#/* */#include "../param.h"#include "../systm.h"#include "../user.h"#include "../inode.h"#include "../file.h"#include "../reg.h"/* * Max allowable buffering per pipe. * This is also the max size of the * file created to implement the pipe. * If this size is bigger than 4096, * pipes will be implemented in LARG * files, which is probably not good. */#define	PIPSIZ	4096/* * The sys-pipe entry. * Allocate an inode on the root device. * Allocate 2 file structures. * Put it all together with flags. */pipe(){	register *ip, *rf, *wf;	int r;	ip = ialloc(rootdev);	if(ip == NULL)		return;	rf = falloc();	if(rf == NULL) {		iput(ip);		return;	}	r = u.u_ar0[R0];	wf = falloc();	if(wf == NULL) {		rf->f_count = 0;		u.u_ofile[r] = NULL;		iput(ip);		return;	}	u.u_ar0[R1] = u.u_ar0[R0];	u.u_ar0[R0] = r;	wf->f_flag = FWRITE|FPIPE;	wf->f_inode = ip;	rf->f_flag = FREAD|FPIPE;	rf->f_inode = ip;	ip->i_count = 2;	ip->i_flag = IACC|IUPD;	ip->i_mode = IALLOC;}/* * Read call directed to a pipe. */readp(fp)int *fp;{	register *rp, *ip;	rp = fp;	ip = rp->f_inode;loop:	/*	 * Very conservative locking.	 */	plock(ip);	/*	 * If the head (read) has caught up with	 * the tail (write), reset both to 0.	 */	if(rp->f_offset[1] == ip->i_size1) {		if(rp->f_offset[1] != 0) {			rp->f_offset[1] = 0;			ip->i_size1 = 0;			if(ip->i_mode&IWRITE) {				ip->i_mode =& ~IWRITE;				wakeup(ip+1);			}		}		/*		 * If there are not both reader and		 * writer active, return without		 * satisfying read.		 */		prele(ip);		if(ip->i_count < 2)			return;		ip->i_mode =| IREAD;		sleep(ip+2, PPIPE);		goto loop;	}	/*	 * Read and return	 */	u.u_offset[0] = 0;	u.u_offset[1] = rp->f_offset[1];	readi(ip);	rp->f_offset[1] = u.u_offset[1];	prele(ip);}/* * Write call directed to a pipe. */writep(fp){	register *rp, *ip, c;	rp = fp;	ip = rp->f_inode;	c = u.u_count;loop:	/*	 * If all done, return.	 */	plock(ip);	if(c == 0) {		prele(ip);		u.u_count = 0;		return;	}	/*	 * If there are not both read and	 * write sides of the pipe active,	 * return error and signal too.	 */	if(ip->i_count < 2) {		prele(ip);		u.u_error = EPIPE;		psignal(u.u_procp, SIGPIPE);		return;	}	/*	 * If the pipe is full,	 * wait for reads to deplete	 * and truncate it.	 */	if(ip->i_size1 == PIPSIZ) {		ip->i_mode =| IWRITE;		prele(ip);		sleep(ip+1, PPIPE);		goto loop;	}	/*	 * Write what is possible and	 * loop back.	 */	u.u_offset[0] = 0;	u.u_offset[1] = ip->i_size1;	u.u_count = min(c, PIPSIZ-u.u_offset[1]);	c =- u.u_count;	writei(ip);	prele(ip);	if(ip->i_mode&IREAD) {		ip->i_mode =& ~IREAD;		wakeup(ip+2);	}	goto loop;}/* * Lock a pipe. * If its already locked, * set the WANT bit and sleep. */plock(ip)int *ip;{	register *rp;	rp = ip;	while(rp->i_flag&ILOCK) {		rp->i_flag =| IWANT;		sleep(rp, PPIPE);	}	rp->i_flag =| ILOCK;}/* * Unlock a pipe. * If WANT bit is on, * wakeup. * This routine is also used * to unlock inodes in general. */prele(ip)int *ip;{	register *rp;	rp = ip;	rp->i_flag =& ~ILOCK;	if(rp->i_flag&IWANT) {		rp->i_flag =& ~IWANT;		wakeup(rp);	}}