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
  16 static void wait_for_partner(struct inode* inode, unsigned int* cnt)
  17 {
  18         int cur = *cnt;
  19         while(cur == *cnt) {
  20                 pipe_wait(inode);
  21                 if(signal_pending(current))
  22                         break;
  23         }
  24 }
  25
  26 static void wake_up_partner(struct inode* inode)
  27 {
  28         wake_up_interruptible(PIPE_WAIT(*inode));
  29 }
  30
  31 static int fifo_open(struct inode *inode, struct file *filp)
  32 {
  33         int ret;
  34
  35         ret = -ERESTARTSYS;
  36         lock_kernel();
  37         if (down_interruptible(PIPE_SEM(*inode)))
  38                 goto err_nolock_nocleanup;
  39
  40         if (!inode->i_pipe) {
  41                 ret = -ENOMEM;
  42                 if(!pipe_new(inode))
  43                         goto err_nocleanup;
  44         }
  45         filp->f_version = 0;
  46
  47         switch (filp->f_mode) {
  48         case 1:
  49         /*
  50          *  O_RDONLY
  51          *  POSIX.1 says that O_NONBLOCK means return with the FIFO
  52          *  opened, even when there is no process writing the FIFO.
  53          */
  54                 filp->f_op = &read_fifo_fops;
  55                 PIPE_RCOUNTER(*inode)++;
  56                 if (PIPE_READERS(*inode)++ == 0)
  57                         wake_up_partner(inode);
  58
  59                 if (!PIPE_WRITERS(*inode)) {
  60                         if ((filp->f_flags & O_NONBLOCK)) {
  61                                 /* suppress POLLHUP until we have
  62                                  * seen a writer */
  63                                 filp->f_version = PIPE_WCOUNTER(*inode);
  64                         } else
  65                         {
  66                                 wait_for_partner(inode, &PIPE_WCOUNTER(*inode));
  67                                 if(signal_pending(current))
  68                                         goto err_rd;
  69                         }
  70                 }
  71                 break;
  72
  73         case 2:
  74         /*
  75          *  O_WRONLY
  76          *  POSIX.1 says that O_NONBLOCK means return -1 with
  77          *  errno=ENXIO when there is no process reading the FIFO.
  78          */
  79                 ret = -ENXIO;
  80                 if ((filp->f_flags & O_NONBLOCK) && !PIPE_READERS(*inode))
  81                         goto err;
  82
  83                 filp->f_op = &write_fifo_fops;
  84                 PIPE_WCOUNTER(*inode)++;
  85                 if (!PIPE_WRITERS(*inode)++)
  86                         wake_up_partner(inode);
  87
  88                 if (!PIPE_READERS(*inode)) {
  89                         wait_for_partner(inode, &PIPE_RCOUNTER(*inode));
  90                         if (signal_pending(current))
  91                                 goto err_wr;
  92                 }
  93                 break;
  94
  95         case 3:
  96         /*
  97          *  O_RDWR
  98          *  POSIX.1 leaves this case "undefined" when O_NONBLOCK is set.
  99          *  This implementation will NEVER block on a O_RDWR open, since
 100          *  the process can at least talk to itself.
 101          */
 102                 filp->f_op = &rdwr_fifo_fops;
 103
 104                 PIPE_READERS(*inode)++;
 105                 PIPE_WRITERS(*inode)++;
 106                 PIPE_RCOUNTER(*inode)++;
 107                 PIPE_WCOUNTER(*inode)++;
 108                 if (PIPE_READERS(*inode) == 1 || PIPE_WRITERS(*inode) == 1)
 109                         wake_up_partner(inode);
 110                 break;
 111
 112         default:
 113                 ret = -EINVAL;
 114                 goto err;
 115         }
 116
 117         /* Ok! */
 118         up(PIPE_SEM(*inode));
 119         unlock_kernel();
 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                 struct pipe_inode_info *info = inode->i_pipe;
 137                 inode->i_pipe = NULL;
 138                 free_page((unsigned long)info->base);
 139                 kfree(info);
 140         }
 141
 142 err_nocleanup:
 143         up(PIPE_SEM(*inode));
 144
 145 err_nolock_nocleanup:
 146         unlock_kernel();
 147         return ret;
 148 }
 149
 150 /*
 151  * Dummy default file-operations: the only thing this does
 152  * is contain the open that then fills in the correct operations
 153  * depending on the access mode of the file...
 154  */
 155 struct file_operations def_fifo_fops = {
 156         open:           fifo_open,      /* will set read or write pipe_fops */
 157 };