move kernel-doc comment for might_sleep directly before its defining block

[linux-2.6/mini2440.git] / fs / fuse / dev.c

/*
  FUSE: Filesystem in Userspace
  Copyright (C) 2001-2006  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>

MODULE_ALIAS_MISCDEV(FUSE_MINOR);

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)
{
        memset(req, 0, sizeof(*req));
        INIT_LIST_HEAD(&req->list);
        INIT_LIST_HEAD(&req->intr_entry);
        init_waitqueue_head(&req->waitq);
        atomic_set(&req->count, 1);
}

struct fuse_req *fuse_request_alloc(void)
{
        struct fuse_req *req = kmem_cache_alloc(fuse_req_cachep, GFP_KERNEL);
        if (req)
                fuse_request_init(req);
        return req;
}

struct fuse_req *fuse_request_alloc_nofs(void)
{
        struct fuse_req *req = kmem_cache_alloc(fuse_req_cachep, GFP_NOFS);
        if (req)
                fuse_request_init(req);
        return req;
}

void fuse_request_free(struct fuse_req *req)
{
        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);
}

static 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 = current->fsuid;
        req->in.h.gid = current->fsgid;
        req->in.h.pid = current->pid;
}

struct fuse_req *fuse_get_req(struct fuse_conn *fc)
{
        struct fuse_req *req;
        sigset_t oldset;
        int intr;
        int err;

        atomic_inc(&fc->num_waiting);
        block_sigs(&oldset);
        intr = wait_event_interruptible(fc->blocked_waitq, !fc->blocked);
        restore_sigs(&oldset);
        err = -EINTR;
        if (intr)
                goto out;

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

        req = fuse_request_alloc();
        err = -ENOMEM;
        if (!req)
                goto out;

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

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

/*
 * 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;
                        get_file(file);
                        req->stolen_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);
        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(struct fuse_conn *fc, struct file *file)
{
        struct fuse_req *req;

        atomic_inc(&fc->num_waiting);
        wait_event(fc->blocked_waitq, !fc->blocked);
        req = fuse_request_alloc();
        if (!req)
                req = get_reserved_req(fc, file);

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

void fuse_put_request(struct fuse_conn *fc, struct fuse_req *req)
{
        if (atomic_dec_and_test(&req->count)) {
                if (req->waiting)
                        atomic_dec(&fc->num_waiting);

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

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.unique = fuse_get_unique(fc);
        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);
}

static void flush_bg_queue(struct fuse_conn *fc)
{
        while (fc->active_background < FUSE_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++;
                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) {
                if (fc->num_background == FUSE_MAX_BACKGROUND) {
                        fc->blocked = 0;
                        wake_up_all(&fc->blocked_waitq);
                }
                if (fc->num_background == FUSE_CONGESTION_THRESHOLD) {
                        clear_bdi_congested(&fc->bdi, READ);
                        clear_bdi_congested(&fc->bdi, WRITE);
                }
                fc->num_background--;
                fc->active_background--;
                flush_bg_queue(fc);
        }
        spin_unlock(&fc->lock);
        wake_up(&req->waitq);
        if (end)
                end(fc, req);
        else
                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);
        }
}

void request_send(struct fuse_conn *fc, struct fuse_req *req)
{
        req->isreply = 1;
        spin_lock(&fc->lock);
        if (!fc->connected)
                req->out.h.error = -ENOTCONN;
        else if (fc->conn_error)
                req->out.h.error = -ECONNREFUSED;
        else {
                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);
}

static void request_send_nowait_locked(struct fuse_conn *fc,
                                       struct fuse_req *req)
{
        req->background = 1;
        fc->num_background++;
        if (fc->num_background == FUSE_MAX_BACKGROUND)
                fc->blocked = 1;
        if (fc->num_background == FUSE_CONGESTION_THRESHOLD) {
                set_bdi_congested(&fc->bdi, READ);
                set_bdi_congested(&fc->bdi, WRITE);
        }
        list_add_tail(&req->list, &fc->bg_queue);
        flush_bg_queue(fc);
}

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

void request_send_noreply(struct fuse_conn *fc, struct fuse_req *req)
{
        req->isreply = 0;
        request_send_nowait(fc, req);
}

void request_send_background(struct fuse_conn *fc, struct fuse_req *req)
{
        req->isreply = 1;
        request_send_nowait(fc, req);
}

/*
 * Called under fc->lock
 *
 * fc->connected must have been checked previously
 */
void request_send_background_locked(struct fuse_conn *fc, struct fuse_req *req)
{
        req->isreply = 1;
        request_send_nowait_locked(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;
        unsigned long nr_segs;
        unsigned long seglen;
        unsigned long addr;
        struct page *pg;
        void *mapaddr;
        void *buf;
        unsigned len;
};

static void fuse_copy_init(struct fuse_copy_state *cs, struct fuse_conn *fc,
                           int write, struct fuse_req *req,
                           const struct iovec *iov, unsigned long nr_segs)
{
        memset(cs, 0, sizeof(*cs));
        cs->fc = fc;
        cs->write = write;
        cs->req = req;
        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->mapaddr) {
                kunmap_atomic(cs->mapaddr, KM_USER0);
                if (cs->write) {
                        flush_dcache_page(cs->pg);
                        set_page_dirty_lock(cs->pg);
                }
                put_page(cs->pg);
                cs->mapaddr = 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)
{
        unsigned long offset;
        int err;

        unlock_request(cs->fc, cs->req);
        fuse_copy_finish(cs);
        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 --;
        }
        down_read(&current->mm->mmap_sem);
        err = get_user_pages(current, current->mm, cs->addr, 1, cs->write, 0,
                             &cs->pg, NULL);
        up_read(&current->mm->mmap_sem);
        if (err < 0)
                return err;
        BUG_ON(err != 1);
        offset = cs->addr % PAGE_SIZE;
        cs->mapaddr = kmap_atomic(cs->pg, KM_USER0);
        cs->buf = cs->mapaddr + offset;
        cs->len = min(PAGE_SIZE - 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) {
                if (cs->write)
                        memcpy(cs->buf, *val, ncpy);
                else
                        memcpy(*val, cs->buf, ncpy);
                *val += ncpy;
        }
        *size -= ncpy;
        cs->len -= ncpy;
        cs->buf += ncpy;
        return ncpy;
}

/*
 * 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 *page,
                          unsigned offset, unsigned count, int zeroing)
{
        if (page && zeroing && count < PAGE_SIZE) {
                void *mapaddr = kmap_atomic(page, KM_USER1);
                memset(mapaddr, 0, PAGE_SIZE);
                kunmap_atomic(mapaddr, KM_USER1);
        }
        while (count) {
                int err;
                if (!cs->len && (err = fuse_copy_fill(cs)))
                        return err;
                if (page) {
                        void *mapaddr = kmap_atomic(page, KM_USER1);
                        void *buf = mapaddr + offset;
                        offset += fuse_copy_do(cs, &buf, &count);
                        kunmap_atomic(mapaddr, KM_USER1);
                } 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;
        unsigned offset = req->page_offset;
        unsigned count = min(nbytes, (unsigned) PAGE_SIZE - offset);

        for (i = 0; i < req->num_pages && (nbytes || zeroing); i++) {
                struct page *page = req->pages[i];
                int err = fuse_copy_page(cs, page, offset, count, zeroing);
                if (err)
                        return err;

                nbytes -= count;
                count = min(nbytes, (unsigned) PAGE_SIZE);
                offset = 0;
        }
        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) {
                int err;
                if (!cs->len && (err = fuse_copy_fill(cs)))
                        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 request_pending(struct fuse_conn *fc)
{
        return !list_empty(&fc->pending) || !list_empty(&fc->interrupts);
}

/* Wait until a request is available on the pending list */
static void request_wait(struct fuse_conn *fc)
{
        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_req *req,
                               const struct iovec *iov, unsigned long nr_segs)
        __releases(fc->lock)
{
        struct fuse_copy_state cs;
        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 (iov_length(iov, nr_segs) < reqsize)
                return -EINVAL;

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

/*
 * 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_read(struct kiocb *iocb, const struct iovec *iov,
                              unsigned long nr_segs, loff_t pos)
{
        int err;
        struct fuse_req *req;
        struct fuse_in *in;
        struct fuse_copy_state cs;
        unsigned reqsize;
        struct file *file = iocb->ki_filp;
        struct fuse_conn *fc = fuse_get_conn(file);
        if (!fc)
                return -EPERM;

 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, req, iov, nr_segs);
        }

        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 (iov_length(iov, nr_segs) < 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);
        fuse_copy_init(&cs, fc, 1, req, iov, nr_segs);
        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;
}

/* Look up request on processing list by unique ID */
static struct fuse_req *request_find(struct fuse_conn *fc, u64 unique)
{
        struct list_head *entry;

        list_for_each(entry, &fc->processing) {
                struct fuse_req *req;
                req = list_entry(entry, struct fuse_req, 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_write(struct kiocb *iocb, const struct iovec *iov,
                               unsigned long nr_segs, loff_t pos)
{
        int err;
        unsigned nbytes = iov_length(iov, nr_segs);
        struct fuse_req *req;
        struct fuse_out_header oh;
        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, NULL, iov, nr_segs);
        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.unique || oh.error <= -1000 || oh.error > 0 ||
            oh.len != nbytes)
                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;
        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 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)
{
        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;
                        /* The end function will consume this reference */
                        __fuse_get_request(req);
                        spin_unlock(&fc->lock);
                        wait_event(req->waitq, !req->locked);
                        end(fc, req);
                        spin_lock(&fc->lock);
                }
        }
}

/*
 * 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;
                end_io_requests(fc);
                end_requests(fc, &fc->pending);
                end_requests(fc, &fc->processing);
                wake_up_all(&fc->waitq);
                wake_up_all(&fc->blocked_waitq);
                kill_fasync(&fc->fasync, SIGIO, POLL_IN);
        }
        spin_unlock(&fc->lock);
}

static 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;
                end_requests(fc, &fc->pending);
                end_requests(fc, &fc->processing);
                spin_unlock(&fc->lock);
                fasync_helper(-1, file, 0, &fc->fasync);
                fuse_conn_put(fc);
        }

        return 0;
}

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,
        .write          = do_sync_write,
        .aio_write      = fuse_dev_write,
        .poll           = fuse_dev_poll,
        .release        = fuse_dev_release,
        .fasync         = fuse_dev_fasync,
};

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);
}