LXR linux/fs/fifo.c

   1/*
   2 *  linux/fs/fifo.c
   3 *
   4 *  written by Paul H. Hargrove
   5 *
   6 *  Fixes:
   7 *      10-06-1999, AV: fixed OOM handling in fifo_open(), moved
   8 *                      initialization there, switched to external
   9 *                      allocation of pipe_inode_info.
  10 */
  11
  12#include <linux/mm.h>
  13#include <linux/slab.h>
  14#include <linux/fs.h>
  15#include <linux/sched.h>
  16#include <linux/pipe_fs_i.h>
  17
  18static void wait_for_partner(struct inode* inode, unsigned int *cnt)
  19{
  20        int cur = *cnt; 
  21
  22        while (cur == *cnt) {
  23                pipe_wait(inode->i_pipe);
  24                if (signal_pending(current))
  25                        break;
  26        }
  27}
  28
  29static void wake_up_partner(struct inode* inode)
  30{
  31        wake_up_interruptible(&inode->i_pipe->wait);
  32}
  33
  34static int fifo_open(struct inode *inode, struct file *filp)
  35{
  36        struct pipe_inode_info *pipe;
  37        int ret;
  38
  39        mutex_lock(&inode->i_mutex);
  40        pipe = inode->i_pipe;
  41        if (!pipe) {
  42                ret = -ENOMEM;
  43                pipe = alloc_pipe_info(inode);
  44                if (!pipe)
  45                        goto err_nocleanup;
  46                inode->i_pipe = pipe;
  47        }
  48        filp->f_version = 0;
  49
  50        /* We can only do regular read/write on fifos */
  51        filp->f_mode &= (FMODE_READ | FMODE_WRITE);
  52
  53        switch (filp->f_mode) {
  54        case FMODE_READ:
  55        /*
  56         *  O_RDONLY
  57         *  POSIX.1 says that O_NONBLOCK means return with the FIFO
  58         *  opened, even when there is no process writing the FIFO.
  59         */
  60                filp->f_op = &read_pipefifo_fops;
  61                pipe->r_counter++;
  62                if (pipe->readers++ == 0)
  63                        wake_up_partner(inode);
  64
  65                if (!pipe->writers) {
  66                        if ((filp->f_flags & O_NONBLOCK)) {
  67                                /* suppress POLLHUP until we have
  68                                 * seen a writer */
  69                                filp->f_version = pipe->w_counter;
  70                        } else 
  71                        {
  72                                wait_for_partner(inode, &pipe->w_counter);
  73                                if(signal_pending(current))
  74                                        goto err_rd;
  75                        }
  76                }
  77                break;
  78        
  79        case FMODE_WRITE:
  80        /*
  81         *  O_WRONLY
  82         *  POSIX.1 says that O_NONBLOCK means return -1 with
  83         *  errno=ENXIO when there is no process reading the FIFO.
  84         */
  85                ret = -ENXIO;
  86                if ((filp->f_flags & O_NONBLOCK) && !pipe->readers)
  87                        goto err;
  88
  89                filp->f_op = &write_pipefifo_fops;
  90                pipe->w_counter++;
  91                if (!pipe->writers++)
  92                        wake_up_partner(inode);
  93
  94                if (!pipe->readers) {
  95                        wait_for_partner(inode, &pipe->r_counter);
  96                        if (signal_pending(current))
  97                                goto err_wr;
  98                }
  99                break;
 100        
 101        case FMODE_READ | FMODE_WRITE:
 102        /*
 103         *  O_RDWR
 104         *  POSIX.1 leaves this case "undefined" when O_NONBLOCK is set.
 105         *  This implementation will NEVER block on a O_RDWR open, since
 106         *  the process can at least talk to itself.
 107         */
 108                filp->f_op = &rdwr_pipefifo_fops;
 109
 110                pipe->readers++;
 111                pipe->writers++;
 112                pipe->r_counter++;
 113                pipe->w_counter++;
 114                if (pipe->readers == 1 || pipe->writers == 1)
 115                        wake_up_partner(inode);
 116                break;
 117
 118        default:
 119                ret = -EINVAL;
 120                goto err;
 121        }
 122
 123        /* Ok! */
 124        mutex_unlock(&inode->i_mutex);
 125        return 0;
 126
 127err_rd:
 128        if (!--pipe->readers)
 129                wake_up_interruptible(&pipe->wait);
 130        ret = -ERESTARTSYS;
 131        goto err;
 132
 133err_wr:
 134        if (!--pipe->writers)
 135                wake_up_interruptible(&pipe->wait);
 136        ret = -ERESTARTSYS;
 137        goto err;
 138
 139err:
 140        if (!pipe->readers && !pipe->writers)
 141                free_pipe_info(inode);
 142
 143err_nocleanup:
 144        mutex_unlock(&inode->i_mutex);
 145        return ret;
 146}
 147
 148/*
 149 * Dummy default file-operations: the only thing this does
 150 * is contain the open that then fills in the correct operations
 151 * depending on the access mode of the file...
 152 */
 153const struct file_operations def_fifo_fops = {
 154        .open           = fifo_open,    /* will set read_ or write_pipefifo_fops */
 155};
 156