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/smp_lock.h>
  15 #include <linux/fs.h>
  16 #include <linux/pipe_fs_i.h>
  17
  18 static 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
  29 static void wake_up_partner(struct inode* inode)
  30 {
  31         wake_up_interruptible(&inode->i_pipe->wait);
  32 }
  33
  34 static 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 1:
  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_fifo_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 2:
  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_fifo_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 3:
 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_fifo_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
 127 err_rd:
 128         if (!--pipe->readers)
 129                 wake_up_interruptible(&pipe->wait);
 130         ret = -ERESTARTSYS;
 131         goto err;
 132
 133 err_wr:
 134         if (!--pipe->writers)
 135                 wake_up_interruptible(&pipe->wait);
 136         ret = -ERESTARTSYS;
 137         goto err;
 138
 139 err:
 140         if (!pipe->readers && !pipe->writers)
 141                 free_pipe_info(inode);
 142
 143 err_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  */
 153 const struct file_operations def_fifo_fops = {
 154         .open           = fifo_open,    /* will set read or write pipe_fops */
 155 };