dirread.c

这是一个同样来自贝尔实验室的和UNIX有着渊源的操作系统, 其简洁的设计和实现易于我们学习和理解

#include "lib.h"
#include <string.h>
#include <stdlib.h>
#include "sys9.h"
#include "dir.h"

static int
statcheck(uchar *buf, uint nbuf)
{
	uchar *ebuf;
	int i;

	ebuf = buf + nbuf;

	buf += STATFIXLEN - 4 * BIT16SZ;

	for(i = 0; i < 4; i++){
		if(buf + BIT16SZ > ebuf)
			return -1;
		buf += BIT16SZ + GBIT16(buf);
	}

	if(buf != ebuf)
		return -1;

	return 0;
}

static
long
dirpackage(uchar *buf, long ts, Dir **d)
{
	char *s;
	long ss, i, n, nn, m;

	if(ts == 0){
		*d = nil;
		return 0;
	}

	/*
	 * first find number of all stats, check they look like stats, & size all associated strings
	 */
	ss = 0;
	n = 0;
	for(i = 0; i < ts; i += m){
		m = BIT16SZ + GBIT16(&buf[i]);
		if(statcheck(&buf[i], m) < 0)
			break;
		ss += m;
		n++;
	}

	if(i != ts)
		return -1;

	*d = malloc(n * sizeof(Dir) + ss);
	if(*d == nil)
		return -1;

	/*
	 * then convert all buffers
	 */
	s = (char*)*d + n * sizeof(Dir);
	nn = 0;
	for(i = 0; i < ts; i += m){
		m = BIT16SZ + GBIT16((uchar*)&buf[i]);
		if(nn >= n || _convM2D(&buf[i], m, *d + nn, s) != m){
			free(*d);
			return -1;
		}
		nn++;
		s += m;
	}

	return nn;
}

long
_dirread(int fd, Dir **d)
{
	uchar *buf;
	long ts;

	buf = malloc(DIRMAX);
	if(buf == nil)
		return -1;
	ts = _READ(fd, buf, DIRMAX);
	if(ts >= 0)
		ts = dirpackage(buf, ts, d);
	free(buf);
	return ts;
}

long
_dirreadall(int fd, Dir **d)
{
	uchar *buf, *nbuf;
	long n, ts;

	buf = nil;
	ts = 0;
	for(;;){
		nbuf = realloc(buf, ts+DIRMAX);
		if(nbuf == nil){
			free(buf);
			return -1;
		}
		buf = nbuf;
		n = _READ(fd, buf+ts, DIRMAX);
		if(n <= 0)
			break;
		ts += n;
	}
	if(ts >= 0)
		ts = dirpackage(buf, ts, d);
	free(buf);
	return ts;
}