/*
  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/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/aio.h>

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

static struct kmem_cache *fuse_req_cachep;

static struct fuse_conn *fuse_get_conn(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 file->private_data;
}

static void fuse_request_init(struct fuse_req *req, struct page **pages,
                              struct fuse_page_desc *page_descs,
                              unsigned npages)
{
        memset(req, 0, sizeof(*req));
        memset(pages, 0, sizeof(*pages) * npages);
        memset(page_descs, 0, sizeof(*page_descs) * npages);
        INIT_LIST_HEAD(&req->list);
        INIT_LIST_HEAD(&req->intr_entry);
        init_waitqueue_head(&req->waitq);
        atomic_set(&req->count, 1);
        req->pages = pages;
        req->page_descs = page_descs;
        req->max_pages = npages;
}

static struct fuse_req *__fuse_request_alloc(unsigned npages, gfp_t flags)
{
        struct fuse_req *req = kmem_cache_alloc(fuse_req_cachep, flags);
        if (req) {
                struct page **pages;
                struct fuse_page_desc *page_descs;

                if (npages <= FUSE_REQ_INLINE_PAGES) {
                        pages = req->inline_pages;
                        page_descs = req->inline_page_descs;
                } else {
                        pages = kmalloc(sizeof(struct page *) * npages, flags);
                        page_descs = kmalloc(sizeof(struct fuse_page_desc) *
                                             npages, flags);
                }

                if (!pages || !page_descs) {
                        kfree(pages);
                        kfree(page_descs);
                        kmem_cache_free(fuse_req_cachep, req);
                        return NULL;
                }

                fuse_request_init(req, pages, page_descs, npages);
        }
        return req;
}

struct fuse_req *fuse_request_alloc(unsigned npages)
{
        return __fuse_request_alloc(npages, GFP_KERNEL);
}
EXPORT_SYMBOL_GPL(fuse_request_alloc);

struct fuse_req *fuse_request_alloc_nofs(unsigned npages)
{
        return __fuse_request_alloc(npages, GFP_NOFS);
}

void fuse_request_free(struct fuse_req *req)
{
        if (req->pages != req->inline_pages) {
                kfree(req->pages);
                kfree(req->page_descs);
        }
        kmem_cache_free(fuse_req_cachep, req);
}

static void block_sigs(sigset_t *oldset)
{
        sigset_t mask;

        siginitsetinv(&mask, sigmask(SIGKILL));
        sigprocmask(SIG_BLOCK, &mask, oldset);
}

static void restore_sigs(sigset_t *oldset)
{
        sigprocmask(SIG_SETMASK, oldset, NULL);
}

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

/* Must be called with > 1 refcount */
static void __fuse_put_request(struct fuse_req *req)
{
        BUG_ON(atomic_read(&req->count) < 2);
        atomic_dec(&req->count);
}

static void fuse_req_init_context(struct fuse_req *req)
{
        req->in.h.uid = from_kuid_munged(&init_user_ns, current_fsuid());
        req->in.h.gid = from_kgid_munged(&init_user_ns, current_fsgid());
        req->in.h.pid = current->pid;
}

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 struct fuse_req *__fuse_get_req(struct fuse_conn *fc, unsigned npages,
                                       bool for_background)
{
        struct fuse_req *req;
        int err;
        atomic_inc(&fc->num_waiting);

        if (fuse_block_alloc(fc, for_background)) {
                sigset_t oldset;
                int intr;

                block_sigs(&oldset);
                intr = wait_event_interruptible_exclusive(fc->blocked_waitq,
                                !fuse_block_alloc(fc, for_background));
                restore_sigs(&oldset);
                err = -EINTR;
                if (intr)
                        goto out;
        }
        /* Matches smp_wmb() in fuse_set_initialized() */
        smp_rmb();

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

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

        fuse_req_init_context(req);
        req->waiting = 1;
        req->background = for_background;
        return req;

 out:
        atomic_dec(&fc->num_waiting);
        return ERR_PTR(err);
}

struct fuse_req *fuse_get_req(struct fuse_conn *fc, unsigned npages)
{
        return __fuse_get_req(fc, npages, false);
}
EXPORT_SYMBOL_GPL(fuse_get_req);

struct fuse_req *fuse_get_req_for_background(struct fuse_conn *fc,
                                             unsigned npages)
{
        return __fuse_get_req(fc, npages, true);
}
EXPORT_SYMBOL_GPL(fuse_get_req_for_background);

/*
 * Return request in fuse_file->reserved_req.  However that may
 * currently be in use.  If that is the case, wait for it to become
 * available.
 */
static struct fuse_req *get_reserved_req(struct fuse_conn *fc,
                                         struct file *file)
{
        struct fuse_req *req = NULL;
        struct fuse_file *ff = file->private_data;

        do {
                wait_event(fc->reserved_req_waitq, ff->reserved_req);
                spin_lock(&fc->lock);
                if (ff->reserved_req) {
                        req = ff->reserved_req;
                        ff->reserved_req = NULL;
                        req->stolen_file = get_file(file);
                }
                spin_unlock(&fc->lock);
        } while (!req);

        return req;
}

/*
 * Put stolen request back into fuse_file->reserved_req
 */
static void put_reserved_req(struct fuse_conn *fc, struct fuse_req *req)
{
        struct file *file = req->stolen_file;
        struct fuse_file *ff = file->private_data;

        spin_lock(&fc->lock);
        fuse_request_init(req, req->pages, req->page_descs, req->max_pages);
        BUG_ON(ff->reserved_req);
        ff->reserved_req = req;
        wake_up_all(&fc->reserved_req_waitq);
        spin_unlock(&fc->lock);
        fput(file);
}

/*
 * Gets a requests for a file operation, always succeeds
 *
 * This is used for sending the FLUSH request, which must get to
 * userspace, due to POSIX locks which may need to be unlocked.
 *
 * If allocation fails due to OOM, use the reserved request in
 * fuse_file.
 *
 * This is very unlikely to deadlock accidentally, since the
 * filesystem should not have it's own file open.  If deadlock is
 * intentional, it can still be broken by "aborting" the filesystem.
 */
struct fuse_req *fuse_get_req_nofail_nopages(struct fuse_conn *fc,
                                             struct file *file)
{
        struct fuse_req *req;

        atomic_inc(&fc->num_waiting);
        wait_event(fc->blocked_waitq, fc->initialized);
        /* Matches smp_wmb() in fuse_set_initialized() */
        smp_rmb();
        req = fuse_request_alloc(0);
        if (!req)
                req = get_reserved_req(fc, file);

        fuse_req_init_context(req);
        req->waiting = 1;
        req->background = 0;
        return req;
}

void fuse_put_request(struct fuse_conn *fc, struct fuse_req *req)
{
        if (atomic_dec_and_test(&req->count)) {
                if (unlikely(req->background)) {
                        /*
                         * We get here in the unlikely case that a background
                         * request was allocated but not sent
                         */
                        spin_lock(&fc->lock);
                        if (!fc->blocked)
                                wake_up(&fc->blocked_waitq);
                        spin_unlock(&fc->lock);
                }

                if (req->waiting)
                        atomic_dec(&fc->num_waiting);

                if (req->stolen_file)
                        put_reserved_req(fc, req);
                else
                        fuse_request_free(req);
        }
}
EXPORT_SYMBOL_GPL(fuse_put_request);

static unsigned len_args(unsigned numargs, struct fuse_arg *args)
{
        unsigned nbytes = 0;
        unsigned i;

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

        return nbytes;
}

static u64 fuse_get_unique(struct fuse_conn *fc)
{
        fc->reqctr++;
        /* zero is special */
        if (fc->reqctr == 0)
                fc->reqctr = 1;

        return fc->reqctr;
}

static void queue_request(struct fuse_conn *fc, struct fuse_req *req)
{
        req->in.h.len = sizeof(struct fuse_in_header) +
                len_args(req->in.numargs, (struct fuse_arg *) req->in.args);
        list_add_tail(&req->list, &fc->pending);
        req->state = FUSE_REQ_PENDING;
        if (!req->waiting) {
                req->waiting = 1;
                atomic_inc(&fc->num_waiting);
        }
        wake_up(&fc->waitq);
        kill_fasync(&fc->fasync, SIGIO, POLL_IN);
}

void fuse_queue_forget(struct fuse_conn *fc, struct fuse_forget_link *forget,
                       u64 nodeid, u64 nlookup)
{
        forget->forget_one.nodeid = nodeid;
        forget->forget_one.nlookup = nlookup;

        spin_lock(&fc->lock);
        if (fc->connected) {
                fc->forget_list_tail->next = forget;
                fc->forget_list_tail = forget;
                wake_up(&fc->waitq);
                kill_fasync(&fc->fasync, SIGIO, POLL_IN);
        } else {
                kfree(forget);
        }
        spin_unlock(&fc->lock);
}

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

                req = list_entry(fc->bg_queue.next, struct fuse_req, list);
                list_del(&req->list);
                fc->active_background++;
                req->in.h.unique = fuse_get_unique(fc);
                queue_request(fc, 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
 *
 * Called with fc->lock, unlocks it
 */
static void request_end(struct fuse_conn *fc, struct fuse_req *req)
__releases(fc->lock)
{
        void (*end) (struct fuse_conn *, struct fuse_req *) = req->end;
        req->end = NULL;
        list_del(&req->list);
        list_del(&req->intr_entry);
        req->state = FUSE_REQ_FINISHED;
        if (req->background) {
                req->background = 0;

                if (fc->num_background == fc->max_background)
                        fc->blocked = 0;

                /* Wake up next waiter, if any */
                if (!fc->blocked && waitqueue_active(&fc->blocked_waitq))
                        wake_up(&fc->blocked_waitq);

                if (fc->num_background == fc->congestion_threshold &&
                    fc->connected && fc->bdi_initialized) {
                        clear_bdi_congested(&fc->bdi, BLK_RW_SYNC);
                        clear_bdi_congested(&fc->bdi, BLK_RW_ASYNC);
                }
                fc->num_background--;
                fc->active_background--;
                flush_bg_queue(fc);
        }
        spin_unlock(&fc->lock);
        wake_up(&req->waitq);
        if (end)
                end(fc, req);
        fuse_put_request(fc, req);
}

static void wait_answer_interruptible(struct fuse_conn *fc,
                                      struct fuse_req *req)
__releases(fc->lock)
__acquires(fc->lock)
{
        if (signal_pending(current))
                return;

        spin_unlock(&fc->lock);
        wait_event_interruptible(req->waitq, req->state == FUSE_REQ_FINISHED);
        spin_lock(&fc->lock);
}

static void queue_interrupt(struct fuse_conn *fc, struct fuse_req *req)
{
        list_add_tail(&req->intr_entry, &fc->interrupts);
        wake_up(&fc->waitq);
        kill_fasync(&fc->fasync, SIGIO, POLL_IN);
}

static void request_wait_answer(struct fuse_conn *fc, struct fuse_req *req)
__releases(fc->lock)
__acquires(fc->lock)
{
        if (!fc->no_interrupt) {
                /* Any signal may interrupt this */
                wait_answer_interruptible(fc, req);

                if (req->aborted)
                        goto aborted;
                if (req->state == FUSE_REQ_FINISHED)
                        return;

                req->interrupted = 1;
                if (req->state == FUSE_REQ_SENT)
                        queue_interrupt(fc, req);
        }

        if (!req->force) {
                sigset_t oldset;

                /* Only fatal signals may interrupt this */
                block_sigs(&oldset);
                wait_answer_interruptible(fc, req);
                restore_sigs(&oldset);

                if (req->aborted)
                        goto aborted;
                if (req->state == FUSE_REQ_FINISHED)
                        return;

                /* Request is not yet in userspace, bail out */
                if (req->state == FUSE_REQ_PENDING) {
                        list_del(&req->list);
                        __fuse_put_request(req);
                        req->out.h.error = -EINTR;
                        return;
                }
        }

        /*
         * Either request is already in userspace, or it was forced.
         * Wait it out.
         */
        spin_unlock(&fc->lock);
        wait_event(req->waitq, req->state == FUSE_REQ_FINISHED);
        spin_lock(&fc->lock);

        if (!req->aborted)
                return;

 aborted:
        BUG_ON(req->state != FUSE_REQ_FINISHED);
        if (req->locked) {
                /* This is uninterruptible sleep, because data is
                   being copied to/from the buffers of req.  During
                   locked state, there mustn't be any filesystem
                   operation (e.g. page fault), since that could lead
                   to deadlock */
                spin_unlock(&fc->lock);
                wait_event(req->waitq, !req->locked);
                spin_lock(&fc->lock);
        }
}

static void __fuse_request_send(struct fuse_conn *fc, struct fuse_req *req)
{
        BUG_ON(req->background);
        spin_lock(&fc->lock);
        if (!fc->connected)
                req->out.h.error = -ENOTCONN;
        else if (fc->conn_error)
                req->out.h.error = -ECONNREFUSED;
        else {
                req->in.h.unique = fuse_get_unique(fc);
                queue_request(fc, req);
                /* acquire extra reference, since request is still needed
                   after request_end() */
                __fuse_get_request(req);

                request_wait_answer(fc, req);
        }
        spin_unlock(&fc->lock);
}

void fuse_request_send(struct fuse_conn *fc, struct fuse_req *req)
{
        req->isreply = 1;
        __fuse_request_send(fc, req);
}
EXPORT_SYMBOL_GPL(fuse_request_send);

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

        if (fc->minor < 9) {
                switch (args->in.h.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->in.h.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;
                }
        }
}

ssize_t fuse_simple_request(struct fuse_conn *fc, struct fuse_args *args)
{
        struct fuse_req *req;
        ssize_t ret;

        req = fuse_get_req(fc, 0);
        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);

        req->in.h.opcode = args->in.h.opcode;
        req->in.h.nodeid = args->in.h.nodeid;
        req->in.numargs = args->in.numargs;
        memcpy(req->in.args, args->in.args,
               args->in.numargs * sizeof(struct fuse_in_arg));
        req->out.argvar = args->out.argvar;
        req->out.numargs = args->out.numargs;
        memcpy(req->out.args, args->out.args,
               args->out.numargs * sizeof(struct fuse_arg));
        fuse_request_send(fc, req);
        ret = req->out.h.error;
        if (!ret && args->out.argvar) {
                BUG_ON(args->out.numargs != 1);
                ret = req->out.args[0].size;
        }
        fuse_put_request(fc, req);

        return ret;
}

static void fuse_request_send_nowait_locked(struct fuse_conn *fc,
                                            struct fuse_req *req)
{
        BUG_ON(!req->background);
        fc->num_background++;
        if (fc->num_background == fc->max_background)
                fc->blocked = 1;
        if (fc->num_background == fc->congestion_threshold &&
            fc->bdi_initialized) {
                set_bdi_congested(&fc->bdi, BLK_RW_SYNC);
                set_bdi_congested(&fc->bdi, BLK_RW_ASYNC);
        }
        list_add_tail(&req->list, &fc->bg_queue);
        flush_bg_queue(fc);
}

static void fuse_request_send_nowait(struct fuse_conn *fc, struct fuse_req *req)
{
        spin_lock(&fc->lock);
        if (fc->connected) {
                fuse_request_send_nowait_locked(fc, req);
                spin_unlock(&fc->lock);
        } else {
                req->out.h.error = -ENOTCONN;
                request_end(fc, req);
        }
}

void fuse_request_send_background(struct fuse_conn *fc, struct fuse_req *req)
{
        req->isreply = 1;
        fuse_request_send_nowait(fc, req);
}
EXPORT_SYMBOL_GPL(fuse_request_send_background);

static int fuse_request_send_notify_reply(struct fuse_conn *fc,
                                          struct fuse_req *req, u64 unique)
{
        int err = -ENODEV;

        req->isreply = 0;
        req->in.h.unique = unique;
        spin_lock(&fc->lock);
        if (fc->connected) {
                queue_request(fc, req);
                err = 0;
        }
        spin_unlock(&fc->lock);

        return err;
}

/*
 * Called under fc->lock
 *
 * fc->connected must have been checked previously
 */
void fuse_request_send_background_locked(struct fuse_conn *fc,
                                         struct fuse_req *req)
{
        req->isreply = 1;
        fuse_request_send_nowait_locked(fc, req);
}

void fuse_force_forget(struct file *file, u64 nodeid)
{
        struct inode *inode = file_inode(file);
        struct fuse_conn *fc = get_fuse_conn(inode);
        struct fuse_req *req;
        struct fuse_forget_in inarg;

        memset(&inarg, 0, sizeof(inarg));
        inarg.nlookup = 1;
        req = fuse_get_req_nofail_nopages(fc, file);
        req->in.h.opcode = FUSE_FORGET;
        req->in.h.nodeid = nodeid;
        req->in.numargs = 1;
        req->in.args[0].size = sizeof(inarg);
        req->in.args[0].value = &inarg;
        req->isreply = 0;
        __fuse_request_send(fc, req);
        /* ignore errors */
        fuse_put_request(fc, req);
}

/*
 * 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_conn *fc, struct fuse_req *req)
{
        int err = 0;
        if (req) {
                spin_lock(&fc->lock);
                if (req->aborted)
                        err = -ENOENT;
                else
                        req->locked = 1;
                spin_unlock(&fc->lock);
        }
        return err;
}

/*
 * Unlock request.  If it was aborted during being locked, the
 * requester thread is currently waiting for it to be unlocked, so
 * wake it up.
 */
static void unlock_request(struct fuse_conn *fc, struct fuse_req *req)
{
        if (req) {
                spin_lock(&fc->lock);
                req->locked = 0;
                if (req->aborted)
                        wake_up(&req->waitq);
                spin_unlock(&fc->lock);
        }
}

struct fuse_copy_state {
        struct fuse_conn *fc;
        int write;
        struct fuse_req *req;
        const struct iovec *iov;
        struct pipe_buffer *pipebufs;
        struct pipe_buffer *currbuf;
        struct pipe_inode_info *pipe;
        unsigned long nr_segs;
        unsigned long seglen;
        unsigned long addr;
        struct page *pg;
        unsigned len;
        unsigned offset;
        unsigned move_pages:1;
};

static void fuse_copy_init(struct fuse_copy_state *cs, struct fuse_conn *fc,
                           int write,
                           const struct iovec *iov, unsigned long nr_segs)
{
        memset(cs, 0, sizeof(*cs));
        cs->fc = fc;
        cs->write = write;
        cs->iov = iov;
        cs->nr_segs = nr_segs;
}

/* 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;

        unlock_request(cs->fc, cs->req);
        fuse_copy_finish(cs);
        if (cs->pipebufs) {
                struct pipe_buffer *buf = cs->pipebufs;

                if (!cs->write) {
                        err = buf->ops->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->buffers)
                                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 {
                if (!cs->seglen) {
                        BUG_ON(!cs->nr_segs);
                        cs->seglen = cs->iov[0].iov_len;
                        cs->addr = (unsigned long) cs->iov[0].iov_base;
                        cs->iov++;
                        cs->nr_segs--;
                }
                err = get_user_pages_fast(cs->addr, 1, cs->write, &page);
                if (err < 0)
                        return err;
                BUG_ON(err != 1);
                cs->pg = page;
                cs->offset = cs->addr % PAGE_SIZE;
                cs->len = min(PAGE_SIZE - cs->offset, cs->seglen);
                cs->seglen -= cs->len;
                cs->addr += cs->len;
        }

        return lock_request(cs->fc, 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_atomic(cs->pg);
                void *buf = pgaddr + cs->offset;

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

                kunmap_atomic(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_count(page) != 1 ||
            (page->flags & PAGE_FLAGS_CHECK_AT_PREP &
             ~(1 << PG_locked |
               1 << PG_referenced |
               1 << PG_uptodate |
               1 << PG_lru |
               1 << PG_active |
               1 << PG_reclaim))) {
                printk(KERN_WARNING "fuse: trying to steal weird page\n");
                printk(KERN_WARNING "  page=%p index=%li flags=%08lx, count=%i, mapcount=%i, mapping=%p\n", page, page->index, page->flags, page_count(page), page_mapcount(page), page->mapping);
                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;

        unlock_request(cs->fc, cs->req);
        fuse_copy_finish(cs);

        err = buf->ops->confirm(cs->pipe, buf);
        if (err)
                return err;

        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 (buf->ops->steal(cs->pipe, buf) != 0)
                goto out_fallback;

        newpage = buf->page;

        if (WARN_ON(!PageUptodate(newpage)))
                return -EIO;

        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;

        err = replace_page_cache_page(oldpage, newpage, GFP_KERNEL);
        if (err) {
                unlock_page(newpage);
                return err;
        }

        page_cache_get(newpage);

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

        err = 0;
        spin_lock(&cs->fc->lock);
        if (cs->req->aborted)
                err = -ENOENT;
        else
                *pagep = newpage;
        spin_unlock(&cs->fc->lock);

        if (err) {
                unlock_page(newpage);
                page_cache_release(newpage);
                return err;
        }

        unlock_page(oldpage);
        page_cache_release(oldpage);
        cs->len = 0;

        return 0;

out_fallback_unlock:
        unlock_page(newpage);
out_fallback:
        cs->pg = buf->page;
        cs->offset = buf->offset;

        err = lock_request(cs->fc, cs->req);
        if (err)
                return err;

        return 1;
}

static int fuse_ref_page(struct fuse_copy_state *cs, struct page *page,
                         unsigned offset, unsigned count)
{
        struct pipe_buffer *buf;

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

        unlock_request(cs->fc, cs->req);
        fuse_copy_finish(cs);

        buf = cs->pipebufs;
        page_cache_get(page);
        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) {
                        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_atomic(page);
                        void *buf = mapaddr + offset;
                        offset += fuse_copy_do(cs, &buf, &count);
                        kunmap_atomic(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;

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

                err = fuse_copy_page(cs, &req->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_conn *fc)
{
        return fc->forget_list_head.next != NULL;
}

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

/* Wait until a request is available on the pending list */
static void request_wait(struct fuse_conn *fc)
__releases(fc->lock)
__acquires(fc->lock)
{
        DECLARE_WAITQUEUE(wait, current);

        add_wait_queue_exclusive(&fc->waitq, &wait);
        while (fc->connected && !request_pending(fc)) {
                set_current_state(TASK_INTERRUPTIBLE);
                if (signal_pending(current))
                        break;

                spin_unlock(&fc->lock);
                schedule();
                spin_lock(&fc->lock);
        }
        set_current_state(TASK_RUNNING);
        remove_wait_queue(&fc->waitq, &wait);
}

/*
 * 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 fc->lock held, releases it
 */
static int fuse_read_interrupt(struct fuse_conn *fc, struct fuse_copy_state *cs,
                               size_t nbytes, struct fuse_req *req)
__releases(fc->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);
        req->intr_unique = fuse_get_unique(fc);
        memset(&ih, 0, sizeof(ih));
        memset(&arg, 0, sizeof(arg));
        ih.len = reqsize;
        ih.opcode = FUSE_INTERRUPT;
        ih.unique = req->intr_unique;
        arg.unique = req->in.h.unique;

        spin_unlock(&fc->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;
}

static struct fuse_forget_link *dequeue_forget(struct fuse_conn *fc,
                                               unsigned max,
                                               unsigned *countp)
{
        struct fuse_forget_link *head = fc->forget_list_head.next;
        struct fuse_forget_link **newhead = &head;
        unsigned count;

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

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

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

        return head;
}

static int fuse_read_single_forget(struct fuse_conn *fc,
                                   struct fuse_copy_state *cs,
                                   size_t nbytes)
__releases(fc->lock)
{
        int err;
        struct fuse_forget_link *forget = dequeue_forget(fc, 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(fc),
                .len = sizeof(ih) + sizeof(arg),
        };

        spin_unlock(&fc->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_conn *fc,
                                   struct fuse_copy_state *cs, size_t nbytes)
__releases(fc->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(fc),
                .len = sizeof(ih) + sizeof(arg),
        };

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

        max_forgets = (nbytes - ih.len) / sizeof(struct fuse_forget_one);
        head = dequeue_forget(fc, max_forgets, &count);
        spin_unlock(&fc->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_copy_state *cs,
                            size_t nbytes)
__releases(fc->lock)
{
        if (fc->minor < 16 || fc->forget_list_head.next->next == NULL)
                return fuse_read_single_forget(fc, cs, nbytes);
        else
                return fuse_read_batch_forget(fc, 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
 * request_end().  Otherwise add it to the processing list, and set
 * the 'sent' flag.
 */
static ssize_t fuse_dev_do_read(struct fuse_conn *fc, struct file *file,
                                struct fuse_copy_state *cs, size_t nbytes)
{
        int err;
        struct fuse_req *req;
        struct fuse_in *in;
        unsigned reqsize;

 restart:
        spin_lock(&fc->lock);
        err = -EAGAIN;
        if ((file->f_flags & O_NONBLOCK) && fc->connected &&
            !request_pending(fc))
                goto err_unlock;

        request_wait(fc);
        err = -ENODEV;
        if (!fc->connected)
                goto err_unlock;
        err = -ERESTARTSYS;
        if (!request_pending(fc))
                goto err_unlock;

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

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

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

        req = list_entry(fc->pending.next, struct fuse_req, list);
        req->state = FUSE_REQ_READING;
        list_move(&req->list, &fc->io);

        in = &req->in;
        reqsize = 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 (in->h.opcode == FUSE_SETXATTR)
                        req->out.h.error = -E2BIG;
                request_end(fc, req);
                goto restart;
        }
        spin_unlock(&fc->lock);
        cs->req = req;
        err = fuse_copy_one(cs, &in->h, sizeof(in->h));
        if (!err)
                err = fuse_copy_args(cs, in->numargs, in->argpages,
                                     (struct fuse_arg *) in->args, 0);
        fuse_copy_finish(cs);
        spin_lock(&fc->lock);
        req->locked = 0;
        if (req->aborted) {
                request_end(fc, req);
                return -ENODEV;
        }
        if (err) {
                req->out.h.error = -EIO;
                request_end(fc, req);
                return err;
        }
        if (!req->isreply)
                request_end(fc, req);
        else {
                req->state = FUSE_REQ_SENT;
                list_move_tail(&req->list, &fc->processing);
                if (req->interrupted)
                        queue_interrupt(fc, req);
                spin_unlock(&fc->lock);
        }
        return reqsize;

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

static ssize_t fuse_dev_read(struct kiocb *iocb, const struct iovec *iov,
                              unsigned long nr_segs, loff_t pos)
{
        struct fuse_copy_state cs;
        struct file *file = iocb->ki_filp;
        struct fuse_conn *fc = fuse_get_conn(file);
        if (!fc)
                return -EPERM;

        fuse_copy_init(&cs, fc, 1, iov, nr_segs);

        return fuse_dev_do_read(fc, file, &cs, iov_length(iov, nr_segs));
}

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 ret;
        int page_nr = 0;
        int do_wakeup = 0;
        struct pipe_buffer *bufs;
        struct fuse_copy_state cs;
        struct fuse_conn *fc = fuse_get_conn(in);
        if (!fc)
                return -EPERM;

        bufs = kmalloc(pipe->buffers * sizeof(struct pipe_buffer), GFP_KERNEL);
        if (!bufs)
                return -ENOMEM;

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

        ret = 0;
        pipe_lock(pipe);

        if (!pipe->readers) {
                send_sig(SIGPIPE, current, 0);
                if (!ret)
                        ret = -EPIPE;
                goto out_unlock;
        }

        if (pipe->nrbufs + cs.nr_segs > pipe->buffers) {
                ret = -EIO;
                goto out_unlock;
        }

        while (page_nr < cs.nr_segs) {
                int newbuf = (pipe->curbuf + pipe->nrbufs) & (pipe->buffers - 1);
                struct pipe_buffer *buf = pipe->bufs + newbuf;

                buf->page = bufs[page_nr].page;
                buf->offset = bufs[page_nr].offset;
                buf->len = bufs[page_nr].len;
                /*
                 * Need to be careful about this.  Having buf->ops in module
                 * code can Oops if the buffer persists after module unload.
                 */
                buf->ops = &nosteal_pipe_buf_ops;

                pipe->nrbufs++;
                page_nr++;
                ret += buf->len;

                if (pipe->files)
                        do_wakeup = 1;
        }

out_unlock:
        pipe_unlock(pipe);

        if (do_wakeup) {
                smp_mb();
                if (waitqueue_active(&pipe->wait))
                        wake_up_interruptible(&pipe->wait);
                kill_fasync(&pipe->fasync_readers, SIGIO, POLL_IN);
        }

out:
        for (; page_nr < cs.nr_segs; page_nr++)
                page_cache_release(bufs[page_nr].page);

        kfree(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 = -ENOENT;
        if (fc->sb) {
                err = fuse_reverse_inval_inode(fc->sb, 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;
        name.hash = full_name_hash(name.name, name.len);

        down_read(&fc->killsb);
        err = -ENOENT;
        if (fc->sb)
                err = fuse_reverse_inval_entry(fc->sb, 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;
        name.hash = full_name_hash(name.name, name.len);

        down_read(&fc->killsb);
        err = -ENOENT;
        if (fc->sb)
                err = fuse_reverse_inval_entry(fc->sb, 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;
        if (!fc->sb)
                goto out_up_killsb;

        inode = ilookup5(fc->sb, nodeid, fuse_inode_eq, &nodeid);
        if (!inode)
                goto out_up_killsb;

        mapping = inode->i_mapping;
        index = outarg.offset >> PAGE_CACHE_SHIFT;
        offset = outarg.offset & ~PAGE_CACHE_MASK;
        file_size = i_size_read(inode);
        end = outarg.offset + outarg.size;
        if (end > file_size) {
                file_size = end;
                fuse_write_update_size(inode, file_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_CACHE_SIZE - offset);
                err = fuse_copy_page(cs, &page, offset, this_num, 0);
                if (!err && offset == 0 &&
                    (this_num == PAGE_CACHE_SIZE || file_size == end))
                        SetPageUptodate(page);
                unlock_page(page);
                page_cache_release(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;
}

static void fuse_retrieve_end(struct fuse_conn *fc, struct fuse_req *req)
{
        release_pages(req->pages, req->num_pages, false);
}

static int fuse_retrieve(struct fuse_conn *fc, struct inode *inode,
                         struct fuse_notify_retrieve_out *outarg)
{
        int err;
        struct address_space *mapping = inode->i_mapping;
        struct fuse_req *req;
        pgoff_t index;
        loff_t file_size;
        unsigned int num;
        unsigned int offset;
        size_t total_len = 0;
        int num_pages;

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

        num = outarg->size;
        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, FUSE_MAX_PAGES_PER_REQ);

        req = fuse_get_req(fc, num_pages);
        if (IS_ERR(req))
                return PTR_ERR(req);

        req->in.h.opcode = FUSE_NOTIFY_REPLY;
        req->in.h.nodeid = outarg->nodeid;
        req->in.numargs = 2;
        req->in.argpages = 1;
        req->page_descs[0].offset = offset;
        req->end = fuse_retrieve_end;

        index = outarg->offset >> PAGE_CACHE_SHIFT;

        while (num && req->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_CACHE_SIZE - offset);
                req->pages[req->num_pages] = page;
                req->page_descs[req->num_pages].length = this_num;
                req->num_pages++;

                offset = 0;
                num -= this_num;
                total_len += this_num;
                index++;
        }
        req->misc.retrieve_in.offset = outarg->offset;
        req->misc.retrieve_in.size = total_len;
        req->in.args[0].size = sizeof(req->misc.retrieve_in);
        req->in.args[0].value = &req->misc.retrieve_in;
        req->in.args[1].size = total_len;

        err = fuse_request_send_notify_reply(fc, req, outarg->notify_unique);
        if (err)
                fuse_retrieve_end(fc, req);

        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 inode *inode;
        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;
        if (fc->sb) {
                u64 nodeid = outarg.nodeid;

                inode = ilookup5(fc->sb, nodeid, fuse_inode_eq, &nodeid);
                if (inode) {
                        err = fuse_retrieve(fc, 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)
{
        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_conn *fc, u64 unique)
{
        struct fuse_req *req;

        list_for_each_entry(req, &fc->processing, list) {
                if (req->in.h.unique == unique || req->intr_unique == unique)
                        return req;
        }
        return NULL;
}

static int copy_out_args(struct fuse_copy_state *cs, struct fuse_out *out,
                         unsigned nbytes)
{
        unsigned reqsize = sizeof(struct fuse_out_header);

        if (out->h.error)
                return nbytes != reqsize ? -EINVAL : 0;

        reqsize += len_args(out->numargs, out->args);

        if (reqsize < nbytes || (reqsize > nbytes && !out->argvar))
                return -EINVAL;
        else if (reqsize > nbytes) {
                struct fuse_arg *lastarg = &out->args[out->numargs-1];
                unsigned diffsize = reqsize - nbytes;
                if (diffsize > lastarg->size)
                        return -EINVAL;
                lastarg->size -= diffsize;
        }
        return fuse_copy_args(cs, out->numargs, out->argpages, out->args,
                              out->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 request_end()
 */
static ssize_t fuse_dev_do_write(struct fuse_conn *fc,
                                 struct fuse_copy_state *cs, size_t nbytes)
{
        int err;
        struct fuse_req *req;
        struct fuse_out_header oh;

        if (nbytes < sizeof(struct fuse_out_header))
                return -EINVAL;

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

        err = -EINVAL;
        if (oh.len != nbytes)
                goto err_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);
                return err ? err : nbytes;
        }

        err = -EINVAL;
        if (oh.error <= -1000 || oh.error > 0)
                goto err_finish;

        spin_lock(&fc->lock);
        err = -ENOENT;
        if (!fc->connected)
                goto err_unlock;

        req = request_find(fc, oh.unique);
        if (!req)
                goto err_unlock;

        if (req->aborted) {
                spin_unlock(&fc->lock);
                fuse_copy_finish(cs);
                spin_lock(&fc->lock);
                request_end(fc, req);
                return -ENOENT;
        }
        /* Is it an interrupt reply? */
        if (req->intr_unique == oh.unique) {
                err = -EINVAL;
                if (nbytes != sizeof(struct fuse_out_header))
                        goto err_unlock;

                if (oh.error == -ENOSYS)
                        fc->no_interrupt = 1;
                else if (oh.error == -EAGAIN)
                        queue_interrupt(fc, req);

                spin_unlock(&fc->lock);
                fuse_copy_finish(cs);
                return nbytes;
        }

        req->state = FUSE_REQ_WRITING;
        list_move(&req->list, &fc->io);
        req->out.h = oh;
        req->locked = 1;
        cs->req = req;
        if (!req->out.page_replace)
                cs->move_pages = 0;
        spin_unlock(&fc->lock);

        err = copy_out_args(cs, &req->out, nbytes);
        fuse_copy_finish(cs);

        spin_lock(&fc->lock);
        req->locked = 0;
        if (!err) {
                if (req->aborted)
                        err = -ENOENT;
        } else if (!req->aborted)
                req->out.h.error = -EIO;
        request_end(fc, req);

        return err ? err : nbytes;

 err_unlock:
        spin_unlock(&fc->lock);
 err_finish:
        fuse_copy_finish(cs);
        return err;
}

static ssize_t fuse_dev_write(struct kiocb *iocb, const struct iovec *iov,
                              unsigned long nr_segs, loff_t pos)
{
        struct fuse_copy_state cs;
        struct fuse_conn *fc = fuse_get_conn(iocb->ki_filp);
        if (!fc)
                return -EPERM;

        fuse_copy_init(&cs, fc, 0, iov, nr_segs);

        return fuse_dev_do_write(fc, &cs, iov_length(iov, nr_segs));
}

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 nbuf;
        unsigned idx;
        struct pipe_buffer *bufs;
        struct fuse_copy_state cs;
        struct fuse_conn *fc;
        size_t rem;
        ssize_t ret;

        fc = fuse_get_conn(out);
        if (!fc)
                return -EPERM;

        bufs = kmalloc(pipe->buffers * sizeof(struct pipe_buffer), GFP_KERNEL);
        if (!bufs)
                return -ENOMEM;

        pipe_lock(pipe);
        nbuf = 0;
        rem = 0;
        for (idx = 0; idx < pipe->nrbufs && rem < len; idx++)
                rem += pipe->bufs[(pipe->curbuf + idx) & (pipe->buffers - 1)].len;

        ret = -EINVAL;
        if (rem < len) {

                pipe_unlock(pipe);
                goto out;
        }

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

                BUG_ON(nbuf >= pipe->buffers);
                BUG_ON(!pipe->nrbufs);
                ibuf = &pipe->bufs[pipe->curbuf];
                obuf = &bufs[nbuf];

                if (rem >= ibuf->len) {
                        *obuf = *ibuf;
                        ibuf->ops = NULL;
                        pipe->curbuf = (pipe->curbuf + 1) & (pipe->buffers - 1);
                        pipe->nrbufs--;
                } else {
                        ibuf->ops->get(pipe, ibuf);
                        *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, fc, 0, NULL, nbuf);
        cs.pipebufs = bufs;
        cs.pipe = pipe;

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

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

        for (idx = 0; idx < nbuf; idx++) {
                struct pipe_buffer *buf = &bufs[idx];
                buf->ops->release(pipe, buf);
        }
out:
        kfree(bufs);
        return ret;
}

static unsigned fuse_dev_poll(struct file *file, poll_table *wait)
{
        unsigned mask = POLLOUT | POLLWRNORM;
        struct fuse_conn *fc = fuse_get_conn(file);
        if (!fc)
                return POLLERR;

        poll_wait(file, &fc->waitq, wait);

        spin_lock(&fc->lock);
        if (!fc->connected)
                mask = POLLERR;
        else if (request_pending(fc))
                mask |= POLLIN | POLLRDNORM;
        spin_unlock(&fc->lock);

        return mask;
}

/*
 * Abort all requests on the given list (pending or processing)
 *
 * This function releases and reacquires fc->lock
 */
static void end_requests(struct fuse_conn *fc, struct list_head *head)
__releases(fc->lock)
__acquires(fc->lock)
{
        while (!list_empty(head)) {
                struct fuse_req *req;
                req = list_entry(head->next, struct fuse_req, list);
                req->out.h.error = -ECONNABORTED;
                request_end(fc, req);
                spin_lock(&fc->lock);
        }
}

/*
 * Abort requests under I/O
 *
 * The requests are set to aborted and finished, and the request
 * waiter is woken up.  This will make request_wait_answer() wait
 * until the request is unlocked and then return.
 *
 * If the request is asynchronous, then the end function needs to be
 * called after waiting for the request to be unlocked (if it was
 * locked).
 */
static void end_io_requests(struct fuse_conn *fc)
__releases(fc->lock)
__acquires(fc->lock)
{
        while (!list_empty(&fc->io)) {
                struct fuse_req *req =
                        list_entry(fc->io.next, struct fuse_req, list);
                void (*end) (struct fuse_conn *, struct fuse_req *) = req->end;

                req->aborted = 1;
                req->out.h.error = -ECONNABORTED;
                req->state = FUSE_REQ_FINISHED;
                list_del_init(&req->list);
                wake_up(&req->waitq);
                if (end) {
                        req->end = NULL;
                        __fuse_get_request(req);
                        spin_unlock(&fc->lock);
                        wait_event(req->waitq, !req->locked);
                        end(fc, req);
                        fuse_put_request(fc, req);
                        spin_lock(&fc->lock);
                }
        }
}

static void end_queued_requests(struct fuse_conn *fc)
__releases(fc->lock)
__acquires(fc->lock)
{
        fc->max_background = UINT_MAX;
        flush_bg_queue(fc);
        end_requests(fc, &fc->pending);
        end_requests(fc, &fc->processing);
        while (forget_pending(fc))
                kfree(dequeue_forget(fc, 1, NULL));
}

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.txt).
 *
 * During the aborting, progression of requests from the pending and
 * processing lists onto the io list, and progression of new requests
 * onto the pending list is prevented by req->connected being false.
 *
 * Progression of requests under I/O to the processing list is
 * prevented by the req->aborted flag being true for these requests.
 * For this reason requests on the io list must be aborted first.
 */
void fuse_abort_conn(struct fuse_conn *fc)
{
        spin_lock(&fc->lock);
        if (fc->connected) {
                fc->connected = 0;
                fc->blocked = 0;
                fuse_set_initialized(fc);
                end_io_requests(fc);
                end_queued_requests(fc);
                end_polls(fc);
                wake_up_all(&fc->waitq);
                wake_up_all(&fc->blocked_waitq);
                kill_fasync(&fc->fasync, SIGIO, POLL_IN);
        }
        spin_unlock(&fc->lock);
}
EXPORT_SYMBOL_GPL(fuse_abort_conn);

int fuse_dev_release(struct inode *inode, struct file *file)
{
        struct fuse_conn *fc = fuse_get_conn(file);
        if (fc) {
                spin_lock(&fc->lock);
                fc->connected = 0;
                fc->blocked = 0;
                fuse_set_initialized(fc);
                end_queued_requests(fc);
                end_polls(fc);
                wake_up_all(&fc->blocked_waitq);
                spin_unlock(&fc->lock);
                fuse_conn_put(fc);
        }

        return 0;
}
EXPORT_SYMBOL_GPL(fuse_dev_release);

static int fuse_dev_fasync(int fd, struct file *file, int on)
{
        struct fuse_conn *fc = fuse_get_conn(file);
        if (!fc)
                return -EPERM;

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

const struct file_operations fuse_dev_operations = {
        .owner          = THIS_MODULE,
        .llseek         = no_llseek,
        .read           = do_sync_read,
        .aio_read       = fuse_dev_read,
        .splice_read    = fuse_dev_splice_read,
        .write          = do_sync_write,
        .aio_write      = fuse_dev_write,
        .splice_write   = fuse_dev_splice_write,
        .poll           = fuse_dev_poll,
        .release        = fuse_dev_release,
        .fasync         = fuse_dev_fasync,
};
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);
}