pipe.c

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/*
 *  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>

/*
 * 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 <[email protected]> 2001-08-16
 *
 * pipe_read & write cleanup
 * -- Manfred Spraul <[email protected]> 2002-05-09
 */

static void pipe_lock_nested(struct pipe_inode_info *pipe, int subclass)
{
    if (pipe->inode)
        mutex_lock_nested(&pipe->inode->i_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->inode)
        mutex_unlock(&pipe->inode->i_mutex);
}
EXPORT_SYMBOL(pipe_unlock);

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

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

        if (atomic) {
            if (__copy_from_user_inatomic(to, iov->iov_base, copy))
                return -EFAULT;
        } else {
            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,
              int atomic)
{
    unsigned long copy;

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

        if (atomic) {
            if (__copy_to_user_inatomic(iov->iov_base, from, copy))
                return -EFAULT;
        } else {
            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;
}

/*
 * Attempt to pre-fault in the user memory, so we can use atomic copies.
 * Returns the number of bytes not faulted in.
 */
static int iov_fault_in_pages_write(struct iovec *iov, unsigned long len)
{
    while (!iov->iov_len)
        iov++;

    while (len > 0) {
        unsigned long this_len;

        this_len = min_t(unsigned long, len, iov->iov_len);
        if (fault_in_pages_writeable(iov->iov_base, this_len))
            break;

        len -= this_len;
        iov++;
    }

    return len;
}

/*
 * Pre-fault in the user memory, so we can use atomic copies.
 */
static void iov_fault_in_pages_read(struct iovec *iov, unsigned long len)
{
    while (!iov->iov_len)
        iov++;

    while (len > 0) {
        unsigned long this_len;

        this_len = min_t(unsigned long, len, iov->iov_len);
        fault_in_pages_readable(iov->iov_base, this_len);
        len -= this_len;
        iov++;
    }
}

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);
}

void *generic_pipe_buf_map(struct pipe_inode_info *pipe,
               struct pipe_buffer *buf, int atomic)
{
    if (atomic) {
        buf->flags |= PIPE_BUF_FLAG_ATOMIC;
        return kmap_atomic(buf->page);
    }

    return kmap(buf->page);
}
EXPORT_SYMBOL(generic_pipe_buf_map);

void generic_pipe_buf_unmap(struct pipe_inode_info *pipe,
                struct pipe_buffer *buf, void *map_data)
{
    if (buf->flags & PIPE_BUF_FLAG_ATOMIC) {
        buf->flags &= ~PIPE_BUF_FLAG_ATOMIC;
        kunmap_atomic(map_data);
    } else
        kunmap(buf->page);
}
EXPORT_SYMBOL(generic_pipe_buf_unmap);

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);

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);

int generic_pipe_buf_confirm(struct pipe_inode_info *info,
                 struct pipe_buffer *buf)
{
    return 0;
}
EXPORT_SYMBOL(generic_pipe_buf_confirm);

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,
    .map = generic_pipe_buf_map,
    .unmap = generic_pipe_buf_unmap,
    .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,
    .map = generic_pipe_buf_map,
    .unmap = generic_pipe_buf_unmap,
    .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, const struct iovec *_iov,
       unsigned long nr_segs, loff_t pos)
{
    struct file *filp = iocb->ki_filp;
    struct inode *inode = filp->f_path.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;
            const struct pipe_buf_operations *ops = buf->ops;
            void *addr;
            size_t chars = buf->len;
            int error, atomic;

            if (chars > total_len)
                chars = total_len;

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

            atomic = !iov_fault_in_pages_write(iov, chars);
redo:
            addr = ops->map(pipe, buf, atomic);
            error = pipe_iov_copy_to_user(iov, addr + buf->offset, chars, atomic);
            ops->unmap(pipe, buf, addr);
            if (unlikely(error)) {
                /*
                 * Just retry with the slow path if we failed.
                 */
                if (atomic) {
                    atomic = 0;
                    goto redo;
                }
                if (!ret)
                    ret = error;
                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);
    }
    mutex_unlock(&inode->i_mutex);

    /* 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, const struct iovec *_iov,
        unsigned long nr_segs, loff_t ppos)
{
    struct file *filp = iocb->ki_filp;
    struct inode *inode = filp->f_path.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;
        const struct pipe_buf_operations *ops = buf->ops;
        int offset = buf->offset + buf->len;

        if (ops->can_merge && offset + chars <= PAGE_SIZE) {
            int error, atomic = 1;
            void *addr;

            error = ops->confirm(pipe, buf);
            if (error)
                goto out;

            iov_fault_in_pages_read(iov, chars);
redo1:
            addr = ops->map(pipe, buf, atomic);
            error = pipe_iov_copy_from_user(offset + addr, iov,
                            chars, atomic);
            ops->unmap(pipe, buf, addr);
            ret = error;
            do_wakeup = 1;
            if (error) {
                if (atomic) {
                    atomic = 0;
                    goto redo1;
                }
                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;
            char *src;
            int error, atomic = 1;

            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;

            iov_fault_in_pages_read(iov, chars);
redo2:
            if (atomic)
                src = kmap_atomic(page);
            else
                src = kmap(page);

            error = pipe_iov_copy_from_user(src, iov, chars,
                            atomic);
            if (atomic)
                kunmap_atomic(src);
            else
                kunmap(page);

            if (unlikely(error)) {
                if (atomic) {
                    atomic = 0;
                    goto redo2;
                }
                if (!ret)
                    ret = error;
                break;
            }
            ret += chars;

            /* Insert it into the buffer array */
            buf->page = page;
            buf->ops = &anon_pipe_buf_ops;
            buf->offset = 0;
            buf->len = chars;
            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;

            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_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:
    mutex_unlock(&inode->i_mutex);
    if (do_wakeup) {
        wake_up_interruptible_sync_poll(&pipe->wait, POLLIN | POLLRDNORM);
        kill_fasync(&pipe->fasync_readers, SIGIO, POLL_IN);
    }
    if (ret > 0) {
        int err = file_update_time(filp);
        if (err)
            ret = err;
    }
    return ret;
}

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 long pipe_ioctl(struct file *filp, unsigned int cmd, unsigned long arg)
{
    struct inode *inode = filp->f_path.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 -ENOIOCTLCMD;
    }
}

/* No kernel lock held - fine */
static unsigned int
pipe_poll(struct file *filp, poll_table *wait)
{
    unsigned int mask;
    struct inode *inode = filp->f_path.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_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);
    }
    mutex_unlock(&inode->i_mutex);

    return 0;
}

static int
pipe_read_fasync(int fd, struct file *filp, int on)
{
    struct inode *inode = filp->f_path.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);

    return retval;
}


static int
pipe_write_fasync(int fd, struct file *filp, int on)
{
    struct inode *inode = filp->f_path.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);

    return retval;
}


static int
pipe_rdwr_fasync(int fd, struct file *filp, int on)
{
    struct inode *inode = filp->f_path.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);
        if (retval < 0) /* this can happen only if on == T */
            fasync_helper(-1, filp, 0, &pipe->fasync_readers);
    }
    mutex_unlock(&inode->i_mutex);
    return retval;
}


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

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

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

    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)
{
    int ret = -ENOENT;

    mutex_lock(&inode->i_mutex);

    if (inode->i_pipe) {
        ret = 0;
        inode->i_pipe->readers++;
    }

    mutex_unlock(&inode->i_mutex);

    return ret;
}

static int
pipe_write_open(struct inode *inode, struct file *filp)
{
    int ret = -ENOENT;

    mutex_lock(&inode->i_mutex);

    if (inode->i_pipe) {
        ret = 0;
        inode->i_pipe->writers++;
    }

    mutex_unlock(&inode->i_mutex);

    return ret;
}

static int
pipe_rdwr_open(struct inode *inode, struct file *filp)
{
    int ret = -ENOENT;

    mutex_lock(&inode->i_mutex);

    if (inode->i_pipe) {
        ret = 0;
        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 ret;
}

/*
 * The file_operations structs are not static because they
 * are also used in linux/fs/fifo.c to do operations on FIFOs.
 *
 * Pipes reuse fifos' file_operations structs.
 */
const struct file_operations read_pipefifo_fops = {
    .llseek     = no_llseek,
    .read       = do_sync_read,
    .aio_read   = pipe_read,
    .write      = bad_pipe_w,
    .poll       = pipe_poll,
    .unlocked_ioctl = pipe_ioctl,
    .open       = pipe_read_open,
    .release    = pipe_read_release,
    .fasync     = pipe_read_fasync,
};

const struct file_operations write_pipefifo_fops = {
    .llseek     = no_llseek,
    .read       = bad_pipe_r,
    .write      = do_sync_write,
    .aio_write  = pipe_write,
    .poll       = pipe_poll,
    .unlocked_ioctl = pipe_ioctl,
    .open       = pipe_write_open,
    .release    = pipe_write_release,
    .fasync     = pipe_write_fasync,
};

const struct file_operations rdwr_pipefifo_fops = {
    .llseek     = no_llseek,
    .read       = do_sync_read,
    .aio_read   = pipe_read,
    .write      = do_sync_write,
    .aio_write  = pipe_write,
    .poll       = pipe_poll,
    .unlocked_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) {
        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->inode = inode;
            pipe->buffers = PIPE_DEF_BUFFERS;
            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);
}

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

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]",
                dentry->d_inode->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(inode);
    if (!pipe)
        goto fail_iput;
    inode->i_pipe = pipe;

    pipe->readers = pipe->writers = 1;
    inode->i_fop = &rdwr_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, &write_pipefifo_fops);
    if (!f)
        goto err_dentry;

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

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

    path_get(&path);
    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);
    path_put(&path);
    return err;

err_inode:
    free_pipe_info(inode);
    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);
}

/*
 * 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)
{
    struct inode *i = file->f_path.dentry->d_inode;

    return S_ISFIFO(i->i_mode) ? i->i_pipe : 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;

    mutex_lock(&pipe->inode->i_mutex);

    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:
    mutex_unlock(&pipe->inode->i_mutex);
    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);