// SPDX-License-Identifier: GPL-2.0
/*
  FUSE: Filesystem in Userspace
  Copyright (C) 2001-2008  Miklos Szeredi <miklos@szeredi.hu>
*/

#include "dev.h"
#include "args.h"
#include "dev_uring_i.h"

#include <linux/init.h>
#include <linux/module.h>
#include <linux/poll.h>
#include <linux/sched/signal.h>
#include <linux/uio.h>
#include <linux/miscdevice.h>
#include <linux/pagemap.h>
#include <linux/file.h>
#include <linux/slab.h>
#include <linux/pipe_fs_i.h>
#include <linux/swap.h>
#include <linux/splice.h>
#include <linux/sched.h>
#include <linux/seq_file.h>

#include "fuse_trace.h"

MODULE_ALIAS_MISCDEV(FUSE_MINOR);
MODULE_ALIAS("devname:fuse");

static DECLARE_WAIT_QUEUE_HEAD(fuse_dev_waitq);

static struct kmem_cache *fuse_req_cachep;

static void fuse_request_init(struct fuse_chan *fch, struct fuse_req *req)
{
        INIT_LIST_HEAD(&req->list);
        INIT_LIST_HEAD(&req->intr_entry);
        init_waitqueue_head(&req->waitq);
        refcount_set(&req->count, 1);
        __set_bit(FR_PENDING, &req->flags);
        req->chan = fch;
        req->create_time = jiffies;
}

static struct fuse_req *fuse_request_alloc(struct fuse_chan *fch, gfp_t flags)
{
        struct fuse_req *req = kmem_cache_zalloc(fuse_req_cachep, flags);
        if (req)
                fuse_request_init(fch, req);

        return req;
}

static void fuse_request_free(struct fuse_req *req)
{
        WARN_ON(!list_empty(&req->intr_entry));
        kmem_cache_free(fuse_req_cachep, req);
}

static void __fuse_get_request(struct fuse_req *req)
{
        refcount_inc(&req->count);
}

/* Must be called with > 1 refcount */
static void __fuse_put_request(struct fuse_req *req)
{
        refcount_dec(&req->count);
}

void fuse_chan_set_initialized(struct fuse_chan *fch, struct fuse_chan_param *param)
{
        if (param) {
                fch->minor = param->minor;
                fch->max_write = param->max_write;
                fch->max_pages = param->max_pages;
        }

        /* Make sure stores before this are seen on another CPU */
        smp_wmb();
        fch->initialized = 1;
        wake_up_all(&fch->blocked_waitq);
}

static bool fuse_block_alloc(struct fuse_chan *fch, bool for_background)
{
        return !fch->initialized || (for_background && fch->blocked) ||
               (fch->io_uring && fch->connected && !fuse_uring_ready(fch));
}

static void fuse_drop_waiting(struct fuse_chan *fch)
{
        /*
         * lockess check of fch->connected is okay, because atomic_dec_and_test()
         * provides a memory barrier matched with the one in fuse_chan_wait_aborted()
         * to ensure no wake-up is missed.
         */
        if (atomic_dec_and_test(&fch->num_waiting) &&
            !READ_ONCE(fch->connected)) {
                /* wake up aborters */
                wake_up_all(&fch->blocked_waitq);
        }
}

static void fuse_put_request(struct fuse_req *req);

static struct fuse_req *fuse_get_req(struct fuse_chan *fch, bool for_background)
{
        struct fuse_req *req;
        int err;

        atomic_inc(&fch->num_waiting);

        if (fuse_block_alloc(fch, for_background)) {
                err = -EINTR;
                if (wait_event_state_exclusive(fch->blocked_waitq,
                                !fuse_block_alloc(fch, for_background),
                                (TASK_KILLABLE | TASK_FREEZABLE)))
                        goto out;
        }

        /* Matches smp_wmb() in fuse_chan_set_initialized() */
        smp_rmb();

        err = -ENOTCONN;
        if (!fch->connected)
                goto out;

        req = fuse_request_alloc(fch, GFP_KERNEL);
        err = -ENOMEM;
        if (!req) {
                if (for_background)
                        wake_up(&fch->blocked_waitq);
                goto out;
        }

        __set_bit(FR_WAITING, &req->flags);
        if (for_background)
                __set_bit(FR_BACKGROUND, &req->flags);

        return req;

 out:
        fuse_drop_waiting(fch);
        return ERR_PTR(err);
}

static void fuse_put_request(struct fuse_req *req)
{
        struct fuse_chan *fch = req->chan;

        if (refcount_dec_and_test(&req->count)) {
                if (test_bit(FR_BACKGROUND, &req->flags)) {
                        /*
                         * We get here in the unlikely case that a background
                         * request was allocated but not sent
                         */
                        spin_lock(&fch->bg_lock);
                        if (!fch->blocked)
                                wake_up(&fch->blocked_waitq);
                        spin_unlock(&fch->bg_lock);
                }

                if (test_bit(FR_WAITING, &req->flags)) {
                        __clear_bit(FR_WAITING, &req->flags);
                        fuse_drop_waiting(fch);
                }

                fuse_request_free(req);
        }
}

unsigned int fuse_len_args(unsigned int numargs, struct fuse_arg *args)
{
        unsigned nbytes = 0;
        unsigned i;

        for (i = 0; i < numargs; i++)
                nbytes += args[i].size;

        return nbytes;
}
EXPORT_SYMBOL_GPL(fuse_len_args);

static u64 fuse_get_unique_locked(struct fuse_iqueue *fiq)
{
        fiq->reqctr += FUSE_REQ_ID_STEP;
        return fiq->reqctr;
}

u64 fuse_get_unique(struct fuse_iqueue *fiq)
{
        u64 ret;

        spin_lock(&fiq->lock);
        ret = fuse_get_unique_locked(fiq);
        spin_unlock(&fiq->lock);

        return ret;
}
EXPORT_SYMBOL_GPL(fuse_get_unique);

unsigned int fuse_req_hash(u64 unique)
{
        return hash_long(unique & ~FUSE_INT_REQ_BIT, FUSE_PQ_HASH_BITS);
}
EXPORT_SYMBOL_GPL(fuse_req_hash);

/*
 * A new request is available, wake fiq->waitq
 */
static void fuse_dev_wake_and_unlock(struct fuse_iqueue *fiq)
__releases(fiq->lock)
{
        wake_up(&fiq->waitq);
        kill_fasync(&fiq->fasync, SIGIO, POLL_IN);
        spin_unlock(&fiq->lock);
}

struct fuse_forget_link *fuse_alloc_forget(void)
{
        return kzalloc_obj(struct fuse_forget_link, GFP_KERNEL_ACCOUNT);
}

void fuse_dev_queue_forget(struct fuse_iqueue *fiq,
                           struct fuse_forget_link *forget)
{
        spin_lock(&fiq->lock);
        if (fiq->connected) {
                fiq->forget_list_tail->next = forget;
                fiq->forget_list_tail = forget;
                fuse_dev_wake_and_unlock(fiq);
        } else {
                kfree(forget);
                spin_unlock(&fiq->lock);
        }
}

void fuse_dev_queue_interrupt(struct fuse_iqueue *fiq, struct fuse_req *req)
{
        spin_lock(&fiq->lock);
        if (list_empty(&req->intr_entry)) {
                list_add_tail(&req->intr_entry, &fiq->interrupts);
                /*
                 * Pairs with smp_mb() implied by test_and_set_bit()
                 * from fuse_request_end().
                 */
                smp_mb();
                if (test_bit(FR_FINISHED, &req->flags)) {
                        list_del_init(&req->intr_entry);
                        spin_unlock(&fiq->lock);
                } else  {
                        fuse_dev_wake_and_unlock(fiq);
                }
        } else {
                spin_unlock(&fiq->lock);
        }
}

static inline void fuse_request_assign_unique_locked(struct fuse_iqueue *fiq,
                                                     struct fuse_req *req)
{
        if (req->in.h.opcode != FUSE_NOTIFY_REPLY)
                req->in.h.unique = fuse_get_unique_locked(fiq);

        /* tracepoint captures in.h.unique and in.h.len */
        trace_fuse_request_send(req);
}

inline void fuse_request_assign_unique(struct fuse_iqueue *fiq,
                                       struct fuse_req *req)
{
        if (req->in.h.opcode != FUSE_NOTIFY_REPLY)
                req->in.h.unique = fuse_get_unique(fiq);

        /* tracepoint captures in.h.unique and in.h.len */
        trace_fuse_request_send(req);
}
EXPORT_SYMBOL_GPL(fuse_request_assign_unique);

static void fuse_dev_queue_req(struct fuse_iqueue *fiq, struct fuse_req *req)
{
        spin_lock(&fiq->lock);
        if (fiq->connected) {
                fuse_request_assign_unique_locked(fiq, req);
                list_add_tail(&req->list, &fiq->pending);
                fuse_dev_wake_and_unlock(fiq);
        } else {
                spin_unlock(&fiq->lock);
                req->out.h.error = -ENOTCONN;
                clear_bit(FR_PENDING, &req->flags);
                fuse_request_end(req);
        }
}

static const struct fuse_iqueue_ops fuse_dev_fiq_ops = {
        .send_forget    = fuse_dev_queue_forget,
        .send_interrupt = fuse_dev_queue_interrupt,
        .send_req       = fuse_dev_queue_req,
};

void fuse_iqueue_init(struct fuse_iqueue *fiq, const struct fuse_iqueue_ops *ops, void *priv)
{
        spin_lock_init(&fiq->lock);
        init_waitqueue_head(&fiq->waitq);
        INIT_LIST_HEAD(&fiq->pending);
        INIT_LIST_HEAD(&fiq->interrupts);
        fiq->forget_list_tail = &fiq->forget_list_head;
        fiq->connected = 1;
        fiq->ops = ops;
        fiq->priv = priv;
}
EXPORT_SYMBOL_GPL(fuse_iqueue_init);

void fuse_chan_release(struct fuse_chan *fch)
{
        struct fuse_iqueue *fiq = &fch->iq;

        if (fiq->ops->release)
                fiq->ops->release(fiq);

        if (fch->timeout.req_timeout)
                cancel_delayed_work_sync(&fch->timeout.work);
}

void fuse_chan_free(struct fuse_chan *fch)
{
        WARN_ON(!list_empty(&fch->devices));
        kfree(fch->pq_prealloc);
        kfree(fch);
}
EXPORT_SYMBOL_GPL(fuse_chan_free);

struct fuse_chan *fuse_chan_new(void)
{
        struct fuse_chan *fch = kzalloc_obj(struct fuse_chan);
        if (!fch)
                return NULL;

        spin_lock_init(&fch->lock);
        INIT_LIST_HEAD(&fch->devices);
        spin_lock_init(&fch->bg_lock);
        INIT_LIST_HEAD(&fch->bg_queue);
        init_waitqueue_head(&fch->blocked_waitq);
        atomic_set(&fch->num_waiting, 0);
        fch->max_background = FUSE_DEFAULT_MAX_BACKGROUND;
        fch->initialized = 0;
        fch->blocked = 0;
        fch->connected = 1;
        fch->timeout.req_timeout = 0;

        return fch;
}
EXPORT_SYMBOL_GPL(fuse_chan_new);

struct list_head *fuse_pqueue_alloc(void)
{
        struct list_head *pq = kzalloc_objs(struct list_head, FUSE_PQ_HASH_SIZE);

        if (pq) {
                for (int i = 0; i < FUSE_PQ_HASH_SIZE; i++)
                        INIT_LIST_HEAD(&pq[i]);
        }
        return pq;
}

struct fuse_chan *fuse_dev_chan_new(void)
{
        struct fuse_chan *fch __free(kfree) = fuse_chan_new();
        if (!fch)
                return NULL;

        fch->pq_prealloc = fuse_pqueue_alloc();
        if (!fch->pq_prealloc)
                return NULL;

        fuse_iqueue_init(&fch->iq, &fuse_dev_fiq_ops, NULL);

        return no_free_ptr(fch);
}
EXPORT_SYMBOL_GPL(fuse_dev_chan_new);

unsigned int fuse_chan_num_background(struct fuse_chan *fch)
{
        return READ_ONCE(fch->num_background);
}

unsigned int fuse_chan_max_background(struct fuse_chan *fch)
{
        return READ_ONCE(fch->max_background);
}

void fuse_chan_max_background_set(struct fuse_chan *fch, unsigned int val)
{
        spin_lock(&fch->bg_lock);
        fch->max_background = val;
        fch->blocked = fch->num_background >= fch->max_background;
        if (!fch->blocked)
                wake_up(&fch->blocked_waitq);
        spin_unlock(&fch->bg_lock);
}

unsigned int fuse_chan_num_waiting(struct fuse_chan *fch)
{
        return atomic_read(&fch->num_waiting);
}

void fuse_chan_set_fc(struct fuse_chan *fch, struct fuse_conn *fc)
{
        fch->conn = fc;
}

void fuse_chan_io_uring_enable(struct fuse_chan *fch)
{
        fch->io_uring = 1;
}

void fuse_pqueue_init(struct fuse_pqueue *fpq)
{
        spin_lock_init(&fpq->lock);
        INIT_LIST_HEAD(&fpq->io);
        fpq->connected = 1;
        fpq->processing = NULL;
}

static struct fuse_dev *fuse_dev_alloc_no_pq(void)
{
        struct fuse_dev *fud;

        fud = kzalloc_obj(struct fuse_dev);
        if (!fud)
                return NULL;

        refcount_set(&fud->ref, 1);
        fuse_pqueue_init(&fud->pq);

        return fud;
}

struct fuse_dev *fuse_dev_alloc(void)
{
        struct fuse_dev *fud __free(kfree) = fuse_dev_alloc_no_pq();
        if (!fud)
                return NULL;

        fud->pq.processing = fuse_pqueue_alloc();
        if (!fud->pq.processing)
                return NULL;

        return no_free_ptr(fud);
}
EXPORT_SYMBOL_GPL(fuse_dev_alloc);

/*
 * Installs @fch into @fud, return true on success.  "Consumes" @pq in either case.
 */
static bool fuse_dev_install_with_pq(struct fuse_dev *fud, struct fuse_chan *fch,
                                     struct list_head *pq)
{
        struct fuse_chan *old_fch;

        guard(spinlock)(&fch->lock);
        /*
         * Pairs with:
         *  - xchg() in fuse_dev_release()
         *  - smp_load_acquire() in fuse_dev_fc_get()
         */
        old_fch = cmpxchg(&fud->chan, NULL, fch);
        if (old_fch) {
                /*
                 * failed to set fud->chan because
                 *  - it was already set to a different fc
                 *  - it was set to disconneted
                 */
                kfree(pq);
                return false;
        }
        if (pq) {
                WARN_ON(fud->pq.processing);
                fud->pq.processing = pq;
        }
        list_add_tail(&fud->entry, &fch->devices);
        fuse_conn_get(fch->conn);
        wake_up_all(&fuse_dev_waitq);
        return true;
}

void fuse_dev_install(struct fuse_dev *fud, struct fuse_chan *fch)
{
        struct list_head *pq = fch->pq_prealloc;

        fch->pq_prealloc = NULL;
        if (!fuse_dev_install_with_pq(fud, fch, pq)) {
                /* Channel is not usable without a dev */
                fuse_chan_abort(fch, false);
        }
}
EXPORT_SYMBOL_GPL(fuse_dev_install);

struct fuse_dev *fuse_dev_alloc_install(struct fuse_chan *fch)
{
        struct fuse_dev *fud;

        fud = fuse_dev_alloc_no_pq();
        if (!fud)
                return NULL;

        fuse_dev_install(fud, fch);
        return fud;
}
EXPORT_SYMBOL_GPL(fuse_dev_alloc_install);

void fuse_dev_put(struct fuse_dev *fud)
{
        struct fuse_chan *fch;

        if (!refcount_dec_and_test(&fud->ref))
                return;

        fch = fuse_dev_chan_get(fud);
        if (fch && fch != FUSE_DEV_CHAN_DISCONNECTED) {
                /* This is the virtiofs case (fuse_dev_release() not called) */
                spin_lock(&fch->lock);
                list_del(&fud->entry);
                spin_unlock(&fch->lock);

                fuse_conn_put(fch->conn);
        }
        kfree(fud->pq.processing);
        kfree(fud);
}
EXPORT_SYMBOL_GPL(fuse_dev_put);

bool fuse_dev_is_installed(struct fuse_dev *fud)
{
        struct fuse_chan *fch = fuse_dev_chan_get(fud);

        return fch != NULL && fch != FUSE_DEV_CHAN_DISCONNECTED;
}

/*
 * Checks if @fc matches the one installed in @fud
 */
bool fuse_dev_verify(struct fuse_dev *fud, struct fuse_chan *fch)
{
        return fuse_dev_chan_get(fud) == fch;
}

bool fuse_dev_is_sync_init(struct fuse_dev *fud)
{
        return fud->sync_init;
}

struct fuse_dev *fuse_dev_grab(struct file *file)
{
        struct fuse_dev *fud = fuse_file_to_fud(file);

        refcount_inc(&fud->ref);
        return fud;
}

static void fuse_send_one(struct fuse_iqueue *fiq, struct fuse_req *req)
{
        req->in.h.len = sizeof(struct fuse_in_header) +
                fuse_len_args(req->args->in_numargs,
                              (struct fuse_arg *) req->args->in_args);
        fiq->ops->send_req(fiq, req);
}

void fuse_chan_queue_forget(struct fuse_chan *fch, struct fuse_forget_link *forget,
                            u64 nodeid, u64 nlookup)
{
        struct fuse_iqueue *fiq = &fch->iq;

        forget->forget_one.nodeid = nodeid;
        forget->forget_one.nlookup = nlookup;

        fiq->ops->send_forget(fiq, forget);
}

static void flush_bg_queue(struct fuse_chan *fch)
{
        struct fuse_iqueue *fiq = &fch->iq;

        while (fch->active_background < fch->max_background &&
               !list_empty(&fch->bg_queue)) {
                struct fuse_req *req;

                req = list_first_entry(&fch->bg_queue, struct fuse_req, list);
                list_del(&req->list);
                fch->active_background++;
                fuse_send_one(fiq, req);
        }
}

void fuse_request_bg_finish(struct fuse_chan *fch, struct fuse_req *req)
{
        lockdep_assert_held(&fch->bg_lock);

        clear_bit(FR_BACKGROUND, &req->flags);
        if (fch->num_background == fch->max_background) {
                fch->blocked = 0;
                wake_up(&fch->blocked_waitq);
        } else if (!fch->blocked) {
                /*
                 * Wake up next waiter, if any.  It's okay to use
                 * waitqueue_active(), as we've already synced up
                 * fch->blocked with waiters with the wake_up() call
                 * above.
                 */
                if (waitqueue_active(&fch->blocked_waitq))
                        wake_up(&fch->blocked_waitq);
        }

        fch->num_background--;
        fch->active_background--;
}

/*
 * This function is called when a request is finished.  Either a reply
 * has arrived or it was aborted (and not yet sent) or some error
 * occurred during communication with userspace, or the device file
 * was closed.  The requester thread is woken up (if still waiting),
 * the 'end' callback is called if given, else the reference to the
 * request is released
 */
void fuse_request_end(struct fuse_req *req)
{
        struct fuse_chan *fch = req->chan;
        struct fuse_iqueue *fiq = &fch->iq;

        if (test_and_set_bit(FR_FINISHED, &req->flags))
                goto put_request;

        trace_fuse_request_end(req);
        /*
         * test_and_set_bit() implies smp_mb() between bit
         * changing and below FR_INTERRUPTED check. Pairs with
         * smp_mb() from queue_interrupt().
         */
        if (test_bit(FR_INTERRUPTED, &req->flags)) {
                spin_lock(&fiq->lock);
                list_del_init(&req->intr_entry);
                spin_unlock(&fiq->lock);
        }
        WARN_ON(test_bit(FR_PENDING, &req->flags));
        WARN_ON(test_bit(FR_SENT, &req->flags));
        if (test_bit(FR_BACKGROUND, &req->flags)) {
                spin_lock(&fch->bg_lock);
                fuse_request_bg_finish(fch, req);
                flush_bg_queue(fch);
                spin_unlock(&fch->bg_lock);
        } else {
                /* Wake up waiter sleeping in request_wait_answer() */
                wake_up(&req->waitq);
        }

        if (test_bit(FR_ASYNC, &req->flags))
                req->args->end(req->args, req->out.h.error);
put_request:
        fuse_put_request(req);
}
EXPORT_SYMBOL_GPL(fuse_request_end);

static int queue_interrupt(struct fuse_req *req)
{
        struct fuse_iqueue *fiq = &req->chan->iq;

        /* Check for we've sent request to interrupt this req */
        if (unlikely(!test_bit(FR_INTERRUPTED, &req->flags)))
                return -EINVAL;

        fiq->ops->send_interrupt(fiq, req);

        return 0;
}

bool fuse_remove_pending_req(struct fuse_req *req, spinlock_t *lock)
{
        spin_lock(lock);
        if (test_bit(FR_PENDING, &req->flags)) {
                /*
                 * FR_PENDING does not get cleared as the request will end
                 * up in destruction anyway.
                 */
                list_del(&req->list);
                spin_unlock(lock);
                __fuse_put_request(req);
                req->out.h.error = -EINTR;
                return true;
        }
        spin_unlock(lock);
        return false;
}

static void request_wait_answer(struct fuse_req *req)
{
        struct fuse_chan *fch = req->chan;
        struct fuse_iqueue *fiq = &fch->iq;
        int err;

        if (!fch->no_interrupt) {
                /* Any signal may interrupt this */
                err = wait_event_interruptible(req->waitq,
                                        test_bit(FR_FINISHED, &req->flags));
                if (!err)
                        return;

                set_bit(FR_INTERRUPTED, &req->flags);
                /* matches barrier in fuse_dev_do_read() */
                smp_mb__after_atomic();
                if (test_bit(FR_SENT, &req->flags))
                        queue_interrupt(req);
        }

        if (!test_bit(FR_FORCE, &req->flags)) {
                bool removed;

                /* Only fatal signals may interrupt this */
                err = wait_event_killable(req->waitq,
                                        test_bit(FR_FINISHED, &req->flags));
                if (!err)
                        return;

                if (req->args->abort_on_kill) {
                        fuse_chan_abort(fch, false);
                        return;
                }

                if (test_bit(FR_URING, &req->flags))
                        removed = fuse_uring_remove_pending_req(req);
                else
                        removed = fuse_remove_pending_req(req, &fiq->lock);
                if (removed)
                        return;
        }

        /*
         * Either request is already in userspace, or it was forced.
         * Wait it out.
         */
        wait_event(req->waitq, test_bit(FR_FINISHED, &req->flags));
}

static void __fuse_request_send(struct fuse_req *req)
{
        struct fuse_iqueue *fiq = &req->chan->iq;

        BUG_ON(test_bit(FR_BACKGROUND, &req->flags));

        /* acquire extra reference, since request is still needed after
           fuse_request_end() */
        __fuse_get_request(req);
        fuse_send_one(fiq, req);

        request_wait_answer(req);
        /* Pairs with smp_wmb() in fuse_request_end() */
        smp_rmb();
}

static void fuse_adjust_compat(struct fuse_chan *fch, struct fuse_args *args)
{
        if (fch->minor < 4 && args->opcode == FUSE_STATFS)
                args->out_args[0].size = FUSE_COMPAT_STATFS_SIZE;

        if (fch->minor < 9) {
                switch (args->opcode) {
                case FUSE_LOOKUP:
                case FUSE_CREATE:
                case FUSE_MKNOD:
                case FUSE_MKDIR:
                case FUSE_SYMLINK:
                case FUSE_LINK:
                        args->out_args[0].size = FUSE_COMPAT_ENTRY_OUT_SIZE;
                        break;
                case FUSE_GETATTR:
                case FUSE_SETATTR:
                        args->out_args[0].size = FUSE_COMPAT_ATTR_OUT_SIZE;
                        break;
                }
        }
        if (fch->minor < 12) {
                switch (args->opcode) {
                case FUSE_CREATE:
                        args->in_args[0].size = sizeof(struct fuse_open_in);
                        break;
                case FUSE_MKNOD:
                        args->in_args[0].size = FUSE_COMPAT_MKNOD_IN_SIZE;
                        break;
                }
        }
}

static void fuse_args_to_req(struct fuse_req *req, struct fuse_args *args)
{
        req->in.h.opcode = args->opcode;
        req->in.h.nodeid = args->nodeid;
        req->in.h.uid = args->uid;
        req->in.h.gid = args->gid;
        req->in.h.pid = args->pid;
        req->args = args;
        if (args->is_ext)
                req->in.h.total_extlen = args->in_args[args->ext_idx].size / 8;
        if (args->end)
                __set_bit(FR_ASYNC, &req->flags);
}

ssize_t fuse_chan_send(struct fuse_chan *fch, struct fuse_args *args)
{
        struct fuse_req *req;
        ssize_t ret;

        if (args->force) {
                atomic_inc(&fch->num_waiting);
                req = fuse_request_alloc(fch, GFP_KERNEL | __GFP_NOFAIL);

                __set_bit(FR_WAITING, &req->flags);
                if (!args->abort_on_kill)
                        __set_bit(FR_FORCE, &req->flags);
        } else {
                req = fuse_get_req(fch, false);
                if (IS_ERR(req))
                        return PTR_ERR(req);
        }

        /* Needs to be done after fuse_get_req() so that fch->minor is valid */
        fuse_adjust_compat(fch, args);
        fuse_args_to_req(req, args);

        if (!args->noreply)
                __set_bit(FR_ISREPLY, &req->flags);
        __fuse_request_send(req);
        ret = req->out.h.error;
        if (!ret && args->out_argvar) {
                BUG_ON(args->out_numargs == 0);
                ret = args->out_args[args->out_numargs - 1].size;
        }
        fuse_put_request(req);

        return ret;
}

#ifdef CONFIG_FUSE_IO_URING
static bool fuse_request_queue_background_uring(struct fuse_req *req)
{
        struct fuse_iqueue *fiq = &req->chan->iq;

        req->in.h.len = sizeof(struct fuse_in_header) +
                fuse_len_args(req->args->in_numargs,
                              (struct fuse_arg *) req->args->in_args);
        fuse_request_assign_unique(fiq, req);

        return fuse_uring_queue_bq_req(req);
}
#endif

/*
 * @return true if queued
 */
static int fuse_request_queue_background(struct fuse_req *req)
{
        struct fuse_chan *fch = req->chan;
        bool queued = false;

        WARN_ON(!test_bit(FR_BACKGROUND, &req->flags));
        if (!test_bit(FR_WAITING, &req->flags)) {
                __set_bit(FR_WAITING, &req->flags);
                atomic_inc(&fch->num_waiting);
        }
        __set_bit(FR_ISREPLY, &req->flags);

#ifdef CONFIG_FUSE_IO_URING
        if (fuse_uring_ready(fch))
                return fuse_request_queue_background_uring(req);
#endif

        spin_lock(&fch->bg_lock);
        if (likely(fch->connected)) {
                fch->num_background++;
                if (fch->num_background == fch->max_background)
                        fch->blocked = 1;
                list_add_tail(&req->list, &fch->bg_queue);
                flush_bg_queue(fch);
                queued = true;
        }
        spin_unlock(&fch->bg_lock);

        return queued;
}

int fuse_chan_send_bg(struct fuse_chan *fch, struct fuse_args *args, gfp_t gfp_flags)
{
        struct fuse_req *req;

        if (args->force) {
                req = fuse_request_alloc(fch, gfp_flags);
                if (!req)
                        return -ENOMEM;
                __set_bit(FR_BACKGROUND, &req->flags);
        } else {
                req = fuse_get_req(fch, true);
                if (IS_ERR(req))
                        return PTR_ERR(req);
        }

        fuse_args_to_req(req, args);

        if (!fuse_request_queue_background(req)) {
                fuse_put_request(req);
                return -ENOTCONN;
        }

        return 0;
}

int fuse_chan_send_notify_reply(struct fuse_chan *fch, struct fuse_args *args, u64 unique)
{
        struct fuse_req *req;
        struct fuse_iqueue *fiq = &fch->iq;

        req = fuse_get_req(fch, false);
        if (IS_ERR(req))
                return PTR_ERR(req);

        __clear_bit(FR_ISREPLY, &req->flags);
        req->in.h.unique = unique;

        fuse_args_to_req(req, args);

        fuse_send_one(fiq, req);

        return 0;
}

/*
 * Lock the request.  Up to the next unlock_request() there mustn't be
 * anything that could cause a page-fault.  If the request was already
 * aborted bail out.
 */
static int lock_request(struct fuse_req *req)
{
        int err = 0;
        if (req) {
                spin_lock(&req->waitq.lock);
                if (test_bit(FR_ABORTED, &req->flags))
                        err = -ENOENT;
                else
                        set_bit(FR_LOCKED, &req->flags);
                spin_unlock(&req->waitq.lock);
        }
        return err;
}

/*
 * Unlock request.  If it was aborted while locked, caller is responsible
 * for unlocking and ending the request.
 */
static int unlock_request(struct fuse_req *req)
{
        int err = 0;
        if (req) {
                spin_lock(&req->waitq.lock);
                if (test_bit(FR_ABORTED, &req->flags))
                        err = -ENOENT;
                else
                        clear_bit(FR_LOCKED, &req->flags);
                spin_unlock(&req->waitq.lock);
        }
        return err;
}

void fuse_copy_init(struct fuse_copy_state *cs, bool write,
                    struct iov_iter *iter)
{
        memset(cs, 0, sizeof(*cs));
        cs->write = write;
        cs->iter = iter;
}

/* Unmap and put previous page of userspace buffer */
void fuse_copy_finish(struct fuse_copy_state *cs)
{
        if (cs->currbuf) {
                struct pipe_buffer *buf = cs->currbuf;

                if (cs->write)
                        buf->len = PAGE_SIZE - cs->len;
                cs->currbuf = NULL;
        } else if (cs->pg) {
                if (cs->write) {
                        flush_dcache_page(cs->pg);
                        set_page_dirty_lock(cs->pg);
                }
                put_page(cs->pg);
        }
        cs->pg = NULL;
}

/*
 * Get another pagefull of userspace buffer, and map it to kernel
 * address space, and lock request
 */
static int fuse_copy_fill(struct fuse_copy_state *cs)
{
        struct page *page;
        int err;

        err = unlock_request(cs->req);
        if (err)
                return err;

        fuse_copy_finish(cs);
        if (cs->pipebufs) {
                struct pipe_buffer *buf = cs->pipebufs;

                if (!cs->write) {
                        err = pipe_buf_confirm(cs->pipe, buf);
                        if (err)
                                return err;

                        BUG_ON(!cs->nr_segs);
                        cs->currbuf = buf;
                        cs->pg = buf->page;
                        cs->offset = buf->offset;
                        cs->len = buf->len;
                        cs->pipebufs++;
                        cs->nr_segs--;
                } else {
                        if (cs->nr_segs >= cs->pipe->max_usage)
                                return -EIO;

                        page = alloc_page(GFP_HIGHUSER);
                        if (!page)
                                return -ENOMEM;

                        buf->page = page;
                        buf->offset = 0;
                        buf->len = 0;

                        cs->currbuf = buf;
                        cs->pg = page;
                        cs->offset = 0;
                        cs->len = PAGE_SIZE;
                        cs->pipebufs++;
                        cs->nr_segs++;
                }
        } else {
                size_t off;
                err = iov_iter_get_pages2(cs->iter, &page, PAGE_SIZE, 1, &off);
                if (err < 0)
                        return err;
                BUG_ON(!err);
                cs->len = err;
                cs->offset = off;
                cs->pg = page;
        }

        return lock_request(cs->req);
}

/* Do as much copy to/from userspace buffer as we can */
static int fuse_copy_do(struct fuse_copy_state *cs, void **val, unsigned *size)
{
        unsigned ncpy = min(*size, cs->len);
        if (val) {
                void *pgaddr = kmap_local_page(cs->pg);
                void *buf = pgaddr + cs->offset;

                if (cs->write)
                        memcpy(buf, *val, ncpy);
                else
                        memcpy(*val, buf, ncpy);

                kunmap_local(pgaddr);
                *val += ncpy;
        }
        *size -= ncpy;
        cs->len -= ncpy;
        cs->offset += ncpy;
        if (cs->is_uring)
                cs->ring.copied_sz += ncpy;

        return ncpy;
}

static int fuse_check_folio(struct folio *folio)
{
        if (folio_mapped(folio) ||
            folio->mapping != NULL ||
            (folio->flags.f & PAGE_FLAGS_CHECK_AT_PREP &
             ~(1 << PG_locked |
               1 << PG_referenced |
               1 << PG_lru |
               1 << PG_active |
               1 << PG_workingset |
               1 << PG_reclaim |
               1 << PG_waiters |
               LRU_GEN_MASK | LRU_REFS_MASK))) {
                dump_page(&folio->page, "fuse: trying to steal weird page");
                return 1;
        }
        return 0;
}

/*
 * Attempt to steal a page from the splice() pipe and move it into the
 * pagecache. If successful, the pointer in @pagep will be updated. The
 * folio that was originally in @pagep will lose a reference and the new
 * folio returned in @pagep will carry a reference.
 */
static int fuse_try_move_folio(struct fuse_copy_state *cs, struct folio **foliop)
{
        int err;
        struct folio *oldfolio = *foliop;
        struct folio *newfolio;
        struct pipe_buffer *buf = cs->pipebufs;

        folio_get(oldfolio);
        err = unlock_request(cs->req);
        if (err)
                goto out_put_old;

        fuse_copy_finish(cs);

        err = pipe_buf_confirm(cs->pipe, buf);
        if (err)
                goto out_put_old;

        BUG_ON(!cs->nr_segs);
        cs->currbuf = buf;
        cs->len = buf->len;
        cs->pipebufs++;
        cs->nr_segs--;

        if (cs->len != folio_size(oldfolio))
                goto out_fallback;

        if (!pipe_buf_try_steal(cs->pipe, buf))
                goto out_fallback;

        newfolio = page_folio(buf->page);

        folio_clear_uptodate(newfolio);
        folio_clear_mappedtodisk(newfolio);

        if (folio_test_large(newfolio))
                goto out_fallback_unlock;

        if (fuse_check_folio(newfolio) != 0)
                goto out_fallback_unlock;

        /*
         * This is a new and locked page, it shouldn't be mapped or
         * have any special flags on it
         */
        if (WARN_ON(folio_mapped(oldfolio)))
                goto out_fallback_unlock;
        if (WARN_ON(folio_has_private(oldfolio)))
                goto out_fallback_unlock;
        if (WARN_ON(folio_test_dirty(oldfolio) ||
                                folio_test_writeback(oldfolio)))
                goto out_fallback_unlock;
        if (WARN_ON(folio_test_mlocked(oldfolio)))
                goto out_fallback_unlock;

        err = lock_request(cs->req);
        if (err)
                goto out_fallback_unlock;

        replace_page_cache_folio(oldfolio, newfolio);

        folio_get(newfolio);

        if (!(buf->flags & PIPE_BUF_FLAG_LRU))
                folio_add_lru(newfolio);

        /*
         * Release while we have extra ref on stolen page.  Otherwise
         * anon_pipe_buf_release() might think the page can be reused.
         */
        pipe_buf_release(cs->pipe, buf);

        *foliop = newfolio;
        folio_unlock(oldfolio);
        /* Drop ref for ap->pages[] array */
        folio_put(oldfolio);
        cs->len = 0;

        err = 0;
out_put_old:
        /* Drop ref obtained in this function */
        folio_put(oldfolio);
        return err;

out_fallback_unlock:
        folio_unlock(newfolio);
out_fallback:
        cs->pg = buf->page;
        cs->offset = buf->offset;

        err = lock_request(cs->req);
        if (!err)
                err = 1;

        goto out_put_old;
}

static int fuse_ref_folio(struct fuse_copy_state *cs, struct folio *folio,
                          unsigned offset, unsigned count)
{
        struct pipe_buffer *buf;
        int err;

        if (cs->nr_segs >= cs->pipe->max_usage)
                return -EIO;

        folio_get(folio);
        err = unlock_request(cs->req);
        if (err) {
                folio_put(folio);
                return err;
        }

        fuse_copy_finish(cs);

        buf = cs->pipebufs;
        buf->page = &folio->page;
        buf->offset = offset;
        buf->len = count;

        cs->pipebufs++;
        cs->nr_segs++;
        cs->len = 0;

        return lock_request(cs->req);
}

/*
 * Copy a folio in the request to/from the userspace buffer.  Must be
 * done atomically
 */
int fuse_copy_folio(struct fuse_copy_state *cs, struct folio **foliop,
                    unsigned offset, unsigned count, int zeroing)
{
        int err;
        struct folio *folio = *foliop;
        size_t size;

        if (folio) {
                size = folio_size(folio);
                if (zeroing && count < size)
                        folio_zero_range(folio, 0, size);
        }

        while (count) {
                if (cs->write && cs->pipebufs && folio) {
                        /*
                         * Can't control lifetime of pipe buffers, so always
                         * copy user pages.
                         */
                        if (cs->req->args->user_pages) {
                                err = fuse_copy_fill(cs);
                                if (err)
                                        return err;
                        } else {
                                return fuse_ref_folio(cs, folio, offset, count);
                        }
                } else if (!cs->len) {
                        if (cs->move_folios && folio &&
                            offset == 0 && count == size) {
                                err = fuse_try_move_folio(cs, foliop);
                                if (err <= 0)
                                        return err;
                        } else {
                                err = fuse_copy_fill(cs);
                                if (err)
                                        return err;
                        }
                }
                if (folio) {
                        void *mapaddr = kmap_local_folio(folio, offset);
                        void *buf = mapaddr;
                        unsigned int copy = count;
                        unsigned int bytes_copied;

                        if (folio_test_highmem(folio) && count > PAGE_SIZE - offset_in_page(offset))
                                copy = PAGE_SIZE - offset_in_page(offset);

                        bytes_copied = fuse_copy_do(cs, &buf, &copy);
                        kunmap_local(mapaddr);
                        offset += bytes_copied;
                        count -= bytes_copied;
                } else
                        offset += fuse_copy_do(cs, NULL, &count);
        }
        if (folio && !cs->write)
                flush_dcache_folio(folio);
        return 0;
}

/* Copy folios in the request to/from userspace buffer */
static int fuse_copy_folios(struct fuse_copy_state *cs, unsigned nbytes,
                            int zeroing)
{
        unsigned i;
        struct fuse_req *req = cs->req;
        struct fuse_args_pages *ap = container_of(req->args, typeof(*ap), args);

        for (i = 0; i < ap->num_folios && (nbytes || zeroing); i++) {
                int err;
                unsigned int offset = ap->descs[i].offset;
                unsigned int count = min(nbytes, ap->descs[i].length);

                err = fuse_copy_folio(cs, &ap->folios[i], offset, count, zeroing);
                if (err)
                        return err;

                nbytes -= count;
        }
        return 0;
}

/* Copy a single argument in the request to/from userspace buffer */
int fuse_copy_one(struct fuse_copy_state *cs, void *val, unsigned size)
{
        while (size) {
                if (!cs->len) {
                        int err = fuse_copy_fill(cs);
                        if (err)
                                return err;
                }
                fuse_copy_do(cs, &val, &size);
        }
        return 0;
}

/* Copy request arguments to/from userspace buffer */
int fuse_copy_args(struct fuse_copy_state *cs, unsigned numargs,
                   unsigned argpages, struct fuse_arg *args,
                   int zeroing)
{
        int err = 0;
        unsigned i;

        for (i = 0; !err && i < numargs; i++)  {
                struct fuse_arg *arg = &args[i];
                if (i == numargs - 1 && argpages)
                        err = fuse_copy_folios(cs, arg->size, zeroing);
                else
                        err = fuse_copy_one(cs, arg->value, arg->size);
        }
        return err;
}

static int forget_pending(struct fuse_iqueue *fiq)
{
        return fiq->forget_list_head.next != NULL;
}

static int request_pending(struct fuse_iqueue *fiq)
{
        return !list_empty(&fiq->pending) || !list_empty(&fiq->interrupts) ||
                forget_pending(fiq);
}

/*
 * Transfer an interrupt request to userspace
 *
 * Unlike other requests this is assembled on demand, without a need
 * to allocate a separate fuse_req structure.
 *
 * Called with fiq->lock held, releases it
 */
static int fuse_read_interrupt(struct fuse_iqueue *fiq, struct fuse_copy_state *cs)
__releases(fiq->lock)
{
        struct fuse_req *req = list_first_entry(&fiq->interrupts, struct fuse_req, intr_entry);
        struct fuse_interrupt_in arg = {
                .unique = req->in.h.unique,
        };
        struct fuse_in_header ih = {
                .opcode = FUSE_INTERRUPT,
                .unique = (req->in.h.unique | FUSE_INT_REQ_BIT),
                .len = sizeof(ih) + sizeof(arg),
        };
        int err;

        list_del_init(&req->intr_entry);
        spin_unlock(&fiq->lock);

        err = fuse_copy_one(cs, &ih, sizeof(ih));
        if (!err)
                err = fuse_copy_one(cs, &arg, sizeof(arg));
        fuse_copy_finish(cs);

        return err ? err : ih.len;
}

static struct fuse_forget_link *fuse_dequeue_forget(struct fuse_iqueue *fiq,
                                                    unsigned int max,
                                                    unsigned int *countp)
{
        struct fuse_forget_link *head = fiq->forget_list_head.next;
        struct fuse_forget_link **newhead = &head;
        unsigned count;

        for (count = 0; *newhead != NULL && count < max; count++)
                newhead = &(*newhead)->next;

        fiq->forget_list_head.next = *newhead;
        *newhead = NULL;
        if (fiq->forget_list_head.next == NULL)
                fiq->forget_list_tail = &fiq->forget_list_head;

        if (countp != NULL)
                *countp = count;

        return head;
}

static int fuse_read_single_forget(struct fuse_iqueue *fiq,
                                   struct fuse_copy_state *cs)
__releases(fiq->lock)
{
        int err;
        struct fuse_forget_link *forget = fuse_dequeue_forget(fiq, 1, NULL);
        struct fuse_forget_in arg = {
                .nlookup = forget->forget_one.nlookup,
        };
        struct fuse_in_header ih = {
                .opcode = FUSE_FORGET,
                .nodeid = forget->forget_one.nodeid,
                .unique = fuse_get_unique_locked(fiq),
                .len = sizeof(ih) + sizeof(arg),
        };

        spin_unlock(&fiq->lock);
        kfree(forget);

        err = fuse_copy_one(cs, &ih, sizeof(ih));
        if (!err)
                err = fuse_copy_one(cs, &arg, sizeof(arg));
        fuse_copy_finish(cs);

        if (err)
                return err;

        return ih.len;
}

static int fuse_read_batch_forget(struct fuse_iqueue *fiq,
                                   struct fuse_copy_state *cs, size_t nbytes)
__releases(fiq->lock)
{
        int err;
        unsigned max_forgets;
        unsigned count;
        struct fuse_forget_link *head;
        struct fuse_batch_forget_in arg = { .count = 0 };
        struct fuse_in_header ih = {
                .opcode = FUSE_BATCH_FORGET,
                .unique = fuse_get_unique_locked(fiq),
                .len = sizeof(ih) + sizeof(arg),
        };

        max_forgets = (nbytes - ih.len) / sizeof(struct fuse_forget_one);
        head = fuse_dequeue_forget(fiq, max_forgets, &count);
        spin_unlock(&fiq->lock);

        arg.count = count;
        ih.len += count * sizeof(struct fuse_forget_one);
        err = fuse_copy_one(cs, &ih, sizeof(ih));
        if (!err)
                err = fuse_copy_one(cs, &arg, sizeof(arg));

        while (head) {
                struct fuse_forget_link *forget = head;

                if (!err) {
                        err = fuse_copy_one(cs, &forget->forget_one,
                                            sizeof(forget->forget_one));
                }
                head = forget->next;
                kfree(forget);
        }

        fuse_copy_finish(cs);

        if (err)
                return err;

        return ih.len;
}

static int fuse_read_forget(struct fuse_chan *fch, struct fuse_iqueue *fiq,
                            struct fuse_copy_state *cs,
                            size_t nbytes)
__releases(fiq->lock)
{
        if (fch->minor < 16 || fiq->forget_list_head.next->next == NULL)
                return fuse_read_single_forget(fiq, cs);
        else
                return fuse_read_batch_forget(fiq, cs, nbytes);
}

/*
 * Read a single request into the userspace filesystem's buffer.  This
 * function waits until a request is available, then removes it from
 * the pending list and copies request data to userspace buffer.  If
 * no reply is needed (FORGET) or request has been aborted or there
 * was an error during the copying then it's finished by calling
 * fuse_request_end().  Otherwise add it to the processing list, and set
 * the 'sent' flag.
 */
static ssize_t fuse_dev_do_read(struct fuse_dev *fud, struct file *file,
                                struct fuse_copy_state *cs, size_t nbytes)
{
        ssize_t err;
        struct fuse_chan *fch = fud->chan;
        struct fuse_iqueue *fiq = &fch->iq;
        struct fuse_pqueue *fpq = &fud->pq;
        struct fuse_req *req;
        struct fuse_args *args;
        unsigned reqsize;
        unsigned int hash;

        /*
         * Require sane minimum read buffer - that has capacity for fixed part
         * of any request header + negotiated max_write room for data.
         *
         * Historically libfuse reserves 4K for fixed header room, but e.g.
         * GlusterFS reserves only 80 bytes
         *
         *      = `sizeof(fuse_in_header) + sizeof(fuse_write_in)`
         *
         * which is the absolute minimum any sane filesystem should be using
         * for header room.
         */
        if (nbytes < max_t(size_t, FUSE_MIN_READ_BUFFER,
                           sizeof(struct fuse_in_header) +
                           sizeof(struct fuse_write_in) +
                           fch->max_write))
                return -EINVAL;

 restart:
        for (;;) {
                spin_lock(&fiq->lock);
                if (!fiq->connected || request_pending(fiq))
                        break;
                spin_unlock(&fiq->lock);

                if (file->f_flags & O_NONBLOCK)
                        return -EAGAIN;
                err = wait_event_interruptible_exclusive(fiq->waitq,
                                !fiq->connected || request_pending(fiq));
                if (err)
                        return err;
        }

        if (!fiq->connected) {
                err = fch->abort_with_err ? -ECONNABORTED : -ENODEV;
                goto err_unlock;
        }

        if (!list_empty(&fiq->interrupts))
                return fuse_read_interrupt(fiq, cs);

        if (forget_pending(fiq)) {
                if (list_empty(&fiq->pending) || fiq->forget_batch-- > 0)
                        return fuse_read_forget(fch, fiq, cs, nbytes);

                if (fiq->forget_batch <= -8)
                        fiq->forget_batch = 16;
        }

        req = list_entry(fiq->pending.next, struct fuse_req, list);
        clear_bit(FR_PENDING, &req->flags);
        list_del_init(&req->list);
        spin_unlock(&fiq->lock);

        args = req->args;
        reqsize = req->in.h.len;

        /* If request is too large, reply with an error and restart the read */
        if (nbytes < reqsize) {
                req->out.h.error = -EIO;
                /* SETXATTR is special, since it may contain too large data */
                if (args->opcode == FUSE_SETXATTR)
                        req->out.h.error = -E2BIG;
                fuse_request_end(req);
                goto restart;
        }
        spin_lock(&fpq->lock);
        /*
         *  Must not put request on fpq->io queue after having been shut down by
         *  fuse_chan_abort()
         */
        if (!fpq->connected) {
                req->out.h.error = err = -ECONNABORTED;
                goto out_end;
        }
        list_add(&req->list, &fpq->io);
        spin_unlock(&fpq->lock);
        cs->req = req;
        err = fuse_copy_one(cs, &req->in.h, sizeof(req->in.h));
        if (!err)
                err = fuse_copy_args(cs, args->in_numargs, args->in_pages,
                                     (struct fuse_arg *) args->in_args, 0);
        fuse_copy_finish(cs);
        spin_lock(&fpq->lock);
        clear_bit(FR_LOCKED, &req->flags);
        if (!fpq->connected) {
                err = fch->abort_with_err ? -ECONNABORTED : -ENODEV;
                goto out_end;
        }
        if (err) {
                req->out.h.error = -EIO;
                goto out_end;
        }
        if (!test_bit(FR_ISREPLY, &req->flags)) {
                err = reqsize;
                goto out_end;
        }
        hash = fuse_req_hash(req->in.h.unique);
        list_move_tail(&req->list, &fpq->processing[hash]);
        __fuse_get_request(req);
        set_bit(FR_SENT, &req->flags);
        trace_fuse_request_sent(req);
        spin_unlock(&fpq->lock);
        /* matches barrier in request_wait_answer() */
        smp_mb__after_atomic();
        if (test_bit(FR_INTERRUPTED, &req->flags))
                queue_interrupt(req);
        fuse_put_request(req);

        return reqsize;

out_end:
        if (!test_bit(FR_PRIVATE, &req->flags))
                list_del_init(&req->list);
        spin_unlock(&fpq->lock);
        fuse_request_end(req);
        return err;

 err_unlock:
        spin_unlock(&fiq->lock);
        return err;
}

static int fuse_dev_open(struct inode *inode, struct file *file)
{
        struct fuse_dev *fud = fuse_dev_alloc_no_pq();

        if (!fud)
                return -ENOMEM;

        file->private_data = fud;
        return 0;
}

struct fuse_dev *fuse_get_dev(struct file *file)
{
        struct fuse_dev *fud = fuse_file_to_fud(file);
        int err;

        if (unlikely(!fuse_dev_chan_get(fud))) {
                /* only block waiting for mount if sync init was requested */
                if (!fud->sync_init)
                        return ERR_PTR(-EPERM);

                err = wait_event_interruptible(fuse_dev_waitq, fuse_dev_chan_get(fud) != NULL);
                if (err)
                        return ERR_PTR(err);
        }

        return fud;
}

static ssize_t fuse_dev_read(struct kiocb *iocb, struct iov_iter *to)
{
        struct fuse_copy_state cs;
        struct file *file = iocb->ki_filp;
        struct fuse_dev *fud = fuse_get_dev(file);

        if (IS_ERR(fud))
                return PTR_ERR(fud);

        if (!user_backed_iter(to))
                return -EINVAL;

        fuse_copy_init(&cs, true, to);

        return fuse_dev_do_read(fud, file, &cs, iov_iter_count(to));
}

static ssize_t fuse_dev_splice_read(struct file *in, loff_t *ppos,
                                    struct pipe_inode_info *pipe,
                                    size_t len, unsigned int flags)
{
        int total, ret;
        int page_nr = 0;
        struct pipe_buffer *bufs;
        struct fuse_copy_state cs;
        struct fuse_dev *fud = fuse_get_dev(in);

        if (IS_ERR(fud))
                return PTR_ERR(fud);

        bufs = kvmalloc_objs(struct pipe_buffer, pipe->max_usage);
        if (!bufs)
                return -ENOMEM;

        fuse_copy_init(&cs, true, NULL);
        cs.pipebufs = bufs;
        cs.pipe = pipe;
        ret = fuse_dev_do_read(fud, in, &cs, len);
        if (ret < 0)
                goto out;

        if (pipe_buf_usage(pipe) + cs.nr_segs > pipe->max_usage) {
                ret = -EIO;
                goto out;
        }

        for (ret = total = 0; page_nr < cs.nr_segs; total += ret) {
                /*
                 * Need to be careful about this.  Having buf->ops in module
                 * code can Oops if the buffer persists after module unload.
                 */
                bufs[page_nr].ops = &nosteal_pipe_buf_ops;
                bufs[page_nr].flags = 0;
                ret = add_to_pipe(pipe, &bufs[page_nr++]);
                if (unlikely(ret < 0))
                        break;
        }
        if (total)
                ret = total;
out:
        for (; page_nr < cs.nr_segs; page_nr++)
                put_page(bufs[page_nr].page);

        kvfree(bufs);
        return ret;
}

/*
 * Resending all processing queue requests.
 *
 * During a FUSE daemon panics and failover, it is possible for some inflight
 * requests to be lost and never returned. As a result, applications awaiting
 * replies would become stuck forever. To address this, we can use notification
 * to trigger resending of these pending requests to the FUSE daemon, ensuring
 * they are properly processed again.
 *
 * Please note that this strategy is applicable only to idempotent requests or
 * if the FUSE daemon takes careful measures to avoid processing duplicated
 * non-idempotent requests.
 */
void fuse_chan_resend(struct fuse_chan *fch)
{
        struct fuse_dev *fud;
        struct fuse_req *req, *next;
        struct fuse_iqueue *fiq = &fch->iq;
        LIST_HEAD(to_queue);
        unsigned int i;

        spin_lock(&fch->lock);
        if (!fch->connected) {
                spin_unlock(&fch->lock);
                return;
        }

        list_for_each_entry(fud, &fch->devices, entry) {
                struct fuse_pqueue *fpq = &fud->pq;

                spin_lock(&fpq->lock);
                for (i = 0; i < FUSE_PQ_HASH_SIZE; i++)
                        list_splice_tail_init(&fpq->processing[i], &to_queue);
                spin_unlock(&fpq->lock);
        }
        spin_unlock(&fch->lock);

        list_for_each_entry_safe(req, next, &to_queue, list) {
                set_bit(FR_PENDING, &req->flags);
                clear_bit(FR_SENT, &req->flags);
                /* mark the request as resend request */
                req->in.h.unique |= FUSE_UNIQUE_RESEND;
        }

        spin_lock(&fiq->lock);
        if (!fiq->connected) {
                spin_unlock(&fiq->lock);
                list_for_each_entry(req, &to_queue, list)
                        clear_bit(FR_PENDING, &req->flags);
                fuse_dev_end_requests(&to_queue);
                return;
        }
        /*
         * Remove interrupt entries for resent requests to prevent stale
         * intr_entry on fiq->interrupts after the request is re-queued.
         */
        list_for_each_entry(req, &to_queue, list) {
                if (test_bit(FR_INTERRUPTED, &req->flags))
                        list_del_init(&req->intr_entry);
        }
        /* iq and pq requests are both oldest to newest */
        list_splice(&to_queue, &fiq->pending);
        fuse_dev_wake_and_unlock(fiq);
}

/* Look up request on processing list by unique ID */
struct fuse_req *fuse_request_find(struct fuse_pqueue *fpq, u64 unique)
{
        unsigned int hash = fuse_req_hash(unique);
        struct fuse_req *req;

        list_for_each_entry(req, &fpq->processing[hash], list) {
                if (req->in.h.unique == unique)
                        return req;
        }
        return NULL;
}

int fuse_copy_out_args(struct fuse_copy_state *cs, struct fuse_args *args,
                       unsigned nbytes)
{

        unsigned int reqsize = 0;

        /*
         * Uring has all headers separated from args - args is payload only
         */
        if (!cs->is_uring)
                reqsize = sizeof(struct fuse_out_header);

        reqsize += fuse_len_args(args->out_numargs, args->out_args);

        if (reqsize < nbytes || (reqsize > nbytes && !args->out_argvar))
                return -EINVAL;
        else if (reqsize > nbytes) {
                struct fuse_arg *lastarg = &args->out_args[args->out_numargs-1];
                unsigned diffsize = reqsize - nbytes;

                if (diffsize > lastarg->size)
                        return -EINVAL;
                lastarg->size -= diffsize;
        }
        return fuse_copy_args(cs, args->out_numargs, args->out_pages,
                              args->out_args, args->page_zeroing);
}

/*
 * Write a single reply to a request.  First the header is copied from
 * the write buffer.  The request is then searched on the processing
 * list by the unique ID found in the header.  If found, then remove
 * it from the list and copy the rest of the buffer to the request.
 * The request is finished by calling fuse_request_end().
 */
static ssize_t fuse_dev_do_write(struct fuse_dev *fud,
                                 struct fuse_copy_state *cs, size_t nbytes)
{
        int err;
        struct fuse_chan *fch = fud->chan;
        struct fuse_pqueue *fpq = &fud->pq;
        struct fuse_req *req;
        struct fuse_out_header oh;

        err = -EINVAL;
        if (nbytes < sizeof(struct fuse_out_header))
                goto out;

        err = fuse_copy_one(cs, &oh, sizeof(oh));
        if (err)
                goto copy_finish;

        err = -EINVAL;
        if (oh.len != nbytes)
                goto copy_finish;

        /*
         * Zero oh.unique indicates unsolicited notification message
         * and error contains notification code.
         */
        if (!oh.unique) {
                /*
                 * Only allow notifications during while the connection is in an
                 * initialized and connected state
                 */
                err = -EINVAL;
                if (!fch->initialized || !fch->connected)
                        goto copy_finish;

                /* Don't try to move folios (yet) */
                cs->move_folios = false;

                err = fuse_notify(fch->conn, oh.error, nbytes - sizeof(oh), cs);
                goto copy_finish;
        }

        err = -EINVAL;
        if (oh.error <= -512 || oh.error > 0)
                goto copy_finish;

        spin_lock(&fpq->lock);
        req = NULL;
        if (fpq->connected)
                req = fuse_request_find(fpq, oh.unique & ~FUSE_INT_REQ_BIT);

        err = -ENOENT;
        if (!req) {
                spin_unlock(&fpq->lock);
                goto copy_finish;
        }

        /* Is it an interrupt reply ID? */
        if (oh.unique & FUSE_INT_REQ_BIT) {
                __fuse_get_request(req);
                spin_unlock(&fpq->lock);

                err = 0;
                if (nbytes != sizeof(struct fuse_out_header))
                        err = -EINVAL;
                else if (oh.error == -ENOSYS)
                        fch->no_interrupt = 1;
                else if (oh.error == -EAGAIN)
                        err = queue_interrupt(req);

                fuse_put_request(req);

                goto copy_finish;
        }

        clear_bit(FR_SENT, &req->flags);
        list_move(&req->list, &fpq->io);
        req->out.h = oh;
        set_bit(FR_LOCKED, &req->flags);
        spin_unlock(&fpq->lock);
        cs->req = req;
        if (!req->args->page_replace)
                cs->move_folios = false;

        if (oh.error)
                err = nbytes != sizeof(oh) ? -EINVAL : 0;
        else
                err = fuse_copy_out_args(cs, req->args, nbytes);
        fuse_copy_finish(cs);

        spin_lock(&fpq->lock);
        clear_bit(FR_LOCKED, &req->flags);
        if (!fpq->connected)
                err = -ENOENT;
        else if (err)
                req->out.h.error = -EIO;
        if (!test_bit(FR_PRIVATE, &req->flags))
                list_del_init(&req->list);
        spin_unlock(&fpq->lock);

        fuse_request_end(req);
out:
        return err ? err : nbytes;

copy_finish:
        fuse_copy_finish(cs);
        goto out;
}

static ssize_t fuse_dev_write(struct kiocb *iocb, struct iov_iter *from)
{
        struct fuse_copy_state cs;
        struct fuse_dev *fud = __fuse_get_dev(iocb->ki_filp);

        if (!fud)
                return -EPERM;

        if (!user_backed_iter(from))
                return -EINVAL;

        fuse_copy_init(&cs, false, from);

        return fuse_dev_do_write(fud, &cs, iov_iter_count(from));
}

static ssize_t fuse_dev_splice_write(struct pipe_inode_info *pipe,
                                     struct file *out, loff_t *ppos,
                                     size_t len, unsigned int flags)
{
        unsigned int head, tail, count;
        unsigned nbuf;
        unsigned idx;
        struct pipe_buffer *bufs;
        struct fuse_copy_state cs;
        struct fuse_dev *fud = __fuse_get_dev(out);
        size_t rem;
        ssize_t ret;

        if (!fud)
                return -EPERM;

        pipe_lock(pipe);

        head = pipe->head;
        tail = pipe->tail;
        count = pipe_occupancy(head, tail);

        bufs = kvmalloc_objs(struct pipe_buffer, count);
        if (!bufs) {
                pipe_unlock(pipe);
                return -ENOMEM;
        }

        nbuf = 0;
        rem = 0;
        for (idx = tail; !pipe_empty(head, idx) && rem < len; idx++)
                rem += pipe_buf(pipe, idx)->len;

        ret = -EINVAL;
        if (rem < len)
                goto out_free;

        rem = len;
        while (rem) {
                struct pipe_buffer *ibuf;
                struct pipe_buffer *obuf;

                if (WARN_ON(nbuf >= count || pipe_empty(head, tail)))
                        goto out_free;

                ibuf = pipe_buf(pipe, tail);
                obuf = &bufs[nbuf];

                if (rem >= ibuf->len) {
                        *obuf = *ibuf;
                        ibuf->ops = NULL;
                        tail++;
                        pipe->tail = tail;
                } else {
                        if (!pipe_buf_get(pipe, ibuf))
                                goto out_free;

                        *obuf = *ibuf;
                        obuf->flags &= ~PIPE_BUF_FLAG_GIFT;
                        obuf->len = rem;
                        ibuf->offset += obuf->len;
                        ibuf->len -= obuf->len;
                }
                nbuf++;
                rem -= obuf->len;
        }
        pipe_unlock(pipe);

        fuse_copy_init(&cs, false, NULL);
        cs.pipebufs = bufs;
        cs.nr_segs = nbuf;
        cs.pipe = pipe;

        if (flags & SPLICE_F_MOVE)
                cs.move_folios = true;

        ret = fuse_dev_do_write(fud, &cs, len);

        pipe_lock(pipe);
out_free:
        for (idx = 0; idx < nbuf; idx++) {
                struct pipe_buffer *buf = &bufs[idx];

                if (buf->ops)
                        pipe_buf_release(pipe, buf);
        }
        pipe_unlock(pipe);

        kvfree(bufs);
        return ret;
}

static __poll_t fuse_dev_poll(struct file *file, poll_table *wait)
{
        __poll_t mask = EPOLLOUT | EPOLLWRNORM;
        struct fuse_iqueue *fiq;
        struct fuse_dev *fud = fuse_get_dev(file);

        if (IS_ERR(fud))
                return EPOLLERR;

        fiq = &fud->chan->iq;
        poll_wait(file, &fiq->waitq, wait);

        spin_lock(&fiq->lock);
        if (!fiq->connected)
                mask = EPOLLERR;
        else if (request_pending(fiq))
                mask |= EPOLLIN | EPOLLRDNORM;
        spin_unlock(&fiq->lock);

        return mask;
}

/* Abort all requests on the given list (pending or processing) */
void fuse_dev_end_requests(struct list_head *head)
{
        while (!list_empty(head)) {
                struct fuse_req *req;
                req = list_entry(head->next, struct fuse_req, list);
                req->out.h.error = -ECONNABORTED;
                clear_bit(FR_SENT, &req->flags);
                list_del_init(&req->list);
                fuse_request_end(req);
        }
}

/*
 * Abort all requests.
 *
 * Emergency exit in case of a malicious or accidental deadlock, or just a hung
 * filesystem.
 *
 * The same effect is usually achievable through killing the filesystem daemon
 * and all users of the filesystem.  The exception is the combination of an
 * asynchronous request and the tricky deadlock (see
 * Documentation/filesystems/fuse/fuse.rst).
 *
 * Aborting requests under I/O goes as follows: 1: Separate out unlocked
 * requests, they should be finished off immediately.  Locked requests will be
 * finished after unlock; see unlock_request(). 2: Finish off the unlocked
 * requests.  It is possible that some request will finish before we can.  This
 * is OK, the request will in that case be removed from the list before we touch
 * it.
 */
void fuse_chan_abort(struct fuse_chan *fch, bool abort_with_err)
{
        struct fuse_iqueue *fiq = &fch->iq;

        fch->abort_with_err = abort_with_err;

        spin_lock(&fch->lock);
        if (fch->connected) {
                struct fuse_dev *fud;
                struct fuse_req *req, *next;
                LIST_HEAD(to_end);
                unsigned int i;

                if (fch->timeout.req_timeout)
                        cancel_delayed_work(&fch->timeout.work);

                /* Background queuing checks fch->connected under bg_lock */
                spin_lock(&fch->bg_lock);
                fch->connected = 0;
                spin_unlock(&fch->bg_lock);

                fuse_chan_set_initialized(fch, NULL);
                list_for_each_entry(fud, &fch->devices, entry) {
                        struct fuse_pqueue *fpq = &fud->pq;

                        spin_lock(&fpq->lock);
                        fpq->connected = 0;
                        list_for_each_entry_safe(req, next, &fpq->io, list) {
                                req->out.h.error = -ECONNABORTED;
                                spin_lock(&req->waitq.lock);
                                set_bit(FR_ABORTED, &req->flags);
                                if (!test_bit(FR_LOCKED, &req->flags)) {
                                        set_bit(FR_PRIVATE, &req->flags);
                                        __fuse_get_request(req);
                                        list_move(&req->list, &to_end);
                                }
                                spin_unlock(&req->waitq.lock);
                        }
                        for (i = 0; i < FUSE_PQ_HASH_SIZE; i++)
                                list_splice_tail_init(&fpq->processing[i],
                                                      &to_end);
                        spin_unlock(&fpq->lock);
                }
                spin_lock(&fch->bg_lock);
                fch->blocked = 0;
                fch->max_background = UINT_MAX;
                flush_bg_queue(fch);
                spin_unlock(&fch->bg_lock);

                spin_lock(&fiq->lock);
                fiq->connected = 0;
                list_for_each_entry(req, &fiq->pending, list)
                        clear_bit(FR_PENDING, &req->flags);
                list_splice_tail_init(&fiq->pending, &to_end);
                while (forget_pending(fiq))
                        kfree(fuse_dequeue_forget(fiq, 1, NULL));
                wake_up_all(&fiq->waitq);
                spin_unlock(&fiq->lock);
                kill_fasync(&fiq->fasync, SIGIO, POLL_IN);
                fuse_end_polls(fch->conn);
                wake_up_all(&fch->blocked_waitq);
                spin_unlock(&fch->lock);

                fuse_dev_end_requests(&to_end);

                /*
                 * fch->lock must not be taken to avoid conflicts with io-uring
                 * locks
                 */
                fuse_uring_abort(fch);
        } else {
                spin_unlock(&fch->lock);
        }
}
EXPORT_SYMBOL_GPL(fuse_chan_abort);

void fuse_chan_wait_aborted(struct fuse_chan *fch)
{
        /* matches implicit memory barrier in fuse_drop_waiting() */
        smp_mb();
        wait_event(fch->blocked_waitq, fuse_chan_num_waiting(fch) == 0);

        fuse_uring_wait_stopped_queues(fch);
}

int fuse_dev_release(struct inode *inode, struct file *file)
{
        struct fuse_dev *fud = fuse_file_to_fud(file);
        /* Pairs with cmpxchg() in fuse_dev_install() */
        struct fuse_chan *fch = xchg(&fud->chan, FUSE_DEV_CHAN_DISCONNECTED);

        if (fch) {
                struct fuse_pqueue *fpq = &fud->pq;
                LIST_HEAD(to_end);
                unsigned int i;
                bool last;

                /* Make sure fuse_dev_install_with_pq() has finished */
                spin_lock(&fch->lock);
                spin_lock(&fpq->lock);
                WARN_ON(!list_empty(&fpq->io));
                for (i = 0; i < FUSE_PQ_HASH_SIZE; i++)
                        list_splice_init(&fpq->processing[i], &to_end);
                spin_unlock(&fpq->lock);

                list_del(&fud->entry);
                /* Are we the last open device? */
                last = list_empty(&fch->devices);
                spin_unlock(&fch->lock);

                fuse_dev_end_requests(&to_end);

                if (last) {
                        WARN_ON(fch->iq.fasync != NULL);
                        fuse_chan_abort(fch, false);
                }
                fuse_conn_put(fch->conn);
        }
        fuse_dev_put(fud);
        return 0;
}
EXPORT_SYMBOL_GPL(fuse_dev_release);

static int fuse_dev_fasync(int fd, struct file *file, int on)
{
        struct fuse_dev *fud = fuse_get_dev(file);

        if (IS_ERR(fud))
                return PTR_ERR(fud);

        /* No locking - fasync_helper does its own locking */
        return fasync_helper(fd, file, on, &fud->chan->iq.fasync);
}

static long fuse_dev_ioctl_clone(struct file *file, __u32 __user *argp)
{
        int oldfd;
        struct fuse_dev *fud, *new_fud;
        struct list_head *pq;

        if (get_user(oldfd, argp))
                return -EFAULT;

        CLASS(fd, f)(oldfd);
        if (fd_empty(f))
                return -EINVAL;

        /*
         * Check against file->f_op because CUSE
         * uses the same ioctl handler.
         */
        if (fd_file(f)->f_op != file->f_op)
                return -EINVAL;

        fud = fuse_get_dev(fd_file(f));
        if (IS_ERR(fud))
                return PTR_ERR(fud);

        pq = fuse_pqueue_alloc();
        if (!pq)
                return -ENOMEM;

        new_fud = fuse_file_to_fud(file);
        if (!fuse_dev_install_with_pq(new_fud, fud->chan, pq))
                return -EINVAL;

        return 0;
}

static long fuse_dev_ioctl_backing_open(struct file *file,
                                        struct fuse_backing_map __user *argp)
{
        struct fuse_dev *fud = fuse_get_dev(file);
        struct fuse_backing_map map;

        if (IS_ERR(fud))
                return PTR_ERR(fud);

        if (!IS_ENABLED(CONFIG_FUSE_PASSTHROUGH))
                return -EOPNOTSUPP;

        if (copy_from_user(&map, argp, sizeof(map)))
                return -EFAULT;

        return fuse_backing_open(fud->chan->conn, &map);
}

static long fuse_dev_ioctl_backing_close(struct file *file, __u32 __user *argp)
{
        struct fuse_dev *fud = fuse_get_dev(file);
        int backing_id;

        if (IS_ERR(fud))
                return PTR_ERR(fud);

        if (!IS_ENABLED(CONFIG_FUSE_PASSTHROUGH))
                return -EOPNOTSUPP;

        if (get_user(backing_id, argp))
                return -EFAULT;

        return fuse_backing_close(fud->chan->conn, backing_id);
}

static long fuse_dev_ioctl_sync_init(struct file *file)
{
        struct fuse_dev *fud = fuse_file_to_fud(file);

        if (fuse_dev_chan_get(fud))
                return -EINVAL;

        fud->sync_init = true;
        return 0;
}

static long fuse_dev_ioctl(struct file *file, unsigned int cmd,
                           unsigned long arg)
{
        void __user *argp = (void __user *)arg;

        switch (cmd) {
        case FUSE_DEV_IOC_CLONE:
                return fuse_dev_ioctl_clone(file, argp);

        case FUSE_DEV_IOC_BACKING_OPEN:
                return fuse_dev_ioctl_backing_open(file, argp);

        case FUSE_DEV_IOC_BACKING_CLOSE:
                return fuse_dev_ioctl_backing_close(file, argp);

        case FUSE_DEV_IOC_SYNC_INIT:
                return fuse_dev_ioctl_sync_init(file);

        default:
                return -ENOTTY;
        }
}

#ifdef CONFIG_PROC_FS
static void fuse_dev_show_fdinfo(struct seq_file *seq, struct file *file)
{
        struct fuse_dev *fud = __fuse_get_dev(file);
        if (!fud)
                return;

        seq_printf(seq, "fuse_connection:\t%u\n", fuse_conn_get_id(fud->chan->conn));
}
#endif

const struct file_operations fuse_dev_operations = {
        .owner          = THIS_MODULE,
        .open           = fuse_dev_open,
        .read_iter      = fuse_dev_read,
        .splice_read    = fuse_dev_splice_read,
        .write_iter     = fuse_dev_write,
        .splice_write   = fuse_dev_splice_write,
        .poll           = fuse_dev_poll,
        .release        = fuse_dev_release,
        .fasync         = fuse_dev_fasync,
        .unlocked_ioctl = fuse_dev_ioctl,
        .compat_ioctl   = compat_ptr_ioctl,
#ifdef CONFIG_FUSE_IO_URING
        .uring_cmd      = fuse_uring_cmd,
#endif
#ifdef CONFIG_PROC_FS
        .show_fdinfo    = fuse_dev_show_fdinfo,
#endif
};
EXPORT_SYMBOL_GPL(fuse_dev_operations);

static struct miscdevice fuse_miscdevice = {
        .minor = FUSE_MINOR,
        .name  = "fuse",
        .fops = &fuse_dev_operations,
};

int __init fuse_dev_init(void)
{
        int err = -ENOMEM;
        fuse_req_cachep = kmem_cache_create("fuse_request",
                                            sizeof(struct fuse_req),
                                            0, 0, NULL);
        if (!fuse_req_cachep)
                goto out;

        err = misc_register(&fuse_miscdevice);
        if (err)
                goto out_cache_clean;

        return 0;

 out_cache_clean:
        kmem_cache_destroy(fuse_req_cachep);
 out:
        return err;
}

void fuse_dev_cleanup(void)
{
        misc_deregister(&fuse_miscdevice);
        kmem_cache_destroy(fuse_req_cachep);
}