linux/fs/fifo.c
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   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/fs.h>
  14#include <linux/sched.h>
  15#include <linux/pipe_fs_i.h>
  16
  17static int wait_for_partner(struct inode* inode, unsigned int *cnt)
  18{
  19        int cur = *cnt; 
  20
  21        while (cur == *cnt) {
  22                pipe_wait(inode->i_pipe);
  23                if (signal_pending(current))
  24                        break;
  25        }
  26        return cur == *cnt ? -ERESTARTSYS : 0;
  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                                if (wait_for_partner(inode, &pipe->w_counter))
  72                                        goto err_rd;
  73                        }
  74                }
  75                break;
  76        
  77        case FMODE_WRITE:
  78        /*
  79         *  O_WRONLY
  80         *  POSIX.1 says that O_NONBLOCK means return -1 with
  81         *  errno=ENXIO when there is no process reading the FIFO.
  82         */
  83                ret = -ENXIO;
  84                if ((filp->f_flags & O_NONBLOCK) && !pipe->readers)
  85                        goto err;
  86
  87                filp->f_op = &write_pipefifo_fops;
  88                pipe->w_counter++;
  89                if (!pipe->writers++)
  90                        wake_up_partner(inode);
  91
  92                if (!pipe->readers) {
  93                        if (wait_for_partner(inode, &pipe->r_counter))
  94                                goto err_wr;
  95                }
  96                break;
  97        
  98        case FMODE_READ | FMODE_WRITE:
  99        /*
 100         *  O_RDWR
 101         *  POSIX.1 leaves this case "undefined" when O_NONBLOCK is set.
 102         *  This implementation will NEVER block on a O_RDWR open, since
 103         *  the process can at least talk to itself.
 104         */
 105                filp->f_op = &rdwr_pipefifo_fops;
 106
 107                pipe->readers++;
 108                pipe->writers++;
 109                pipe->r_counter++;
 110                pipe->w_counter++;
 111                if (pipe->readers == 1 || pipe->writers == 1)
 112                        wake_up_partner(inode);
 113                break;
 114
 115        default:
 116                ret = -EINVAL;
 117                goto err;
 118        }
 119
 120        /* Ok! */
 121        mutex_unlock(&inode->i_mutex);
 122        return 0;
 123
 124err_rd:
 125        if (!--pipe->readers)
 126                wake_up_interruptible(&pipe->wait);
 127        ret = -ERESTARTSYS;
 128        goto err;
 129
 130err_wr:
 131        if (!--pipe->writers)
 132                wake_up_interruptible(&pipe->wait);
 133        ret = -ERESTARTSYS;
 134        goto err;
 135
 136err:
 137        if (!pipe->readers && !pipe->writers)
 138                free_pipe_info(inode);
 139
 140err_nocleanup:
 141        mutex_unlock(&inode->i_mutex);
 142        return ret;
 143}
 144
 145/*
 146 * Dummy default file-operations: the only thing this does
 147 * is contain the open that then fills in the correct operations
 148 * depending on the access mode of the file...
 149 */
 150const struct file_operations def_fifo_fops = {
 151        .open           = fifo_open,    /* will set read_ or write_pipefifo_fops */
 152        .llseek         = noop_llseek,
 153};
 154
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