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

  This program can be distributed under the terms of the GNU GPL.
  See the file COPYING.
*/

#include "fuse_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>

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

/* Ordinary requests have even IDs, while interrupts IDs are odd */
#define FUSE_INT_REQ_BIT (1ULL << 0)
#define FUSE_REQ_ID_STEP (1ULL << 1)

static struct kmem_cache *fuse_req_cachep;

static struct fuse_dev *fuse_get_dev(struct file *file)
{
        /*
         * Lockless access is OK, because file->private data is set
         * once during mount and is valid until the file is released.
         */
        return READ_ONCE(file->private_data);
}

static void fuse_request_init(struct fuse_mount *fm, 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->fm = fm;
}

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

        return req;
}

static void fuse_request_free(struct fuse_req *req)
{
        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_set_initialized(struct fuse_conn *fc)
{
        /* Make sure stores before this are seen on another CPU */
        smp_wmb();
        fc->initialized = 1;
}

static bool fuse_block_alloc(struct fuse_conn *fc, bool for_background)
{
        return !fc->initialized || (for_background && fc->blocked);
}

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

static void fuse_put_request(struct fuse_req *req);

static struct fuse_req *fuse_get_req(struct fuse_mount *fm, bool for_background)
{
        struct fuse_conn *fc = fm->fc;
        struct fuse_req *req;
        int err;
        atomic_inc(&fc->num_waiting);

        if (fuse_block_alloc(fc, for_background)) {
                err = -EINTR;
                if (wait_event_killable_exclusive(fc->blocked_waitq,
                                !fuse_block_alloc(fc, for_background)))
                        goto out;
        }
        /* Matches smp_wmb() in fuse_set_initialized() */
        smp_rmb();

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

        err = -ECONNREFUSED;
        if (fc->conn_error)
                goto out;

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

        req->in.h.uid = from_kuid(fc->user_ns, current_fsuid());
        req->in.h.gid = from_kgid(fc->user_ns, current_fsgid());
        req->in.h.pid = pid_nr_ns(task_pid(current), fc->pid_ns);

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

        if (unlikely(req->in.h.uid == ((uid_t)-1) ||
                     req->in.h.gid == ((gid_t)-1))) {
                fuse_put_request(req);
                return ERR_PTR(-EOVERFLOW);
        }
        return req;

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

static void fuse_put_request(struct fuse_req *req)
{
        struct fuse_conn *fc = req->fm->fc;

        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(&fc->bg_lock);
                        if (!fc->blocked)
                                wake_up(&fc->blocked_waitq);
                        spin_unlock(&fc->bg_lock);
                }

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

                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);

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

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

/**
 * 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);
}

const struct fuse_iqueue_ops fuse_dev_fiq_ops = {
        .wake_forget_and_unlock         = fuse_dev_wake_and_unlock,
        .wake_interrupt_and_unlock      = fuse_dev_wake_and_unlock,
        .wake_pending_and_unlock        = fuse_dev_wake_and_unlock,
};
EXPORT_SYMBOL_GPL(fuse_dev_fiq_ops);

static void queue_request_and_unlock(struct fuse_iqueue *fiq,
                                     struct fuse_req *req)
__releases(fiq->lock)
{
        req->in.h.len = sizeof(struct fuse_in_header) +
                fuse_len_args(req->args->in_numargs,
                              (struct fuse_arg *) req->args->in_args);
        list_add_tail(&req->list, &fiq->pending);
        fiq->ops->wake_pending_and_unlock(fiq);
}

void fuse_queue_forget(struct fuse_conn *fc, struct fuse_forget_link *forget,
                       u64 nodeid, u64 nlookup)
{
        struct fuse_iqueue *fiq = &fc->iq;

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

        spin_lock(&fiq->lock);
        if (fiq->connected) {
                fiq->forget_list_tail->next = forget;
                fiq->forget_list_tail = forget;
                fiq->ops->wake_forget_and_unlock(fiq);
        } else {
                kfree(forget);
                spin_unlock(&fiq->lock);
        }
}

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

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

                req = list_first_entry(&fc->bg_queue, struct fuse_req, list);
                list_del(&req->list);
                fc->active_background++;
                spin_lock(&fiq->lock);
                req->in.h.unique = fuse_get_unique(fiq);
                queue_request_and_unlock(fiq, req);
        }
}

/*
 * 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_mount *fm = req->fm;
        struct fuse_conn *fc = fm->fc;
        struct fuse_iqueue *fiq = &fc->iq;

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

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

                fc->num_background--;
                fc->active_background--;
                flush_bg_queue(fc);
                spin_unlock(&fc->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(fm, 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->fm->fc->iq;

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

        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);
                        return 0;
                }
                fiq->ops->wake_interrupt_and_unlock(fiq);
        } else {
                spin_unlock(&fiq->lock);
        }
        return 0;
}

static void request_wait_answer(struct fuse_req *req)
{
        struct fuse_conn *fc = req->fm->fc;
        struct fuse_iqueue *fiq = &fc->iq;
        int err;

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

                spin_lock(&fiq->lock);
                /* Request is not yet in userspace, bail out */
                if (test_bit(FR_PENDING, &req->flags)) {
                        list_del(&req->list);
                        spin_unlock(&fiq->lock);
                        __fuse_put_request(req);
                        req->out.h.error = -EINTR;
                        return;
                }
                spin_unlock(&fiq->lock);
        }

        /*
         * 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->fm->fc->iq;

        BUG_ON(test_bit(FR_BACKGROUND, &req->flags));
        spin_lock(&fiq->lock);
        if (!fiq->connected) {
                spin_unlock(&fiq->lock);
                req->out.h.error = -ENOTCONN;
        } else {
                req->in.h.unique = fuse_get_unique(fiq);
                /* acquire extra reference, since request is still needed
                   after fuse_request_end() */
                __fuse_get_request(req);
                queue_request_and_unlock(fiq, req);

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

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

        if (fc->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 (fc->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_force_creds(struct fuse_req *req)
{
        struct fuse_conn *fc = req->fm->fc;

        req->in.h.uid = from_kuid_munged(fc->user_ns, current_fsuid());
        req->in.h.gid = from_kgid_munged(fc->user_ns, current_fsgid());
        req->in.h.pid = pid_nr_ns(task_pid(current), fc->pid_ns);
}

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->args = args;
        if (args->end)
                __set_bit(FR_ASYNC, &req->flags);
}

ssize_t fuse_simple_request(struct fuse_mount *fm, struct fuse_args *args)
{
        struct fuse_conn *fc = fm->fc;
        struct fuse_req *req;
        ssize_t ret;

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

                if (!args->nocreds)
                        fuse_force_creds(req);

                __set_bit(FR_WAITING, &req->flags);
                __set_bit(FR_FORCE, &req->flags);
        } else {
                WARN_ON(args->nocreds);
                req = fuse_get_req(fm, false);
                if (IS_ERR(req))
                        return PTR_ERR(req);
        }

        /* Needs to be done after fuse_get_req() so that fc->minor is valid */
        fuse_adjust_compat(fc, 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;
}

static bool fuse_request_queue_background(struct fuse_req *req)
{
        struct fuse_mount *fm = req->fm;
        struct fuse_conn *fc = fm->fc;
        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(&fc->num_waiting);
        }
        __set_bit(FR_ISREPLY, &req->flags);
        spin_lock(&fc->bg_lock);
        if (likely(fc->connected)) {
                fc->num_background++;
                if (fc->num_background == fc->max_background)
                        fc->blocked = 1;
                list_add_tail(&req->list, &fc->bg_queue);
                flush_bg_queue(fc);
                queued = true;
        }
        spin_unlock(&fc->bg_lock);

        return queued;
}

int fuse_simple_background(struct fuse_mount *fm, struct fuse_args *args,
                            gfp_t gfp_flags)
{
        struct fuse_req *req;

        if (args->force) {
                WARN_ON(!args->nocreds);
                req = fuse_request_alloc(fm, gfp_flags);
                if (!req)
                        return -ENOMEM;
                __set_bit(FR_BACKGROUND, &req->flags);
        } else {
                WARN_ON(args->nocreds);
                req = fuse_get_req(fm, 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;
}
EXPORT_SYMBOL_GPL(fuse_simple_background);

static int fuse_simple_notify_reply(struct fuse_mount *fm,
                                    struct fuse_args *args, u64 unique)
{
        struct fuse_req *req;
        struct fuse_iqueue *fiq = &fm->fc->iq;
        int err = 0;

        req = fuse_get_req(fm, 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);

        spin_lock(&fiq->lock);
        if (fiq->connected) {
                queue_request_and_unlock(fiq, req);
        } else {
                err = -ENODEV;
                spin_unlock(&fiq->lock);
                fuse_put_request(req);
        }

        return err;
}

/*
 * 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;
}

struct fuse_copy_state {
        int write;
        struct fuse_req *req;
        struct iov_iter *iter;
        struct pipe_buffer *pipebufs;
        struct pipe_buffer *currbuf;
        struct pipe_inode_info *pipe;
        unsigned long nr_segs;
        struct page *pg;
        unsigned len;
        unsigned offset;
        unsigned move_pages:1;
};

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

/* Unmap and put previous page of userspace buffer */
static 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_pages(cs->iter, &page, PAGE_SIZE, 1, &off);
                if (err < 0)
                        return err;
                BUG_ON(!err);
                cs->len = err;
                cs->offset = off;
                cs->pg = page;
                iov_iter_advance(cs->iter, err);
        }

        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;
        return ncpy;
}

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

static int fuse_try_move_page(struct fuse_copy_state *cs, struct page **pagep)
{
        int err;
        struct page *oldpage = *pagep;
        struct page *newpage;
        struct pipe_buffer *buf = cs->pipebufs;

        get_page(oldpage);
        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 != PAGE_SIZE)
                goto out_fallback;

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

        newpage = buf->page;

        if (!PageUptodate(newpage))
                SetPageUptodate(newpage);

        ClearPageMappedToDisk(newpage);

        if (fuse_check_page(newpage) != 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(page_mapped(oldpage)))
                goto out_fallback_unlock;
        if (WARN_ON(page_has_private(oldpage)))
                goto out_fallback_unlock;
        if (WARN_ON(PageDirty(oldpage) || PageWriteback(oldpage)))
                goto out_fallback_unlock;
        if (WARN_ON(PageMlocked(oldpage)))
                goto out_fallback_unlock;

        replace_page_cache_page(oldpage, newpage);

        get_page(newpage);

        if (!(buf->flags & PIPE_BUF_FLAG_LRU))
                lru_cache_add(newpage);

        /*
         * 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);

        err = 0;
        spin_lock(&cs->req->waitq.lock);
        if (test_bit(FR_ABORTED, &cs->req->flags))
                err = -ENOENT;
        else
                *pagep = newpage;
        spin_unlock(&cs->req->waitq.lock);

        if (err) {
                unlock_page(newpage);
                put_page(newpage);
                goto out_put_old;
        }

        unlock_page(oldpage);
        /* Drop ref for ap->pages[] array */
        put_page(oldpage);
        cs->len = 0;

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

out_fallback_unlock:
        unlock_page(newpage);
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_page(struct fuse_copy_state *cs, struct page *page,
                         unsigned offset, unsigned count)
{
        struct pipe_buffer *buf;
        int err;

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

        get_page(page);
        err = unlock_request(cs->req);
        if (err) {
                put_page(page);
                return err;
        }

        fuse_copy_finish(cs);

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

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

        return 0;
}

/*
 * Copy a page in the request to/from the userspace buffer.  Must be
 * done atomically
 */
static int fuse_copy_page(struct fuse_copy_state *cs, struct page **pagep,
                          unsigned offset, unsigned count, int zeroing)
{
        int err;
        struct page *page = *pagep;

        if (page && zeroing && count < PAGE_SIZE)
                clear_highpage(page);

        while (count) {
                if (cs->write && cs->pipebufs && page) {
                        /*
                         * 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_page(cs, page, offset, count);
                        }
                } else if (!cs->len) {
                        if (cs->move_pages && page &&
                            offset == 0 && count == PAGE_SIZE) {
                                err = fuse_try_move_page(cs, pagep);
                                if (err <= 0)
                                        return err;
                        } else {
                                err = fuse_copy_fill(cs);
                                if (err)
                                        return err;
                        }
                }
                if (page) {
                        void *mapaddr = kmap_local_page(page);
                        void *buf = mapaddr + offset;
                        offset += fuse_copy_do(cs, &buf, &count);
                        kunmap_local(mapaddr);
                } else
                        offset += fuse_copy_do(cs, NULL, &count);
        }
        if (page && !cs->write)
                flush_dcache_page(page);
        return 0;
}

/* Copy pages in the request to/from userspace buffer */
static int fuse_copy_pages(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_pages && (nbytes || zeroing); i++) {
                int err;
                unsigned int offset = ap->descs[i].offset;
                unsigned int count = min(nbytes, ap->descs[i].length);

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

                nbytes -= count;
        }
        return 0;
}

/* Copy a single argument in the request to/from userspace buffer */
static 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 */
static 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_pages(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,
                               size_t nbytes, struct fuse_req *req)
__releases(fiq->lock)
{
        struct fuse_in_header ih;
        struct fuse_interrupt_in arg;
        unsigned reqsize = sizeof(ih) + sizeof(arg);
        int err;

        list_del_init(&req->intr_entry);
        memset(&ih, 0, sizeof(ih));
        memset(&arg, 0, sizeof(arg));
        ih.len = reqsize;
        ih.opcode = FUSE_INTERRUPT;
        ih.unique = (req->in.h.unique | FUSE_INT_REQ_BIT);
        arg.unique = req->in.h.unique;

        spin_unlock(&fiq->lock);
        if (nbytes < reqsize)
                return -EINVAL;

        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 : reqsize;
}

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;
}
EXPORT_SYMBOL(fuse_dequeue_forget);

static int fuse_read_single_forget(struct fuse_iqueue *fiq,
                                   struct fuse_copy_state *cs,
                                   size_t nbytes)
__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(fiq),
                .len = sizeof(ih) + sizeof(arg),
        };

        spin_unlock(&fiq->lock);
        kfree(forget);
        if (nbytes < ih.len)
                return -EINVAL;

        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(fiq),
                .len = sizeof(ih) + sizeof(arg),
        };

        if (nbytes < ih.len) {
                spin_unlock(&fiq->lock);
                return -EINVAL;
        }

        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_conn *fc, struct fuse_iqueue *fiq,
                            struct fuse_copy_state *cs,
                            size_t nbytes)
__releases(fiq->lock)
{
        if (fc->minor < 16 || fiq->forget_list_head.next->next == NULL)
                return fuse_read_single_forget(fiq, cs, nbytes);
        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_conn *fc = fud->fc;
        struct fuse_iqueue *fiq = &fc->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) +
                           fc->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 = fc->aborted ? -ECONNABORTED : -ENODEV;
                goto err_unlock;
        }

        if (!list_empty(&fiq->interrupts)) {
                req = list_entry(fiq->interrupts.next, struct fuse_req,
                                 intr_entry);
                return fuse_read_interrupt(fiq, cs, nbytes, req);
        }

        if (forget_pending(fiq)) {
                if (list_empty(&fiq->pending) || fiq->forget_batch-- > 0)
                        return fuse_read_forget(fc, 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_abort_conn()
         */
        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 = fc->aborted ? -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);
        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)
{
        /*
         * The fuse device's file's private_data is used to hold
         * the fuse_conn(ection) when it is mounted, and is used to
         * keep track of whether the file has been mounted already.
         */
        file->private_data = NULL;
        return 0;
}

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 (!fud)
                return -EPERM;

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

        fuse_copy_init(&cs, 1, 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 (!fud)
                return -EPERM;

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

        fuse_copy_init(&cs, 1, NULL);
        cs.pipebufs = bufs;
        cs.pipe = pipe;
        ret = fuse_dev_do_read(fud, in, &cs, len);
        if (ret < 0)
                goto out;

        if (pipe_occupancy(pipe->head, pipe->tail) + 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;
}

static int fuse_notify_poll(struct fuse_conn *fc, unsigned int size,
                            struct fuse_copy_state *cs)
{
        struct fuse_notify_poll_wakeup_out outarg;
        int err = -EINVAL;

        if (size != sizeof(outarg))
                goto err;

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

        fuse_copy_finish(cs);
        return fuse_notify_poll_wakeup(fc, &outarg);

err:
        fuse_copy_finish(cs);
        return err;
}

static int fuse_notify_inval_inode(struct fuse_conn *fc, unsigned int size,
                                   struct fuse_copy_state *cs)
{
        struct fuse_notify_inval_inode_out outarg;
        int err = -EINVAL;

        if (size != sizeof(outarg))
                goto err;

        err = fuse_copy_one(cs, &outarg, sizeof(outarg));
        if (err)
                goto err;
        fuse_copy_finish(cs);

        down_read(&fc->killsb);
        err = fuse_reverse_inval_inode(fc, outarg.ino,
                                       outarg.off, outarg.len);
        up_read(&fc->killsb);
        return err;

err:
        fuse_copy_finish(cs);
        return err;
}

static int fuse_notify_inval_entry(struct fuse_conn *fc, unsigned int size,
                                   struct fuse_copy_state *cs)
{
        struct fuse_notify_inval_entry_out outarg;
        int err = -ENOMEM;
        char *buf;
        struct qstr name;

        buf = kzalloc(FUSE_NAME_MAX + 1, GFP_KERNEL);
        if (!buf)
                goto err;

        err = -EINVAL;
        if (size < sizeof(outarg))
                goto err;

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

        err = -ENAMETOOLONG;
        if (outarg.namelen > FUSE_NAME_MAX)
                goto err;

        err = -EINVAL;
        if (size != sizeof(outarg) + outarg.namelen + 1)
                goto err;

        name.name = buf;
        name.len = outarg.namelen;
        err = fuse_copy_one(cs, buf, outarg.namelen + 1);
        if (err)
                goto err;
        fuse_copy_finish(cs);
        buf[outarg.namelen] = 0;

        down_read(&fc->killsb);
        err = fuse_reverse_inval_entry(fc, outarg.parent, 0, &name);
        up_read(&fc->killsb);
        kfree(buf);
        return err;

err:
        kfree(buf);
        fuse_copy_finish(cs);
        return err;
}

static int fuse_notify_delete(struct fuse_conn *fc, unsigned int size,
                              struct fuse_copy_state *cs)
{
        struct fuse_notify_delete_out outarg;
        int err = -ENOMEM;
        char *buf;
        struct qstr name;

        buf = kzalloc(FUSE_NAME_MAX + 1, GFP_KERNEL);
        if (!buf)
                goto err;

        err = -EINVAL;
        if (size < sizeof(outarg))
                goto err;

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

        err = -ENAMETOOLONG;
        if (outarg.namelen > FUSE_NAME_MAX)
                goto err;

        err = -EINVAL;
        if (size != sizeof(outarg) + outarg.namelen + 1)
                goto err;

        name.name = buf;
        name.len = outarg.namelen;
        err = fuse_copy_one(cs, buf, outarg.namelen + 1);
        if (err)
                goto err;
        fuse_copy_finish(cs);
        buf[outarg.namelen] = 0;

        down_read(&fc->killsb);
        err = fuse_reverse_inval_entry(fc, outarg.parent, outarg.child, &name);
        up_read(&fc->killsb);
        kfree(buf);
        return err;

err:
        kfree(buf);
        fuse_copy_finish(cs);
        return err;
}

static int fuse_notify_store(struct fuse_conn *fc, unsigned int size,
                             struct fuse_copy_state *cs)
{
        struct fuse_notify_store_out outarg;
        struct inode *inode;
        struct address_space *mapping;
        u64 nodeid;
        int err;
        pgoff_t index;
        unsigned int offset;
        unsigned int num;
        loff_t file_size;
        loff_t end;

        err = -EINVAL;
        if (size < sizeof(outarg))
                goto out_finish;

        err = fuse_copy_one(cs, &outarg, sizeof(outarg));
        if (err)
                goto out_finish;

        err = -EINVAL;
        if (size - sizeof(outarg) != outarg.size)
                goto out_finish;

        nodeid = outarg.nodeid;

        down_read(&fc->killsb);

        err = -ENOENT;
        inode = fuse_ilookup(fc, nodeid,  NULL);
        if (!inode)
                goto out_up_killsb;

        mapping = inode->i_mapping;
        index = outarg.offset >> PAGE_SHIFT;
        offset = outarg.offset & ~PAGE_MASK;
        file_size = i_size_read(inode);
        end = outarg.offset + outarg.size;
        if (end > file_size) {
                file_size = end;
                fuse_write_update_attr(inode, file_size, outarg.size);
        }

        num = outarg.size;
        while (num) {
                struct page *page;
                unsigned int this_num;

                err = -ENOMEM;
                page = find_or_create_page(mapping, index,
                                           mapping_gfp_mask(mapping));
                if (!page)
                        goto out_iput;

                this_num = min_t(unsigned, num, PAGE_SIZE - offset);
                err = fuse_copy_page(cs, &page, offset, this_num, 0);
                if (!err && offset == 0 &&
                    (this_num == PAGE_SIZE || file_size == end))
                        SetPageUptodate(page);
                unlock_page(page);
                put_page(page);

                if (err)
                        goto out_iput;

                num -= this_num;
                offset = 0;
                index++;
        }

        err = 0;

out_iput:
        iput(inode);
out_up_killsb:
        up_read(&fc->killsb);
out_finish:
        fuse_copy_finish(cs);
        return err;
}

struct fuse_retrieve_args {
        struct fuse_args_pages ap;
        struct fuse_notify_retrieve_in inarg;
};

static void fuse_retrieve_end(struct fuse_mount *fm, struct fuse_args *args,
                              int error)
{
        struct fuse_retrieve_args *ra =
                container_of(args, typeof(*ra), ap.args);

        release_pages(ra->ap.pages, ra->ap.num_pages);
        kfree(ra);
}

static int fuse_retrieve(struct fuse_mount *fm, struct inode *inode,
                         struct fuse_notify_retrieve_out *outarg)
{
        int err;
        struct address_space *mapping = inode->i_mapping;
        pgoff_t index;
        loff_t file_size;
        unsigned int num;
        unsigned int offset;
        size_t total_len = 0;
        unsigned int num_pages;
        struct fuse_conn *fc = fm->fc;
        struct fuse_retrieve_args *ra;
        size_t args_size = sizeof(*ra);
        struct fuse_args_pages *ap;
        struct fuse_args *args;

        offset = outarg->offset & ~PAGE_MASK;
        file_size = i_size_read(inode);

        num = min(outarg->size, fc->max_write);
        if (outarg->offset > file_size)
                num = 0;
        else if (outarg->offset + num > file_size)
                num = file_size - outarg->offset;

        num_pages = (num + offset + PAGE_SIZE - 1) >> PAGE_SHIFT;
        num_pages = min(num_pages, fc->max_pages);

        args_size += num_pages * (sizeof(ap->pages[0]) + sizeof(ap->descs[0]));

        ra = kzalloc(args_size, GFP_KERNEL);
        if (!ra)
                return -ENOMEM;

        ap = &ra->ap;
        ap->pages = (void *) (ra + 1);
        ap->descs = (void *) (ap->pages + num_pages);

        args = &ap->args;
        args->nodeid = outarg->nodeid;
        args->opcode = FUSE_NOTIFY_REPLY;
        args->in_numargs = 2;
        args->in_pages = true;
        args->end = fuse_retrieve_end;

        index = outarg->offset >> PAGE_SHIFT;

        while (num && ap->num_pages < num_pages) {
                struct page *page;
                unsigned int this_num;

                page = find_get_page(mapping, index);
                if (!page)
                        break;

                this_num = min_t(unsigned, num, PAGE_SIZE - offset);
                ap->pages[ap->num_pages] = page;
                ap->descs[ap->num_pages].offset = offset;
                ap->descs[ap->num_pages].length = this_num;
                ap->num_pages++;

                offset = 0;
                num -= this_num;
                total_len += this_num;
                index++;
        }
        ra->inarg.offset = outarg->offset;
        ra->inarg.size = total_len;
        args->in_args[0].size = sizeof(ra->inarg);
        args->in_args[0].value = &ra->inarg;
        args->in_args[1].size = total_len;

        err = fuse_simple_notify_reply(fm, args, outarg->notify_unique);
        if (err)
                fuse_retrieve_end(fm, args, err);

        return err;
}

static int fuse_notify_retrieve(struct fuse_conn *fc, unsigned int size,
                                struct fuse_copy_state *cs)
{
        struct fuse_notify_retrieve_out outarg;
        struct fuse_mount *fm;
        struct inode *inode;
        u64 nodeid;
        int err;

        err = -EINVAL;
        if (size != sizeof(outarg))
                goto copy_finish;

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

        fuse_copy_finish(cs);

        down_read(&fc->killsb);
        err = -ENOENT;
        nodeid = outarg.nodeid;

        inode = fuse_ilookup(fc, nodeid, &fm);
        if (inode) {
                err = fuse_retrieve(fm, inode, &outarg);
                iput(inode);
        }
        up_read(&fc->killsb);

        return err;

copy_finish:
        fuse_copy_finish(cs);
        return err;
}

static int fuse_notify(struct fuse_conn *fc, enum fuse_notify_code code,
                       unsigned int size, struct fuse_copy_state *cs)
{
        /* Don't try to move pages (yet) */
        cs->move_pages = 0;

        switch (code) {
        case FUSE_NOTIFY_POLL:
                return fuse_notify_poll(fc, size, cs);

        case FUSE_NOTIFY_INVAL_INODE:
                return fuse_notify_inval_inode(fc, size, cs);

        case FUSE_NOTIFY_INVAL_ENTRY:
                return fuse_notify_inval_entry(fc, size, cs);

        case FUSE_NOTIFY_STORE:
                return fuse_notify_store(fc, size, cs);

        case FUSE_NOTIFY_RETRIEVE:
                return fuse_notify_retrieve(fc, size, cs);

        case FUSE_NOTIFY_DELETE:
                return fuse_notify_delete(fc, size, cs);

        default:
                fuse_copy_finish(cs);
                return -EINVAL;
        }
}

/* Look up request on processing list by unique ID */
static struct fuse_req *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;
}

static int copy_out_args(struct fuse_copy_state *cs, struct fuse_args *args,
                         unsigned nbytes)
{
        unsigned 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_conn *fc = fud->fc;
        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) {
                err = fuse_notify(fc, oh.error, nbytes - sizeof(oh), cs);
                goto out;
        }

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

        spin_lock(&fpq->lock);
        req = NULL;
        if (fpq->connected)
                req = 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)
                        fc->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_pages = 0;

        if (oh.error)
                err = nbytes != sizeof(oh) ? -EINVAL : 0;
        else
                err = 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 (!iter_is_iovec(from))
                return -EINVAL;

        fuse_copy_init(&cs, 0, 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, mask, count;
        unsigned nbuf;
        unsigned idx;
        struct pipe_buffer *bufs;
        struct fuse_copy_state cs;
        struct fuse_dev *fud;
        size_t rem;
        ssize_t ret;

        fud = fuse_get_dev(out);
        if (!fud)
                return -EPERM;

        pipe_lock(pipe);

        head = pipe->head;
        tail = pipe->tail;
        mask = pipe->ring_size - 1;
        count = head - tail;

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

        nbuf = 0;
        rem = 0;
        for (idx = tail; idx != head && rem < len; idx++)
                rem += pipe->bufs[idx & mask].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 || tail == head))
                        goto out_free;

                ibuf = &pipe->bufs[tail & mask];
                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, 0, NULL);
        cs.pipebufs = bufs;
        cs.nr_segs = nbuf;
        cs.pipe = pipe;

        if (flags & SPLICE_F_MOVE)
                cs.move_pages = 1;

        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 (!fud)
                return EPOLLERR;

        fiq = &fud->fc->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) */
static void 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);
        }
}

static void end_polls(struct fuse_conn *fc)
{
        struct rb_node *p;

        p = rb_first(&fc->polled_files);

        while (p) {
                struct fuse_file *ff;
                ff = rb_entry(p, struct fuse_file, polled_node);
                wake_up_interruptible_all(&ff->poll_wait);

                p = rb_next(p);
        }
}

/*
 * 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.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_abort_conn(struct fuse_conn *fc)
{
        struct fuse_iqueue *fiq = &fc->iq;

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

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

                fuse_set_initialized(fc);
                list_for_each_entry(fud, &fc->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(&fc->bg_lock);
                fc->blocked = 0;
                fc->max_background = UINT_MAX;
                flush_bg_queue(fc);
                spin_unlock(&fc->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);
                end_polls(fc);
                wake_up_all(&fc->blocked_waitq);
                spin_unlock(&fc->lock);

                end_requests(&to_end);
        } else {
                spin_unlock(&fc->lock);
        }
}
EXPORT_SYMBOL_GPL(fuse_abort_conn);

void fuse_wait_aborted(struct fuse_conn *fc)
{
        /* matches implicit memory barrier in fuse_drop_waiting() */
        smp_mb();
        wait_event(fc->blocked_waitq, atomic_read(&fc->num_waiting) == 0);
}

int fuse_dev_release(struct inode *inode, struct file *file)
{
        struct fuse_dev *fud = fuse_get_dev(file);

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

                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);

                end_requests(&to_end);

                /* Are we the last open device? */
                if (atomic_dec_and_test(&fc->dev_count)) {
                        WARN_ON(fc->iq.fasync != NULL);
                        fuse_abort_conn(fc);
                }
                fuse_dev_free(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 (!fud)
                return -EPERM;

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

static int fuse_device_clone(struct fuse_conn *fc, struct file *new)
{
        struct fuse_dev *fud;

        if (new->private_data)
                return -EINVAL;

        fud = fuse_dev_alloc_install(fc);
        if (!fud)
                return -ENOMEM;

        new->private_data = fud;
        atomic_inc(&fc->dev_count);

        return 0;
}

static long fuse_dev_ioctl(struct file *file, unsigned int cmd,
                           unsigned long arg)
{
        int res;
        int oldfd;
        struct fuse_dev *fud = NULL;

        switch (cmd) {
        case FUSE_DEV_IOC_CLONE:
                res = -EFAULT;
                if (!get_user(oldfd, (__u32 __user *)arg)) {
                        struct file *old = fget(oldfd);

                        res = -EINVAL;
                        if (old) {
                                /*
                                 * Check against file->f_op because CUSE
                                 * uses the same ioctl handler.
                                 */
                                if (old->f_op == file->f_op &&
                                    old->f_cred->user_ns == file->f_cred->user_ns)
                                        fud = fuse_get_dev(old);

                                if (fud) {
                                        mutex_lock(&fuse_mutex);
                                        res = fuse_device_clone(fud->fc, file);
                                        mutex_unlock(&fuse_mutex);
                                }
                                fput(old);
                        }
                }
                break;
        default:
                res = -ENOTTY;
                break;
        }
        return res;
}

const struct file_operations fuse_dev_operations = {
        .owner          = THIS_MODULE,
        .open           = fuse_dev_open,
        .llseek         = no_llseek,
        .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,
};
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);
}