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 void 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}
  27
  28static void wake_up_partner(struct inode* inode)
  29{
  30        wake_up_interruptible(&inode->i_pipe->wait);
  31}
  32
  33static int fifo_open(struct inode *inode, struct file *filp)
  34{
  35        struct pipe_inode_info *pipe;
  36        int ret;
  37
  38        mutex_lock(&inode->i_mutex);
  39        pipe = inode->i_pipe;
  40        if (!pipe) {
  41                ret = -ENOMEM;
  42                pipe = alloc_pipe_info(inode);
  43                if (!pipe)
  44                        goto err_nocleanup;
  45                inode->i_pipe = pipe;
  46        }
  47        filp->f_version = 0;
  48
  49        /* We can only do regular read/write on fifos */
  50        filp->f_mode &= (FMODE_READ | FMODE_WRITE);
  51
  52        switch (filp->f_mode) {
  53        case FMODE_READ:
  54        /*
  55         *  O_RDONLY
  56         *  POSIX.1 says that O_NONBLOCK means return with the FIFO
  57         *  opened, even when there is no process writing the FIFO.
  58         */
  59                filp->f_op = &read_pipefifo_fops;
  60                pipe->r_counter++;
  61                if (pipe->readers++ == 0)
  62                        wake_up_partner(inode);
  63
  64                if (!pipe->writers) {
  65                        if ((filp->f_flags & O_NONBLOCK)) {
  66                                /* suppress POLLHUP until we have
  67                                 * seen a writer */
  68                                filp->f_version = pipe->w_counter;
  69                        } else {
  70                                wait_for_partner(inode, &pipe->w_counter);
  71                                if(signal_pending(current))
  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                        wait_for_partner(inode, &pipe->r_counter);
  94                        if (signal_pending(current))
  95                                goto err_wr;
  96                }
  97                break;
  98        
  99        case FMODE_READ | FMODE_WRITE:
 100        /*
 101         *  O_RDWR
 102         *  POSIX.1 leaves this case "undefined" when O_NONBLOCK is set.
 103         *  This implementation will NEVER block on a O_RDWR open, since
 104         *  the process can at least talk to itself.
 105         */
 106                filp->f_op = &rdwr_pipefifo_fops;
 107
 108                pipe->readers++;
 109                pipe->writers++;
 110                pipe->r_counter++;
 111                pipe->w_counter++;
 112                if (pipe->readers == 1 || pipe->writers == 1)
 113                        wake_up_partner(inode);
 114                break;
 115
 116        default:
 117                ret = -EINVAL;
 118                goto err;
 119        }
 120
 121        /* Ok! */
 122        mutex_unlock(&inode->i_mutex);
 123        return 0;
 124
 125err_rd:
 126        if (!--pipe->readers)
 127                wake_up_interruptible(&pipe->wait);
 128        ret = -ERESTARTSYS;
 129        goto err;
 130
 131err_wr:
 132        if (!--pipe->writers)
 133                wake_up_interruptible(&pipe->wait);
 134        ret = -ERESTARTSYS;
 135        goto err;
 136
 137err:
 138        if (!pipe->readers && !pipe->writers)
 139                free_pipe_info(inode);
 140
 141err_nocleanup:
 142        mutex_unlock(&inode->i_mutex);
 143        return ret;
 144}
 145
 146/*
 147 * Dummy default file-operations: the only thing this does
 148 * is contain the open that then fills in the correct operations
 149 * depending on the access mode of the file...
 150 */
 151const struct file_operations def_fifo_fops = {
 152        .open           = fifo_open,    /* will set read_ or write_pipefifo_fops */
 153        .llseek         = noop_llseek,
 154};
 155
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