/* *  linux/fs/pipe.c * *  (C) 1991  Linus Torvalds */#include <signal.h>#include <linux/sched.h>#include <linux/mm.h>	/* for get_free_page */#include <asm/segment.h>int read_pipe(struct m_inode * inode, char * buf, int count){	int chars, size, read = 0;	while (count>0) {		while (!(size=PIPE_SIZE(*inode))) {			wake_up(&inode->i_wait);			if (inode->i_count != 2) /* are there any writers? */				return read;			sleep_on(&inode->i_wait);		}		chars = PAGE_SIZE-PIPE_TAIL(*inode);		if (chars > count)			chars = count;		if (chars > size)			chars = size;		count -= chars;		read += chars;		size = PIPE_TAIL(*inode);		PIPE_TAIL(*inode) += chars;		PIPE_TAIL(*inode) &= (PAGE_SIZE-1);		while (chars-->0)			put_fs_byte(((char *)inode->i_size)[size++],buf++);	}	wake_up(&inode->i_wait);	return read;}	int write_pipe(struct m_inode * inode, char * buf, int count){	int chars, size, written = 0;	while (count>0) {		while (!(size=(PAGE_SIZE-1)-PIPE_SIZE(*inode))) {			wake_up(&inode->i_wait);			if (inode->i_count != 2) { /* no readers */				current->signal |= (1<<(SIGPIPE-1));				return written?written:-1;			}			sleep_on(&inode->i_wait);		}		chars = PAGE_SIZE-PIPE_HEAD(*inode);		if (chars > count)			chars = count;		if (chars > size)			chars = size;		count -= chars;		written += chars;		size = PIPE_HEAD(*inode);		PIPE_HEAD(*inode) += chars;		PIPE_HEAD(*inode) &= (PAGE_SIZE-1);		while (chars-->0)			((char *)inode->i_size)[size++]=get_fs_byte(buf++);	}	wake_up(&inode->i_wait);	return written;}int sys_pipe(unsigned long * fildes){	struct m_inode * inode;	struct file * f[2];	int fd[2];	int i,j;	j=0;	for(i=0;j<2 && i<NR_FILE;i++)		if (!file_table[i].f_count)			(f[j++]=i+file_table)->f_count++;	if (j==1)		f[0]->f_count=0;	if (j<2)		return -1;	j=0;	for(i=0;j<2 && i<NR_OPEN;i++)		if (!current->filp[i]) {			current->filp[ fd[j]=i ] = f[j];			j++;		}	if (j==1)		current->filp[fd[0]]=NULL;	if (j<2) {		f[0]->f_count=f[1]->f_count=0;		return -1;	}	if (!(inode=get_pipe_inode())) {		current->filp[fd[0]] =			current->filp[fd[1]] = NULL;		f[0]->f_count = f[1]->f_count = 0;		return -1;	}	f[0]->f_inode = f[1]->f_inode = inode;	f[0]->f_pos = f[1]->f_pos = 0;	f[0]->f_mode = 1;		/* read */	f[1]->f_mode = 2;		/* write */	put_fs_long(fd[0],0+fildes);	put_fs_long(fd[1],1+fildes);	return 0;}