/*
 * net/sunrpc/rpc_pipe.c
 *
 * Userland/kernel interface for rpcauth_gss.
 * Code shamelessly plagiarized from fs/nfsd/nfsctl.c
 * and fs/sysfs/inode.c
 *
 * Copyright (c) 2002, Trond Myklebust <trond.myklebust@fys.uio.no>
 *
 */
#include <linux/module.h>
#include <linux/slab.h>
#include <linux/string.h>
#include <linux/pagemap.h>
#include <linux/mount.h>
#include <linux/namei.h>
#include <linux/fsnotify.h>
#include <linux/kernel.h>

#include <asm/ioctls.h>
#include <linux/fs.h>
#include <linux/poll.h>
#include <linux/wait.h>
#include <linux/seq_file.h>

#include <linux/sunrpc/clnt.h>
#include <linux/workqueue.h>
#include <linux/sunrpc/rpc_pipe_fs.h>

static struct vfsmount *rpc_mount __read_mostly;
static int rpc_mount_count;

static struct file_system_type rpc_pipe_fs_type;


static struct kmem_cache *rpc_inode_cachep __read_mostly;

#define RPC_UPCALL_TIMEOUT (30*HZ)

static void rpc_purge_list(struct rpc_inode *rpci, struct list_head *head,
                void (*destroy_msg)(struct rpc_pipe_msg *), int err)
{
        struct rpc_pipe_msg *msg;

        if (list_empty(head))
                return;
        do {
                msg = list_entry(head->next, struct rpc_pipe_msg, list);
                list_del(&msg->list);
                msg->errno = err;
                destroy_msg(msg);
        } while (!list_empty(head));
        wake_up(&rpci->waitq);
}

static void
rpc_timeout_upcall_queue(struct work_struct *work)
{
        LIST_HEAD(free_list);
        struct rpc_inode *rpci =
                container_of(work, struct rpc_inode, queue_timeout.work);
        struct inode *inode = &rpci->vfs_inode;
        void (*destroy_msg)(struct rpc_pipe_msg *);

        spin_lock(&inode->i_lock);
        if (rpci->ops == NULL) {
                spin_unlock(&inode->i_lock);
                return;
        }
        destroy_msg = rpci->ops->destroy_msg;
        if (rpci->nreaders == 0) {
                list_splice_init(&rpci->pipe, &free_list);
                rpci->pipelen = 0;
        }
        spin_unlock(&inode->i_lock);
        rpc_purge_list(rpci, &free_list, destroy_msg, -ETIMEDOUT);
}

/**
 * rpc_queue_upcall
 * @inode: inode of upcall pipe on which to queue given message
 * @msg: message to queue
 *
 * Call with an @inode created by rpc_mkpipe() to queue an upcall.
 * A userspace process may then later read the upcall by performing a
 * read on an open file for this inode.  It is up to the caller to
 * initialize the fields of @msg (other than @msg->list) appropriately.
 */
int
rpc_queue_upcall(struct inode *inode, struct rpc_pipe_msg *msg)
{
        struct rpc_inode *rpci = RPC_I(inode);
        int res = -EPIPE;

        spin_lock(&inode->i_lock);
        if (rpci->ops == NULL)
                goto out;
        if (rpci->nreaders) {
                list_add_tail(&msg->list, &rpci->pipe);
                rpci->pipelen += msg->len;
                res = 0;
        } else if (rpci->flags & RPC_PIPE_WAIT_FOR_OPEN) {
                if (list_empty(&rpci->pipe))
                        queue_delayed_work(rpciod_workqueue,
                                        &rpci->queue_timeout,
                                        RPC_UPCALL_TIMEOUT);
                list_add_tail(&msg->list, &rpci->pipe);
                rpci->pipelen += msg->len;
                res = 0;
        }
out:
        spin_unlock(&inode->i_lock);
        wake_up(&rpci->waitq);
        return res;
}
EXPORT_SYMBOL(rpc_queue_upcall);

static inline void
rpc_inode_setowner(struct inode *inode, void *private)
{
        RPC_I(inode)->private = private;
}

static void
rpc_close_pipes(struct inode *inode)
{
        struct rpc_inode *rpci = RPC_I(inode);
        struct rpc_pipe_ops *ops;

        mutex_lock(&inode->i_mutex);
        ops = rpci->ops;
        if (ops != NULL) {
                LIST_HEAD(free_list);

                spin_lock(&inode->i_lock);
                rpci->nreaders = 0;
                list_splice_init(&rpci->in_upcall, &free_list);
                list_splice_init(&rpci->pipe, &free_list);
                rpci->pipelen = 0;
                rpci->ops = NULL;
                spin_unlock(&inode->i_lock);
                rpc_purge_list(rpci, &free_list, ops->destroy_msg, -EPIPE);
                rpci->nwriters = 0;
                if (ops->release_pipe)
                        ops->release_pipe(inode);
                cancel_delayed_work_sync(&rpci->queue_timeout);
        }
        rpc_inode_setowner(inode, NULL);
        mutex_unlock(&inode->i_mutex);
}

static struct inode *
rpc_alloc_inode(struct super_block *sb)
{
        struct rpc_inode *rpci;
        rpci = (struct rpc_inode *)kmem_cache_alloc(rpc_inode_cachep, GFP_KERNEL);
        if (!rpci)
                return NULL;
        return &rpci->vfs_inode;
}

static void
rpc_destroy_inode(struct inode *inode)
{
        kmem_cache_free(rpc_inode_cachep, RPC_I(inode));
}

static int
rpc_pipe_open(struct inode *inode, struct file *filp)
{
        struct rpc_inode *rpci = RPC_I(inode);
        int res = -ENXIO;

        mutex_lock(&inode->i_mutex);
        if (rpci->ops != NULL) {
                if (filp->f_mode & FMODE_READ)
                        rpci->nreaders ++;
                if (filp->f_mode & FMODE_WRITE)
                        rpci->nwriters ++;
                res = 0;
        }
        mutex_unlock(&inode->i_mutex);
        return res;
}

static int
rpc_pipe_release(struct inode *inode, struct file *filp)
{
        struct rpc_inode *rpci = RPC_I(inode);
        struct rpc_pipe_msg *msg;

        mutex_lock(&inode->i_mutex);
        if (rpci->ops == NULL)
                goto out;
        msg = (struct rpc_pipe_msg *)filp->private_data;
        if (msg != NULL) {
                spin_lock(&inode->i_lock);
                msg->errno = -EAGAIN;
                list_del(&msg->list);
                spin_unlock(&inode->i_lock);
                rpci->ops->destroy_msg(msg);
        }
        if (filp->f_mode & FMODE_WRITE)
                rpci->nwriters --;
        if (filp->f_mode & FMODE_READ) {
                rpci->nreaders --;
                if (rpci->nreaders == 0) {
                        LIST_HEAD(free_list);
                        spin_lock(&inode->i_lock);
                        list_splice_init(&rpci->pipe, &free_list);
                        rpci->pipelen = 0;
                        spin_unlock(&inode->i_lock);
                        rpc_purge_list(rpci, &free_list,
                                        rpci->ops->destroy_msg, -EAGAIN);
                }
        }
        if (rpci->ops->release_pipe)
                rpci->ops->release_pipe(inode);
out:
        mutex_unlock(&inode->i_mutex);
        return 0;
}

static ssize_t
rpc_pipe_read(struct file *filp, char __user *buf, size_t len, loff_t *offset)
{
        struct inode *inode = filp->f_path.dentry->d_inode;
        struct rpc_inode *rpci = RPC_I(inode);
        struct rpc_pipe_msg *msg;
        int res = 0;

        mutex_lock(&inode->i_mutex);
        if (rpci->ops == NULL) {
                res = -EPIPE;
                goto out_unlock;
        }
        msg = filp->private_data;
        if (msg == NULL) {
                spin_lock(&inode->i_lock);
                if (!list_empty(&rpci->pipe)) {
                        msg = list_entry(rpci->pipe.next,
                                        struct rpc_pipe_msg,
                                        list);
                        list_move(&msg->list, &rpci->in_upcall);
                        rpci->pipelen -= msg->len;
                        filp->private_data = msg;
                        msg->copied = 0;
                }
                spin_unlock(&inode->i_lock);
                if (msg == NULL)
                        goto out_unlock;
        }
        /* NOTE: it is up to the callback to update msg->copied */
        res = rpci->ops->upcall(filp, msg, buf, len);
        if (res < 0 || msg->len == msg->copied) {
                filp->private_data = NULL;
                spin_lock(&inode->i_lock);
                list_del(&msg->list);
                spin_unlock(&inode->i_lock);
                rpci->ops->destroy_msg(msg);
        }
out_unlock:
        mutex_unlock(&inode->i_mutex);
        return res;
}

static ssize_t
rpc_pipe_write(struct file *filp, const char __user *buf, size_t len, loff_t *offset)
{
        struct inode *inode = filp->f_path.dentry->d_inode;
        struct rpc_inode *rpci = RPC_I(inode);
        int res;

        mutex_lock(&inode->i_mutex);
        res = -EPIPE;
        if (rpci->ops != NULL)
                res = rpci->ops->downcall(filp, buf, len);
        mutex_unlock(&inode->i_mutex);
        return res;
}

static unsigned int
rpc_pipe_poll(struct file *filp, struct poll_table_struct *wait)
{
        struct rpc_inode *rpci;
        unsigned int mask = 0;

        rpci = RPC_I(filp->f_path.dentry->d_inode);
        poll_wait(filp, &rpci->waitq, wait);

        mask = POLLOUT | POLLWRNORM;
        if (rpci->ops == NULL)
                mask |= POLLERR | POLLHUP;
        if (filp->private_data || !list_empty(&rpci->pipe))
                mask |= POLLIN | POLLRDNORM;
        return mask;
}

static int
rpc_pipe_ioctl(struct inode *ino, struct file *filp,
                unsigned int cmd, unsigned long arg)
{
        struct rpc_inode *rpci = RPC_I(filp->f_path.dentry->d_inode);
        int len;

        switch (cmd) {
        case FIONREAD:
                if (rpci->ops == NULL)
                        return -EPIPE;
                len = rpci->pipelen;
                if (filp->private_data) {
                        struct rpc_pipe_msg *msg;
                        msg = (struct rpc_pipe_msg *)filp->private_data;
                        len += msg->len - msg->copied;
                }
                return put_user(len, (int __user *)arg);
        default:
                return -EINVAL;
        }
}

static const struct file_operations rpc_pipe_fops = {
        .owner          = THIS_MODULE,
        .llseek         = no_llseek,
        .read           = rpc_pipe_read,
        .write          = rpc_pipe_write,
        .poll           = rpc_pipe_poll,
        .ioctl          = rpc_pipe_ioctl,
        .open           = rpc_pipe_open,
        .release        = rpc_pipe_release,
};

static int
rpc_show_info(struct seq_file *m, void *v)
{
        struct rpc_clnt *clnt = m->private;

        seq_printf(m, "RPC server: %s\n", clnt->cl_server);
        seq_printf(m, "service: %s (%d) version %d\n", clnt->cl_protname,
                        clnt->cl_prog, clnt->cl_vers);
        seq_printf(m, "address: %s\n", rpc_peeraddr2str(clnt, RPC_DISPLAY_ADDR));
        seq_printf(m, "protocol: %s\n", rpc_peeraddr2str(clnt, RPC_DISPLAY_PROTO));
        seq_printf(m, "port: %s\n", rpc_peeraddr2str(clnt, RPC_DISPLAY_PORT));
        return 0;
}

static int
rpc_info_open(struct inode *inode, struct file *file)
{
        struct rpc_clnt *clnt;
        int ret = single_open(file, rpc_show_info, NULL);

        if (!ret) {
                struct seq_file *m = file->private_data;
                mutex_lock(&inode->i_mutex);
                clnt = RPC_I(inode)->private;
                if (clnt) {
                        kref_get(&clnt->cl_kref);
                        m->private = clnt;
                } else {
                        single_release(inode, file);
                        ret = -EINVAL;
                }
                mutex_unlock(&inode->i_mutex);
        }
        return ret;
}

static int
rpc_info_release(struct inode *inode, struct file *file)
{
        struct seq_file *m = file->private_data;
        struct rpc_clnt *clnt = (struct rpc_clnt *)m->private;

        if (clnt)
                rpc_release_client(clnt);
        return single_release(inode, file);
}

static const struct file_operations rpc_info_operations = {
        .owner          = THIS_MODULE,
        .open           = rpc_info_open,
        .read           = seq_read,
        .llseek         = seq_lseek,
        .release        = rpc_info_release,
};


/*
 * We have a single directory with 1 node in it.
 */
enum {
        RPCAUTH_Root = 1,
        RPCAUTH_lockd,
        RPCAUTH_mount,
        RPCAUTH_nfs,
        RPCAUTH_portmap,
        RPCAUTH_statd,
        RPCAUTH_RootEOF
};

/*
 * Description of fs contents.
 */
struct rpc_filelist {
        char *name;
        const struct file_operations *i_fop;
        int mode;
};

static struct rpc_filelist files[] = {
        [RPCAUTH_lockd] = {
                .name = "lockd",
                .mode = S_IFDIR | S_IRUGO | S_IXUGO,
        },
        [RPCAUTH_mount] = {
                .name = "mount",
                .mode = S_IFDIR | S_IRUGO | S_IXUGO,
        },
        [RPCAUTH_nfs] = {
                .name = "nfs",
                .mode = S_IFDIR | S_IRUGO | S_IXUGO,
        },
        [RPCAUTH_portmap] = {
                .name = "portmap",
                .mode = S_IFDIR | S_IRUGO | S_IXUGO,
        },
        [RPCAUTH_statd] = {
                .name = "statd",
                .mode = S_IFDIR | S_IRUGO | S_IXUGO,
        },
};

enum {
        RPCAUTH_info = 2,
        RPCAUTH_EOF
};

static struct rpc_filelist authfiles[] = {
        [RPCAUTH_info] = {
                .name = "info",
                .i_fop = &rpc_info_operations,
                .mode = S_IFREG | S_IRUSR,
        },
};

struct vfsmount *rpc_get_mount(void)
{
        int err;

        err = simple_pin_fs(&rpc_pipe_fs_type, &rpc_mount, &rpc_mount_count);
        if (err != 0)
                return ERR_PTR(err);
        return rpc_mount;
}

void rpc_put_mount(void)
{
        simple_release_fs(&rpc_mount, &rpc_mount_count);
}

static int rpc_delete_dentry(struct dentry *dentry)
{
        return 1;
}

static struct dentry_operations rpc_dentry_operations = {
        .d_delete = rpc_delete_dentry,
};

static int
rpc_lookup_parent(char *path, struct nameidata *nd)
{
        struct vfsmount *mnt;

        if (path[0] == '\0')
                return -ENOENT;

        mnt = rpc_get_mount();
        if (IS_ERR(mnt)) {
                printk(KERN_WARNING "%s: %s failed to mount "
                               "pseudofilesystem \n", __FILE__, __func__);
                return PTR_ERR(mnt);
        }

        if (vfs_path_lookup(mnt->mnt_root, mnt, path, LOOKUP_PARENT, nd)) {
                printk(KERN_WARNING "%s: %s failed to find path %s\n",
                                __FILE__, __func__, path);
                rpc_put_mount();
                return -ENOENT;
        }
        return 0;
}

static void
rpc_release_path(struct nameidata *nd)
{
        path_put(&nd->path);
        rpc_put_mount();
}

static struct inode *
rpc_get_inode(struct super_block *sb, int mode)
{
        struct inode *inode = new_inode(sb);
        if (!inode)
                return NULL;
        inode->i_mode = mode;
        inode->i_uid = inode->i_gid = 0;
        inode->i_blocks = 0;
        inode->i_atime = inode->i_mtime = inode->i_ctime = CURRENT_TIME;
        switch(mode & S_IFMT) {
                case S_IFDIR:
                        inode->i_fop = &simple_dir_operations;
                        inode->i_op = &simple_dir_inode_operations;
                        inc_nlink(inode);
                default:
                        break;
        }
        return inode;
}

/*
 * FIXME: This probably has races.
 */
static void rpc_depopulate(struct dentry *parent,
                           unsigned long start, unsigned long eof)
{
        struct inode *dir = parent->d_inode;
        struct list_head *pos, *next;
        struct dentry *dentry, *dvec[10];
        int n = 0;

        mutex_lock_nested(&dir->i_mutex, I_MUTEX_CHILD);
repeat:
        spin_lock(&dcache_lock);
        list_for_each_safe(pos, next, &parent->d_subdirs) {
                dentry = list_entry(pos, struct dentry, d_u.d_child);
                if (!dentry->d_inode ||
                                dentry->d_inode->i_ino < start ||
                                dentry->d_inode->i_ino >= eof)
                        continue;
                spin_lock(&dentry->d_lock);
                if (!d_unhashed(dentry)) {
                        dget_locked(dentry);
                        __d_drop(dentry);
                        spin_unlock(&dentry->d_lock);
                        dvec[n++] = dentry;
                        if (n == ARRAY_SIZE(dvec))
                                break;
                } else
                        spin_unlock(&dentry->d_lock);
        }
        spin_unlock(&dcache_lock);
        if (n) {
                do {
                        dentry = dvec[--n];
                        if (S_ISREG(dentry->d_inode->i_mode))
                                simple_unlink(dir, dentry);
                        else if (S_ISDIR(dentry->d_inode->i_mode))
                                simple_rmdir(dir, dentry);
                        d_delete(dentry);
                        dput(dentry);
                } while (n);
                goto repeat;
        }
        mutex_unlock(&dir->i_mutex);
}

static int
rpc_populate(struct dentry *parent,
                struct rpc_filelist *files,
                int start, int eof)
{
        struct inode *inode, *dir = parent->d_inode;
        void *private = RPC_I(dir)->private;
        struct dentry *dentry;
        int mode, i;

        mutex_lock(&dir->i_mutex);
        for (i = start; i < eof; i++) {
                dentry = d_alloc_name(parent, files[i].name);
                if (!dentry)
                        goto out_bad;
                dentry->d_op = &rpc_dentry_operations;
                mode = files[i].mode;
                inode = rpc_get_inode(dir->i_sb, mode);
                if (!inode) {
                        dput(dentry);
                        goto out_bad;
                }
                inode->i_ino = i;
                if (files[i].i_fop)
                        inode->i_fop = files[i].i_fop;
                if (private)
                        rpc_inode_setowner(inode, private);
                if (S_ISDIR(mode))
                        inc_nlink(dir);
                d_add(dentry, inode);
                fsnotify_create(dir, dentry);
        }
        mutex_unlock(&dir->i_mutex);
        return 0;
out_bad:
        mutex_unlock(&dir->i_mutex);
        printk(KERN_WARNING "%s: %s failed to populate directory %s\n",
                        __FILE__, __func__, parent->d_name.name);
        return -ENOMEM;
}

static int
__rpc_mkdir(struct inode *dir, struct dentry *dentry)
{
        struct inode *inode;

        inode = rpc_get_inode(dir->i_sb, S_IFDIR | S_IRUGO | S_IXUGO);
        if (!inode)
                goto out_err;
        inode->i_ino = iunique(dir->i_sb, 100);
        d_instantiate(dentry, inode);
        inc_nlink(dir);
        fsnotify_mkdir(dir, dentry);
        return 0;
out_err:
        printk(KERN_WARNING "%s: %s failed to allocate inode for dentry %s\n",
                        __FILE__, __func__, dentry->d_name.name);
        return -ENOMEM;
}

static int
__rpc_rmdir(struct inode *dir, struct dentry *dentry)
{
        int error;
        error = simple_rmdir(dir, dentry);
        if (!error)
                d_delete(dentry);
        return error;
}

static struct dentry *
rpc_lookup_create(struct dentry *parent, const char *name, int len, int exclusive)
{
        struct inode *dir = parent->d_inode;
        struct dentry *dentry;

        mutex_lock_nested(&dir->i_mutex, I_MUTEX_PARENT);
        dentry = lookup_one_len(name, parent, len);
        if (IS_ERR(dentry))
                goto out_err;
        if (!dentry->d_inode)
                dentry->d_op = &rpc_dentry_operations;
        else if (exclusive) {
                dput(dentry);
                dentry = ERR_PTR(-EEXIST);
                goto out_err;
        }
        return dentry;
out_err:
        mutex_unlock(&dir->i_mutex);
        return dentry;
}

static struct dentry *
rpc_lookup_negative(char *path, struct nameidata *nd)
{
        struct dentry *dentry;
        int error;

        if ((error = rpc_lookup_parent(path, nd)) != 0)
                return ERR_PTR(error);
        dentry = rpc_lookup_create(nd->path.dentry, nd->last.name, nd->last.len,
                                   1);
        if (IS_ERR(dentry))
                rpc_release_path(nd);
        return dentry;
}

/**
 * rpc_mkdir - Create a new directory in rpc_pipefs
 * @path: path from the rpc_pipefs root to the new directory
 * @rpc_client: rpc client to associate with this directory
 *
 * This creates a directory at the given @path associated with
 * @rpc_clnt, which will contain a file named "info" with some basic
 * information about the client, together with any "pipes" that may
 * later be created using rpc_mkpipe().
 */
struct dentry *
rpc_mkdir(char *path, struct rpc_clnt *rpc_client)
{
        struct nameidata nd;
        struct dentry *dentry;
        struct inode *dir;
        int error;

        dentry = rpc_lookup_negative(path, &nd);
        if (IS_ERR(dentry))
                return dentry;
        dir = nd.path.dentry->d_inode;
        if ((error = __rpc_mkdir(dir, dentry)) != 0)
                goto err_dput;
        RPC_I(dentry->d_inode)->private = rpc_client;
        error = rpc_populate(dentry, authfiles,
                        RPCAUTH_info, RPCAUTH_EOF);
        if (error)
                goto err_depopulate;
        dget(dentry);
out:
        mutex_unlock(&dir->i_mutex);
        rpc_release_path(&nd);
        return dentry;
err_depopulate:
        rpc_depopulate(dentry, RPCAUTH_info, RPCAUTH_EOF);
        __rpc_rmdir(dir, dentry);
err_dput:
        dput(dentry);
        printk(KERN_WARNING "%s: %s() failed to create directory %s (errno = %d)\n",
                        __FILE__, __func__, path, error);
        dentry = ERR_PTR(error);
        goto out;
}

/**
 * rpc_rmdir - Remove a directory created with rpc_mkdir()
 * @dentry: directory to remove
 */
int
rpc_rmdir(struct dentry *dentry)
{
        struct dentry *parent;
        struct inode *dir;
        int error;

        parent = dget_parent(dentry);
        dir = parent->d_inode;
        mutex_lock_nested(&dir->i_mutex, I_MUTEX_PARENT);
        rpc_depopulate(dentry, RPCAUTH_info, RPCAUTH_EOF);
        error = __rpc_rmdir(dir, dentry);
        dput(dentry);
        mutex_unlock(&dir->i_mutex);
        dput(parent);
        return error;
}

/**
 * rpc_mkpipe - make an rpc_pipefs file for kernel<->userspace communication
 * @parent: dentry of directory to create new "pipe" in
 * @name: name of pipe
 * @private: private data to associate with the pipe, for the caller's use
 * @ops: operations defining the behavior of the pipe: upcall, downcall,
 *      release_pipe, and destroy_msg.
 * @flags: rpc_inode flags
 *
 * Data is made available for userspace to read by calls to
 * rpc_queue_upcall().  The actual reads will result in calls to
 * @ops->upcall, which will be called with the file pointer,
 * message, and userspace buffer to copy to.
 *
 * Writes can come at any time, and do not necessarily have to be
 * responses to upcalls.  They will result in calls to @msg->downcall.
 *
 * The @private argument passed here will be available to all these methods
 * from the file pointer, via RPC_I(file->f_dentry->d_inode)->private.
 */
struct dentry *
rpc_mkpipe(struct dentry *parent, const char *name, void *private, struct rpc_pipe_ops *ops, int flags)
{
        struct dentry *dentry;
        struct inode *dir, *inode;
        struct rpc_inode *rpci;

        dentry = rpc_lookup_create(parent, name, strlen(name), 0);
        if (IS_ERR(dentry))
                return dentry;
        dir = parent->d_inode;
        if (dentry->d_inode) {
                rpci = RPC_I(dentry->d_inode);
                if (rpci->private != private ||
                                rpci->ops != ops ||
                                rpci->flags != flags) {
                        dput (dentry);
                        dentry = ERR_PTR(-EBUSY);
                }
                rpci->nkern_readwriters++;
                goto out;
        }
        inode = rpc_get_inode(dir->i_sb, S_IFIFO | S_IRUSR | S_IWUSR);
        if (!inode)
                goto err_dput;
        inode->i_ino = iunique(dir->i_sb, 100);
        inode->i_fop = &rpc_pipe_fops;
        d_instantiate(dentry, inode);
        rpci = RPC_I(inode);
        rpci->private = private;
        rpci->flags = flags;
        rpci->ops = ops;
        rpci->nkern_readwriters = 1;
        fsnotify_create(dir, dentry);
        dget(dentry);
out:
        mutex_unlock(&dir->i_mutex);
        return dentry;
err_dput:
        dput(dentry);
        dentry = ERR_PTR(-ENOMEM);
        printk(KERN_WARNING "%s: %s() failed to create pipe %s/%s (errno = %d)\n",
                        __FILE__, __func__, parent->d_name.name, name,
                        -ENOMEM);
        goto out;
}
EXPORT_SYMBOL(rpc_mkpipe);

/**
 * rpc_unlink - remove a pipe
 * @dentry: dentry for the pipe, as returned from rpc_mkpipe
 *
 * After this call, lookups will no longer find the pipe, and any
 * attempts to read or write using preexisting opens of the pipe will
 * return -EPIPE.
 */
int
rpc_unlink(struct dentry *dentry)
{
        struct dentry *parent;
        struct inode *dir;
        int error = 0;

        parent = dget_parent(dentry);
        dir = parent->d_inode;
        mutex_lock_nested(&dir->i_mutex, I_MUTEX_PARENT);
        if (--RPC_I(dentry->d_inode)->nkern_readwriters == 0) {
                rpc_close_pipes(dentry->d_inode);
                error = simple_unlink(dir, dentry);
                if (!error)
                        d_delete(dentry);
        }
        dput(dentry);
        mutex_unlock(&dir->i_mutex);
        dput(parent);
        return error;
}
EXPORT_SYMBOL(rpc_unlink);

/*
 * populate the filesystem
 */
static struct super_operations s_ops = {
        .alloc_inode    = rpc_alloc_inode,
        .destroy_inode  = rpc_destroy_inode,
        .statfs         = simple_statfs,
};

#define RPCAUTH_GSSMAGIC 0x67596969

static int
rpc_fill_super(struct super_block *sb, void *data, int silent)
{
        struct inode *inode;
        struct dentry *root;

        sb->s_blocksize = PAGE_CACHE_SIZE;
        sb->s_blocksize_bits = PAGE_CACHE_SHIFT;
        sb->s_magic = RPCAUTH_GSSMAGIC;
        sb->s_op = &s_ops;
        sb->s_time_gran = 1;

        inode = rpc_get_inode(sb, S_IFDIR | 0755);
        if (!inode)
                return -ENOMEM;
        root = d_alloc_root(inode);
        if (!root) {
                iput(inode);
                return -ENOMEM;
        }
        if (rpc_populate(root, files, RPCAUTH_Root + 1, RPCAUTH_RootEOF))
                goto out;
        sb->s_root = root;
        return 0;
out:
        d_genocide(root);
        dput(root);
        return -ENOMEM;
}

static int
rpc_get_sb(struct file_system_type *fs_type,
                int flags, const char *dev_name, void *data, struct vfsmount *mnt)
{
        return get_sb_single(fs_type, flags, data, rpc_fill_super, mnt);
}

static struct file_system_type rpc_pipe_fs_type = {
        .owner          = THIS_MODULE,
        .name           = "rpc_pipefs",
        .get_sb         = rpc_get_sb,
        .kill_sb        = kill_litter_super,
};

static void
init_once(void *foo)
{
        struct rpc_inode *rpci = (struct rpc_inode *) foo;

        inode_init_once(&rpci->vfs_inode);
        rpci->private = NULL;
        rpci->nreaders = 0;
        rpci->nwriters = 0;
        INIT_LIST_HEAD(&rpci->in_upcall);
        INIT_LIST_HEAD(&rpci->in_downcall);
        INIT_LIST_HEAD(&rpci->pipe);
        rpci->pipelen = 0;
        init_waitqueue_head(&rpci->waitq);
        INIT_DELAYED_WORK(&rpci->queue_timeout,
                            rpc_timeout_upcall_queue);
        rpci->ops = NULL;
}

int register_rpc_pipefs(void)
{
        int err;

        rpc_inode_cachep = kmem_cache_create("rpc_inode_cache",
                                sizeof(struct rpc_inode),
                                0, (SLAB_HWCACHE_ALIGN|SLAB_RECLAIM_ACCOUNT|
                                                SLAB_MEM_SPREAD),
                                init_once);
        if (!rpc_inode_cachep)
                return -ENOMEM;
        err = register_filesystem(&rpc_pipe_fs_type);
        if (err) {
                kmem_cache_destroy(rpc_inode_cachep);
                return err;
        }

        return 0;
}

void unregister_rpc_pipefs(void)
{
        kmem_cache_destroy(rpc_inode_cachep);
        unregister_filesystem(&rpc_pipe_fs_type);
}