[PATCH] another round of fs/pipe.c cleanups

[deliverable/linux.git] / fs / pipe.c

/*
 *  linux/fs/pipe.c
 *
 *  Copyright (C) 1991, 1992, 1999  Linus Torvalds
 */

#include <linux/mm.h>
#include <linux/file.h>
#include <linux/poll.h>
#include <linux/slab.h>
#include <linux/module.h>
#include <linux/init.h>
#include <linux/fs.h>
#include <linux/mount.h>
#include <linux/pipe_fs_i.h>
#include <linux/uio.h>
#include <linux/highmem.h>
#include <linux/pagemap.h>

#include <asm/uaccess.h>
#include <asm/ioctls.h>

/*
 * We use a start+len construction, which provides full use of the 
 * allocated memory.
 * -- Florian Coosmann (FGC)
 * 
 * Reads with count = 0 should always return 0.
 * -- Julian Bradfield 1999-06-07.
 *
 * FIFOs and Pipes now generate SIGIO for both readers and writers.
 * -- Jeremy Elson <jelson@circlemud.org> 2001-08-16
 *
 * pipe_read & write cleanup
 * -- Manfred Spraul <manfred@colorfullife.com> 2002-05-09
 */

/* Drop the inode semaphore and wait for a pipe event, atomically */
void pipe_wait(struct pipe_inode_info *pipe)
{
        DEFINE_WAIT(wait);

        /*
         * Pipes are system-local resources, so sleeping on them
         * is considered a noninteractive wait:
         */
        prepare_to_wait(&pipe->wait, &wait,
                        TASK_INTERRUPTIBLE | TASK_NONINTERACTIVE);
        if (pipe->inode)
                mutex_unlock(&pipe->inode->i_mutex);
        schedule();
        finish_wait(&pipe->wait, &wait);
        if (pipe->inode)
                mutex_lock(&pipe->inode->i_mutex);
}

static int
pipe_iov_copy_from_user(void *to, struct iovec *iov, unsigned long len)
{
        unsigned long copy;

        while (len > 0) {
                while (!iov->iov_len)
                        iov++;
                copy = min_t(unsigned long, len, iov->iov_len);

                if (copy_from_user(to, iov->iov_base, copy))
                        return -EFAULT;
                to += copy;
                len -= copy;
                iov->iov_base += copy;
                iov->iov_len -= copy;
        }
        return 0;
}

static int
pipe_iov_copy_to_user(struct iovec *iov, const void *from, unsigned long len)
{
        unsigned long copy;

        while (len > 0) {
                while (!iov->iov_len)
                        iov++;
                copy = min_t(unsigned long, len, iov->iov_len);

                if (copy_to_user(iov->iov_base, from, copy))
                        return -EFAULT;
                from += copy;
                len -= copy;
                iov->iov_base += copy;
                iov->iov_len -= copy;
        }
        return 0;
}

static void anon_pipe_buf_release(struct pipe_inode_info *pipe,
                                  struct pipe_buffer *buf)
{
        struct page *page = buf->page;

        buf->flags &= ~PIPE_BUF_FLAG_STOLEN;

        /*
         * If nobody else uses this page, and we don't already have a
         * temporary page, let's keep track of it as a one-deep
         * allocation cache. (Otherwise just release our reference to it)
         */
        if (page_count(page) == 1 && !pipe->tmp_page)
                pipe->tmp_page = page;
        else
                page_cache_release(page);
}

static void * anon_pipe_buf_map(struct file *file, struct pipe_inode_info *pipe,
                                struct pipe_buffer *buf)
{
        return kmap(buf->page);
}

static void anon_pipe_buf_unmap(struct pipe_inode_info *pipe,
                                struct pipe_buffer *buf)
{
        kunmap(buf->page);
}

static int anon_pipe_buf_steal(struct pipe_inode_info *pipe,
                               struct pipe_buffer *buf)
{
        buf->flags |= PIPE_BUF_FLAG_STOLEN;
        return 0;
}

static struct pipe_buf_operations anon_pipe_buf_ops = {
        .can_merge = 1,
        .map = anon_pipe_buf_map,
        .unmap = anon_pipe_buf_unmap,
        .release = anon_pipe_buf_release,
        .steal = anon_pipe_buf_steal,
};

static ssize_t
pipe_readv(struct file *filp, const struct iovec *_iov,
           unsigned long nr_segs, loff_t *ppos)
{
        struct inode *inode = filp->f_dentry->d_inode;
        struct pipe_inode_info *pipe;
        int do_wakeup;
        ssize_t ret;
        struct iovec *iov = (struct iovec *)_iov;
        size_t total_len;

        total_len = iov_length(iov, nr_segs);
        /* Null read succeeds. */
        if (unlikely(total_len == 0))
                return 0;

        do_wakeup = 0;
        ret = 0;
        mutex_lock(&inode->i_mutex);
        pipe = inode->i_pipe;
        for (;;) {
                int bufs = pipe->nrbufs;
                if (bufs) {
                        int curbuf = pipe->curbuf;
                        struct pipe_buffer *buf = pipe->bufs + curbuf;
                        struct pipe_buf_operations *ops = buf->ops;
                        void *addr;
                        size_t chars = buf->len;
                        int error;

                        if (chars > total_len)
                                chars = total_len;

                        addr = ops->map(filp, pipe, buf);
                        if (IS_ERR(addr)) {
                                if (!ret)
                                        ret = PTR_ERR(addr);
                                break;
                        }
                        error = pipe_iov_copy_to_user(iov, addr + buf->offset, chars);
                        ops->unmap(pipe, buf);
                        if (unlikely(error)) {
                                if (!ret)
                                        ret = -EFAULT;
                                break;
                        }
                        ret += chars;
                        buf->offset += chars;
                        buf->len -= chars;
                        if (!buf->len) {
                                buf->ops = NULL;
                                ops->release(pipe, buf);
                                curbuf = (curbuf + 1) & (PIPE_BUFFERS-1);
                                pipe->curbuf = curbuf;
                                pipe->nrbufs = --bufs;
                                do_wakeup = 1;
                        }
                        total_len -= chars;
                        if (!total_len)
                                break;  /* common path: read succeeded */
                }
                if (bufs)       /* More to do? */
                        continue;
                if (!pipe->writers)
                        break;
                if (!pipe->waiting_writers) {
                        /* syscall merging: Usually we must not sleep
                         * if O_NONBLOCK is set, or if we got some data.
                         * But if a writer sleeps in kernel space, then
                         * we can wait for that data without violating POSIX.
                         */
                        if (ret)
                                break;
                        if (filp->f_flags & O_NONBLOCK) {
                                ret = -EAGAIN;
                                break;
                        }
                }
                if (signal_pending(current)) {
                        if (!ret)
                                ret = -ERESTARTSYS;
                        break;
                }
                if (do_wakeup) {
                        wake_up_interruptible_sync(&pipe->wait);
                        kill_fasync(&pipe->fasync_writers, SIGIO, POLL_OUT);
                }
                pipe_wait(pipe);
        }
        mutex_unlock(&inode->i_mutex);

        /* Signal writers asynchronously that there is more room. */
        if (do_wakeup) {
                wake_up_interruptible(&pipe->wait);
                kill_fasync(&pipe->fasync_writers, SIGIO, POLL_OUT);
        }
        if (ret > 0)
                file_accessed(filp);
        return ret;
}

static ssize_t
pipe_read(struct file *filp, char __user *buf, size_t count, loff_t *ppos)
{
        struct iovec iov = { .iov_base = buf, .iov_len = count };

        return pipe_readv(filp, &iov, 1, ppos);
}

static ssize_t
pipe_writev(struct file *filp, const struct iovec *_iov,
            unsigned long nr_segs, loff_t *ppos)
{
        struct inode *inode = filp->f_dentry->d_inode;
        struct pipe_inode_info *pipe;
        ssize_t ret;
        int do_wakeup;
        struct iovec *iov = (struct iovec *)_iov;
        size_t total_len;
        ssize_t chars;

        total_len = iov_length(iov, nr_segs);
        /* Null write succeeds. */
        if (unlikely(total_len == 0))
                return 0;

        do_wakeup = 0;
        ret = 0;
        mutex_lock(&inode->i_mutex);
        pipe = inode->i_pipe;

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

        /* We try to merge small writes */
        chars = total_len & (PAGE_SIZE-1); /* size of the last buffer */
        if (pipe->nrbufs && chars != 0) {
                int lastbuf = (pipe->curbuf + pipe->nrbufs - 1) &
                                                        (PIPE_BUFFERS-1);
                struct pipe_buffer *buf = pipe->bufs + lastbuf;
                struct pipe_buf_operations *ops = buf->ops;
                int offset = buf->offset + buf->len;

                if (ops->can_merge && offset + chars <= PAGE_SIZE) {
                        void *addr;
                        int error;

                        addr = ops->map(filp, pipe, buf);
                        if (IS_ERR(addr)) {
                                error = PTR_ERR(addr);
                                goto out;
                        }
                        error = pipe_iov_copy_from_user(offset + addr, iov,
                                                        chars);
                        ops->unmap(pipe, buf);
                        ret = error;
                        do_wakeup = 1;
                        if (error)
                                goto out;
                        buf->len += chars;
                        total_len -= chars;
                        ret = chars;
                        if (!total_len)
                                goto out;
                }
        }

        for (;;) {
                int bufs;

                if (!pipe->readers) {
                        send_sig(SIGPIPE, current, 0);
                        if (!ret)
                                ret = -EPIPE;
                        break;
                }
                bufs = pipe->nrbufs;
                if (bufs < PIPE_BUFFERS) {
                        int newbuf = (pipe->curbuf + bufs) & (PIPE_BUFFERS-1);
                        struct pipe_buffer *buf = pipe->bufs + newbuf;
                        struct page *page = pipe->tmp_page;
                        int error;

                        if (!page) {
                                page = alloc_page(GFP_HIGHUSER);
                                if (unlikely(!page)) {
                                        ret = ret ? : -ENOMEM;
                                        break;
                                }
                                pipe->tmp_page = page;
                        }
                        /* Always wake up, even if the copy fails. Otherwise
                         * we lock up (O_NONBLOCK-)readers that sleep due to
                         * syscall merging.
                         * FIXME! Is this really true?
                         */
                        do_wakeup = 1;
                        chars = PAGE_SIZE;
                        if (chars > total_len)
                                chars = total_len;

                        error = pipe_iov_copy_from_user(kmap(page), iov, chars);
                        kunmap(page);
                        if (unlikely(error)) {
                                if (!ret)
                                        ret = -EFAULT;
                                break;
                        }
                        ret += chars;

                        /* Insert it into the buffer array */
                        buf->page = page;
                        buf->ops = &anon_pipe_buf_ops;
                        buf->offset = 0;
                        buf->len = chars;
                        pipe->nrbufs = ++bufs;
                        pipe->tmp_page = NULL;

                        total_len -= chars;
                        if (!total_len)
                                break;
                }
                if (bufs < PIPE_BUFFERS)
                        continue;
                if (filp->f_flags & O_NONBLOCK) {
                        if (!ret)
                                ret = -EAGAIN;
                        break;
                }
                if (signal_pending(current)) {
                        if (!ret)
                                ret = -ERESTARTSYS;
                        break;
                }
                if (do_wakeup) {
                        wake_up_interruptible_sync(&pipe->wait);
                        kill_fasync(&pipe->fasync_readers, SIGIO, POLL_IN);
                        do_wakeup = 0;
                }
                pipe->waiting_writers++;
                pipe_wait(pipe);
                pipe->waiting_writers--;
        }
out:
        mutex_unlock(&inode->i_mutex);
        if (do_wakeup) {
                wake_up_interruptible(&pipe->wait);
                kill_fasync(&pipe->fasync_readers, SIGIO, POLL_IN);
        }
        if (ret > 0)
                file_update_time(filp);
        return ret;
}

static ssize_t
pipe_write(struct file *filp, const char __user *buf,
           size_t count, loff_t *ppos)
{
        struct iovec iov = { .iov_base = (void __user *)buf, .iov_len = count };

        return pipe_writev(filp, &iov, 1, ppos);
}

static ssize_t
bad_pipe_r(struct file *filp, char __user *buf, size_t count, loff_t *ppos)
{
        return -EBADF;
}

static ssize_t
bad_pipe_w(struct file *filp, const char __user *buf, size_t count,
           loff_t *ppos)
{
        return -EBADF;
}

static int
pipe_ioctl(struct inode *pino, struct file *filp,
           unsigned int cmd, unsigned long arg)
{
        struct inode *inode = filp->f_dentry->d_inode;
        struct pipe_inode_info *pipe;
        int count, buf, nrbufs;

        switch (cmd) {
                case FIONREAD:
                        mutex_lock(&inode->i_mutex);
                        pipe = inode->i_pipe;
                        count = 0;
                        buf = pipe->curbuf;
                        nrbufs = pipe->nrbufs;
                        while (--nrbufs >= 0) {
                                count += pipe->bufs[buf].len;
                                buf = (buf+1) & (PIPE_BUFFERS-1);
                        }
                        mutex_unlock(&inode->i_mutex);

                        return put_user(count, (int __user *)arg);
                default:
                        return -EINVAL;
        }
}

/* No kernel lock held - fine */
static unsigned int
pipe_poll(struct file *filp, poll_table *wait)
{
        unsigned int mask;
        struct inode *inode = filp->f_dentry->d_inode;
        struct pipe_inode_info *pipe = inode->i_pipe;
        int nrbufs;

        poll_wait(filp, &pipe->wait, wait);

        /* Reading only -- no need for acquiring the semaphore.  */
        nrbufs = pipe->nrbufs;
        mask = 0;
        if (filp->f_mode & FMODE_READ) {
                mask = (nrbufs > 0) ? POLLIN | POLLRDNORM : 0;
                if (!pipe->writers && filp->f_version != pipe->w_counter)
                        mask |= POLLHUP;
        }

        if (filp->f_mode & FMODE_WRITE) {
                mask |= (nrbufs < PIPE_BUFFERS) ? POLLOUT | POLLWRNORM : 0;
                /*
                 * Most Unices do not set POLLERR for FIFOs but on Linux they
                 * behave exactly like pipes for poll().
                 */
                if (!pipe->readers)
                        mask |= POLLERR;
        }

        return mask;
}

static int
pipe_release(struct inode *inode, int decr, int decw)
{
        struct pipe_inode_info *pipe;

        mutex_lock(&inode->i_mutex);
        pipe = inode->i_pipe;
        pipe->readers -= decr;
        pipe->writers -= decw;

        if (!pipe->readers && !pipe->writers) {
                free_pipe_info(inode);
        } else {
                wake_up_interruptible(&pipe->wait);
                kill_fasync(&pipe->fasync_readers, SIGIO, POLL_IN);
                kill_fasync(&pipe->fasync_writers, SIGIO, POLL_OUT);
        }
        mutex_unlock(&inode->i_mutex);

        return 0;
}

static int
pipe_read_fasync(int fd, struct file *filp, int on)
{
        struct inode *inode = filp->f_dentry->d_inode;
        int retval;

        mutex_lock(&inode->i_mutex);
        retval = fasync_helper(fd, filp, on, &inode->i_pipe->fasync_readers);
        mutex_unlock(&inode->i_mutex);

        if (retval < 0)
                return retval;

        return 0;
}


static int
pipe_write_fasync(int fd, struct file *filp, int on)
{
        struct inode *inode = filp->f_dentry->d_inode;
        int retval;

        mutex_lock(&inode->i_mutex);
        retval = fasync_helper(fd, filp, on, &inode->i_pipe->fasync_writers);
        mutex_unlock(&inode->i_mutex);

        if (retval < 0)
                return retval;

        return 0;
}


static int
pipe_rdwr_fasync(int fd, struct file *filp, int on)
{
        struct inode *inode = filp->f_dentry->d_inode;
        struct pipe_inode_info *pipe = inode->i_pipe;
        int retval;

        mutex_lock(&inode->i_mutex);

        retval = fasync_helper(fd, filp, on, &pipe->fasync_readers);

        if (retval >= 0)
                retval = fasync_helper(fd, filp, on, &pipe->fasync_writers);

        mutex_unlock(&inode->i_mutex);

        if (retval < 0)
                return retval;

        return 0;
}


static int
pipe_read_release(struct inode *inode, struct file *filp)
{
        pipe_read_fasync(-1, filp, 0);
        return pipe_release(inode, 1, 0);
}

static int
pipe_write_release(struct inode *inode, struct file *filp)
{
        pipe_write_fasync(-1, filp, 0);
        return pipe_release(inode, 0, 1);
}

static int
pipe_rdwr_release(struct inode *inode, struct file *filp)
{
        int decr, decw;

        pipe_rdwr_fasync(-1, filp, 0);
        decr = (filp->f_mode & FMODE_READ) != 0;
        decw = (filp->f_mode & FMODE_WRITE) != 0;
        return pipe_release(inode, decr, decw);
}

static int
pipe_read_open(struct inode *inode, struct file *filp)
{
        /* We could have perhaps used atomic_t, but this and friends
           below are the only places.  So it doesn't seem worthwhile.  */
        mutex_lock(&inode->i_mutex);
        inode->i_pipe->readers++;
        mutex_unlock(&inode->i_mutex);

        return 0;
}

static int
pipe_write_open(struct inode *inode, struct file *filp)
{
        mutex_lock(&inode->i_mutex);
        inode->i_pipe->writers++;
        mutex_unlock(&inode->i_mutex);

        return 0;
}

static int
pipe_rdwr_open(struct inode *inode, struct file *filp)
{
        mutex_lock(&inode->i_mutex);
        if (filp->f_mode & FMODE_READ)
                inode->i_pipe->readers++;
        if (filp->f_mode & FMODE_WRITE)
                inode->i_pipe->writers++;
        mutex_unlock(&inode->i_mutex);

        return 0;
}

/*
 * The file_operations structs are not static because they
 * are also used in linux/fs/fifo.c to do operations on FIFOs.
 */
const struct file_operations read_fifo_fops = {
        .llseek         = no_llseek,
        .read           = pipe_read,
        .readv          = pipe_readv,
        .write          = bad_pipe_w,
        .poll           = pipe_poll,
        .ioctl          = pipe_ioctl,
        .open           = pipe_read_open,
        .release        = pipe_read_release,
        .fasync         = pipe_read_fasync,
};

const struct file_operations write_fifo_fops = {
        .llseek         = no_llseek,
        .read           = bad_pipe_r,
        .write          = pipe_write,
        .writev         = pipe_writev,
        .poll           = pipe_poll,
        .ioctl          = pipe_ioctl,
        .open           = pipe_write_open,
        .release        = pipe_write_release,
        .fasync         = pipe_write_fasync,
};

const struct file_operations rdwr_fifo_fops = {
        .llseek         = no_llseek,
        .read           = pipe_read,
        .readv          = pipe_readv,
        .write          = pipe_write,
        .writev         = pipe_writev,
        .poll           = pipe_poll,
        .ioctl          = pipe_ioctl,
        .open           = pipe_rdwr_open,
        .release        = pipe_rdwr_release,
        .fasync         = pipe_rdwr_fasync,
};

static struct file_operations read_pipe_fops = {
        .llseek         = no_llseek,
        .read           = pipe_read,
        .readv          = pipe_readv,
        .write          = bad_pipe_w,
        .poll           = pipe_poll,
        .ioctl          = pipe_ioctl,
        .open           = pipe_read_open,
        .release        = pipe_read_release,
        .fasync         = pipe_read_fasync,
};

static struct file_operations write_pipe_fops = {
        .llseek         = no_llseek,
        .read           = bad_pipe_r,
        .write          = pipe_write,
        .writev         = pipe_writev,
        .poll           = pipe_poll,
        .ioctl          = pipe_ioctl,
        .open           = pipe_write_open,
        .release        = pipe_write_release,
        .fasync         = pipe_write_fasync,
};

static struct file_operations rdwr_pipe_fops = {
        .llseek         = no_llseek,
        .read           = pipe_read,
        .readv          = pipe_readv,
        .write          = pipe_write,
        .writev         = pipe_writev,
        .poll           = pipe_poll,
        .ioctl          = pipe_ioctl,
        .open           = pipe_rdwr_open,
        .release        = pipe_rdwr_release,
        .fasync         = pipe_rdwr_fasync,
};

struct pipe_inode_info * alloc_pipe_info(struct inode *inode)
{
        struct pipe_inode_info *pipe;

        pipe = kzalloc(sizeof(struct pipe_inode_info), GFP_KERNEL);
        if (pipe) {
                init_waitqueue_head(&pipe->wait);
                pipe->r_counter = pipe->w_counter = 1;
                pipe->inode = inode;
        }

        return pipe;
}

void __free_pipe_info(struct pipe_inode_info *pipe)
{
        int i;

        for (i = 0; i < PIPE_BUFFERS; i++) {
                struct pipe_buffer *buf = pipe->bufs + i;
                if (buf->ops)
                        buf->ops->release(pipe, buf);
        }
        if (pipe->tmp_page)
                __free_page(pipe->tmp_page);
        kfree(pipe);
}

void free_pipe_info(struct inode *inode)
{
        __free_pipe_info(inode->i_pipe);
        inode->i_pipe = NULL;
}

static struct vfsmount *pipe_mnt __read_mostly;
static int pipefs_delete_dentry(struct dentry *dentry)
{
        return 1;
}

static struct dentry_operations pipefs_dentry_operations = {
        .d_delete       = pipefs_delete_dentry,
};

static struct inode * get_pipe_inode(void)
{
        struct inode *inode = new_inode(pipe_mnt->mnt_sb);
        struct pipe_inode_info *pipe;

        if (!inode)
                goto fail_inode;

        pipe = alloc_pipe_info(inode);
        if (!pipe)
                goto fail_iput;
        inode->i_pipe = pipe;

        pipe->readers = pipe->writers = 1;
        inode->i_fop = &rdwr_pipe_fops;

        /*
         * Mark the inode dirty from the very beginning,
         * that way it will never be moved to the dirty
         * list because "mark_inode_dirty()" will think
         * that it already _is_ on the dirty list.
         */
        inode->i_state = I_DIRTY;
        inode->i_mode = S_IFIFO | S_IRUSR | S_IWUSR;
        inode->i_uid = current->fsuid;
        inode->i_gid = current->fsgid;
        inode->i_atime = inode->i_mtime = inode->i_ctime = CURRENT_TIME;
        inode->i_blksize = PAGE_SIZE;

        return inode;

fail_iput:
        iput(inode);

fail_inode:
        return NULL;
}

int do_pipe(int *fd)
{
        struct qstr this;
        char name[32];
        struct dentry *dentry;
        struct inode * inode;
        struct file *f1, *f2;
        int error;
        int i, j;

        error = -ENFILE;
        f1 = get_empty_filp();
        if (!f1)
                goto no_files;

        f2 = get_empty_filp();
        if (!f2)
                goto close_f1;

        inode = get_pipe_inode();
        if (!inode)
                goto close_f12;

        error = get_unused_fd();
        if (error < 0)
                goto close_f12_inode;
        i = error;

        error = get_unused_fd();
        if (error < 0)
                goto close_f12_inode_i;
        j = error;

        error = -ENOMEM;
        sprintf(name, "[%lu]", inode->i_ino);
        this.name = name;
        this.len = strlen(name);
        this.hash = inode->i_ino; /* will go */
        dentry = d_alloc(pipe_mnt->mnt_sb->s_root, &this);
        if (!dentry)
                goto close_f12_inode_i_j;

        dentry->d_op = &pipefs_dentry_operations;
        d_add(dentry, inode);
        f1->f_vfsmnt = f2->f_vfsmnt = mntget(mntget(pipe_mnt));
        f1->f_dentry = f2->f_dentry = dget(dentry);
        f1->f_mapping = f2->f_mapping = inode->i_mapping;

        /* read file */
        f1->f_pos = f2->f_pos = 0;
        f1->f_flags = O_RDONLY;
        f1->f_op = &read_pipe_fops;
        f1->f_mode = FMODE_READ;
        f1->f_version = 0;

        /* write file */
        f2->f_flags = O_WRONLY;
        f2->f_op = &write_pipe_fops;
        f2->f_mode = FMODE_WRITE;
        f2->f_version = 0;

        fd_install(i, f1);
        fd_install(j, f2);
        fd[0] = i;
        fd[1] = j;

        return 0;

close_f12_inode_i_j:
        put_unused_fd(j);
close_f12_inode_i:
        put_unused_fd(i);
close_f12_inode:
        free_pipe_info(inode);
        iput(inode);
close_f12:
        put_filp(f2);
close_f1:
        put_filp(f1);
no_files:
        return error;   
}

/*
 * pipefs should _never_ be mounted by userland - too much of security hassle,
 * no real gain from having the whole whorehouse mounted. So we don't need
 * any operations on the root directory. However, we need a non-trivial
 * d_name - pipe: will go nicely and kill the special-casing in procfs.
 */

static struct super_block *
pipefs_get_sb(struct file_system_type *fs_type, int flags,
              const char *dev_name, void *data)
{
        return get_sb_pseudo(fs_type, "pipe:", NULL, PIPEFS_MAGIC);
}

static struct file_system_type pipe_fs_type = {
        .name           = "pipefs",
        .get_sb         = pipefs_get_sb,
        .kill_sb        = kill_anon_super,
};

static int __init init_pipe_fs(void)
{
        int err = register_filesystem(&pipe_fs_type);

        if (!err) {
                pipe_mnt = kern_mount(&pipe_fs_type);
                if (IS_ERR(pipe_mnt)) {
                        err = PTR_ERR(pipe_mnt);
                        unregister_filesystem(&pipe_fs_type);
                }
        }
        return err;
}

static void __exit exit_pipe_fs(void)
{
        unregister_filesystem(&pipe_fs_type);
        mntput(pipe_mnt);
}

fs_initcall(init_pipe_fs);
module_exit(exit_pipe_fs);