/* * linux/fs/fifo.c * * written by Paul H. Hargrove * * Fixes: * 10-06-1999, AV: fixed OOM handling in fifo_open(), moved * initialization there, switched to external * allocation of pipe_inode_info. */ #include <linux/mm.h> #include <linux/slab.h> #include <linux/smp_lock.h> #include <linux/fs.h> #include <linux/pipe_fs_i.h> static void wait_for_partner(struct inode* inode, unsigned int *cnt) { int cur = *cnt; while (cur == *cnt) { pipe_wait(inode->i_pipe); if (signal_pending(current)) break; } } static void wake_up_partner(struct inode* inode) { wake_up_interruptible(&inode->i_pipe->wait); } static int fifo_open(struct inode *inode, struct file *filp) { struct pipe_inode_info *pipe; int ret; mutex_lock(&inode->i_mutex); pipe = inode->i_pipe; if (!pipe) { ret = -ENOMEM; pipe = alloc_pipe_info(inode); if (!pipe) goto err_nocleanup; inode->i_pipe = pipe; } filp->f_version = 0; /* We can only do regular read/write on fifos */ filp->f_mode &= (FMODE_READ | FMODE_WRITE); switch (filp->f_mode) { case 1: /* * O_RDONLY * POSIX.1 says that O_NONBLOCK means return with the FIFO * opened, even when there is no process writing the FIFO. */ filp->f_op = &read_fifo_fops; pipe->r_counter++; if (pipe->readers++ == 0) wake_up_partner(inode); if (!pipe->writers) { if ((filp->f_flags & O_NONBLOCK)) { /* suppress POLLHUP until we have * seen a writer */ filp->f_version = pipe->w_counter; } else { wait_for_partner(inode, &pipe->w_counter); if(signal_pending(current)) goto err_rd; } } break; case 2: /* * O_WRONLY * POSIX.1 says that O_NONBLOCK means return -1 with * errno=ENXIO when there is no process reading the FIFO. */ ret = -ENXIO; if ((filp->f_flags & O_NONBLOCK) && !pipe->readers) goto err; filp->f_op = &write_fifo_fops; pipe->w_counter++; if (!pipe->writers++) wake_up_partner(inode); if (!pipe->readers) { wait_for_partner(inode, &pipe->r_counter); if (signal_pending(current)) goto err_wr; } break; case 3: /* * O_RDWR * POSIX.1 leaves this case "undefined" when O_NONBLOCK is set. * This implementation will NEVER block on a O_RDWR open, since * the process can at least talk to itself. */ filp->f_op = &rdwr_fifo_fops; pipe->readers++; pipe->writers++; pipe->r_counter++; pipe->w_counter++; if (pipe->readers == 1 || pipe->writers == 1) wake_up_partner(inode); break; default: ret = -EINVAL; goto err; } /* Ok! */ mutex_unlock(&inode->i_mutex); return 0; err_rd: if (!--pipe->readers) wake_up_interruptible(&pipe->wait); ret = -ERESTARTSYS; goto err; err_wr: if (!--pipe->writers) wake_up_interruptible(&pipe->wait); ret = -ERESTARTSYS; goto err; err: if (!pipe->readers && !pipe->writers) free_pipe_info(inode); err_nocleanup: mutex_unlock(&inode->i_mutex); return ret; } /* * Dummy default file-operations: the only thing this does * is contain the open that then fills in the correct operations * depending on the access mode of the file... */ const struct file_operations def_fifo_fops = { .open = fifo_open, /* will set read or write pipe_fops */ };