/*
 *  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 <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.
 */

/* Drop the inode semaphore and wait for a pipe event, atomically */
void pipe_wait(struct inode * inode)
{
        DECLARE_WAITQUEUE(wait, current);
        current->state = TASK_INTERRUPTIBLE;
        add_wait_queue(PIPE_WAIT(*inode), &wait);
        up(PIPE_SEM(*inode));
        schedule();
        remove_wait_queue(PIPE_WAIT(*inode), &wait);
        current->state = TASK_RUNNING;
        down(PIPE_SEM(*inode));
}

static ssize_t
pipe_read(struct file *filp, char *buf, size_t count, loff_t *ppos)
{
        struct inode *inode = filp->f_dentry->d_inode;
        ssize_t size, read, ret;

        /* Seeks are not allowed on pipes.  */
        ret = -ESPIPE;
        read = 0;
        if (ppos != &filp->f_pos)
                goto out_nolock;

        /* Always return 0 on null read.  */
        ret = 0;
        if (count == 0)
                goto out_nolock;

        /* Get the pipe semaphore */
        ret = -ERESTARTSYS;
        if (down_interruptible(PIPE_SEM(*inode)))
                goto out_nolock;

        if (PIPE_EMPTY(*inode)) {
do_more_read:
                ret = 0;
                if (!PIPE_WRITERS(*inode))
                        goto out;

                ret = -EAGAIN;
                if (filp->f_flags & O_NONBLOCK)
                        goto out;

                for (;;) {
                        PIPE_WAITING_READERS(*inode)++;
                        pipe_wait(inode);
                        PIPE_WAITING_READERS(*inode)--;
                        ret = -ERESTARTSYS;
                        if (signal_pending(current))
                                goto out;
                        ret = 0;
                        if (!PIPE_EMPTY(*inode))
                                break;
                        if (!PIPE_WRITERS(*inode))
                                goto out;
                }
        }

        /* Read what data is available.  */
        ret = -EFAULT;
        while (count > 0 && (size = PIPE_LEN(*inode))) {
                char *pipebuf = PIPE_BASE(*inode) + PIPE_START(*inode);
                ssize_t chars = PIPE_MAX_RCHUNK(*inode);

                if (chars > count)
                        chars = count;
                if (chars > size)
                        chars = size;

                if (copy_to_user(buf, pipebuf, chars))
                        goto out;

                read += chars;
                PIPE_START(*inode) += chars;
                PIPE_START(*inode) &= (PIPE_SIZE - 1);
                PIPE_LEN(*inode) -= chars;
                count -= chars;
                buf += chars;
        }

        /* Cache behaviour optimization */
        if (!PIPE_LEN(*inode))
                PIPE_START(*inode) = 0;

        if (count && PIPE_WAITING_WRITERS(*inode) && !(filp->f_flags & O_NONBLOCK)) {
                /*
                 * We know that we are going to sleep: signal
                 * writers synchronously that there is more
                 * room.
                 */
                wake_up_interruptible_sync(PIPE_WAIT(*inode));
                if (!PIPE_EMPTY(*inode))
                        BUG();
                goto do_more_read;
        }
        /* Signal writers asynchronously that there is more room.  */
        wake_up_interruptible(PIPE_WAIT(*inode));

        ret = read;
out:
        up(PIPE_SEM(*inode));
out_nolock:
        if (read)
                ret = read;

        UPDATE_ATIME(inode);
        return ret;
}

static ssize_t
pipe_write(struct file *filp, const char *buf, size_t count, loff_t *ppos)
{
        struct inode *inode = filp->f_dentry->d_inode;
        ssize_t free, written, ret;

        /* Seeks are not allowed on pipes.  */
        ret = -ESPIPE;
        written = 0;
        if (ppos != &filp->f_pos)
                goto out_nolock;

        /* Null write succeeds.  */
        ret = 0;
        if (count == 0)
                goto out_nolock;

        ret = -ERESTARTSYS;
        if (down_interruptible(PIPE_SEM(*inode)))
                goto out_nolock;

        /* No readers yields SIGPIPE.  */
        if (!PIPE_READERS(*inode))
                goto sigpipe;

        /* If count <= PIPE_BUF, we have to make it atomic.  */
        free = (count <= PIPE_BUF ? count : 1);

        /* Wait, or check for, available space.  */
        if (filp->f_flags & O_NONBLOCK) {
                ret = -EAGAIN;
                if (PIPE_FREE(*inode) < free)
                        goto out;
        } else {
                while (PIPE_FREE(*inode) < free) {
                        PIPE_WAITING_WRITERS(*inode)++;
                        pipe_wait(inode);
                        PIPE_WAITING_WRITERS(*inode)--;
                        ret = -ERESTARTSYS;
                        if (signal_pending(current))
                                goto out;

                        if (!PIPE_READERS(*inode))
                                goto sigpipe;
                }
        }

        /* Copy into available space.  */
        ret = -EFAULT;
        while (count > 0) {
                int space;
                char *pipebuf = PIPE_BASE(*inode) + PIPE_END(*inode);
                ssize_t chars = PIPE_MAX_WCHUNK(*inode);

                if ((space = PIPE_FREE(*inode)) != 0) {
                        if (chars > count)
                                chars = count;
                        if (chars > space)
                                chars = space;

                        if (copy_from_user(pipebuf, buf, chars))
                                goto out;

                        written += chars;
                        PIPE_LEN(*inode) += chars;
                        count -= chars;
                        buf += chars;
                        space = PIPE_FREE(*inode);
                        continue;
                }

                ret = written;
                if (filp->f_flags & O_NONBLOCK)
                        break;

                do {
                        /*
                         * Synchronous wake-up: it knows that this process
                         * is going to give up this CPU, so it doesn't have
                         * to do idle reschedules.
                         */
                        wake_up_interruptible_sync(PIPE_WAIT(*inode));
                        PIPE_WAITING_WRITERS(*inode)++;
                        pipe_wait(inode);
                        PIPE_WAITING_WRITERS(*inode)--;
                        if (signal_pending(current))
                                goto out;
                        if (!PIPE_READERS(*inode))
                                goto sigpipe;
                } while (!PIPE_FREE(*inode));
                ret = -EFAULT;
        }

        /* Signal readers asynchronously that there is more data.  */
        wake_up_interruptible(PIPE_WAIT(*inode));

        inode->i_ctime = inode->i_mtime = CURRENT_TIME;
        mark_inode_dirty(inode);

out:
        up(PIPE_SEM(*inode));
out_nolock:
        if (written)
                ret = written;
        return ret;

sigpipe:
        if (written)
                goto out;
        up(PIPE_SEM(*inode));
        send_sig(SIGPIPE, current, 0);
        return -EPIPE;
}

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

static ssize_t
bad_pipe_w(struct file *filp, const char *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)
{
        switch (cmd) {
                case FIONREAD:
                        return put_user(PIPE_LEN(*pino), (int *)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;

        poll_wait(filp, PIPE_WAIT(*inode), wait);

        /* Reading only -- no need for acquiring the semaphore.  */
        mask = POLLIN | POLLRDNORM;
        if (PIPE_EMPTY(*inode))
                mask = POLLOUT | POLLWRNORM;
        if (!PIPE_WRITERS(*inode) && filp->f_version != PIPE_WCOUNTER(*inode))
                mask |= POLLHUP;
        if (!PIPE_READERS(*inode))
                mask |= POLLERR;

        return mask;
}

/* FIXME: most Unices do not set POLLERR for fifos */
#define fifo_poll pipe_poll

static int
pipe_release(struct inode *inode, int decr, int decw)
{
        down(PIPE_SEM(*inode));
        PIPE_READERS(*inode) -= decr;
        PIPE_WRITERS(*inode) -= decw;
        if (!PIPE_READERS(*inode) && !PIPE_WRITERS(*inode)) {
                struct pipe_inode_info *info = inode->i_pipe;
                inode->i_pipe = NULL;
                free_page((unsigned long) info->base);
                kfree(info);
        } else {
                wake_up_interruptible(PIPE_WAIT(*inode));
        }
        up(PIPE_SEM(*inode));

        return 0;
}

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)
{
        /* We could have perhaps used atomic_t, but this and friends
           below are the only places.  So it doesn't seem worthwhile.  */
        down(PIPE_SEM(*inode));
        PIPE_READERS(*inode)++;
        up(PIPE_SEM(*inode));

        return 0;
}

static int
pipe_write_open(struct inode *inode, struct file *filp)
{
        down(PIPE_SEM(*inode));
        PIPE_WRITERS(*inode)++;
        up(PIPE_SEM(*inode));

        return 0;
}

static int
pipe_rdwr_open(struct inode *inode, struct file *filp)
{
        down(PIPE_SEM(*inode));
        if (filp->f_mode & FMODE_READ)
                PIPE_READERS(*inode)++;
        if (filp->f_mode & FMODE_WRITE)
                PIPE_WRITERS(*inode)++;
        up(PIPE_SEM(*inode));

        return 0;
}

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

struct file_operations write_fifo_fops = {
        llseek:         no_llseek,
        read:           bad_pipe_r,
        write:          pipe_write,
        poll:           fifo_poll,
        ioctl:          pipe_ioctl,
        open:           pipe_write_open,
        release:        pipe_write_release,
};

struct file_operations rdwr_fifo_fops = {
        llseek:         no_llseek,
        read:           pipe_read,
        write:          pipe_write,
        poll:           fifo_poll,
        ioctl:          pipe_ioctl,
        open:           pipe_rdwr_open,
        release:        pipe_rdwr_release,
};

struct file_operations read_pipe_fops = {
        llseek:         no_llseek,
        read:           pipe_read,
        write:          bad_pipe_w,
        poll:           pipe_poll,
        ioctl:          pipe_ioctl,
        open:           pipe_read_open,
        release:        pipe_read_release,
};

struct file_operations write_pipe_fops = {
        llseek:         no_llseek,
        read:           bad_pipe_r,
        write:          pipe_write,
        poll:           pipe_poll,
        ioctl:          pipe_ioctl,
        open:           pipe_write_open,
        release:        pipe_write_release,
};

struct file_operations rdwr_pipe_fops = {
        llseek:         no_llseek,
        read:           pipe_read,
        write:          pipe_write,
        poll:           pipe_poll,
        ioctl:          pipe_ioctl,
        open:           pipe_rdwr_open,
        release:        pipe_rdwr_release,
};

struct inode* pipe_new(struct inode* inode)
{
        unsigned long page;

        page = __get_free_page(GFP_USER);
        if (!page)
                return NULL;

        inode->i_pipe = kmalloc(sizeof(struct pipe_inode_info), GFP_KERNEL);
        if (!inode->i_pipe)
                goto fail_page;

        init_waitqueue_head(PIPE_WAIT(*inode));
        PIPE_BASE(*inode) = (char*) page;
        PIPE_START(*inode) = PIPE_LEN(*inode) = 0;
        PIPE_READERS(*inode) = PIPE_WRITERS(*inode) = 0;
        PIPE_WAITING_READERS(*inode) = PIPE_WAITING_WRITERS(*inode) = 0;
        PIPE_RCOUNTER(*inode) = PIPE_WCOUNTER(*inode) = 1;

        return inode;
fail_page:
        free_page(page);
        return NULL;
}

static struct vfsmount *pipe_mnt;
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);

        if (!inode)
                goto fail_inode;

        if(!pipe_new(inode))
                goto fail_iput;
        PIPE_READERS(*inode) = PIPE_WRITERS(*inode) = 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);

        /* read file */
        f1->f_pos = f2->f_pos = 0;
        f1->f_flags = O_RDONLY;
        f1->f_op = &read_pipe_fops;
        f1->f_mode = 1;
        f1->f_version = 0;

        /* write file */
        f2->f_flags = O_WRONLY;
        f2->f_op = &write_pipe_fops;
        f2->f_mode = 2;
        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_page((unsigned long) PIPE_BASE(*inode));
        kfree(inode->i_pipe);
        inode->i_pipe = NULL;
        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 int pipefs_statfs(struct super_block *sb, struct statfs *buf)
{
        buf->f_type = PIPEFS_MAGIC;
        buf->f_bsize = 1024;
        buf->f_namelen = 255;
        return 0;
}

static struct super_operations pipefs_ops = {
        statfs:         pipefs_statfs,
};

static struct super_block * pipefs_read_super(struct super_block *sb, void *data, int silent)
{
        struct inode *root = new_inode(sb);
        if (!root)
                return NULL;
        root->i_mode = S_IFDIR | S_IRUSR | S_IWUSR;
        root->i_uid = root->i_gid = 0;
        root->i_atime = root->i_mtime = root->i_ctime = CURRENT_TIME;
        sb->s_blocksize = 1024;
        sb->s_blocksize_bits = 10;
        sb->s_magic = PIPEFS_MAGIC;
        sb->s_op        = &pipefs_ops;
        sb->s_root = d_alloc(NULL, &(const struct qstr) { "pipe:", 5, 0 });
        if (!sb->s_root) {
                iput(root);
                return NULL;
        }
        sb->s_root->d_sb = sb;
        sb->s_root->d_parent = sb->s_root;
        d_instantiate(sb->s_root, root);
        return sb;
}

static DECLARE_FSTYPE(pipe_fs_type, "pipefs", pipefs_read_super, FS_NOMOUNT);

static int __init init_pipe_fs(void)
{
        int err = register_filesystem(&pipe_fs_type);
        if (!err) {
                pipe_mnt = kern_mount(&pipe_fs_type);
                err = PTR_ERR(pipe_mnt);
                if (IS_ERR(pipe_mnt))
                        unregister_filesystem(&pipe_fs_type);
                else
                        err = 0;
        }
        return err;
}

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

module_init(init_pipe_fs)
module_exit(exit_pipe_fs)