Linux 4.2.1

[linux/fpc-iii.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/log2.h>
#include <linux/mount.h>
#include <linux/magic.h>
#include <linux/pipe_fs_i.h>
#include <linux/uio.h>
#include <linux/highmem.h>
#include <linux/pagemap.h>
#include <linux/audit.h>
#include <linux/syscalls.h>
#include <linux/fcntl.h>

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

#include "internal.h"

/*
 * The max size that a non-root user is allowed to grow the pipe. Can
 * be set by root in /proc/sys/fs/pipe-max-size
 */
unsigned int pipe_max_size = 1048576;

/*
 * Minimum pipe size, as required by POSIX
 */
unsigned int pipe_min_size = PAGE_SIZE;

/*
 * 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
 */

static void pipe_lock_nested(struct pipe_inode_info *pipe, int subclass)
{
        if (pipe->files)
                mutex_lock_nested(&pipe->mutex, subclass);
}

void pipe_lock(struct pipe_inode_info *pipe)
{
        /*
         * pipe_lock() nests non-pipe inode locks (for writing to a file)
         */
        pipe_lock_nested(pipe, I_MUTEX_PARENT);
}
EXPORT_SYMBOL(pipe_lock);

void pipe_unlock(struct pipe_inode_info *pipe)
{
        if (pipe->files)
                mutex_unlock(&pipe->mutex);
}
EXPORT_SYMBOL(pipe_unlock);

static inline void __pipe_lock(struct pipe_inode_info *pipe)
{
        mutex_lock_nested(&pipe->mutex, I_MUTEX_PARENT);
}

static inline void __pipe_unlock(struct pipe_inode_info *pipe)
{
        mutex_unlock(&pipe->mutex);
}

void pipe_double_lock(struct pipe_inode_info *pipe1,
                      struct pipe_inode_info *pipe2)
{
        BUG_ON(pipe1 == pipe2);

        if (pipe1 < pipe2) {
                pipe_lock_nested(pipe1, I_MUTEX_PARENT);
                pipe_lock_nested(pipe2, I_MUTEX_CHILD);
        } else {
                pipe_lock_nested(pipe2, I_MUTEX_PARENT);
                pipe_lock_nested(pipe1, I_MUTEX_CHILD);
        }
}

/* 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);
        pipe_unlock(pipe);
        schedule();
        finish_wait(&pipe->wait, &wait);
        pipe_lock(pipe);
}

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

        /*
         * 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);
}

/**
 * generic_pipe_buf_steal - attempt to take ownership of a &pipe_buffer
 * @pipe:       the pipe that the buffer belongs to
 * @buf:        the buffer to attempt to steal
 *
 * Description:
 *      This function attempts to steal the &struct page attached to
 *      @buf. If successful, this function returns 0 and returns with
 *      the page locked. The caller may then reuse the page for whatever
 *      he wishes; the typical use is insertion into a different file
 *      page cache.
 */
int generic_pipe_buf_steal(struct pipe_inode_info *pipe,
                           struct pipe_buffer *buf)
{
        struct page *page = buf->page;

        /*
         * A reference of one is golden, that means that the owner of this
         * page is the only one holding a reference to it. lock the page
         * and return OK.
         */
        if (page_count(page) == 1) {
                lock_page(page);
                return 0;
        }

        return 1;
}
EXPORT_SYMBOL(generic_pipe_buf_steal);

/**
 * generic_pipe_buf_get - get a reference to a &struct pipe_buffer
 * @pipe:       the pipe that the buffer belongs to
 * @buf:        the buffer to get a reference to
 *
 * Description:
 *      This function grabs an extra reference to @buf. It's used in
 *      in the tee() system call, when we duplicate the buffers in one
 *      pipe into another.
 */
void generic_pipe_buf_get(struct pipe_inode_info *pipe, struct pipe_buffer *buf)
{
        page_cache_get(buf->page);
}
EXPORT_SYMBOL(generic_pipe_buf_get);

/**
 * generic_pipe_buf_confirm - verify contents of the pipe buffer
 * @info:       the pipe that the buffer belongs to
 * @buf:        the buffer to confirm
 *
 * Description:
 *      This function does nothing, because the generic pipe code uses
 *      pages that are always good when inserted into the pipe.
 */
int generic_pipe_buf_confirm(struct pipe_inode_info *info,
                             struct pipe_buffer *buf)
{
        return 0;
}
EXPORT_SYMBOL(generic_pipe_buf_confirm);

/**
 * generic_pipe_buf_release - put a reference to a &struct pipe_buffer
 * @pipe:       the pipe that the buffer belongs to
 * @buf:        the buffer to put a reference to
 *
 * Description:
 *      This function releases a reference to @buf.
 */
void generic_pipe_buf_release(struct pipe_inode_info *pipe,
                              struct pipe_buffer *buf)
{
        page_cache_release(buf->page);
}
EXPORT_SYMBOL(generic_pipe_buf_release);

static const struct pipe_buf_operations anon_pipe_buf_ops = {
        .can_merge = 1,
        .confirm = generic_pipe_buf_confirm,
        .release = anon_pipe_buf_release,
        .steal = generic_pipe_buf_steal,
        .get = generic_pipe_buf_get,
};

static const struct pipe_buf_operations packet_pipe_buf_ops = {
        .can_merge = 0,
        .confirm = generic_pipe_buf_confirm,
        .release = anon_pipe_buf_release,
        .steal = generic_pipe_buf_steal,
        .get = generic_pipe_buf_get,
};

static ssize_t
pipe_read(struct kiocb *iocb, struct iov_iter *to)
{
        size_t total_len = iov_iter_count(to);
        struct file *filp = iocb->ki_filp;
        struct pipe_inode_info *pipe = filp->private_data;
        int do_wakeup;
        ssize_t ret;

        /* Null read succeeds. */
        if (unlikely(total_len == 0))
                return 0;

        do_wakeup = 0;
        ret = 0;
        __pipe_lock(pipe);
        for (;;) {
                int bufs = pipe->nrbufs;
                if (bufs) {
                        int curbuf = pipe->curbuf;
                        struct pipe_buffer *buf = pipe->bufs + curbuf;
                        const struct pipe_buf_operations *ops = buf->ops;
                        size_t chars = buf->len;
                        size_t written;
                        int error;

                        if (chars > total_len)
                                chars = total_len;

                        error = ops->confirm(pipe, buf);
                        if (error) {
                                if (!ret)
                                        ret = error;
                                break;
                        }

                        written = copy_page_to_iter(buf->page, buf->offset, chars, to);
                        if (unlikely(written < chars)) {
                                if (!ret)
                                        ret = -EFAULT;
                                break;
                        }
                        ret += chars;
                        buf->offset += chars;
                        buf->len -= chars;

                        /* Was it a packet buffer? Clean up and exit */
                        if (buf->flags & PIPE_BUF_FLAG_PACKET) {
                                total_len = chars;
                                buf->len = 0;
                        }

                        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_poll(&pipe->wait, POLLOUT | POLLWRNORM);
                        kill_fasync(&pipe->fasync_writers, SIGIO, POLL_OUT);
                }
                pipe_wait(pipe);
        }
        __pipe_unlock(pipe);

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

static inline int is_packetized(struct file *file)
{
        return (file->f_flags & O_DIRECT) != 0;
}

static ssize_t
pipe_write(struct kiocb *iocb, struct iov_iter *from)
{
        struct file *filp = iocb->ki_filp;
        struct pipe_inode_info *pipe = filp->private_data;
        ssize_t ret = 0;
        int do_wakeup = 0;
        size_t total_len = iov_iter_count(from);
        ssize_t chars;

        /* Null write succeeds. */
        if (unlikely(total_len == 0))
                return 0;

        __pipe_lock(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;
                const struct pipe_buf_operations *ops = buf->ops;
                int offset = buf->offset + buf->len;

                if (ops->can_merge && offset + chars <= PAGE_SIZE) {
                        int error = ops->confirm(pipe, buf);
                        if (error)
                                goto out;

                        ret = copy_page_from_iter(buf->page, offset, chars, from);
                        if (unlikely(ret < chars)) {
                                error = -EFAULT;
                                goto out;
                        }
                        do_wakeup = 1;
                        buf->len += chars;
                        ret = chars;
                        if (!iov_iter_count(from))
                                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 copied;

                        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;
                        copied = copy_page_from_iter(page, 0, PAGE_SIZE, from);
                        if (unlikely(copied < PAGE_SIZE && iov_iter_count(from))) {
                                if (!ret)
                                        ret = -EFAULT;
                                break;
                        }
                        ret += copied;

                        /* Insert it into the buffer array */
                        buf->page = page;
                        buf->ops = &anon_pipe_buf_ops;
                        buf->offset = 0;
                        buf->len = copied;
                        buf->flags = 0;
                        if (is_packetized(filp)) {
                                buf->ops = &packet_pipe_buf_ops;
                                buf->flags = PIPE_BUF_FLAG_PACKET;
                        }
                        pipe->nrbufs = ++bufs;
                        pipe->tmp_page = NULL;

                        if (!iov_iter_count(from))
                                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_poll(&pipe->wait, POLLIN | POLLRDNORM);
                        kill_fasync(&pipe->fasync_readers, SIGIO, POLL_IN);
                        do_wakeup = 0;
                }
                pipe->waiting_writers++;
                pipe_wait(pipe);
                pipe->waiting_writers--;
        }
out:
        __pipe_unlock(pipe);
        if (do_wakeup) {
                wake_up_interruptible_sync_poll(&pipe->wait, POLLIN | POLLRDNORM);
                kill_fasync(&pipe->fasync_readers, SIGIO, POLL_IN);
        }
        if (ret > 0 && sb_start_write_trylock(file_inode(filp)->i_sb)) {
                int err = file_update_time(filp);
                if (err)
                        ret = err;
                sb_end_write(file_inode(filp)->i_sb);
        }
        return ret;
}

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

        switch (cmd) {
                case FIONREAD:
                        __pipe_lock(pipe);
                        count = 0;
                        buf = pipe->curbuf;
                        nrbufs = pipe->nrbufs;
                        while (--nrbufs >= 0) {
                                count += pipe->bufs[buf].len;
                                buf = (buf+1) & (pipe->buffers - 1);
                        }
                        __pipe_unlock(pipe);

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

/* No kernel lock held - fine */
static unsigned int
pipe_poll(struct file *filp, poll_table *wait)
{
        unsigned int mask;
        struct pipe_inode_info *pipe = filp->private_data;
        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 void put_pipe_info(struct inode *inode, struct pipe_inode_info *pipe)
{
        int kill = 0;

        spin_lock(&inode->i_lock);
        if (!--pipe->files) {
                inode->i_pipe = NULL;
                kill = 1;
        }
        spin_unlock(&inode->i_lock);

        if (kill)
                free_pipe_info(pipe);
}

static int
pipe_release(struct inode *inode, struct file *file)
{
        struct pipe_inode_info *pipe = file->private_data;

        __pipe_lock(pipe);
        if (file->f_mode & FMODE_READ)
                pipe->readers--;
        if (file->f_mode & FMODE_WRITE)
                pipe->writers--;

        if (pipe->readers || pipe->writers) {
                wake_up_interruptible_sync_poll(&pipe->wait, POLLIN | POLLOUT | POLLRDNORM | POLLWRNORM | POLLERR | POLLHUP);
                kill_fasync(&pipe->fasync_readers, SIGIO, POLL_IN);
                kill_fasync(&pipe->fasync_writers, SIGIO, POLL_OUT);
        }
        __pipe_unlock(pipe);

        put_pipe_info(inode, pipe);
        return 0;
}

static int
pipe_fasync(int fd, struct file *filp, int on)
{
        struct pipe_inode_info *pipe = filp->private_data;
        int retval = 0;

        __pipe_lock(pipe);
        if (filp->f_mode & FMODE_READ)
                retval = fasync_helper(fd, filp, on, &pipe->fasync_readers);
        if ((filp->f_mode & FMODE_WRITE) && retval >= 0) {
                retval = fasync_helper(fd, filp, on, &pipe->fasync_writers);
                if (retval < 0 && (filp->f_mode & FMODE_READ))
                        /* this can happen only if on == T */
                        fasync_helper(-1, filp, 0, &pipe->fasync_readers);
        }
        __pipe_unlock(pipe);
        return retval;
}

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

        pipe = kzalloc(sizeof(struct pipe_inode_info), GFP_KERNEL);
        if (pipe) {
                pipe->bufs = kzalloc(sizeof(struct pipe_buffer) * PIPE_DEF_BUFFERS, GFP_KERNEL);
                if (pipe->bufs) {
                        init_waitqueue_head(&pipe->wait);
                        pipe->r_counter = pipe->w_counter = 1;
                        pipe->buffers = PIPE_DEF_BUFFERS;
                        mutex_init(&pipe->mutex);
                        return pipe;
                }
                kfree(pipe);
        }

        return NULL;
}

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->bufs);
        kfree(pipe);
}

static struct vfsmount *pipe_mnt __read_mostly;

/*
 * pipefs_dname() is called from d_path().
 */
static char *pipefs_dname(struct dentry *dentry, char *buffer, int buflen)
{
        return dynamic_dname(dentry, buffer, buflen, "pipe:[%lu]",
                                d_inode(dentry)->i_ino);
}

static const struct dentry_operations pipefs_dentry_operations = {
        .d_dname        = pipefs_dname,
};

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

        if (!inode)
                goto fail_inode;

        inode->i_ino = get_next_ino();

        pipe = alloc_pipe_info();
        if (!pipe)
                goto fail_iput;

        inode->i_pipe = pipe;
        pipe->files = 2;
        pipe->readers = pipe->writers = 1;
        inode->i_fop = &pipefifo_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;

        return inode;

fail_iput:
        iput(inode);

fail_inode:
        return NULL;
}

int create_pipe_files(struct file **res, int flags)
{
        int err;
        struct inode *inode = get_pipe_inode();
        struct file *f;
        struct path path;
        static struct qstr name = { .name = "" };

        if (!inode)
                return -ENFILE;

        err = -ENOMEM;
        path.dentry = d_alloc_pseudo(pipe_mnt->mnt_sb, &name);
        if (!path.dentry)
                goto err_inode;
        path.mnt = mntget(pipe_mnt);

        d_instantiate(path.dentry, inode);

        err = -ENFILE;
        f = alloc_file(&path, FMODE_WRITE, &pipefifo_fops);
        if (IS_ERR(f))
                goto err_dentry;

        f->f_flags = O_WRONLY | (flags & (O_NONBLOCK | O_DIRECT));
        f->private_data = inode->i_pipe;

        res[0] = alloc_file(&path, FMODE_READ, &pipefifo_fops);
        if (IS_ERR(res[0]))
                goto err_file;

        path_get(&path);
        res[0]->private_data = inode->i_pipe;
        res[0]->f_flags = O_RDONLY | (flags & O_NONBLOCK);
        res[1] = f;
        return 0;

err_file:
        put_filp(f);
err_dentry:
        free_pipe_info(inode->i_pipe);
        path_put(&path);
        return err;

err_inode:
        free_pipe_info(inode->i_pipe);
        iput(inode);
        return err;
}

static int __do_pipe_flags(int *fd, struct file **files, int flags)
{
        int error;
        int fdw, fdr;

        if (flags & ~(O_CLOEXEC | O_NONBLOCK | O_DIRECT))
                return -EINVAL;

        error = create_pipe_files(files, flags);
        if (error)
                return error;

        error = get_unused_fd_flags(flags);
        if (error < 0)
                goto err_read_pipe;
        fdr = error;

        error = get_unused_fd_flags(flags);
        if (error < 0)
                goto err_fdr;
        fdw = error;

        audit_fd_pair(fdr, fdw);
        fd[0] = fdr;
        fd[1] = fdw;
        return 0;

 err_fdr:
        put_unused_fd(fdr);
 err_read_pipe:
        fput(files[0]);
        fput(files[1]);
        return error;
}

int do_pipe_flags(int *fd, int flags)
{
        struct file *files[2];
        int error = __do_pipe_flags(fd, files, flags);
        if (!error) {
                fd_install(fd[0], files[0]);
                fd_install(fd[1], files[1]);
        }
        return error;
}

/*
 * sys_pipe() is the normal C calling standard for creating
 * a pipe. It's not the way Unix traditionally does this, though.
 */
SYSCALL_DEFINE2(pipe2, int __user *, fildes, int, flags)
{
        struct file *files[2];
        int fd[2];
        int error;

        error = __do_pipe_flags(fd, files, flags);
        if (!error) {
                if (unlikely(copy_to_user(fildes, fd, sizeof(fd)))) {
                        fput(files[0]);
                        fput(files[1]);
                        put_unused_fd(fd[0]);
                        put_unused_fd(fd[1]);
                        error = -EFAULT;
                } else {
                        fd_install(fd[0], files[0]);
                        fd_install(fd[1], files[1]);
                }
        }
        return error;
}

SYSCALL_DEFINE1(pipe, int __user *, fildes)
{
        return sys_pipe2(fildes, 0);
}

static int wait_for_partner(struct pipe_inode_info *pipe, unsigned int *cnt)
{
        int cur = *cnt; 

        while (cur == *cnt) {
                pipe_wait(pipe);
                if (signal_pending(current))
                        break;
        }
        return cur == *cnt ? -ERESTARTSYS : 0;
}

static void wake_up_partner(struct pipe_inode_info *pipe)
{
        wake_up_interruptible(&pipe->wait);
}

static int fifo_open(struct inode *inode, struct file *filp)
{
        struct pipe_inode_info *pipe;
        bool is_pipe = inode->i_sb->s_magic == PIPEFS_MAGIC;
        int ret;

        filp->f_version = 0;

        spin_lock(&inode->i_lock);
        if (inode->i_pipe) {
                pipe = inode->i_pipe;
                pipe->files++;
                spin_unlock(&inode->i_lock);
        } else {
                spin_unlock(&inode->i_lock);
                pipe = alloc_pipe_info();
                if (!pipe)
                        return -ENOMEM;
                pipe->files = 1;
                spin_lock(&inode->i_lock);
                if (unlikely(inode->i_pipe)) {
                        inode->i_pipe->files++;
                        spin_unlock(&inode->i_lock);
                        free_pipe_info(pipe);
                        pipe = inode->i_pipe;
                } else {
                        inode->i_pipe = pipe;
                        spin_unlock(&inode->i_lock);
                }
        }
        filp->private_data = pipe;
        /* OK, we have a pipe and it's pinned down */

        __pipe_lock(pipe);

        /* We can only do regular read/write on fifos */
        filp->f_mode &= (FMODE_READ | FMODE_WRITE);

        switch (filp->f_mode) {
        case FMODE_READ:
        /*
         *  O_RDONLY
         *  POSIX.1 says that O_NONBLOCK means return with the FIFO
         *  opened, even when there is no process writing the FIFO.
         */
                pipe->r_counter++;
                if (pipe->readers++ == 0)
                        wake_up_partner(pipe);

                if (!is_pipe && !pipe->writers) {
                        if ((filp->f_flags & O_NONBLOCK)) {
                                /* suppress POLLHUP until we have
                                 * seen a writer */
                                filp->f_version = pipe->w_counter;
                        } else {
                                if (wait_for_partner(pipe, &pipe->w_counter))
                                        goto err_rd;
                        }
                }
                break;
        
        case FMODE_WRITE:
        /*
         *  O_WRONLY
         *  POSIX.1 says that O_NONBLOCK means return -1 with
         *  errno=ENXIO when there is no process reading the FIFO.
         */
                ret = -ENXIO;
                if (!is_pipe && (filp->f_flags & O_NONBLOCK) && !pipe->readers)
                        goto err;

                pipe->w_counter++;
                if (!pipe->writers++)
                        wake_up_partner(pipe);

                if (!is_pipe && !pipe->readers) {
                        if (wait_for_partner(pipe, &pipe->r_counter))
                                goto err_wr;
                }
                break;
        
        case FMODE_READ | FMODE_WRITE:
        /*
         *  O_RDWR
         *  POSIX.1 leaves this case "undefined" when O_NONBLOCK is set.
         *  This implementation will NEVER block on a O_RDWR open, since
         *  the process can at least talk to itself.
         */

                pipe->readers++;
                pipe->writers++;
                pipe->r_counter++;
                pipe->w_counter++;
                if (pipe->readers == 1 || pipe->writers == 1)
                        wake_up_partner(pipe);
                break;

        default:
                ret = -EINVAL;
                goto err;
        }

        /* Ok! */
        __pipe_unlock(pipe);
        return 0;

err_rd:
        if (!--pipe->readers)
                wake_up_interruptible(&pipe->wait);
        ret = -ERESTARTSYS;
        goto err;

err_wr:
        if (!--pipe->writers)
                wake_up_interruptible(&pipe->wait);
        ret = -ERESTARTSYS;
        goto err;

err:
        __pipe_unlock(pipe);

        put_pipe_info(inode, pipe);
        return ret;
}

const struct file_operations pipefifo_fops = {
        .open           = fifo_open,
        .llseek         = no_llseek,
        .read_iter      = pipe_read,
        .write_iter     = pipe_write,
        .poll           = pipe_poll,
        .unlocked_ioctl = pipe_ioctl,
        .release        = pipe_release,
        .fasync         = pipe_fasync,
};

/*
 * Allocate a new array of pipe buffers and copy the info over. Returns the
 * pipe size if successful, or return -ERROR on error.
 */
static long pipe_set_size(struct pipe_inode_info *pipe, unsigned long nr_pages)
{
        struct pipe_buffer *bufs;

        /*
         * We can shrink the pipe, if arg >= pipe->nrbufs. Since we don't
         * expect a lot of shrink+grow operations, just free and allocate
         * again like we would do for growing. If the pipe currently
         * contains more buffers than arg, then return busy.
         */
        if (nr_pages < pipe->nrbufs)
                return -EBUSY;

        bufs = kcalloc(nr_pages, sizeof(*bufs), GFP_KERNEL | __GFP_NOWARN);
        if (unlikely(!bufs))
                return -ENOMEM;

        /*
         * The pipe array wraps around, so just start the new one at zero
         * and adjust the indexes.
         */
        if (pipe->nrbufs) {
                unsigned int tail;
                unsigned int head;

                tail = pipe->curbuf + pipe->nrbufs;
                if (tail < pipe->buffers)
                        tail = 0;
                else
                        tail &= (pipe->buffers - 1);

                head = pipe->nrbufs - tail;
                if (head)
                        memcpy(bufs, pipe->bufs + pipe->curbuf, head * sizeof(struct pipe_buffer));
                if (tail)
                        memcpy(bufs + head, pipe->bufs, tail * sizeof(struct pipe_buffer));
        }

        pipe->curbuf = 0;
        kfree(pipe->bufs);
        pipe->bufs = bufs;
        pipe->buffers = nr_pages;
        return nr_pages * PAGE_SIZE;
}

/*
 * Currently we rely on the pipe array holding a power-of-2 number
 * of pages.
 */
static inline unsigned int round_pipe_size(unsigned int size)
{
        unsigned long nr_pages;

        nr_pages = (size + PAGE_SIZE - 1) >> PAGE_SHIFT;
        return roundup_pow_of_two(nr_pages) << PAGE_SHIFT;
}

/*
 * This should work even if CONFIG_PROC_FS isn't set, as proc_dointvec_minmax
 * will return an error.
 */
int pipe_proc_fn(struct ctl_table *table, int write, void __user *buf,
                 size_t *lenp, loff_t *ppos)
{
        int ret;

        ret = proc_dointvec_minmax(table, write, buf, lenp, ppos);
        if (ret < 0 || !write)
                return ret;

        pipe_max_size = round_pipe_size(pipe_max_size);
        return ret;
}

/*
 * After the inode slimming patch, i_pipe/i_bdev/i_cdev share the same
 * location, so checking ->i_pipe is not enough to verify that this is a
 * pipe.
 */
struct pipe_inode_info *get_pipe_info(struct file *file)
{
        return file->f_op == &pipefifo_fops ? file->private_data : NULL;
}

long pipe_fcntl(struct file *file, unsigned int cmd, unsigned long arg)
{
        struct pipe_inode_info *pipe;
        long ret;

        pipe = get_pipe_info(file);
        if (!pipe)
                return -EBADF;

        __pipe_lock(pipe);

        switch (cmd) {
        case F_SETPIPE_SZ: {
                unsigned int size, nr_pages;

                size = round_pipe_size(arg);
                nr_pages = size >> PAGE_SHIFT;

                ret = -EINVAL;
                if (!nr_pages)
                        goto out;

                if (!capable(CAP_SYS_RESOURCE) && size > pipe_max_size) {
                        ret = -EPERM;
                        goto out;
                }
                ret = pipe_set_size(pipe, nr_pages);
                break;
                }
        case F_GETPIPE_SZ:
                ret = pipe->buffers * PAGE_SIZE;
                break;
        default:
                ret = -EINVAL;
                break;
        }

out:
        __pipe_unlock(pipe);
        return ret;
}

static const struct super_operations pipefs_ops = {
        .destroy_inode = free_inode_nonrcu,
        .statfs = simple_statfs,
};

/*
 * 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 dentry *pipefs_mount(struct file_system_type *fs_type,
                         int flags, const char *dev_name, void *data)
{
        return mount_pseudo(fs_type, "pipe:", &pipefs_ops,
                        &pipefs_dentry_operations, PIPEFS_MAGIC);
}

static struct file_system_type pipe_fs_type = {
        .name           = "pipefs",
        .mount          = pipefs_mount,
        .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;
}

fs_initcall(init_pipe_fs);