[safe/jmp/linux-2.6] / fs / fuse / dev.c

/*
  FUSE: Filesystem in Userspace
  Copyright (C) 2001-2005  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 kmem_cache_t *fuse_req_cachep;

static struct fuse_conn *fuse_get_conn(struct file *file)
{
        struct fuse_conn *fc;
        spin_lock(&fuse_lock);
        fc = file->private_data;
        if (fc && !fc->connected)
                fc = NULL;
        spin_unlock(&fuse_lock);
        return fc;
}

static void fuse_request_init(struct fuse_req *req)
{
        memset(req, 0, sizeof(*req));
        INIT_LIST_HEAD(&req->list);
        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, SLAB_KERNEL);
        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);
}

/*
 * Reset request, so that it can be reused
 *
 * The caller must be _very_ careful to make sure, that it is holding
 * the only reference to req
 */
void fuse_reset_request(struct fuse_req *req)
{
        int preallocated = req->preallocated;
        BUG_ON(atomic_read(&req->count) != 1);
        fuse_request_init(req);
        req->preallocated = preallocated;
}

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 struct fuse_req *do_get_request(struct fuse_conn *fc)
{
        struct fuse_req *req;

        spin_lock(&fuse_lock);
        BUG_ON(list_empty(&fc->unused_list));
        req = list_entry(fc->unused_list.next, struct fuse_req, list);
        list_del_init(&req->list);
        spin_unlock(&fuse_lock);
        fuse_request_init(req);
        req->preallocated = 1;
        req->in.h.uid = current->fsuid;
        req->in.h.gid = current->fsgid;
        req->in.h.pid = current->pid;
        return req;
}

/* This can return NULL, but only in case it's interrupted by a SIGKILL */
struct fuse_req *fuse_get_request(struct fuse_conn *fc)
{
        int intr;
        sigset_t oldset;

        atomic_inc(&fc->num_waiting);
        block_sigs(&oldset);
        intr = down_interruptible(&fc->outstanding_sem);
        restore_sigs(&oldset);
        if (intr) {
                atomic_dec(&fc->num_waiting);
                return NULL;
        }
        return do_get_request(fc);
}

/* Must be called with fuse_lock held */
static void fuse_putback_request(struct fuse_conn *fc, struct fuse_req *req)
{
        if (req->preallocated) {
                atomic_dec(&fc->num_waiting);
                list_add(&req->list, &fc->unused_list);
        } else
                fuse_request_free(req);

        /* If we are in debt decrease that first */
        if (fc->outstanding_debt)
                fc->outstanding_debt--;
        else
                up(&fc->outstanding_sem);
}

void fuse_put_request(struct fuse_conn *fc, struct fuse_req *req)
{
        if (atomic_dec_and_test(&req->count)) {
                spin_lock(&fuse_lock);
                fuse_putback_request(fc, req);
                spin_unlock(&fuse_lock);
        }
}

static void fuse_put_request_locked(struct fuse_conn *fc, struct fuse_req *req)
{
        if (atomic_dec_and_test(&req->count))
                fuse_putback_request(fc, req);
}

void fuse_release_background(struct fuse_req *req)
{
        iput(req->inode);
        iput(req->inode2);
        if (req->file)
                fput(req->file);
        spin_lock(&fuse_lock);
        list_del(&req->bg_entry);
        spin_unlock(&fuse_lock);
}

/*
 * This function is called when a request is finished.  Either a reply
 * has arrived or it was interrupted (and not yet sent) or some error
 * occurred during communication with userspace, or the device file
 * was closed.  In case of a background request the reference to the
 * stored objects are released.  The requester thread is woken up (if
 * still waiting), the 'end' callback is called if given, else the
 * reference to the request is released
 *
 * Releasing extra reference for foreground requests must be done
 * within the same locked region as setting state to finished.  This
 * is because fuse_reset_request() may be called after request is
 * finished and it must be the sole possessor.  If request is
 * interrupted and put in the background, it will return with an error
 * and hence never be reset and reused.
 *
 * Called with fuse_lock, unlocks it
 */
static void request_end(struct fuse_conn *fc, struct fuse_req *req)
{
        list_del(&req->list);
        req->state = FUSE_REQ_FINISHED;
        if (!req->background) {
                wake_up(&req->waitq);
                fuse_put_request_locked(fc, req);
                spin_unlock(&fuse_lock);
        } else {
                void (*end) (struct fuse_conn *, struct fuse_req *) = req->end;
                req->end = NULL;
                spin_unlock(&fuse_lock);
                down_read(&fc->sbput_sem);
                if (fc->mounted)
                        fuse_release_background(req);
                up_read(&fc->sbput_sem);
                if (end)
                        end(fc, req);
                else
                        fuse_put_request(fc, req);
        }
}

/*
 * Unfortunately request interruption not just solves the deadlock
 * problem, it causes problems too.  These stem from the fact, that an
 * interrupted request is continued to be processed in userspace,
 * while all the locks and object references (inode and file) held
 * during the operation are released.
 *
 * To release the locks is exactly why there's a need to interrupt the
 * request, so there's not a lot that can be done about this, except
 * introduce additional locking in userspace.
 *
 * More important is to keep inode and file references until userspace
 * has replied, otherwise FORGET and RELEASE could be sent while the
 * inode/file is still used by the filesystem.
 *
 * For this reason the concept of "background" request is introduced.
 * An interrupted request is backgrounded if it has been already sent
 * to userspace.  Backgrounding involves getting an extra reference to
 * inode(s) or file used in the request, and adding the request to
 * fc->background list.  When a reply is received for a background
 * request, the object references are released, and the request is
 * removed from the list.  If the filesystem is unmounted while there
 * are still background requests, the list is walked and references
 * are released as if a reply was received.
 *
 * There's one more use for a background request.  The RELEASE message is
 * always sent as background, since it doesn't return an error or
 * data.
 */
static void background_request(struct fuse_conn *fc, struct fuse_req *req)
{
        req->background = 1;
        list_add(&req->bg_entry, &fc->background);
        if (req->inode)
                req->inode = igrab(req->inode);
        if (req->inode2)
                req->inode2 = igrab(req->inode2);
        if (req->file)
                get_file(req->file);
}

/* Called with fuse_lock held.  Releases, and then reacquires it. */
static void request_wait_answer(struct fuse_conn *fc, struct fuse_req *req)
{
        sigset_t oldset;

        spin_unlock(&fuse_lock);
        block_sigs(&oldset);
        wait_event_interruptible(req->waitq, req->state == FUSE_REQ_FINISHED);
        restore_sigs(&oldset);
        spin_lock(&fuse_lock);
        if (req->state == FUSE_REQ_FINISHED && !req->interrupted)
                return;

        if (!req->interrupted) {
                req->out.h.error = -EINTR;
                req->interrupted = 1;
        }
        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(&fuse_lock);
                wait_event(req->waitq, !req->locked);
                spin_lock(&fuse_lock);
        }
        if (req->state == FUSE_REQ_PENDING) {
                list_del(&req->list);
                __fuse_put_request(req);
        } else if (req->state == FUSE_REQ_SENT)
                background_request(fc, 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 void queue_request(struct fuse_conn *fc, struct fuse_req *req)
{
        fc->reqctr++;
        /* zero is special */
        if (fc->reqctr == 0)
                fc->reqctr = 1;
        req->in.h.unique = fc->reqctr;
        req->in.h.len = sizeof(struct fuse_in_header) +
                len_args(req->in.numargs, (struct fuse_arg *) req->in.args);
        if (!req->preallocated) {
                /* If request is not preallocated (either FORGET or
                   RELEASE), then still decrease outstanding_sem, so
                   user can't open infinite number of files while not
                   processing the RELEASE requests.  However for
                   efficiency do it without blocking, so if down()
                   would block, just increase the debt instead */
                if (down_trylock(&fc->outstanding_sem))
                        fc->outstanding_debt++;
        }
        list_add_tail(&req->list, &fc->pending);
        req->state = FUSE_REQ_PENDING;
        wake_up(&fc->waitq);
        kill_fasync(&fc->fasync, SIGIO, POLL_IN);
}

/*
 * This can only be interrupted by a SIGKILL
 */
void request_send(struct fuse_conn *fc, struct fuse_req *req)
{
        req->isreply = 1;
        spin_lock(&fuse_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(&fuse_lock);
}

static void request_send_nowait(struct fuse_conn *fc, struct fuse_req *req)
{
        spin_lock(&fuse_lock);
        if (fc->connected) {
                queue_request(fc, req);
                spin_unlock(&fuse_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;
        spin_lock(&fuse_lock);
        background_request(fc, req);
        spin_unlock(&fuse_lock);
        request_send_nowait(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
 * interrupted bail out.
 */
static int lock_request(struct fuse_req *req)
{
        int err = 0;
        if (req) {
                spin_lock(&fuse_lock);
                if (req->interrupted)
                        err = -ENOENT;
                else
                        req->locked = 1;
                spin_unlock(&fuse_lock);
        }
        return err;
}

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

struct fuse_copy_state {
        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, int write,
                           struct fuse_req *req, const struct iovec *iov,
                           unsigned long nr_segs)
{
        memset(cs, 0, sizeof(*cs));
        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->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->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;
}

/* 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 && list_empty(&fc->pending)) {
                set_current_state(TASK_INTERRUPTIBLE);
                if (signal_pending(current))
                        break;

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

/*
 * 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 interrupted 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_readv(struct file *file, const struct iovec *iov,
                              unsigned long nr_segs, loff_t *off)
{
        int err;
        struct fuse_conn *fc;
        struct fuse_req *req;
        struct fuse_in *in;
        struct fuse_copy_state cs;
        unsigned reqsize;

 restart:
        spin_lock(&fuse_lock);
        fc = file->private_data;
        err = -EPERM;
        if (!fc)
                goto err_unlock;
        request_wait(fc);
        err = -ENODEV;
        if (!fc->connected)
                goto err_unlock;
        err = -ERESTARTSYS;
        if (list_empty(&fc->pending))
                goto err_unlock;

        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(&fuse_lock);
        fuse_copy_init(&cs, 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(&fuse_lock);
        req->locked = 0;
        if (!err && req->interrupted)
                err = -ENOENT;
        if (err) {
                if (!req->interrupted)
                        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);
                spin_unlock(&fuse_lock);
        }
        return reqsize;

 err_unlock:
        spin_unlock(&fuse_lock);
        return err;
}

static ssize_t fuse_dev_read(struct file *file, char __user *buf,
                             size_t nbytes, loff_t *off)
{
        struct iovec iov;
        iov.iov_len = nbytes;
        iov.iov_base = buf;
        return fuse_dev_readv(file, &iov, 1, off);
}

/* 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)
                        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_writev(struct file *file, const struct iovec *iov,
                               unsigned long nr_segs, loff_t *off)
{
        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(file);
        if (!fc)
                return -ENODEV;

        fuse_copy_init(&cs, 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(&fuse_lock);
        err = -ENOENT;
        if (!fc->connected)
                goto err_unlock;

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

        if (req->interrupted) {
                spin_unlock(&fuse_lock);
                fuse_copy_finish(&cs);
                spin_lock(&fuse_lock);
                request_end(fc, req);
                return -ENOENT;
        }
        list_move(&req->list, &fc->io);
        req->out.h = oh;
        req->locked = 1;
        cs.req = req;
        spin_unlock(&fuse_lock);

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

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

        return err ? err : nbytes;

 err_unlock:
        spin_unlock(&fuse_lock);
 err_finish:
        fuse_copy_finish(&cs);
        return err;
}

static ssize_t fuse_dev_write(struct file *file, const char __user *buf,
                              size_t nbytes, loff_t *off)
{
        struct iovec iov;
        iov.iov_len = nbytes;
        iov.iov_base = (char __user *) buf;
        return fuse_dev_writev(file, &iov, 1, off);
}

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(&fuse_lock);
        if (!fc->connected)
                mask = POLLERR;
        else if (!list_empty(&fc->pending))
                mask |= POLLIN | POLLRDNORM;
        spin_unlock(&fuse_lock);

        return mask;
}

/*
 * Abort all requests on the given list (pending or processing)
 *
 * This function releases and reacquires fuse_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(&fuse_lock);
        }
}

/*
 * Abort requests under I/O
 *
 * The requests are set to interrupted 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)
{
        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->interrupted = 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(&fuse_lock);
                        wait_event(req->waitq, !req->locked);
                        end(fc, req);
                        spin_lock(&fuse_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->interrupted 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(&fuse_lock);
        if (fc->connected) {
                fc->connected = 0;
                end_io_requests(fc);
                end_requests(fc, &fc->pending);
                end_requests(fc, &fc->processing);
                wake_up_all(&fc->waitq);
                kill_fasync(&fc->fasync, SIGIO, POLL_IN);
        }
        spin_unlock(&fuse_lock);
}

static int fuse_dev_release(struct inode *inode, struct file *file)
{
        struct fuse_conn *fc;

        spin_lock(&fuse_lock);
        fc = file->private_data;
        if (fc) {
                fc->connected = 0;
                end_requests(fc, &fc->pending);
                end_requests(fc, &fc->processing);
        }
        spin_unlock(&fuse_lock);
        if (fc) {
                fasync_helper(-1, file, 0, &fc->fasync);
                kobject_put(&fc->kobj);
        }

        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 -ENODEV;

        /* 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           = fuse_dev_read,
        .readv          = fuse_dev_readv,
        .write          = fuse_dev_write,
        .writev         = fuse_dev_writev,
        .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, 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);
}