);

	mutex_destroy(&srv_sess->lock);
	kfree(srv_sess);
}

static int create_sess(struct rtrs_srv *rtrs)
{
	struct rnbd_srv_session *srv_sess;
	char sessname[NAME_MAX];
	int err;

	err = rtrs_srv_get_sess_name(rtrs, sessname, sizeof(sessname));
	if (err) {
		pr_err("rtrs_srv_get_sess_name(%s): %d\n", sessname, err);

		return err;
	}
	srv_sess = kzalloc(sizeof(*srv_sess), GFP_KERNEL);
	if (!srv_sess)
		return -ENOMEM;

	srv_sess->queue_depth = rtrs_srv_get_queue_depth(rtrs);
	err = bioset_init(&srv_sess->sess_bio_set, srv_sess->queue_depth,
			  offsetof(struct rnbd_dev_blk_io, bio),
			  BIOSET_NEED_BVECS);
	if (err) {
		pr_err("Allocating srv_session for session %s failed\n",
		       sessname);
		kfree(srv_sess);
		return err;
	}

	xa_init_flags(&srv_sess->index_idr, XA_FLAGS_ALLOC);
	INIT_LIST_HEAD(&srv_sess->sess_dev_list);
	mutex_init(&srv_sess->lock);
	mutex_lock(&sess_lock);
	list_add(&srv_sess->list, &sess_list);
	mutex_unlock(&sess_lock);

	srv_sess->rtrs = rtrs;
	strlcpy(srv_sess->sessname, sessname, sizeof(srv_sess->sessname));

	rtrs_srv_set_sess_priv(rtrs, srv_sess);

	return 0;
}

static int rnbd_srv_link_ev(struct rtrs_srv *rtrs,
			     enum rtrs_srv_link_ev ev, void *priv)
{
	struct rnbd_srv_session *srv_sess = priv;

	switch (ev) {
	case RTRS_SRV_LINK_EV_CONNECTED:
		return create_sess(rtrs);

	case RTRS_SRV_LINK_EV_DISCONNECTED:
		if (WARN_ON_ONCE(!srv_sess))
			return -EINVAL;

		destroy_sess(srv_sess);
		return 0;

	default:
		pr_warn("Received unknown RTRS session event %d from session %s\n",
			ev, srv_sess->sessname);
		return -EINVAL;
	}
}

void rnbd_srv_sess_dev_force_close(struct rnbd_srv_sess_dev *sess_dev,
				   struct kobj_attribute *attr)
{
	struct rnbd_srv_session	*sess = sess_dev->sess;

	sess_dev->keep_id = true;
	/* It is already started to close by client's close message. */
	if (!mutex_trylock(&sess->lock))
		return;
	/* first remove sysfs itself to avoid deadlock */
	sysfs_remove_file_self(&sess_dev->kobj, &attr->attr);
	rnbd_srv_destroy_dev_session_sysfs(sess_dev);
	mutex_unlock(&sess->lock);
}

static int process_msg_close(struct rnbd_srv_session *srv_sess,
			     void *data, size_t datalen, const void *usr,
			     size_t usrlen)
{
	const struct rnbd_msg_close *close_msg = usr;
	struct rnbd_srv_sess_dev *sess_dev;

	sess_dev = rnbd_get_sess_dev(le32_to_cpu(close_msg->device_id),
				      srv_sess);
	if (IS_ERR(sess_dev))
		return 0;

	rnbd_put_sess_dev(sess_dev);
	mutex_lock(&srv_sess->lock);
	rnbd_srv_destroy_dev_session_sysfs(sess_dev);
	mutex_unlock(&srv_sess->lock);
	return 0;
}

static int process_msg_open(struct rnbd_srv_session *srv_sess,
			    const void *msg, size_t len,
			    void *data, size_t datalen);

static int process_msg_sess_info(struct rnbd_srv_session *srv_sess,
				 const void *msg, size_t len,
				 void *data, size_t datalen);

static int rnbd_srv_rdma_ev(void *priv,
			    struct rtrs_srv_op *id, int dir,
			    void *data, size_t datalen, const void *usr,
			    size_t usrlen)
{
	struct rnbd_srv_session *srv_sess = priv;
	const struct rnbd_msg_hdr *hdr = usr;
	int ret = 0;
	u16 type;

	if (WARN_ON_ONCE(!srv_sess))
		return -ENODEV;

	type = le16_to_cpu(hdr->type);

	switch (type) {
	case RNBD_MSG_IO:
		return process_rdma(srv_sess, id, data, datalen, usr, usrlen);
	case RNBD_MSG_CLOSE:
		ret = process_msg_close(srv_sess, data, datalen, usr, usrlen);
		break;
	case RNBD_MSG_OPEN:
		ret = process_msg_open(srv_sess, usr, usrlen, data, datalen);
		break;
	case RNBD_MSG_SESS_INFO:
		ret = process_msg_sess_info(srv_sess, usr, usrlen, data,
					    datalen);
		break;
	default:
		pr_warn("Received unexpected message type %d with dir %d from session %s\n",
			type, dir, srv_sess->sessname);
		return -EINVAL;
	}

	rtrs_srv_resp_rdma(id, ret);
	return 0;
}

static struct rnbd_srv_sess_dev
*rnbd_sess_dev_alloc(struct rnbd_srv_session *srv_sess)
{
	struct rnbd_srv_sess_dev *sess_dev;
	int error;

	sess_dev = kzalloc(sizeof(*sess_dev), GFP_KERNEL);
	if (!sess_dev)
		return ERR_PTR(-ENOMEM);

	error = xa_alloc(&srv_sess->index_idr, &sess_dev->device_id, sess_dev,
			 xa_limit_32b, GFP_NOWAIT);
	if (error < 0) {
		pr_warn("Allocating idr failed, err: %d\n", error);
		kfree(sess_dev);
		return ERR_PTR(error);
	}

	return sess_dev;
}

static struct rnbd_srv_dev *rnbd_srv_init_srv_dev(const char *id)
{
	struct rnbd_srv_dev *dev;

	dev = kzalloc(sizeof(*dev), GFP_KERNEL);
	if (!dev)
		return ERR_PTR(-ENOMEM);

	strlcpy(dev->id, id, sizeof(dev->id));
	kref_init(&dev->kref);
	INIT_LIST_HEAD(&dev->sess_dev_list);
	mutex_init(&dev->lock);

	return dev;
}

static struct rnbd_srv_dev *
rnbd_srv_find_or_add_srv_dev(struct rnbd_srv_dev *new_dev)
{
	struct rnbd_srv_dev *dev;

	spin_lock(&dev_lock);
	list_for_each_entry(dev, &dev_list, list) {
		if (!strncmp(dev->id, new_dev->id, sizeof(dev->id))) {
			if (!kref_get_unless_zero(&dev->kref))
				/*
				 * We lost the race, device is almost dead.
				 *  Continue traversing to find a valid one.
				 */
				continue;
			spin_unlock(&dev_lock);
			return dev;
		}
	}
	list_add(&new_dev->list, &dev_list);
	spin_unlock(&dev_lock);

	return new_dev;
}

static int rnbd_srv_check_update_open_perm(struct rnbd_srv_dev *srv_dev,
					    struct rnbd_srv_session *srv_sess,
					    enum rnbd_access_mode access_mode)
{
	int ret = -EPERM;

	mutex_lock(&srv_dev->lock);

	switch (access_mode) {
	case RNBD_ACCESS_RO:
		ret = 0;
		break;
	case RNBD_ACCESS_RW:
		if (srv_dev->open_write_cnt == 0)  {
			srv_dev->open_write_cnt++;
			ret = 0;
		} else {
			pr_err("Mapping device '%s' for session %s with RW permissions failed. Device already opened as 'RW' by %d client(s), access mode %s.\n",
			       srv_dev->id, srv_sess->sessname,
			       srv_dev->open_write_cnt,
			       rnbd_access_mode_str(access_mode));
		}
		break;
	case RNBD_ACCESS_MIGRATION:
		if (srv_dev->open_write_cnt < 2) {
			srv_dev->open_write_cnt++;
			ret = 0;
		} else {
			pr_err("Mapping device '%s' for session %s with migration permissions failed. Device already opened as 'RW' by %d client(s), access mode %s.\n",
			       srv_dev->id, srv_sess->sessname,
			       srv_dev->open_write_cnt,
			       rnbd_access_mode_str(access_mode));
		}
		break;
	default:
		pr_err("Received mapping request for device '%s' on session %s with invalid access mode: %d\n",
		       srv_dev->id, srv_sess->sessname, access_mode);
		ret = -EINVAL;
	}

	mutex_unlock(&srv_dev->lock);

	return ret;
}

static struct rnbd_srv_dev *
rnbd_srv_get_or_create_srv_dev(struct rnbd_dev *rnbd_dev,
				struct rnbd_srv_session *srv_sess,
				enum rnbd_access_mode access_mode)
{
	int ret;
	struct rnbd_srv_dev *new_dev, *dev;

	new_dev = rnbd_srv_init_srv_dev(rnbd_dev->name);
	if (IS_ERR(new_dev))
		return new_dev;

	dev = rnbd_srv_find_or_add_srv_dev(new_dev);
	if (dev != new_dev)
		kfree(new_dev);

	ret = rnbd_srv_check_update_open_perm(dev, srv_sess, access_mode);
	if (ret) {
		rnbd_put_srv_dev(dev);
		return ERR_PTR(ret);
	}

	return dev;
}

static void rnbd_srv_fill_msg_open_rsp(struct rnbd_msg_open_rsp *rsp,
					struct rnbd_srv_sess_dev *sess_dev)
{
	struct rnbd_dev *rnbd_dev = sess_dev->rnbd_dev;
	struct request_queue *q = bdev_get_queue(rnbd_dev->bdev);

	rsp->hdr.type = cpu_to_le16(RNBD_MSG_OPEN_RSP);
	rsp->device_id =
		cpu_to_le32(sess_dev->device_id);
	rsp->nsectors =
		cpu_to_le64(get_capacity(rnbd_dev->bdev->bd_disk));
	rsp->logical_block_size	=
		cpu_to_le16(bdev_logical_block_size(rnbd_dev->bdev));
	rsp->physical_block_size =
		cpu_to_le16(bdev_physical_block_size(rnbd_dev->bdev));
	rsp->max_segments =
		cpu_to_le16(rnbd_dev_get_max_segs(rnbd_dev));
	rsp->max_hw_sectors =
		cpu_to_le32(rnbd_dev_get_max_hw_sects(rnbd_dev));
	rsp->max_write_same_sectors =
		cpu_to_le32(bdev_write_same(rnbd_dev->bdev));
	rsp->max_discard_sectors =
		cpu_to_le32(rnbd_dev_get_max_discard_sects(rnbd_dev));
	rsp->discard_granularity =
		cpu_to_le32(rnbd_dev_get_discard_granularity(rnbd_dev));
	rsp->discard_alignment =
		cpu_to_le32(rnbd_dev_get_discard_alignment(rnbd_dev));
	rsp->secure_discard =
		cpu_to_le16(rnbd_dev_get_secure_discard(rnbd_dev));
	rsp->rotational = !blk_queue_nonrot(q);
	rsp->cache_policy = 0;
	if (test_bit(QUEUE_FLAG_WC, &q->queue_flags))
		rsp->cache_policy |= RNBD_WRITEBACK;
	if (blk_queue_fua(q))
		rsp->cache_policy |= RNBD_FUA;
}

static struct rnbd_srv_sess_dev *
rnbd_srv_create_set_sess_dev(struct rnbd_srv_session *srv_sess,
			      const struct rnbd_msg_open *open_msg,
			      struct rnbd_dev *rnbd_dev, fmode_t open_flags,
			      struct rnbd_srv_dev *srv_dev)
{
	struct rnbd_srv_sess_dev *sdev = rnbd_sess_dev_alloc(srv_sess);

	if (IS_ERR(sdev))
		return sdev;

	kref_init(&sdev->kref);

	strlcpy(sdev->pathname, open_msg->dev_name, sizeof(sdev->pathname));

	sdev->rnbd_dev		= rnbd_dev;
	sdev->sess		= srv_sess;
	sdev->dev		= srv_dev;
	sdev->open_flags	= open_flags;
	sdev->access_mode	= open_msg->access_mode;

	return sdev;
}

static char *rnbd_srv_get_full_path(struct rnbd_srv_session *srv_sess,
				     const char *dev_name)
{
	char *full_path;
	char *a, *b;

	full_path = kmalloc(PATH_MAX, GFP_KERNEL);
	if (!full_path)
		return ERR_PTR(-ENOMEM);

	/*
	 * Replace %SESSNAME% with a real session name in order to
	 * create device namespace.
	 */
	a = strnstr(dev_search_path, "%SESSNAME%", sizeof(dev_search_path));
	if (a) {
		int len = a - dev_search_path;

		len = snprintf(full_path, PATH_MAX, "%.*s/%s/%s", len,
			       dev_search_path, srv_sess->sessname, dev_name);
		if (len >= PATH_MAX) {
			pr_err("Too long path: %s, %s, %s\n",
			       dev_search_path, srv_sess->sessname, dev_name);
			kfree(full_path);
			return ERR_PTR(-EINVAL);
		}
	} else {
		snprintf(full_path, PATH_MAX, "%s/%s",
			 dev_search_path, dev_name);
	}

	/* eliminitate duplicated slashes */
	a = strchr(full_path, '/');
	b = a;
	while (*b != '\0') {
		if (*b == '/' && *a == '/') {
			b++;
		} else {
			a++;
			*a = *b;
			b++;
		}
	}
	a++;
	*a = '\0';

	return full_path;
}

static int process_msg_sess_info(struct rnbd_srv_session *srv_sess,
				 const void *msg, size_t len,
				 void *data, size_t datalen)
{
	const struct rnbd_msg_sess_info *sess_info_msg = msg;
	struct rnbd_msg_sess_info_rsp *rsp = data;

	srv_sess->ver = min_t(u8, sess_info_msg->ver, RNBD_PROTO_VER_MAJOR);
	pr_debug("Session %s using protocol version %d (client version: %d, server version: %d)\n",
		 srv_sess->sessname, srv_sess->ver,
		 sess_info_msg->ver, RNBD_PROTO_VER_MAJOR);

	rsp->hdr.type = cpu_to_le16(RNBD_MSG_SESS_INFO_RSP);
	rsp->ver = srv_sess->ver;

	return 0;
}

/**
 * find_srv_sess_dev() - a dev is already opened by this name
 * @srv_sess:	the session to search.
 * @dev_name:	string containing the name of the device.
 *
 * Return struct rnbd_srv_sess_dev if srv_sess already opened the dev_name
 * NULL if the session didn't open the device yet.
 */
static struct rnbd_srv_sess_dev *
find_srv_sess_dev(struct rnbd_srv_session *srv_sess, const char *dev_name)
{
	struct rnbd_srv_sess_dev *sess_dev;

	if (list_empty(&srv_sess->sess_dev_list))
		return NULL;

	list_for_each_entry(sess_dev, &srv_sess->sess_dev_list, sess_list)
		if (!strcmp(sess_dev->pathname, dev_name))
			return sess_dev;

	return NULL;
}

static int process_msg_open(struct rnbd_srv_session *srv_sess,
			    const void *msg, size_t len,
			    void *data, size_t datalen)
{
	int ret;
	struct rnbd_srv_dev *srv_dev;
	struct rnbd_srv_sess_dev *srv_sess_dev;
	const struct rnbd_msg_open *open_msg = msg;
	fmode_t open_flags;
	char *full_path;
	struct rnbd_dev *rnbd_dev;
	struct rnbd_msg_open_rsp *rsp = data;

	pr_debug("Open message received: session='%s' path='%s' access_mode=%d\n",
		 srv_sess->sessname, open_msg->dev_name,
		 open_msg->access_mode);
	open_flags = FMODE_READ;
	if (open_msg->access_mode != RNBD_ACCESS_RO)
		open_flags |= FMODE_WRITE;

	mutex_lock(&srv_sess->lock);

	srv_sess_dev = find_srv_sess_dev(srv_sess, open_msg->dev_name);
	if (srv_sess_dev)
		goto fill_response;

	if ((strlen(dev_search_path) + strlen(open_msg->dev_name))
	    >= PATH_MAX) {
		pr_err("Opening device for session %s failed, device path too long. '%s/%s' is longer than PATH_MAX (%d)\n",
		       srv_sess->sessname, dev_search_path, open_msg->dev_name,
		       PATH_MAX);
		ret = -EINVAL;
		goto reject;
	}
	if (strstr(open_msg->dev_name, "..")) {
		pr_err("Opening device for session %s failed, device path %s contains relative path ..\n",
		       srv_sess->sessname, open_msg->dev_name);
		ret = -EINVAL;
		goto reject;
	}
	full_path = rnbd_srv_get_full_path(srv_sess, open_msg->dev_name);
	if (IS_ERR(full_path)) {
		ret = PTR_ERR(full_path);
		pr_err("Opening device '%s' for client %s failed, failed to get device full path, err: %d\n",
		       open_msg->dev_name, srv_sess->sessname, ret);
		goto reject;
	}

	rnbd_dev = rnbd_dev_open(full_path, open_flags,
				 &srv_sess->sess_bio_set);
	if (IS_ERR(rnbd_dev)) {
		pr_err("Opening device '%s' on session %s failed, failed to open the block device, err: %ld\n",
		       full_path, srv_sess->sessname, PTR_ERR(rnbd_dev));
		ret = PTR_ERR(rnbd_dev);
		goto free_path;
	}

	srv_dev = rnbd_srv_get_or_create_srv_dev(rnbd_dev, srv_sess,
						  open_msg->access_mode);
	if (IS_ERR(srv_dev)) {
		pr_err("Opening device '%s' on session %s failed, creating srv_dev failed, err: %ld\n",
		       full_path, srv_sess->sessname, PTR_ERR(srv_dev));
		ret = PTR_ERR(srv_dev);
		goto rnbd_dev_close;
	}

	srv_sess_dev = rnbd_srv_create_set_sess_dev(srv_sess, open_msg,
						     rnbd_dev, open_flags,
						     srv_dev);
	if (IS_ERR(srv_sess_dev)) {
		pr_err("Opening device '%s' on session %s failed, creating sess_dev failed, err: %ld\n",
		       full_path, srv_sess->sessname, PTR_ERR(srv_sess_dev));
		ret = PTR_ERR(srv_sess_dev);
		goto srv_dev_put;
	}

	/* Create the srv_dev sysfs files if they haven't been created yet. The
	 * reason to delay the creation is not to create the sysfs files before
	 * we are sure the device can be opened.
	 */
	mutex_lock(&srv_dev->lock);
	if (!srv_dev->dev_kobj.state_in_sysfs) {
		ret = rnbd_srv_create_dev_sysfs(srv_dev, rnbd_dev->bdev,
						 rnbd_dev->name);
		if (ret) {
			mutex_unlock(&srv_dev->lock);
			rnbd_srv_err(srv_sess_dev,
				      "Opening device failed, failed to create device sysfs files, err: %d\n",
				      ret);
			goto free_srv_sess_dev;
		}
	}

	ret = rnbd_srv_create_dev_session_sysfs(srv_sess_dev);
	if (ret) {
		mutex_unlock(&srv_dev->lock);
		rnbd_srv_err(srv_sess_dev,
			      "Opening device failed, failed to create dev client sysfs files, err: %d\n",
			      ret);
		goto free_srv_sess_dev;
	}

	list_add(&srv_sess_dev->dev_list, &srv_dev->sess_dev_list);
	mutex_unlock(&srv_dev->lock);

	list_add(&srv_sess_dev->sess_list, &srv_sess->sess_dev_list);

	rnbd_srv_info(srv_sess_dev, "Opened device '%s'\n", srv_dev->id);

	kfree(full_path);

fill_response:
	rnbd_srv_fill_msg_open_rsp(rsp, srv_sess_dev);
	mutex_unlock(&srv_sess->lock);
	return 0;

free_srv_sess_dev:
	xa_erase(&srv_sess->index_idr, srv_sess_dev->device_id);
	synchronize_rcu();
	kfree(srv_sess_dev);
srv_dev_put:
	if (open_msg->access_mode != RNBD_ACCESS_RO) {
		mutex_lock(&srv_dev->lock);
		srv_dev->open_write_cnt--;
		mutex_unlock(&srv_dev->lock);
	}
	rnbd_put_srv_dev(srv_dev);
rnbd_dev_close:
	rnbd_dev_close(rnbd_dev);
free_path:
	kfree(full_path);
reject:
	mutex_unlock(&srv_sess->lock);
	return ret;
}

static struct rtrs_srv_ctx *rtrs_ctx;

static struct rtrs_srv_ops rtrs_ops;
static int __init rnbd_srv_init_module(void)
{
	int err;

	BUILD_BUG_ON(sizeof(struct rnbd_msg_hdr) != 4);
	BUILD_BUG_ON(sizeof(struct rnbd_msg_sess_info) != 36);
	BUILD_BUG_ON(sizeof(struct rnbd_msg_sess_info_rsp) != 36);
	BUILD_BUG_ON(sizeof(struct rnbd_msg_open) != 264);
	BUILD_BUG_ON(sizeof(struct rnbd_msg_close) != 8);
	BUILD_BUG_ON(sizeof(struct rnbd_msg_open_rsp) != 56);
	rtrs_ops = (struct rtrs_srv_ops) {
		.rdma_ev = rnbd_srv_rdma_ev,
		.link_ev = rnbd_srv_link_ev,
	};
	rtrs_ctx = rtrs_srv_open(&rtrs_ops, port_nr);
	if (IS_ERR(rtrs_ctx)) {
		err = PTR_ERR(rtrs_ctx);
		pr_err("rtrs_srv_open(), err: %d\n", err);
		return err;
	}

	err = rnbd_srv_create_sysfs_files();
	if (err) {
		pr_err("rnbd_srv_create_sysfs_files(), err: %d\n", err);
		rtrs_srv_close(rtrs_ctx);
		return err;
	}

	return 0;
}

static void __exit rnbd_srv_cleanup_module(void)
{
	rtrs_srv_close(rtrs_ctx);
	WARN_ON(!list_empty(&sess_list));
	rnbd_srv_destroy_sysfs_files();
}

module_init(rnbd_srv_init_module);
module_exit(rnbd_srv_cleanup_module);