BBN-V6/ken/pipe.c

#
/*
 */

#include "../h/param.h"
#include "../h/systm.h"
#include "../h/user.h"
#include "../h/inode.h"
#include "../h/file.h"
#include "../h/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  1024
#define BLKSIZE 512
#define PMAXPAGE 8

/*
 * 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|IPIPE;
}

/*
 * Read call directed to a pipe.

 * Modified 12/5/78 (BBN:mek) to avoid awakei if called from portread

 */
readp(fp,flag)
int *fp,flag;
{
	register *rp, *ip;
	int i,curpage;

	rp = fp;
	ip = rp->f_inode;

loop:
	/*
	 * Very conservative locking.
	 */

	plock(ip);


	if(ip->i_size1 == 0) {
		/* Pipe is empty */

		if (ip->i_flag & IEOFP)         /* rand:bobg--EOF on pipe */
		{
			ip->i_flag =& ~IEOFP;   /* `read' the EOF */
			wakeup(ip+3);           /* allow further writes */
			prele(ip);              /* didn't even need it! */
			return;                 /* EOF simulated */
		}

		/*
		 * 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);


	/* BBN: mek (4/30/79)  -  free all unneeded buffers.
	   Moved from below */

	curpage = u.u_offset[1]/BLKSIZE;
	for ( i =0; i < curpage; i++ )  bdfree(ip,i);

	/* Rand change to reset at end of read instead of beginning *
	 * Some of this code has been moved from above.
	 *
	 * If the head (read) has caught up with
	 * the tail (write), reset both to 0.
	 */
	if ((rp->f_offset[1] = u.u_offset[1]) == ip->i_size1)
	{       rp->f_offset[1] = 0;
		ip->i_size1 = 0;

		/* BBN: mek ( 4/30/79 ) - free the current buffer page */
		bdfree(ip, curpage);

		if (ip->i_mode&IWRITE) {
			ip->i_mode =& ~IWRITE;
			wakeup(ip+1);
		}

	}


	/* avoid awake if called from portread */

	if ( flag != -1 )
		    awakei(ip,-1);          /* bbn:mek---awake other end */
	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;
	}

	/*
	 * rand:bobg--if there is a pending eof, sleep till it is read
	 */

	while (ip->i_flag & IEOFP) /* any other eofs pending? */
	{
		prele(ip);
		sleep(ip+3,PPIPE);  /* sleep till a reader reads an eof */
		plock(ip);
	}

	/*
	 * 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);
	awakei(ip,-1);		/* bbn:mek---awake other end */
	prele(ip);
	if(ip->i_mode&IREAD) {
		ip->i_mode =& ~IREAD;
		wakeup(ip+2);
	}
	goto loop;
}

/*
 * eofp routine (rand:bobg) to write a single eof on a pipe
 * passed a ptr to an inode by eofp/sys1 code
 */
eofp(pin)
{
	register int *ip;

	plock(ip = pin);
	if(ip->i_count < 2)     /* make sure someone will read EOF */
	{
		prele(ip);      /* other end must have died */
		u.u_error = EPIPE;
		psignal(u.u_procp, SIGPIPE); /* let writer know */
		return;
	}
	while (ip->i_flag & IEOFP) /* any other eofs pending? */
	{                       /* sleep till last EOF handled */
		prele(ip);
		sleep(ip+3,PPIPE);  /* sleep till a reader reads an eof */
		plock(ip);
	}
	ip->i_flag =| IEOFP;    /* announce EOF to next read */
	prele(ip);
	if (ip->i_mode & IREAD) /* wakeup any waiting reads */
	{
		ip->i_mode =& ~IREAD;
		wakeup(ip+2);
	}
}

/*
 * 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);
	}
}