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/fs.h>
  14 #include <linux/sched.h>
  15 #include <linux/pipe_fs_i.h>
  16
  17 static 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
  28 static void wake_up_partner(struct inode* inode)
  29 {
  30         wake_up_interruptible(&inode->i_pipe->wait);
  31 }
  32
  33 static 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
 125 err_rd:
 126         if (!--pipe->readers)
 127                 wake_up_interruptible(&pipe->wait);
 128         ret = -ERESTARTSYS;
 129         goto err;
 130
 131 err_wr:
 132         if (!--pipe->writers)
 133                 wake_up_interruptible(&pipe->wait);
 134         ret = -ERESTARTSYS;
 135         goto err;
 136
 137 err:
 138         if (!pipe->readers && !pipe->writers)
 139                 free_pipe_info(inode);
 140
 141 err_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  */
 151 const struct file_operations def_fifo_fops = {
 152         .open           = fifo_open,    /* will set read_ or write_pipefifo_fops */
 153         .llseek         = noop_llseek,
 154 };