root/fs/fifo.c

DEFINITIONS

1. wait_for_partner
2. wake_up_partner
3. fifo_open

/*
 *  linux/fs/fifo.c
 *
 *  written by Paul H. Hargrove
 *
 *  Fixes:
 *      10-06-1999, AV: fixed OOM handling in fifo_open(), moved
 *                      initialization there, switched to external
 *                      allocation of pipe_inode_info.
 */

#include <linux/mm.h>
#include <linux/slab.h>
#include <linux/fs.h>
#include <linux/sched.h>
#include <linux/pipe_fs_i.h>

static void wait_for_partner(struct inode* inode, unsigned int *cnt)
{
        int cur = *cnt; 

        while (cur == *cnt) {
                pipe_wait(inode->i_pipe);
                if (signal_pending(current))
                        break;
        }
}

static void wake_up_partner(struct inode* inode)
{
        wake_up_interruptible(&inode->i_pipe->wait);
}

static int fifo_open(struct inode *inode, struct file *filp)
{
        struct pipe_inode_info *pipe;
        int ret;

        mutex_lock(&inode->i_mutex);
        pipe = inode->i_pipe;
        if (!pipe) {
                ret = -ENOMEM;
                pipe = alloc_pipe_info(inode);
                if (!pipe)
                        goto err_nocleanup;
                inode->i_pipe = pipe;
        }
        filp->f_version = 0;

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

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

                if (!pipe->writers) {
                        if ((filp->f_flags & O_NONBLOCK)) {
                                /* suppress POLLHUP until we have
                                 * seen a writer */
                                filp->f_version = pipe->w_counter;
                        } else 
                        {
                                wait_for_partner(inode, &pipe->w_counter);
                                if(signal_pending(current))
                                        goto err_rd;
                        }
                }
                break;
        
        case 2:
        /*
         *  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 ((filp->f_flags & O_NONBLOCK) && !pipe->readers)
                        goto err;

                filp->f_op = &write_pipefifo_fops;
                pipe->w_counter++;
                if (!pipe->writers++)
                        wake_up_partner(inode);

                if (!pipe->readers) {
                        wait_for_partner(inode, &pipe->r_counter);
                        if (signal_pending(current))
                                goto err_wr;
                }
                break;
        
        case 3:
        /*
         *  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.
         */
                filp->f_op = &rdwr_pipefifo_fops;

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

        default:
                ret = -EINVAL;
                goto err;
        }

        /* Ok! */
        mutex_unlock(&inode->i_mutex);
        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:
        if (!pipe->readers && !pipe->writers)
                free_pipe_info(inode);

err_nocleanup:
        mutex_unlock(&inode->i_mutex);
        return ret;
}

/*
 * Dummy default file-operations: the only thing this does
 * is contain the open that then fills in the correct operations
 * depending on the access mode of the file...
 */
const struct file_operations def_fifo_fops = {
        .open           = fifo_open,    /* will set read_ or write_pipefifo_fops */
};