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 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
  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 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
 124 err_rd:
 125         if (!--pipe->readers)
 126                 wake_up_interruptible(&pipe->wait);
 127         ret = -ERESTARTSYS;
 128         goto err;
 129
 130 err_wr:
 131         if (!--pipe->writers)
 132                 wake_up_interruptible(&pipe->wait);
 133         ret = -ERESTARTSYS;
 134         goto err;
 135
 136 err:
 137         if (!pipe->readers && !pipe->writers)
 138                 free_pipe_info(inode);
 139
 140 err_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  */
 150 const struct file_operations def_fifo_fops = {
 151         .open           = fifo_open,    /* will set read_ or write_pipefifo_fops */
 152         .llseek         = noop_llseek,
 153 };