root/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 <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 inode * inode)
{
        DEFINE_WAIT(wait);

        prepare_to_wait(PIPE_WAIT(*inode), &wait, TASK_INTERRUPTIBLE);
        up(PIPE_SEM(*inode));
        schedule();
        finish_wait(PIPE_WAIT(*inode), &wait);
        down(PIPE_SEM(*inode));
}

static inline 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 inline 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 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;
        int do_wakeup;
        ssize_t ret;
        struct iovec *iov = (struct iovec *)_iov;
        size_t total_len;

        /* pread is not allowed on pipes. */
        if (unlikely(ppos != &filp->f_pos))
                return -ESPIPE;

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

        do_wakeup = 0;
        ret = 0;
        down(PIPE_SEM(*inode));
        for (;;) {
                int size = PIPE_LEN(*inode);
                if (size) {
                        char *pipebuf = PIPE_BASE(*inode) + PIPE_START(*inode);
                        ssize_t chars = PIPE_MAX_RCHUNK(*inode);

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

                        if (pipe_iov_copy_to_user(iov, pipebuf, chars)) {
                                if (!ret) ret = -EFAULT;
                                break;
                        }
                        ret += chars;

                        PIPE_START(*inode) += chars;
                        PIPE_START(*inode) &= (PIPE_SIZE - 1);
                        PIPE_LEN(*inode) -= chars;
                        total_len -= chars;
                        do_wakeup = 1;
                        if (!total_len)
                                break;  /* common path: read succeeded */
                }
                if (PIPE_LEN(*inode)) /* test for cyclic buffers */
                        continue;
                if (!PIPE_WRITERS(*inode))
                        break;
                if (!PIPE_WAITING_WRITERS(*inode)) {
                        /* 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(*inode));
                        kill_fasync(PIPE_FASYNC_WRITERS(*inode), SIGIO, POLL_OUT);
                }
                pipe_wait(inode);
        }
        up(PIPE_SEM(*inode));
        /* Signal writers asynchronously that there is more room.  */
        if (do_wakeup) {
                wake_up_interruptible(PIPE_WAIT(*inode));
                kill_fasync(PIPE_FASYNC_WRITERS(*inode), 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;
        ssize_t ret;
        size_t min;
        int do_wakeup;
        struct iovec *iov = (struct iovec *)_iov;
        size_t total_len;

        /* pwrite is not allowed on pipes. */
        if (unlikely(ppos != &filp->f_pos))
                return -ESPIPE;

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

        do_wakeup = 0;
        ret = 0;
        min = total_len;
        if (min > PIPE_BUF)
                min = 1;
        down(PIPE_SEM(*inode));
        for (;;) {
                int free;
                if (!PIPE_READERS(*inode)) {
                        send_sig(SIGPIPE, current, 0);
                        if (!ret) ret = -EPIPE;
                        break;
                }
                free = PIPE_FREE(*inode);
                if (free >= min) {
                        /* transfer data */
                        ssize_t chars = PIPE_MAX_WCHUNK(*inode);
                        char *pipebuf = PIPE_BASE(*inode) + PIPE_END(*inode);
                        /* Always wakeup, even if the copy fails. Otherwise
                         * we lock up (O_NONBLOCK-)readers that sleep due to
                         * syscall merging.
                         */
                        do_wakeup = 1;
                        if (chars > total_len)
                                chars = total_len;
                        if (chars > free)
                                chars = free;

                        if (pipe_iov_copy_from_user(pipebuf, iov, chars)) {
                                if (!ret) ret = -EFAULT;
                                break;
                        }
                        ret += chars;

                        PIPE_LEN(*inode) += chars;
                        total_len -= chars;
                        if (!total_len)
                                break;
                }
                if (PIPE_FREE(*inode) && ret) {
                        /* handle cyclic data buffers */
                        min = 1;
                        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(*inode));
                        kill_fasync(PIPE_FASYNC_READERS(*inode), SIGIO, POLL_IN);
                        do_wakeup = 0;
                }
                PIPE_WAITING_WRITERS(*inode)++;
                pipe_wait(inode);
                PIPE_WAITING_WRITERS(*inode)--;
        }
        up(PIPE_SEM(*inode));
        if (do_wakeup) {
                wake_up_interruptible(PIPE_WAIT(*inode));
                kill_fasync(PIPE_FASYNC_READERS(*inode), SIGIO, POLL_IN);
        }
        if (ret > 0)
                inode_update_time(inode, 1);    /* mtime and ctime */
        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)
{
        switch (cmd) {
                case FIONREAD:
                        return put_user(PIPE_LEN(*pino), (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;

        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));
                kill_fasync(PIPE_FASYNC_READERS(*inode), SIGIO, POLL_IN);
                kill_fasync(PIPE_FASYNC_WRITERS(*inode), SIGIO, POLL_OUT);
        }
        up(PIPE_SEM(*inode));

        return 0;
}

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

        down(PIPE_SEM(*inode));
        retval = fasync_helper(fd, filp, on, PIPE_FASYNC_READERS(*inode));
        up(PIPE_SEM(*inode));

        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;

        down(PIPE_SEM(*inode));
        retval = fasync_helper(fd, filp, on, PIPE_FASYNC_WRITERS(*inode));
        up(PIPE_SEM(*inode));

        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;
        int retval;

        down(PIPE_SEM(*inode));

        retval = fasync_helper(fd, filp, on, PIPE_FASYNC_READERS(*inode));

        if (retval >= 0)
                retval = fasync_helper(fd, filp, on, PIPE_FASYNC_WRITERS(*inode));

        up(PIPE_SEM(*inode));

        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.  */
        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,
        .readv          = pipe_readv,
        .write          = bad_pipe_w,
        .poll           = fifo_poll,
        .ioctl          = pipe_ioctl,
        .open           = pipe_read_open,
        .release        = pipe_read_release,
        .fasync         = pipe_read_fasync,
};

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

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

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,
};

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,
};

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 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_WRITERS(*inode) = 0;
        PIPE_RCOUNTER(*inode) = PIPE_WCOUNTER(*inode) = 1;
        *PIPE_FASYNC_READERS(*inode) = *PIPE_FASYNC_WRITERS(*inode) = NULL;

        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);
        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 = 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 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);
}

module_init(init_pipe_fs)
module_exit(exit_pipe_fs)