xv6/pipe.c

#include "types.h"
#include "defs.h"
#include "param.h"
#include "mmu.h"
#include "proc.h"
#include "fs.h"
#include "spinlock.h"
#include "sleeplock.h"
#include "file.h"

#define PIPESIZE 512

struct pipe {
    struct spinlock lock;
    char data[PIPESIZE];
    uint nread;     // number of bytes read
    uint nwrite;    // number of bytes written
    int readopen;   // read fd is still open
    int writeopen;  // write fd is still open
};

void cleanuppipealloc(struct pipe *p, struct file **f0, struct file **f1) {
     if (p) {
        kfree((char*)p);
    }
    if (*f0) {
        fileclose(*f0);
    }
    if (*f1) {
        fileclose(*f1);
    }   
}

int pipealloc(struct file **f0, struct file **f1) {
    struct pipe *p;

    p = 0;
    *f0 = *f1 = 0;
    if ((*f0 = filealloc()) == 0 || (*f1 = filealloc()) == 0) {
        cleanuppipealloc(p, f0, f1);
        return -1;
    }
    if ((p = (struct pipe*)kalloc()) == 0) {
        cleanuppipealloc(p, f0, f1);
        return -1;
    }
    p->readopen = 1;
    p->writeopen = 1;
    p->nwrite = 0;
    p->nread = 0;
    initlock(&p->lock, "pipe");
    (*f0)->type = FD_PIPE;
    (*f0)->readable = 1;
    (*f0)->writable = 0;
    (*f0)->pipe = p;
    (*f1)->type = FD_PIPE;
    (*f1)->readable = 0;
    (*f1)->writable = 1;
    (*f1)->pipe = p;
    return 0;
}

void pipeclose(struct pipe *p, int writable) {
    acquire(&p->lock);
    if (writable) {
        p->writeopen = 0;
        wakeup(&p->nread);
    }
    else {
        p->readopen = 0;
        wakeup(&p->nwrite);
    }
    if (p->readopen == 0 && p->writeopen == 0) {
        release(&p->lock);
        kfree((char*)p);
    }
    else {
        release(&p->lock);
    }
}

int pipewrite(struct pipe *p, char *addr, int n) {
    int i;

    acquire(&p->lock);
    for (i = 0; i < n; i++) {
        while (p->nwrite == p->nread + PIPESIZE) { //DOC: pipewrite-full
            if (p->readopen == 0 || myproc()->killed) {
                release(&p->lock);
                return -1;
            }
            wakeup(&p->nread);
            sleep(&p->nwrite, &p->lock);  //DOC: pipewrite-sleep
        }
        p->data[p->nwrite++ % PIPESIZE] = addr[i];
    }
    wakeup(&p->nread);  //DOC: pipewrite-wakeup1
    release(&p->lock);
    return n;
}

int piperead(struct pipe *p, char *addr, int n)     {
    int i;

    acquire(&p->lock);
    while (p->nread == p->nwrite && p->writeopen) { //DOC: pipe-empty
        if (myproc()->killed) {
            release(&p->lock);
            return -1;
        }
        sleep(&p->nread, &p->lock); //DOC: piperead-sleep
    }
    for (i = 0; i < n; i++) {  //DOC: piperead-copy
        if (p->nread == p->nwrite) {
            break;
        }
        addr[i] = p->data[p->nread++ % PIPESIZE];
    }
    wakeup(&p->nwrite);  //DOC: piperead-wakeup
    release(&p->lock);
    return i;
}