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         while(cur == *cnt) {
  22                 pipe_wait(inode);
  23                 if(signal_pending(current))
  24                         break;
  25         }
  26 }
  27
  28 static void wake_up_partner(struct inode* inode)
  29 {
  30         wake_up_interruptible(PIPE_WAIT(*inode));
  31 }
  32
  33 static int fifo_open(struct inode *inode, struct file *filp)
  34 {
  35         int ret;
  36
  37         ret = -ERESTARTSYS;
  38         if (down_interruptible(PIPE_SEM(*inode)))
  39                 goto err_nolock_nocleanup;
  40
  41         if (!inode->i_pipe) {
  42                 ret = -ENOMEM;
  43                 if(!pipe_new(inode))
  44                         goto err_nocleanup;
  45         }
  46         filp->f_version = 0;
  47
  48         /* We can only do regular read/write on fifos */
  49         filp->f_mode &= (FMODE_READ | FMODE_WRITE);
  50
  51         switch (filp->f_mode) {
  52         case 1:
  53         /*
  54          *  O_RDONLY
  55          *  POSIX.1 says that O_NONBLOCK means return with the FIFO
  56          *  opened, even when there is no process writing the FIFO.
  57          */
  58                 filp->f_op = &read_fifo_fops;
  59                 PIPE_RCOUNTER(*inode)++;
  60                 if (PIPE_READERS(*inode)++ == 0)
  61                         wake_up_partner(inode);
  62
  63                 if (!PIPE_WRITERS(*inode)) {
  64                         if ((filp->f_flags & O_NONBLOCK)) {
  65                                 /* suppress POLLHUP until we have
  66                                  * seen a writer */
  67                                 filp->f_version = PIPE_WCOUNTER(*inode);
  68                         } else
  69                         {
  70                                 wait_for_partner(inode, &PIPE_WCOUNTER(*inode));
  71                                 if(signal_pending(current))
  72                                         goto err_rd;
  73                         }
  74                 }
  75                 break;
  76
  77         case 2:
  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(*inode))
  85                         goto err;
  86
  87                 filp->f_op = &write_fifo_fops;
  88                 PIPE_WCOUNTER(*inode)++;
  89                 if (!PIPE_WRITERS(*inode)++)
  90                         wake_up_partner(inode);
  91
  92                 if (!PIPE_READERS(*inode)) {
  93                         wait_for_partner(inode, &PIPE_RCOUNTER(*inode));
  94                         if (signal_pending(current))
  95                                 goto err_wr;
  96                 }
  97                 break;
  98
  99         case 3:
 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_fifo_fops;
 107
 108                 PIPE_READERS(*inode)++;
 109                 PIPE_WRITERS(*inode)++;
 110                 PIPE_RCOUNTER(*inode)++;
 111                 PIPE_WCOUNTER(*inode)++;
 112                 if (PIPE_READERS(*inode) == 1 || PIPE_WRITERS(*inode) == 1)
 113                         wake_up_partner(inode);
 114                 break;
 115
 116         default:
 117                 ret = -EINVAL;
 118                 goto err;
 119         }
 120
 121         /* Ok! */
 122         up(PIPE_SEM(*inode));
 123         return 0;
 124
 125 err_rd:
 126         if (!--PIPE_READERS(*inode))
 127                 wake_up_interruptible(PIPE_WAIT(*inode));
 128         ret = -ERESTARTSYS;
 129         goto err;
 130
 131 err_wr:
 132         if (!--PIPE_WRITERS(*inode))
 133                 wake_up_interruptible(PIPE_WAIT(*inode));
 134         ret = -ERESTARTSYS;
 135         goto err;
 136
 137 err:
 138         if (!PIPE_READERS(*inode) && !PIPE_WRITERS(*inode))
 139                 free_pipe_info(inode);
 140
 141 err_nocleanup:
 142         up(PIPE_SEM(*inode));
 143
 144 err_nolock_nocleanup:
 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 struct file_operations def_fifo_fops = {
 154         .open           = fifo_open,    /* will set read or write pipe_fops */
 155 };