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         mutex_lock(PIPE_MUTEX(*inode));
  38         if (!inode->i_pipe) {
  39                 ret = -ENOMEM;
  40                 if(!pipe_new(inode))
  41                         goto err_nocleanup;
  42         }
  43         filp->f_version = 0;
  44
  45         /* We can only do regular read/write on fifos */
  46         filp->f_mode &= (FMODE_READ | FMODE_WRITE);
  47
  48         switch (filp->f_mode) {
  49         case 1:
  50         /*
  51          *  O_RDONLY
  52          *  POSIX.1 says that O_NONBLOCK means return with the FIFO
  53          *  opened, even when there is no process writing the FIFO.
  54          */
  55                 filp->f_op = &read_fifo_fops;
  56                 PIPE_RCOUNTER(*inode)++;
  57                 if (PIPE_READERS(*inode)++ == 0)
  58                         wake_up_partner(inode);
  59
  60                 if (!PIPE_WRITERS(*inode)) {
  61                         if ((filp->f_flags & O_NONBLOCK)) {
  62                                 /* suppress POLLHUP until we have
  63                                  * seen a writer */
  64                                 filp->f_version = PIPE_WCOUNTER(*inode);
  65                         } else
  66                         {
  67                                 wait_for_partner(inode, &PIPE_WCOUNTER(*inode));
  68                                 if(signal_pending(current))
  69                                         goto err_rd;
  70                         }
  71                 }
  72                 break;
  73
  74         case 2:
  75         /*
  76          *  O_WRONLY
  77          *  POSIX.1 says that O_NONBLOCK means return -1 with
  78          *  errno=ENXIO when there is no process reading the FIFO.
  79          */
  80                 ret = -ENXIO;
  81                 if ((filp->f_flags & O_NONBLOCK) && !PIPE_READERS(*inode))
  82                         goto err;
  83
  84                 filp->f_op = &write_fifo_fops;
  85                 PIPE_WCOUNTER(*inode)++;
  86                 if (!PIPE_WRITERS(*inode)++)
  87                         wake_up_partner(inode);
  88
  89                 if (!PIPE_READERS(*inode)) {
  90                         wait_for_partner(inode, &PIPE_RCOUNTER(*inode));
  91                         if (signal_pending(current))
  92                                 goto err_wr;
  93                 }
  94                 break;
  95
  96         case 3:
  97         /*
  98          *  O_RDWR
  99          *  POSIX.1 leaves this case "undefined" when O_NONBLOCK is set.
 100          *  This implementation will NEVER block on a O_RDWR open, since
 101          *  the process can at least talk to itself.
 102          */
 103                 filp->f_op = &rdwr_fifo_fops;
 104
 105                 PIPE_READERS(*inode)++;
 106                 PIPE_WRITERS(*inode)++;
 107                 PIPE_RCOUNTER(*inode)++;
 108                 PIPE_WCOUNTER(*inode)++;
 109                 if (PIPE_READERS(*inode) == 1 || PIPE_WRITERS(*inode) == 1)
 110                         wake_up_partner(inode);
 111                 break;
 112
 113         default:
 114                 ret = -EINVAL;
 115                 goto err;
 116         }
 117
 118         /* Ok! */
 119         mutex_unlock(PIPE_MUTEX(*inode));
 120         return 0;
 121
 122 err_rd:
 123         if (!--PIPE_READERS(*inode))
 124                 wake_up_interruptible(PIPE_WAIT(*inode));
 125         ret = -ERESTARTSYS;
 126         goto err;
 127
 128 err_wr:
 129         if (!--PIPE_WRITERS(*inode))
 130                 wake_up_interruptible(PIPE_WAIT(*inode));
 131         ret = -ERESTARTSYS;
 132         goto err;
 133
 134 err:
 135         if (!PIPE_READERS(*inode) && !PIPE_WRITERS(*inode))
 136                 free_pipe_info(inode);
 137
 138 err_nocleanup:
 139         mutex_unlock(PIPE_MUTEX(*inode));
 140         return ret;
 141 }
 142
 143 /*
 144  * Dummy default file-operations: the only thing this does
 145  * is contain the open that then fills in the correct operations
 146  * depending on the access mode of the file...
 147  */
 148 struct file_operations def_fifo_fops = {
 149         .open           = fifo_open,    /* will set read or write pipe_fops */
 150 };