// SPDX-License-Identifier: GPL-2.0-or-later
/*
 * Network block device - make block devices work over TCP
 *
 * Note that you can not swap over this thing, yet. Seems to work but
 * deadlocks sometimes - you can not swap over TCP in general.
 * 
 * Copyright 1997-2000, 2008 Pavel Machek <pavel@ucw.cz>
 * Parts copyright 2001 Steven Whitehouse <steve@chygwyn.com>
 *
 * (part of code stolen from loop.c)
 */

#include <linux/major.h>

#include <linux/blkdev.h>
#include <linux/module.h>
#include <linux/init.h>
#include <linux/sched.h>
#include <linux/sched/mm.h>
#include <linux/fs.h>
#include <linux/bio.h>
#include <linux/stat.h>
#include <linux/errno.h>
#include <linux/file.h>
#include <linux/ioctl.h>
#include <linux/mutex.h>
#include <linux/compiler.h>
#include <linux/completion.h>
#include <linux/err.h>
#include <linux/kernel.h>
#include <linux/slab.h>
#include <net/sock.h>
#include <linux/net.h>
#include <linux/kthread.h>
#include <linux/types.h>
#include <linux/debugfs.h>
#include <linux/blk-mq.h>

#include <linux/uaccess.h>
#include <asm/types.h>

#include <linux/nbd.h>
#include <linux/nbd-netlink.h>
#include <net/genetlink.h>

#define CREATE_TRACE_POINTS
#include <trace/events/nbd.h>

static DEFINE_IDR(nbd_index_idr);
static DEFINE_MUTEX(nbd_index_mutex);
static int nbd_total_devices = 0;

struct nbd_sock {
        struct socket *sock;
        struct mutex tx_lock;
        struct request *pending;
        int sent;
        bool dead;
        int fallback_index;
        int cookie;
};

struct recv_thread_args {
        struct work_struct work;
        struct nbd_device *nbd;
        int index;
};

struct link_dead_args {
        struct work_struct work;
        int index;
};

#define NBD_RT_TIMEDOUT                 0
#define NBD_RT_DISCONNECT_REQUESTED     1
#define NBD_RT_DISCONNECTED             2
#define NBD_RT_HAS_PID_FILE             3
#define NBD_RT_HAS_CONFIG_REF           4
#define NBD_RT_BOUND                    5
#define NBD_RT_DISCONNECT_ON_CLOSE      6
#define NBD_RT_HAS_BACKEND_FILE         7

#define NBD_DESTROY_ON_DISCONNECT       0
#define NBD_DISCONNECT_REQUESTED        1

struct nbd_config {
        u32 flags;
        unsigned long runtime_flags;
        u64 dead_conn_timeout;

        struct nbd_sock **socks;
        int num_connections;
        atomic_t live_connections;
        wait_queue_head_t conn_wait;

        atomic_t recv_threads;
        wait_queue_head_t recv_wq;
        loff_t blksize;
        loff_t bytesize;
#if IS_ENABLED(CONFIG_DEBUG_FS)
        struct dentry *dbg_dir;
#endif
};

struct nbd_device {
        struct blk_mq_tag_set tag_set;

        int index;
        refcount_t config_refs;
        refcount_t refs;
        struct nbd_config *config;
        struct mutex config_lock;
        struct gendisk *disk;
        struct workqueue_struct *recv_workq;

        struct list_head list;
        struct task_struct *task_recv;
        struct task_struct *task_setup;

        struct completion *destroy_complete;
        unsigned long flags;

        char *backend;
};

#define NBD_CMD_REQUEUED        1

struct nbd_cmd {
        struct nbd_device *nbd;
        struct mutex lock;
        int index;
        int cookie;
        int retries;
        blk_status_t status;
        unsigned long flags;
        u32 cmd_cookie;
};

#if IS_ENABLED(CONFIG_DEBUG_FS)
static struct dentry *nbd_dbg_dir;
#endif

#define nbd_name(nbd) ((nbd)->disk->disk_name)

#define NBD_MAGIC 0x68797548

#define NBD_DEF_BLKSIZE 1024

static unsigned int nbds_max = 16;
static int max_part = 16;
static int part_shift;

static int nbd_dev_dbg_init(struct nbd_device *nbd);
static void nbd_dev_dbg_close(struct nbd_device *nbd);
static void nbd_config_put(struct nbd_device *nbd);
static void nbd_connect_reply(struct genl_info *info, int index);
static int nbd_genl_status(struct sk_buff *skb, struct genl_info *info);
static void nbd_dead_link_work(struct work_struct *work);
static void nbd_disconnect_and_put(struct nbd_device *nbd);

static inline struct device *nbd_to_dev(struct nbd_device *nbd)
{
        return disk_to_dev(nbd->disk);
}

static void nbd_requeue_cmd(struct nbd_cmd *cmd)
{
        struct request *req = blk_mq_rq_from_pdu(cmd);

        if (!test_and_set_bit(NBD_CMD_REQUEUED, &cmd->flags))
                blk_mq_requeue_request(req, true);
}

#define NBD_COOKIE_BITS 32

static u64 nbd_cmd_handle(struct nbd_cmd *cmd)
{
        struct request *req = blk_mq_rq_from_pdu(cmd);
        u32 tag = blk_mq_unique_tag(req);
        u64 cookie = cmd->cmd_cookie;

        return (cookie << NBD_COOKIE_BITS) | tag;
}

static u32 nbd_handle_to_tag(u64 handle)
{
        return (u32)handle;
}

static u32 nbd_handle_to_cookie(u64 handle)
{
        return (u32)(handle >> NBD_COOKIE_BITS);
}

static const char *nbdcmd_to_ascii(int cmd)
{
        switch (cmd) {
        case  NBD_CMD_READ: return "read";
        case NBD_CMD_WRITE: return "write";
        case  NBD_CMD_DISC: return "disconnect";
        case NBD_CMD_FLUSH: return "flush";
        case  NBD_CMD_TRIM: return "trim/discard";
        }
        return "invalid";
}

static ssize_t pid_show(struct device *dev,
                        struct device_attribute *attr, char *buf)
{
        struct gendisk *disk = dev_to_disk(dev);
        struct nbd_device *nbd = (struct nbd_device *)disk->private_data;

        return sprintf(buf, "%d\n", task_pid_nr(nbd->task_recv));
}

static const struct device_attribute pid_attr = {
        .attr = { .name = "pid", .mode = 0444},
        .show = pid_show,
};

static ssize_t backend_show(struct device *dev,
                struct device_attribute *attr, char *buf)
{
        struct gendisk *disk = dev_to_disk(dev);
        struct nbd_device *nbd = (struct nbd_device *)disk->private_data;

        return sprintf(buf, "%s\n", nbd->backend ?: "");
}

static const struct device_attribute backend_attr = {
        .attr = { .name = "backend", .mode = 0444},
        .show = backend_show,
};

static void nbd_dev_remove(struct nbd_device *nbd)
{
        struct gendisk *disk = nbd->disk;

        if (disk) {
                del_gendisk(disk);
                blk_cleanup_disk(disk);
                blk_mq_free_tag_set(&nbd->tag_set);
        }

        /*
         * Place this in the last just before the nbd is freed to
         * make sure that the disk and the related kobject are also
         * totally removed to avoid duplicate creation of the same
         * one.
         */
        if (test_bit(NBD_DESTROY_ON_DISCONNECT, &nbd->flags) && nbd->destroy_complete)
                complete(nbd->destroy_complete);

        kfree(nbd);
}

static void nbd_put(struct nbd_device *nbd)
{
        if (refcount_dec_and_mutex_lock(&nbd->refs,
                                        &nbd_index_mutex)) {
                idr_remove(&nbd_index_idr, nbd->index);
                nbd_dev_remove(nbd);
                mutex_unlock(&nbd_index_mutex);
        }
}

static int nbd_disconnected(struct nbd_config *config)
{
        return test_bit(NBD_RT_DISCONNECTED, &config->runtime_flags) ||
                test_bit(NBD_RT_DISCONNECT_REQUESTED, &config->runtime_flags);
}

static void nbd_mark_nsock_dead(struct nbd_device *nbd, struct nbd_sock *nsock,
                                int notify)
{
        if (!nsock->dead && notify && !nbd_disconnected(nbd->config)) {
                struct link_dead_args *args;
                args = kmalloc(sizeof(struct link_dead_args), GFP_NOIO);
                if (args) {
                        INIT_WORK(&args->work, nbd_dead_link_work);
                        args->index = nbd->index;
                        queue_work(system_wq, &args->work);
                }
        }
        if (!nsock->dead) {
                kernel_sock_shutdown(nsock->sock, SHUT_RDWR);
                if (atomic_dec_return(&nbd->config->live_connections) == 0) {
                        if (test_and_clear_bit(NBD_RT_DISCONNECT_REQUESTED,
                                               &nbd->config->runtime_flags)) {
                                set_bit(NBD_RT_DISCONNECTED,
                                        &nbd->config->runtime_flags);
                                dev_info(nbd_to_dev(nbd),
                                        "Disconnected due to user request.\n");
                        }
                }
        }
        nsock->dead = true;
        nsock->pending = NULL;
        nsock->sent = 0;
}

static void nbd_size_clear(struct nbd_device *nbd)
{
        if (nbd->config->bytesize) {
                set_capacity(nbd->disk, 0);
                kobject_uevent(&nbd_to_dev(nbd)->kobj, KOBJ_CHANGE);
        }
}

static int nbd_set_size(struct nbd_device *nbd, loff_t bytesize,
                loff_t blksize)
{
        if (!blksize)
                blksize = NBD_DEF_BLKSIZE;
        if (blksize < 512 || blksize > PAGE_SIZE || !is_power_of_2(blksize))
                return -EINVAL;

        nbd->config->bytesize = bytesize;
        nbd->config->blksize = blksize;

        if (!nbd->task_recv)
                return 0;

        if (nbd->config->flags & NBD_FLAG_SEND_TRIM) {
                nbd->disk->queue->limits.discard_granularity = blksize;
                nbd->disk->queue->limits.discard_alignment = blksize;
                blk_queue_max_discard_sectors(nbd->disk->queue, UINT_MAX);
        }
        blk_queue_logical_block_size(nbd->disk->queue, blksize);
        blk_queue_physical_block_size(nbd->disk->queue, blksize);

        if (max_part)
                set_bit(GD_NEED_PART_SCAN, &nbd->disk->state);
        if (!set_capacity_and_notify(nbd->disk, bytesize >> 9))
                kobject_uevent(&nbd_to_dev(nbd)->kobj, KOBJ_CHANGE);
        return 0;
}

static void nbd_complete_rq(struct request *req)
{
        struct nbd_cmd *cmd = blk_mq_rq_to_pdu(req);

        dev_dbg(nbd_to_dev(cmd->nbd), "request %p: %s\n", req,
                cmd->status ? "failed" : "done");

        blk_mq_end_request(req, cmd->status);
}

/*
 * Forcibly shutdown the socket causing all listeners to error
 */
static void sock_shutdown(struct nbd_device *nbd)
{
        struct nbd_config *config = nbd->config;
        int i;

        if (config->num_connections == 0)
                return;
        if (test_and_set_bit(NBD_RT_DISCONNECTED, &config->runtime_flags))
                return;

        for (i = 0; i < config->num_connections; i++) {
                struct nbd_sock *nsock = config->socks[i];
                mutex_lock(&nsock->tx_lock);
                nbd_mark_nsock_dead(nbd, nsock, 0);
                mutex_unlock(&nsock->tx_lock);
        }
        dev_warn(disk_to_dev(nbd->disk), "shutting down sockets\n");
}

static u32 req_to_nbd_cmd_type(struct request *req)
{
        switch (req_op(req)) {
        case REQ_OP_DISCARD:
                return NBD_CMD_TRIM;
        case REQ_OP_FLUSH:
                return NBD_CMD_FLUSH;
        case REQ_OP_WRITE:
                return NBD_CMD_WRITE;
        case REQ_OP_READ:
                return NBD_CMD_READ;
        default:
                return U32_MAX;
        }
}

static enum blk_eh_timer_return nbd_xmit_timeout(struct request *req,
                                                 bool reserved)
{
        struct nbd_cmd *cmd = blk_mq_rq_to_pdu(req);
        struct nbd_device *nbd = cmd->nbd;
        struct nbd_config *config;

        if (!mutex_trylock(&cmd->lock))
                return BLK_EH_RESET_TIMER;

        if (!refcount_inc_not_zero(&nbd->config_refs)) {
                cmd->status = BLK_STS_TIMEOUT;
                mutex_unlock(&cmd->lock);
                goto done;
        }
        config = nbd->config;

        if (config->num_connections > 1 ||
            (config->num_connections == 1 && nbd->tag_set.timeout)) {
                dev_err_ratelimited(nbd_to_dev(nbd),
                                    "Connection timed out, retrying (%d/%d alive)\n",
                                    atomic_read(&config->live_connections),
                                    config->num_connections);
                /*
                 * Hooray we have more connections, requeue this IO, the submit
                 * path will put it on a real connection. Or if only one
                 * connection is configured, the submit path will wait util
                 * a new connection is reconfigured or util dead timeout.
                 */
                if (config->socks) {
                        if (cmd->index < config->num_connections) {
                                struct nbd_sock *nsock =
                                        config->socks[cmd->index];
                                mutex_lock(&nsock->tx_lock);
                                /* We can have multiple outstanding requests, so
                                 * we don't want to mark the nsock dead if we've
                                 * already reconnected with a new socket, so
                                 * only mark it dead if its the same socket we
                                 * were sent out on.
                                 */
                                if (cmd->cookie == nsock->cookie)
                                        nbd_mark_nsock_dead(nbd, nsock, 1);
                                mutex_unlock(&nsock->tx_lock);
                        }
                        mutex_unlock(&cmd->lock);
                        nbd_requeue_cmd(cmd);
                        nbd_config_put(nbd);
                        return BLK_EH_DONE;
                }
        }

        if (!nbd->tag_set.timeout) {
                /*
                 * Userspace sets timeout=0 to disable socket disconnection,
                 * so just warn and reset the timer.
                 */
                struct nbd_sock *nsock = config->socks[cmd->index];
                cmd->retries++;
                dev_info(nbd_to_dev(nbd), "Possible stuck request %p: control (%s@%llu,%uB). Runtime %u seconds\n",
                        req, nbdcmd_to_ascii(req_to_nbd_cmd_type(req)),
                        (unsigned long long)blk_rq_pos(req) << 9,
                        blk_rq_bytes(req), (req->timeout / HZ) * cmd->retries);

                mutex_lock(&nsock->tx_lock);
                if (cmd->cookie != nsock->cookie) {
                        nbd_requeue_cmd(cmd);
                        mutex_unlock(&nsock->tx_lock);
                        mutex_unlock(&cmd->lock);
                        nbd_config_put(nbd);
                        return BLK_EH_DONE;
                }
                mutex_unlock(&nsock->tx_lock);
                mutex_unlock(&cmd->lock);
                nbd_config_put(nbd);
                return BLK_EH_RESET_TIMER;
        }

        dev_err_ratelimited(nbd_to_dev(nbd), "Connection timed out\n");
        set_bit(NBD_RT_TIMEDOUT, &config->runtime_flags);
        cmd->status = BLK_STS_IOERR;
        mutex_unlock(&cmd->lock);
        sock_shutdown(nbd);
        nbd_config_put(nbd);
done:
        blk_mq_complete_request(req);
        return BLK_EH_DONE;
}

/*
 *  Send or receive packet.
 */
static int sock_xmit(struct nbd_device *nbd, int index, int send,
                     struct iov_iter *iter, int msg_flags, int *sent)
{
        struct nbd_config *config = nbd->config;
        struct socket *sock = config->socks[index]->sock;
        int result;
        struct msghdr msg;
        unsigned int noreclaim_flag;

        if (unlikely(!sock)) {
                dev_err_ratelimited(disk_to_dev(nbd->disk),
                        "Attempted %s on closed socket in sock_xmit\n",
                        (send ? "send" : "recv"));
                return -EINVAL;
        }

        msg.msg_iter = *iter;

        noreclaim_flag = memalloc_noreclaim_save();
        do {
                sock->sk->sk_allocation = GFP_NOIO | __GFP_MEMALLOC;
                msg.msg_name = NULL;
                msg.msg_namelen = 0;
                msg.msg_control = NULL;
                msg.msg_controllen = 0;
                msg.msg_flags = msg_flags | MSG_NOSIGNAL;

                if (send)
                        result = sock_sendmsg(sock, &msg);
                else
                        result = sock_recvmsg(sock, &msg, msg.msg_flags);

                if (result <= 0) {
                        if (result == 0)
                                result = -EPIPE; /* short read */
                        break;
                }
                if (sent)
                        *sent += result;
        } while (msg_data_left(&msg));

        memalloc_noreclaim_restore(noreclaim_flag);

        return result;
}

/*
 * Different settings for sk->sk_sndtimeo can result in different return values
 * if there is a signal pending when we enter sendmsg, because reasons?
 */
static inline int was_interrupted(int result)
{
        return result == -ERESTARTSYS || result == -EINTR;
}

/* always call with the tx_lock held */
static int nbd_send_cmd(struct nbd_device *nbd, struct nbd_cmd *cmd, int index)
{
        struct request *req = blk_mq_rq_from_pdu(cmd);
        struct nbd_config *config = nbd->config;
        struct nbd_sock *nsock = config->socks[index];
        int result;
        struct nbd_request request = {.magic = htonl(NBD_REQUEST_MAGIC)};
        struct kvec iov = {.iov_base = &request, .iov_len = sizeof(request)};
        struct iov_iter from;
        unsigned long size = blk_rq_bytes(req);
        struct bio *bio;
        u64 handle;
        u32 type;
        u32 nbd_cmd_flags = 0;
        int sent = nsock->sent, skip = 0;

        iov_iter_kvec(&from, WRITE, &iov, 1, sizeof(request));

        type = req_to_nbd_cmd_type(req);
        if (type == U32_MAX)
                return -EIO;

        if (rq_data_dir(req) == WRITE &&
            (config->flags & NBD_FLAG_READ_ONLY)) {
                dev_err_ratelimited(disk_to_dev(nbd->disk),
                                    "Write on read-only\n");
                return -EIO;
        }

        if (req->cmd_flags & REQ_FUA)
                nbd_cmd_flags |= NBD_CMD_FLAG_FUA;

        /* We did a partial send previously, and we at least sent the whole
         * request struct, so just go and send the rest of the pages in the
         * request.
         */
        if (sent) {
                if (sent >= sizeof(request)) {
                        skip = sent - sizeof(request);

                        /* initialize handle for tracing purposes */
                        handle = nbd_cmd_handle(cmd);

                        goto send_pages;
                }
                iov_iter_advance(&from, sent);
        } else {
                cmd->cmd_cookie++;
        }
        cmd->index = index;
        cmd->cookie = nsock->cookie;
        cmd->retries = 0;
        request.type = htonl(type | nbd_cmd_flags);
        if (type != NBD_CMD_FLUSH) {
                request.from = cpu_to_be64((u64)blk_rq_pos(req) << 9);
                request.len = htonl(size);
        }
        handle = nbd_cmd_handle(cmd);
        memcpy(request.handle, &handle, sizeof(handle));

        trace_nbd_send_request(&request, nbd->index, blk_mq_rq_from_pdu(cmd));

        dev_dbg(nbd_to_dev(nbd), "request %p: sending control (%s@%llu,%uB)\n",
                req, nbdcmd_to_ascii(type),
                (unsigned long long)blk_rq_pos(req) << 9, blk_rq_bytes(req));
        result = sock_xmit(nbd, index, 1, &from,
                        (type == NBD_CMD_WRITE) ? MSG_MORE : 0, &sent);
        trace_nbd_header_sent(req, handle);
        if (result <= 0) {
                if (was_interrupted(result)) {
                        /* If we havne't sent anything we can just return BUSY,
                         * however if we have sent something we need to make
                         * sure we only allow this req to be sent until we are
                         * completely done.
                         */
                        if (sent) {
                                nsock->pending = req;
                                nsock->sent = sent;
                        }
                        set_bit(NBD_CMD_REQUEUED, &cmd->flags);
                        return BLK_STS_RESOURCE;
                }
                dev_err_ratelimited(disk_to_dev(nbd->disk),
                        "Send control failed (result %d)\n", result);
                return -EAGAIN;
        }
send_pages:
        if (type != NBD_CMD_WRITE)
                goto out;

        bio = req->bio;
        while (bio) {
                struct bio *next = bio->bi_next;
                struct bvec_iter iter;
                struct bio_vec bvec;

                bio_for_each_segment(bvec, bio, iter) {
                        bool is_last = !next && bio_iter_last(bvec, iter);
                        int flags = is_last ? 0 : MSG_MORE;

                        dev_dbg(nbd_to_dev(nbd), "request %p: sending %d bytes data\n",
                                req, bvec.bv_len);
                        iov_iter_bvec(&from, WRITE, &bvec, 1, bvec.bv_len);
                        if (skip) {
                                if (skip >= iov_iter_count(&from)) {
                                        skip -= iov_iter_count(&from);
                                        continue;
                                }
                                iov_iter_advance(&from, skip);
                                skip = 0;
                        }
                        result = sock_xmit(nbd, index, 1, &from, flags, &sent);
                        if (result <= 0) {
                                if (was_interrupted(result)) {
                                        /* We've already sent the header, we
                                         * have no choice but to set pending and
                                         * return BUSY.
                                         */
                                        nsock->pending = req;
                                        nsock->sent = sent;
                                        set_bit(NBD_CMD_REQUEUED, &cmd->flags);
                                        return BLK_STS_RESOURCE;
                                }
                                dev_err(disk_to_dev(nbd->disk),
                                        "Send data failed (result %d)\n",
                                        result);
                                return -EAGAIN;
                        }
                        /*
                         * The completion might already have come in,
                         * so break for the last one instead of letting
                         * the iterator do it. This prevents use-after-free
                         * of the bio.
                         */
                        if (is_last)
                                break;
                }
                bio = next;
        }
out:
        trace_nbd_payload_sent(req, handle);
        nsock->pending = NULL;
        nsock->sent = 0;
        return 0;
}

/* NULL returned = something went wrong, inform userspace */
static struct nbd_cmd *nbd_read_stat(struct nbd_device *nbd, int index)
{
        struct nbd_config *config = nbd->config;
        int result;
        struct nbd_reply reply;
        struct nbd_cmd *cmd;
        struct request *req = NULL;
        u64 handle;
        u16 hwq;
        u32 tag;
        struct kvec iov = {.iov_base = &reply, .iov_len = sizeof(reply)};
        struct iov_iter to;
        int ret = 0;

        reply.magic = 0;
        iov_iter_kvec(&to, READ, &iov, 1, sizeof(reply));
        result = sock_xmit(nbd, index, 0, &to, MSG_WAITALL, NULL);
        if (result <= 0) {
                if (!nbd_disconnected(config))
                        dev_err(disk_to_dev(nbd->disk),
                                "Receive control failed (result %d)\n", result);
                return ERR_PTR(result);
        }

        if (ntohl(reply.magic) != NBD_REPLY_MAGIC) {
                dev_err(disk_to_dev(nbd->disk), "Wrong magic (0x%lx)\n",
                                (unsigned long)ntohl(reply.magic));
                return ERR_PTR(-EPROTO);
        }

        memcpy(&handle, reply.handle, sizeof(handle));
        tag = nbd_handle_to_tag(handle);
        hwq = blk_mq_unique_tag_to_hwq(tag);
        if (hwq < nbd->tag_set.nr_hw_queues)
                req = blk_mq_tag_to_rq(nbd->tag_set.tags[hwq],
                                       blk_mq_unique_tag_to_tag(tag));
        if (!req || !blk_mq_request_started(req)) {
                dev_err(disk_to_dev(nbd->disk), "Unexpected reply (%d) %p\n",
                        tag, req);
                return ERR_PTR(-ENOENT);
        }
        trace_nbd_header_received(req, handle);
        cmd = blk_mq_rq_to_pdu(req);

        mutex_lock(&cmd->lock);
        if (cmd->cmd_cookie != nbd_handle_to_cookie(handle)) {
                dev_err(disk_to_dev(nbd->disk), "Double reply on req %p, cmd_cookie %u, handle cookie %u\n",
                        req, cmd->cmd_cookie, nbd_handle_to_cookie(handle));
                ret = -ENOENT;
                goto out;
        }
        if (cmd->status != BLK_STS_OK) {
                dev_err(disk_to_dev(nbd->disk), "Command already handled %p\n",
                        req);
                ret = -ENOENT;
                goto out;
        }
        if (test_bit(NBD_CMD_REQUEUED, &cmd->flags)) {
                dev_err(disk_to_dev(nbd->disk), "Raced with timeout on req %p\n",
                        req);
                ret = -ENOENT;
                goto out;
        }
        if (ntohl(reply.error)) {
                dev_err(disk_to_dev(nbd->disk), "Other side returned error (%d)\n",
                        ntohl(reply.error));
                cmd->status = BLK_STS_IOERR;
                goto out;
        }

        dev_dbg(nbd_to_dev(nbd), "request %p: got reply\n", req);
        if (rq_data_dir(req) != WRITE) {
                struct req_iterator iter;
                struct bio_vec bvec;

                rq_for_each_segment(bvec, req, iter) {
                        iov_iter_bvec(&to, READ, &bvec, 1, bvec.bv_len);
                        result = sock_xmit(nbd, index, 0, &to, MSG_WAITALL, NULL);
                        if (result <= 0) {
                                dev_err(disk_to_dev(nbd->disk), "Receive data failed (result %d)\n",
                                        result);
                                /*
                                 * If we've disconnected, we need to make sure we
                                 * complete this request, otherwise error out
                                 * and let the timeout stuff handle resubmitting
                                 * this request onto another connection.
                                 */
                                if (nbd_disconnected(config)) {
                                        cmd->status = BLK_STS_IOERR;
                                        goto out;
                                }
                                ret = -EIO;
                                goto out;
                        }
                        dev_dbg(nbd_to_dev(nbd), "request %p: got %d bytes data\n",
                                req, bvec.bv_len);
                }
        }
out:
        trace_nbd_payload_received(req, handle);
        mutex_unlock(&cmd->lock);
        return ret ? ERR_PTR(ret) : cmd;
}

static void recv_work(struct work_struct *work)
{
        struct recv_thread_args *args = container_of(work,
                                                     struct recv_thread_args,
                                                     work);
        struct nbd_device *nbd = args->nbd;
        struct nbd_config *config = nbd->config;
        struct nbd_cmd *cmd;
        struct request *rq;

        while (1) {
                cmd = nbd_read_stat(nbd, args->index);
                if (IS_ERR(cmd)) {
                        struct nbd_sock *nsock = config->socks[args->index];

                        mutex_lock(&nsock->tx_lock);
                        nbd_mark_nsock_dead(nbd, nsock, 1);
                        mutex_unlock(&nsock->tx_lock);
                        break;
                }

                rq = blk_mq_rq_from_pdu(cmd);
                if (likely(!blk_should_fake_timeout(rq->q)))
                        blk_mq_complete_request(rq);
        }
        nbd_config_put(nbd);
        atomic_dec(&config->recv_threads);
        wake_up(&config->recv_wq);
        kfree(args);
}

static bool nbd_clear_req(struct request *req, void *data, bool reserved)
{
        struct nbd_cmd *cmd = blk_mq_rq_to_pdu(req);

        /* don't abort one completed request */
        if (blk_mq_request_completed(req))
                return true;

        mutex_lock(&cmd->lock);
        cmd->status = BLK_STS_IOERR;
        mutex_unlock(&cmd->lock);

        blk_mq_complete_request(req);
        return true;
}

static void nbd_clear_que(struct nbd_device *nbd)
{
        blk_mq_quiesce_queue(nbd->disk->queue);
        blk_mq_tagset_busy_iter(&nbd->tag_set, nbd_clear_req, NULL);
        blk_mq_unquiesce_queue(nbd->disk->queue);
        dev_dbg(disk_to_dev(nbd->disk), "queue cleared\n");
}

static int find_fallback(struct nbd_device *nbd, int index)
{
        struct nbd_config *config = nbd->config;
        int new_index = -1;
        struct nbd_sock *nsock = config->socks[index];
        int fallback = nsock->fallback_index;

        if (test_bit(NBD_RT_DISCONNECTED, &config->runtime_flags))
                return new_index;

        if (config->num_connections <= 1) {
                dev_err_ratelimited(disk_to_dev(nbd->disk),
                                    "Dead connection, failed to find a fallback\n");
                return new_index;
        }

        if (fallback >= 0 && fallback < config->num_connections &&
            !config->socks[fallback]->dead)
                return fallback;

        if (nsock->fallback_index < 0 ||
            nsock->fallback_index >= config->num_connections ||
            config->socks[nsock->fallback_index]->dead) {
                int i;
                for (i = 0; i < config->num_connections; i++) {
                        if (i == index)
                                continue;
                        if (!config->socks[i]->dead) {
                                new_index = i;
                                break;
                        }
                }
                nsock->fallback_index = new_index;
                if (new_index < 0) {
                        dev_err_ratelimited(disk_to_dev(nbd->disk),
                                            "Dead connection, failed to find a fallback\n");
                        return new_index;
                }
        }
        new_index = nsock->fallback_index;
        return new_index;
}

static int wait_for_reconnect(struct nbd_device *nbd)
{
        struct nbd_config *config = nbd->config;
        if (!config->dead_conn_timeout)
                return 0;
        if (test_bit(NBD_RT_DISCONNECTED, &config->runtime_flags))
                return 0;
        return wait_event_timeout(config->conn_wait,
                                  atomic_read(&config->live_connections) > 0,
                                  config->dead_conn_timeout) > 0;
}

static int nbd_handle_cmd(struct nbd_cmd *cmd, int index)
{
        struct request *req = blk_mq_rq_from_pdu(cmd);
        struct nbd_device *nbd = cmd->nbd;
        struct nbd_config *config;
        struct nbd_sock *nsock;
        int ret;

        if (!refcount_inc_not_zero(&nbd->config_refs)) {
                dev_err_ratelimited(disk_to_dev(nbd->disk),
                                    "Socks array is empty\n");
                blk_mq_start_request(req);
                return -EINVAL;
        }
        config = nbd->config;

        if (index >= config->num_connections) {
                dev_err_ratelimited(disk_to_dev(nbd->disk),
                                    "Attempted send on invalid socket\n");
                nbd_config_put(nbd);
                blk_mq_start_request(req);
                return -EINVAL;
        }
        cmd->status = BLK_STS_OK;
again:
        nsock = config->socks[index];
        mutex_lock(&nsock->tx_lock);
        if (nsock->dead) {
                int old_index = index;
                index = find_fallback(nbd, index);
                mutex_unlock(&nsock->tx_lock);
                if (index < 0) {
                        if (wait_for_reconnect(nbd)) {
                                index = old_index;
                                goto again;
                        }
                        /* All the sockets should already be down at this point,
                         * we just want to make sure that DISCONNECTED is set so
                         * any requests that come in that were queue'ed waiting
                         * for the reconnect timer don't trigger the timer again
                         * and instead just error out.
                         */
                        sock_shutdown(nbd);
                        nbd_config_put(nbd);
                        blk_mq_start_request(req);
                        return -EIO;
                }
                goto again;
        }

        /* Handle the case that we have a pending request that was partially
         * transmitted that _has_ to be serviced first.  We need to call requeue
         * here so that it gets put _after_ the request that is already on the
         * dispatch list.
         */
        blk_mq_start_request(req);
        if (unlikely(nsock->pending && nsock->pending != req)) {
                nbd_requeue_cmd(cmd);
                ret = 0;
                goto out;
        }
        /*
         * Some failures are related to the link going down, so anything that
         * returns EAGAIN can be retried on a different socket.
         */
        ret = nbd_send_cmd(nbd, cmd, index);
        if (ret == -EAGAIN) {
                dev_err_ratelimited(disk_to_dev(nbd->disk),
                                    "Request send failed, requeueing\n");
                nbd_mark_nsock_dead(nbd, nsock, 1);
                nbd_requeue_cmd(cmd);
                ret = 0;
        }
out:
        mutex_unlock(&nsock->tx_lock);
        nbd_config_put(nbd);
        return ret;
}

static blk_status_t nbd_queue_rq(struct blk_mq_hw_ctx *hctx,
                        const struct blk_mq_queue_data *bd)
{
        struct nbd_cmd *cmd = blk_mq_rq_to_pdu(bd->rq);
        int ret;

        /*
         * Since we look at the bio's to send the request over the network we
         * need to make sure the completion work doesn't mark this request done
         * before we are done doing our send.  This keeps us from dereferencing
         * freed data if we have particularly fast completions (ie we get the
         * completion before we exit sock_xmit on the last bvec) or in the case
         * that the server is misbehaving (or there was an error) before we're
         * done sending everything over the wire.
         */
        mutex_lock(&cmd->lock);
        clear_bit(NBD_CMD_REQUEUED, &cmd->flags);

        /* We can be called directly from the user space process, which means we
         * could possibly have signals pending so our sendmsg will fail.  In
         * this case we need to return that we are busy, otherwise error out as
         * appropriate.
         */
        ret = nbd_handle_cmd(cmd, hctx->queue_num);
        if (ret < 0)
                ret = BLK_STS_IOERR;

        else if (!ret)
                ret = BLK_STS_OK;
        mutex_unlock(&cmd->lock);

        return ret;
}

static struct socket *nbd_get_socket(struct nbd_device *nbd, unsigned long fd,
                                     int *err)
{
        struct socket *sock;

        *err = 0;
        sock = sockfd_lookup(fd, err);
        if (!sock)
                return NULL;

        if (sock->ops->shutdown == sock_no_shutdown) {
                dev_err(disk_to_dev(nbd->disk), "Unsupported socket: shutdown callout must be supported.\n");
                *err = -EINVAL;
                sockfd_put(sock);
                return NULL;
        }

        return sock;
}

static int nbd_add_socket(struct nbd_device *nbd, unsigned long arg,
                          bool netlink)
{
        struct nbd_config *config = nbd->config;
        struct socket *sock;
        struct nbd_sock **socks;
        struct nbd_sock *nsock;
        int err;

        sock = nbd_get_socket(nbd, arg, &err);
        if (!sock)
                return err;

        /*
         * We need to make sure we don't get any errant requests while we're
         * reallocating the ->socks array.
         */
        blk_mq_freeze_queue(nbd->disk->queue);

        if (!netlink && !nbd->task_setup &&
            !test_bit(NBD_RT_BOUND, &config->runtime_flags))
                nbd->task_setup = current;

        if (!netlink &&
            (nbd->task_setup != current ||
             test_bit(NBD_RT_BOUND, &config->runtime_flags))) {
                dev_err(disk_to_dev(nbd->disk),
                        "Device being setup by another task");
                err = -EBUSY;
                goto put_socket;
        }

        nsock = kzalloc(sizeof(*nsock), GFP_KERNEL);
        if (!nsock) {
                err = -ENOMEM;
                goto put_socket;
        }

        socks = krealloc(config->socks, (config->num_connections + 1) *
                         sizeof(struct nbd_sock *), GFP_KERNEL);
        if (!socks) {
                kfree(nsock);
                err = -ENOMEM;
                goto put_socket;
        }

        config->socks = socks;

        nsock->fallback_index = -1;
        nsock->dead = false;
        mutex_init(&nsock->tx_lock);
        nsock->sock = sock;
        nsock->pending = NULL;
        nsock->sent = 0;
        nsock->cookie = 0;
        socks[config->num_connections++] = nsock;
        atomic_inc(&config->live_connections);
        blk_mq_unfreeze_queue(nbd->disk->queue);

        return 0;

put_socket:
        blk_mq_unfreeze_queue(nbd->disk->queue);
        sockfd_put(sock);
        return err;
}

static int nbd_reconnect_socket(struct nbd_device *nbd, unsigned long arg)
{
        struct nbd_config *config = nbd->config;
        struct socket *sock, *old;
        struct recv_thread_args *args;
        int i;
        int err;

        sock = nbd_get_socket(nbd, arg, &err);
        if (!sock)
                return err;

        args = kzalloc(sizeof(*args), GFP_KERNEL);
        if (!args) {
                sockfd_put(sock);
                return -ENOMEM;
        }

        for (i = 0; i < config->num_connections; i++) {
                struct nbd_sock *nsock = config->socks[i];

                if (!nsock->dead)
                        continue;

                mutex_lock(&nsock->tx_lock);
                if (!nsock->dead) {
                        mutex_unlock(&nsock->tx_lock);
                        continue;
                }
                sk_set_memalloc(sock->sk);
                if (nbd->tag_set.timeout)
                        sock->sk->sk_sndtimeo = nbd->tag_set.timeout;
                atomic_inc(&config->recv_threads);
                refcount_inc(&nbd->config_refs);
                old = nsock->sock;
                nsock->fallback_index = -1;
                nsock->sock = sock;
                nsock->dead = false;
                INIT_WORK(&args->work, recv_work);
                args->index = i;
                args->nbd = nbd;
                nsock->cookie++;
                mutex_unlock(&nsock->tx_lock);
                sockfd_put(old);

                clear_bit(NBD_RT_DISCONNECTED, &config->runtime_flags);

                /* We take the tx_mutex in an error path in the recv_work, so we
                 * need to queue_work outside of the tx_mutex.
                 */
                queue_work(nbd->recv_workq, &args->work);

                atomic_inc(&config->live_connections);
                wake_up(&config->conn_wait);
                return 0;
        }
        sockfd_put(sock);
        kfree(args);
        return -ENOSPC;
}

static void nbd_bdev_reset(struct block_device *bdev)
{
        if (bdev->bd_openers > 1)
                return;
        set_capacity(bdev->bd_disk, 0);
}

static void nbd_parse_flags(struct nbd_device *nbd)
{
        struct nbd_config *config = nbd->config;
        if (config->flags & NBD_FLAG_READ_ONLY)
                set_disk_ro(nbd->disk, true);
        else
                set_disk_ro(nbd->disk, false);
        if (config->flags & NBD_FLAG_SEND_TRIM)
                blk_queue_flag_set(QUEUE_FLAG_DISCARD, nbd->disk->queue);
        if (config->flags & NBD_FLAG_SEND_FLUSH) {
                if (config->flags & NBD_FLAG_SEND_FUA)
                        blk_queue_write_cache(nbd->disk->queue, true, true);
                else
                        blk_queue_write_cache(nbd->disk->queue, true, false);
        }
        else
                blk_queue_write_cache(nbd->disk->queue, false, false);
}

static void send_disconnects(struct nbd_device *nbd)
{
        struct nbd_config *config = nbd->config;
        struct nbd_request request = {
                .magic = htonl(NBD_REQUEST_MAGIC),
                .type = htonl(NBD_CMD_DISC),
        };
        struct kvec iov = {.iov_base = &request, .iov_len = sizeof(request)};
        struct iov_iter from;
        int i, ret;

        for (i = 0; i < config->num_connections; i++) {
                struct nbd_sock *nsock = config->socks[i];

                iov_iter_kvec(&from, WRITE, &iov, 1, sizeof(request));
                mutex_lock(&nsock->tx_lock);
                ret = sock_xmit(nbd, i, 1, &from, 0, NULL);
                if (ret <= 0)
                        dev_err(disk_to_dev(nbd->disk),
                                "Send disconnect failed %d\n", ret);
                mutex_unlock(&nsock->tx_lock);
        }
}

static int nbd_disconnect(struct nbd_device *nbd)
{
        struct nbd_config *config = nbd->config;

        dev_info(disk_to_dev(nbd->disk), "NBD_DISCONNECT\n");
        set_bit(NBD_RT_DISCONNECT_REQUESTED, &config->runtime_flags);
        set_bit(NBD_DISCONNECT_REQUESTED, &nbd->flags);
        send_disconnects(nbd);
        return 0;
}

static void nbd_clear_sock(struct nbd_device *nbd)
{
        sock_shutdown(nbd);
        nbd_clear_que(nbd);
        nbd->task_setup = NULL;
}

static void nbd_config_put(struct nbd_device *nbd)
{
        if (refcount_dec_and_mutex_lock(&nbd->config_refs,
                                        &nbd->config_lock)) {
                struct nbd_config *config = nbd->config;
                nbd_dev_dbg_close(nbd);
                nbd_size_clear(nbd);
                if (test_and_clear_bit(NBD_RT_HAS_PID_FILE,
                                       &config->runtime_flags))
                        device_remove_file(disk_to_dev(nbd->disk), &pid_attr);
                nbd->task_recv = NULL;
                if (test_and_clear_bit(NBD_RT_HAS_BACKEND_FILE,
                                       &config->runtime_flags)) {
                        device_remove_file(disk_to_dev(nbd->disk), &backend_attr);
                        kfree(nbd->backend);
                        nbd->backend = NULL;
                }
                nbd_clear_sock(nbd);
                if (config->num_connections) {
                        int i;
                        for (i = 0; i < config->num_connections; i++) {
                                sockfd_put(config->socks[i]->sock);
                                kfree(config->socks[i]);
                        }
                        kfree(config->socks);
                }
                kfree(nbd->config);
                nbd->config = NULL;

                if (nbd->recv_workq)
                        destroy_workqueue(nbd->recv_workq);
                nbd->recv_workq = NULL;

                nbd->tag_set.timeout = 0;
                nbd->disk->queue->limits.discard_granularity = 0;
                nbd->disk->queue->limits.discard_alignment = 0;
                blk_queue_max_discard_sectors(nbd->disk->queue, UINT_MAX);
                blk_queue_flag_clear(QUEUE_FLAG_DISCARD, nbd->disk->queue);

                mutex_unlock(&nbd->config_lock);
                nbd_put(nbd);
                module_put(THIS_MODULE);
        }
}

static int nbd_start_device(struct nbd_device *nbd)
{
        struct nbd_config *config = nbd->config;
        int num_connections = config->num_connections;
        int error = 0, i;

        if (nbd->task_recv)
                return -EBUSY;
        if (!config->socks)
                return -EINVAL;
        if (num_connections > 1 &&
            !(config->flags & NBD_FLAG_CAN_MULTI_CONN)) {
                dev_err(disk_to_dev(nbd->disk), "server does not support multiple connections per device.\n");
                return -EINVAL;
        }

        nbd->recv_workq = alloc_workqueue("knbd%d-recv",
                                          WQ_MEM_RECLAIM | WQ_HIGHPRI |
                                          WQ_UNBOUND, 0, nbd->index);
        if (!nbd->recv_workq) {
                dev_err(disk_to_dev(nbd->disk), "Could not allocate knbd recv work queue.\n");
                return -ENOMEM;
        }

        blk_mq_update_nr_hw_queues(&nbd->tag_set, config->num_connections);
        nbd->task_recv = current;

        nbd_parse_flags(nbd);

        error = device_create_file(disk_to_dev(nbd->disk), &pid_attr);
        if (error) {
                dev_err(disk_to_dev(nbd->disk), "device_create_file failed for pid!\n");
                return error;
        }
        set_bit(NBD_RT_HAS_PID_FILE, &config->runtime_flags);

        nbd_dev_dbg_init(nbd);
        for (i = 0; i < num_connections; i++) {
                struct recv_thread_args *args;

                args = kzalloc(sizeof(*args), GFP_KERNEL);
                if (!args) {
                        sock_shutdown(nbd);
                        /*
                         * If num_connections is m (2 < m),
                         * and NO.1 ~ NO.n(1 < n < m) kzallocs are successful.
                         * But NO.(n + 1) failed. We still have n recv threads.
                         * So, add flush_workqueue here to prevent recv threads
                         * dropping the last config_refs and trying to destroy
                         * the workqueue from inside the workqueue.
                         */
                        if (i)
                                flush_workqueue(nbd->recv_workq);
                        return -ENOMEM;
                }
                sk_set_memalloc(config->socks[i]->sock->sk);
                if (nbd->tag_set.timeout)
                        config->socks[i]->sock->sk->sk_sndtimeo =
                                nbd->tag_set.timeout;
                atomic_inc(&config->recv_threads);
                refcount_inc(&nbd->config_refs);
                INIT_WORK(&args->work, recv_work);
                args->nbd = nbd;
                args->index = i;
                queue_work(nbd->recv_workq, &args->work);
        }
        return nbd_set_size(nbd, config->bytesize, config->blksize);
}

static int nbd_start_device_ioctl(struct nbd_device *nbd, struct block_device *bdev)
{
        struct nbd_config *config = nbd->config;
        int ret;

        ret = nbd_start_device(nbd);
        if (ret)
                return ret;

        if (max_part)
                set_bit(GD_NEED_PART_SCAN, &nbd->disk->state);
        mutex_unlock(&nbd->config_lock);
        ret = wait_event_interruptible(config->recv_wq,
                                         atomic_read(&config->recv_threads) == 0);
        if (ret)
                sock_shutdown(nbd);
        flush_workqueue(nbd->recv_workq);

        mutex_lock(&nbd->config_lock);
        nbd_bdev_reset(bdev);
        /* user requested, ignore socket errors */
        if (test_bit(NBD_RT_DISCONNECT_REQUESTED, &config->runtime_flags))
                ret = 0;
        if (test_bit(NBD_RT_TIMEDOUT, &config->runtime_flags))
                ret = -ETIMEDOUT;
        return ret;
}

static void nbd_clear_sock_ioctl(struct nbd_device *nbd,
                                 struct block_device *bdev)
{
        sock_shutdown(nbd);
        __invalidate_device(bdev, true);
        nbd_bdev_reset(bdev);
        if (test_and_clear_bit(NBD_RT_HAS_CONFIG_REF,
                               &nbd->config->runtime_flags))
                nbd_config_put(nbd);
}

static void nbd_set_cmd_timeout(struct nbd_device *nbd, u64 timeout)
{
        nbd->tag_set.timeout = timeout * HZ;
        if (timeout)
                blk_queue_rq_timeout(nbd->disk->queue, timeout * HZ);
        else
                blk_queue_rq_timeout(nbd->disk->queue, 30 * HZ);
}

/* Must be called with config_lock held */
static int __nbd_ioctl(struct block_device *bdev, struct nbd_device *nbd,
                       unsigned int cmd, unsigned long arg)
{
        struct nbd_config *config = nbd->config;

        switch (cmd) {
        case NBD_DISCONNECT:
                return nbd_disconnect(nbd);
        case NBD_CLEAR_SOCK:
                nbd_clear_sock_ioctl(nbd, bdev);
                return 0;
        case NBD_SET_SOCK:
                return nbd_add_socket(nbd, arg, false);
        case NBD_SET_BLKSIZE:
                return nbd_set_size(nbd, config->bytesize, arg);
        case NBD_SET_SIZE:
                return nbd_set_size(nbd, arg, config->blksize);
        case NBD_SET_SIZE_BLOCKS:
                return nbd_set_size(nbd, arg * config->blksize,
                                    config->blksize);
        case NBD_SET_TIMEOUT:
                nbd_set_cmd_timeout(nbd, arg);
                return 0;

        case NBD_SET_FLAGS:
                config->flags = arg;
                return 0;
        case NBD_DO_IT:
                return nbd_start_device_ioctl(nbd, bdev);
        case NBD_CLEAR_QUE:
                /*
                 * This is for compatibility only.  The queue is always cleared
                 * by NBD_DO_IT or NBD_CLEAR_SOCK.
                 */
                return 0;
        case NBD_PRINT_DEBUG:
                /*
                 * For compatibility only, we no longer keep a list of
                 * outstanding requests.
                 */
                return 0;
        }
        return -ENOTTY;
}

static int nbd_ioctl(struct block_device *bdev, fmode_t mode,
                     unsigned int cmd, unsigned long arg)
{
        struct nbd_device *nbd = bdev->bd_disk->private_data;
        struct nbd_config *config = nbd->config;
        int error = -EINVAL;

        if (!capable(CAP_SYS_ADMIN))
                return -EPERM;

        /* The block layer will pass back some non-nbd ioctls in case we have
         * special handling for them, but we don't so just return an error.
         */
        if (_IOC_TYPE(cmd) != 0xab)
                return -EINVAL;

        mutex_lock(&nbd->config_lock);

        /* Don't allow ioctl operations on a nbd device that was created with
         * netlink, unless it's DISCONNECT or CLEAR_SOCK, which are fine.
         */
        if (!test_bit(NBD_RT_BOUND, &config->runtime_flags) ||
            (cmd == NBD_DISCONNECT || cmd == NBD_CLEAR_SOCK))
                error = __nbd_ioctl(bdev, nbd, cmd, arg);
        else
                dev_err(nbd_to_dev(nbd), "Cannot use ioctl interface on a netlink controlled device.\n");
        mutex_unlock(&nbd->config_lock);
        return error;
}

static struct nbd_config *nbd_alloc_config(void)
{
        struct nbd_config *config;

        config = kzalloc(sizeof(struct nbd_config), GFP_NOFS);
        if (!config)
                return NULL;
        atomic_set(&config->recv_threads, 0);
        init_waitqueue_head(&config->recv_wq);
        init_waitqueue_head(&config->conn_wait);
        config->blksize = NBD_DEF_BLKSIZE;
        atomic_set(&config->live_connections, 0);
        try_module_get(THIS_MODULE);
        return config;
}

static int nbd_open(struct block_device *bdev, fmode_t mode)
{
        struct nbd_device *nbd;
        int ret = 0;

        mutex_lock(&nbd_index_mutex);
        nbd = bdev->bd_disk->private_data;
        if (!nbd) {
                ret = -ENXIO;
                goto out;
        }
        if (!refcount_inc_not_zero(&nbd->refs)) {
                ret = -ENXIO;
                goto out;
        }
        if (!refcount_inc_not_zero(&nbd->config_refs)) {
                struct nbd_config *config;

                mutex_lock(&nbd->config_lock);
                if (refcount_inc_not_zero(&nbd->config_refs)) {
                        mutex_unlock(&nbd->config_lock);
                        goto out;
                }
                config = nbd->config = nbd_alloc_config();
                if (!config) {
                        ret = -ENOMEM;
                        mutex_unlock(&nbd->config_lock);
                        goto out;
                }
                refcount_set(&nbd->config_refs, 1);
                refcount_inc(&nbd->refs);
                mutex_unlock(&nbd->config_lock);
                if (max_part)
                        set_bit(GD_NEED_PART_SCAN, &bdev->bd_disk->state);
        } else if (nbd_disconnected(nbd->config)) {
                if (max_part)
                        set_bit(GD_NEED_PART_SCAN, &bdev->bd_disk->state);
        }
out:
        mutex_unlock(&nbd_index_mutex);
        return ret;
}

static void nbd_release(struct gendisk *disk, fmode_t mode)
{
        struct nbd_device *nbd = disk->private_data;

        if (test_bit(NBD_RT_DISCONNECT_ON_CLOSE, &nbd->config->runtime_flags) &&
                        disk->part0->bd_openers == 0)
                nbd_disconnect_and_put(nbd);

        nbd_config_put(nbd);
        nbd_put(nbd);
}

static const struct block_device_operations nbd_fops =
{
        .owner =        THIS_MODULE,
        .open =         nbd_open,
        .release =      nbd_release,
        .ioctl =        nbd_ioctl,
        .compat_ioctl = nbd_ioctl,
};

#if IS_ENABLED(CONFIG_DEBUG_FS)

static int nbd_dbg_tasks_show(struct seq_file *s, void *unused)
{
        struct nbd_device *nbd = s->private;

        if (nbd->task_recv)
                seq_printf(s, "recv: %d\n", task_pid_nr(nbd->task_recv));

        return 0;
}

DEFINE_SHOW_ATTRIBUTE(nbd_dbg_tasks);

static int nbd_dbg_flags_show(struct seq_file *s, void *unused)
{
        struct nbd_device *nbd = s->private;
        u32 flags = nbd->config->flags;

        seq_printf(s, "Hex: 0x%08x\n\n", flags);

        seq_puts(s, "Known flags:\n");

        if (flags & NBD_FLAG_HAS_FLAGS)
                seq_puts(s, "NBD_FLAG_HAS_FLAGS\n");
        if (flags & NBD_FLAG_READ_ONLY)
                seq_puts(s, "NBD_FLAG_READ_ONLY\n");
        if (flags & NBD_FLAG_SEND_FLUSH)
                seq_puts(s, "NBD_FLAG_SEND_FLUSH\n");
        if (flags & NBD_FLAG_SEND_FUA)
                seq_puts(s, "NBD_FLAG_SEND_FUA\n");
        if (flags & NBD_FLAG_SEND_TRIM)
                seq_puts(s, "NBD_FLAG_SEND_TRIM\n");

        return 0;
}

DEFINE_SHOW_ATTRIBUTE(nbd_dbg_flags);

static int nbd_dev_dbg_init(struct nbd_device *nbd)
{
        struct dentry *dir;
        struct nbd_config *config = nbd->config;

        if (!nbd_dbg_dir)
                return -EIO;

        dir = debugfs_create_dir(nbd_name(nbd), nbd_dbg_dir);
        if (!dir) {
                dev_err(nbd_to_dev(nbd), "Failed to create debugfs dir for '%s'\n",
                        nbd_name(nbd));
                return -EIO;
        }
        config->dbg_dir = dir;

        debugfs_create_file("tasks", 0444, dir, nbd, &nbd_dbg_tasks_fops);
        debugfs_create_u64("size_bytes", 0444, dir, &config->bytesize);
        debugfs_create_u32("timeout", 0444, dir, &nbd->tag_set.timeout);
        debugfs_create_u64("blocksize", 0444, dir, &config->blksize);
        debugfs_create_file("flags", 0444, dir, nbd, &nbd_dbg_flags_fops);

        return 0;
}

static void nbd_dev_dbg_close(struct nbd_device *nbd)
{
        debugfs_remove_recursive(nbd->config->dbg_dir);
}

static int nbd_dbg_init(void)
{
        struct dentry *dbg_dir;

        dbg_dir = debugfs_create_dir("nbd", NULL);
        if (!dbg_dir)
                return -EIO;

        nbd_dbg_dir = dbg_dir;

        return 0;
}

static void nbd_dbg_close(void)
{
        debugfs_remove_recursive(nbd_dbg_dir);
}

#else  /* IS_ENABLED(CONFIG_DEBUG_FS) */

static int nbd_dev_dbg_init(struct nbd_device *nbd)
{
        return 0;
}

static void nbd_dev_dbg_close(struct nbd_device *nbd)
{
}

static int nbd_dbg_init(void)
{
        return 0;
}

static void nbd_dbg_close(void)
{
}

#endif

static int nbd_init_request(struct blk_mq_tag_set *set, struct request *rq,
                            unsigned int hctx_idx, unsigned int numa_node)
{
        struct nbd_cmd *cmd = blk_mq_rq_to_pdu(rq);
        cmd->nbd = set->driver_data;
        cmd->flags = 0;
        mutex_init(&cmd->lock);
        return 0;
}

static const struct blk_mq_ops nbd_mq_ops = {
        .queue_rq       = nbd_queue_rq,
        .complete       = nbd_complete_rq,
        .init_request   = nbd_init_request,
        .timeout        = nbd_xmit_timeout,
};

static int nbd_dev_add(int index)
{
        struct nbd_device *nbd;
        struct gendisk *disk;
        int err = -ENOMEM;

        nbd = kzalloc(sizeof(struct nbd_device), GFP_KERNEL);
        if (!nbd)
                goto out;

        nbd->tag_set.ops = &nbd_mq_ops;
        nbd->tag_set.nr_hw_queues = 1;
        nbd->tag_set.queue_depth = 128;
        nbd->tag_set.numa_node = NUMA_NO_NODE;
        nbd->tag_set.cmd_size = sizeof(struct nbd_cmd);
        nbd->tag_set.flags = BLK_MQ_F_SHOULD_MERGE |
                BLK_MQ_F_BLOCKING;
        nbd->tag_set.driver_data = nbd;
        nbd->destroy_complete = NULL;
        nbd->backend = NULL;

        err = blk_mq_alloc_tag_set(&nbd->tag_set);
        if (err)
                goto out_free_nbd;

        if (index >= 0) {
                err = idr_alloc(&nbd_index_idr, nbd, index, index + 1,
                                GFP_KERNEL);
                if (err == -ENOSPC)
                        err = -EEXIST;
        } else {
                err = idr_alloc(&nbd_index_idr, nbd, 0, 0, GFP_KERNEL);
                if (err >= 0)
                        index = err;
        }
        if (err < 0)
                goto out_free_tags;
        nbd->index = index;

        disk = blk_mq_alloc_disk(&nbd->tag_set, NULL);
        if (IS_ERR(disk)) {
                err = PTR_ERR(disk);
                goto out_free_idr;
        }
        nbd->disk = disk;

        /*
         * Tell the block layer that we are not a rotational device
         */
        blk_queue_flag_set(QUEUE_FLAG_NONROT, disk->queue);
        blk_queue_flag_clear(QUEUE_FLAG_ADD_RANDOM, disk->queue);
        disk->queue->limits.discard_granularity = 0;
        disk->queue->limits.discard_alignment = 0;
        blk_queue_max_discard_sectors(disk->queue, 0);
        blk_queue_max_segment_size(disk->queue, UINT_MAX);
        blk_queue_max_segments(disk->queue, USHRT_MAX);
        blk_queue_max_hw_sectors(disk->queue, 65536);
        disk->queue->limits.max_sectors = 256;

        mutex_init(&nbd->config_lock);
        refcount_set(&nbd->config_refs, 0);
        refcount_set(&nbd->refs, 1);
        INIT_LIST_HEAD(&nbd->list);
        disk->major = NBD_MAJOR;
        disk->first_minor = index << part_shift;
        disk->minors = 1 << part_shift;
        disk->fops = &nbd_fops;
        disk->private_data = nbd;
        sprintf(disk->disk_name, "nbd%d", index);
        add_disk(disk);
        nbd_total_devices++;
        return index;

out_free_idr:
        idr_remove(&nbd_index_idr, index);
out_free_tags:
        blk_mq_free_tag_set(&nbd->tag_set);
out_free_nbd:
        kfree(nbd);
out:
        return err;
}

static int find_free_cb(int id, void *ptr, void *data)
{
        struct nbd_device *nbd = ptr;
        struct nbd_device **found = data;

        if (!refcount_read(&nbd->config_refs)) {
                *found = nbd;
                return 1;
        }
        return 0;
}

/* Netlink interface. */
static const struct nla_policy nbd_attr_policy[NBD_ATTR_MAX + 1] = {
        [NBD_ATTR_INDEX]                =       { .type = NLA_U32 },
        [NBD_ATTR_SIZE_BYTES]           =       { .type = NLA_U64 },
        [NBD_ATTR_BLOCK_SIZE_BYTES]     =       { .type = NLA_U64 },
        [NBD_ATTR_TIMEOUT]              =       { .type = NLA_U64 },
        [NBD_ATTR_SERVER_FLAGS]         =       { .type = NLA_U64 },
        [NBD_ATTR_CLIENT_FLAGS]         =       { .type = NLA_U64 },
        [NBD_ATTR_SOCKETS]              =       { .type = NLA_NESTED},
        [NBD_ATTR_DEAD_CONN_TIMEOUT]    =       { .type = NLA_U64 },
        [NBD_ATTR_DEVICE_LIST]          =       { .type = NLA_NESTED},
        [NBD_ATTR_BACKEND_IDENTIFIER]   =       { .type = NLA_STRING},
};

static const struct nla_policy nbd_sock_policy[NBD_SOCK_MAX + 1] = {
        [NBD_SOCK_FD]                   =       { .type = NLA_U32 },
};

/* We don't use this right now since we don't parse the incoming list, but we
 * still want it here so userspace knows what to expect.
 */
static const struct nla_policy __attribute__((unused))
nbd_device_policy[NBD_DEVICE_ATTR_MAX + 1] = {
        [NBD_DEVICE_INDEX]              =       { .type = NLA_U32 },
        [NBD_DEVICE_CONNECTED]          =       { .type = NLA_U8 },
};

static int nbd_genl_size_set(struct genl_info *info, struct nbd_device *nbd)
{
        struct nbd_config *config = nbd->config;
        u64 bsize = config->blksize;
        u64 bytes = config->bytesize;

        if (info->attrs[NBD_ATTR_SIZE_BYTES])
                bytes = nla_get_u64(info->attrs[NBD_ATTR_SIZE_BYTES]);

        if (info->attrs[NBD_ATTR_BLOCK_SIZE_BYTES])
                bsize = nla_get_u64(info->attrs[NBD_ATTR_BLOCK_SIZE_BYTES]);

        if (bytes != config->bytesize || bsize != config->blksize)
                return nbd_set_size(nbd, bytes, bsize);
        return 0;
}

static int nbd_genl_connect(struct sk_buff *skb, struct genl_info *info)
{
        DECLARE_COMPLETION_ONSTACK(destroy_complete);
        struct nbd_device *nbd = NULL;
        struct nbd_config *config;
        int index = -1;
        int ret;
        bool put_dev = false;

        if (!netlink_capable(skb, CAP_SYS_ADMIN))
                return -EPERM;

        if (info->attrs[NBD_ATTR_INDEX])
                index = nla_get_u32(info->attrs[NBD_ATTR_INDEX]);
        if (!info->attrs[NBD_ATTR_SOCKETS]) {
                printk(KERN_ERR "nbd: must specify at least one socket\n");
                return -EINVAL;
        }
        if (!info->attrs[NBD_ATTR_SIZE_BYTES]) {
                printk(KERN_ERR "nbd: must specify a size in bytes for the device\n");
                return -EINVAL;
        }
again:
        mutex_lock(&nbd_index_mutex);
        if (index == -1) {
                ret = idr_for_each(&nbd_index_idr, &find_free_cb, &nbd);
                if (ret == 0) {
                        int new_index;
                        new_index = nbd_dev_add(-1);
                        if (new_index < 0) {
                                mutex_unlock(&nbd_index_mutex);
                                printk(KERN_ERR "nbd: failed to add new device\n");
                                return new_index;
                        }
                        nbd = idr_find(&nbd_index_idr, new_index);
                }
        } else {
                nbd = idr_find(&nbd_index_idr, index);
                if (!nbd) {
                        ret = nbd_dev_add(index);
                        if (ret < 0) {
                                mutex_unlock(&nbd_index_mutex);
                                printk(KERN_ERR "nbd: failed to add new device\n");
                                return ret;
                        }
                        nbd = idr_find(&nbd_index_idr, index);
                }
        }
        if (!nbd) {
                printk(KERN_ERR "nbd: couldn't find device at index %d\n",
                       index);
                mutex_unlock(&nbd_index_mutex);
                return -EINVAL;
        }

        if (test_bit(NBD_DESTROY_ON_DISCONNECT, &nbd->flags) &&
            test_bit(NBD_DISCONNECT_REQUESTED, &nbd->flags)) {
                nbd->destroy_complete = &destroy_complete;
                mutex_unlock(&nbd_index_mutex);

                /* Wait untill the the nbd stuff is totally destroyed */
                wait_for_completion(&destroy_complete);
                goto again;
        }

        if (!refcount_inc_not_zero(&nbd->refs)) {
                mutex_unlock(&nbd_index_mutex);
                if (index == -1)
                        goto again;
                printk(KERN_ERR "nbd: device at index %d is going down\n",
                       index);
                return -EINVAL;
        }
        mutex_unlock(&nbd_index_mutex);

        mutex_lock(&nbd->config_lock);
        if (refcount_read(&nbd->config_refs)) {
                mutex_unlock(&nbd->config_lock);
                nbd_put(nbd);
                if (index == -1)
                        goto again;
                printk(KERN_ERR "nbd: nbd%d already in use\n", index);
                return -EBUSY;
        }
        if (WARN_ON(nbd->config)) {
                mutex_unlock(&nbd->config_lock);
                nbd_put(nbd);
                return -EINVAL;
        }
        config = nbd->config = nbd_alloc_config();
        if (!nbd->config) {
                mutex_unlock(&nbd->config_lock);
                nbd_put(nbd);
                printk(KERN_ERR "nbd: couldn't allocate config\n");
                return -ENOMEM;
        }
        refcount_set(&nbd->config_refs, 1);
        set_bit(NBD_RT_BOUND, &config->runtime_flags);

        ret = nbd_genl_size_set(info, nbd);
        if (ret)
                goto out;

        if (info->attrs[NBD_ATTR_TIMEOUT])
                nbd_set_cmd_timeout(nbd,
                                    nla_get_u64(info->attrs[NBD_ATTR_TIMEOUT]));
        if (info->attrs[NBD_ATTR_DEAD_CONN_TIMEOUT]) {
                config->dead_conn_timeout =
                        nla_get_u64(info->attrs[NBD_ATTR_DEAD_CONN_TIMEOUT]);
                config->dead_conn_timeout *= HZ;
        }
        if (info->attrs[NBD_ATTR_SERVER_FLAGS])
                config->flags =
                        nla_get_u64(info->attrs[NBD_ATTR_SERVER_FLAGS]);
        if (info->attrs[NBD_ATTR_CLIENT_FLAGS]) {
                u64 flags = nla_get_u64(info->attrs[NBD_ATTR_CLIENT_FLAGS]);
                if (flags & NBD_CFLAG_DESTROY_ON_DISCONNECT) {
                        /*
                         * We have 1 ref to keep the device around, and then 1
                         * ref for our current operation here, which will be
                         * inherited by the config.  If we already have
                         * DESTROY_ON_DISCONNECT set then we know we don't have
                         * that extra ref already held so we don't need the
                         * put_dev.
                         */
                        if (!test_and_set_bit(NBD_DESTROY_ON_DISCONNECT,
                                              &nbd->flags))
                                put_dev = true;
                } else {
                        if (test_and_clear_bit(NBD_DESTROY_ON_DISCONNECT,
                                               &nbd->flags))
                                refcount_inc(&nbd->refs);
                }
                if (flags & NBD_CFLAG_DISCONNECT_ON_CLOSE) {
                        set_bit(NBD_RT_DISCONNECT_ON_CLOSE,
                                &config->runtime_flags);
                }
        }

        if (info->attrs[NBD_ATTR_SOCKETS]) {
                struct nlattr *attr;
                int rem, fd;

                nla_for_each_nested(attr, info->attrs[NBD_ATTR_SOCKETS],
                                    rem) {
                        struct nlattr *socks[NBD_SOCK_MAX+1];

                        if (nla_type(attr) != NBD_SOCK_ITEM) {
                                printk(KERN_ERR "nbd: socks must be embedded in a SOCK_ITEM attr\n");
                                ret = -EINVAL;
                                goto out;
                        }
                        ret = nla_parse_nested_deprecated(socks, NBD_SOCK_MAX,
                                                          attr,
                                                          nbd_sock_policy,
                                                          info->extack);
                        if (ret != 0) {
                                printk(KERN_ERR "nbd: error processing sock list\n");
                                ret = -EINVAL;
                                goto out;
                        }
                        if (!socks[NBD_SOCK_FD])
                                continue;
                        fd = (int)nla_get_u32(socks[NBD_SOCK_FD]);
                        ret = nbd_add_socket(nbd, fd, true);
                        if (ret)
                                goto out;
                }
        }
        ret = nbd_start_device(nbd);
        if (ret)
                goto out;
        if (info->attrs[NBD_ATTR_BACKEND_IDENTIFIER]) {
                nbd->backend = nla_strdup(info->attrs[NBD_ATTR_BACKEND_IDENTIFIER],
                                          GFP_KERNEL);
                if (!nbd->backend) {
                        ret = -ENOMEM;
                        goto out;
                }
        }
        ret = device_create_file(disk_to_dev(nbd->disk), &backend_attr);
        if (ret) {
                dev_err(disk_to_dev(nbd->disk),
                        "device_create_file failed for backend!\n");
                goto out;
        }
        set_bit(NBD_RT_HAS_BACKEND_FILE, &config->runtime_flags);
out:
        mutex_unlock(&nbd->config_lock);
        if (!ret) {
                set_bit(NBD_RT_HAS_CONFIG_REF, &config->runtime_flags);
                refcount_inc(&nbd->config_refs);
                nbd_connect_reply(info, nbd->index);
        }