dgread.c

来自「TCP-IP红宝书源代码」· C语言 代码 · 共 61 行

/* dgread.c - dgread */

#include <conf.h>
#include <kernel.h>
#include <proc.h>
#include <network.h>
#include <ports.h>

/*------------------------------------------------------------------------
 *  dgread  -  read one datagram from a datagram pseudo-device
 *------------------------------------------------------------------------
 */
int
dgread(struct devsw *pdev, char *pxg0, unsigned len)
{
	struct	xgram	*pxg = (struct xgram *)pxg0;
	struct	dgblk	*pdg;
	struct	upq	*pup;
	struct	ep	*pep;
	struct	ip	*pip;
	struct	udp	*pudp;
	unsigned	datalen;

	pdg = (struct dgblk *)pdev->dvioblk;
	if (pdg->dg_mode & DG_TMODE) {
		pup = &upqs[pdg->dg_upq];
		if (!isbadpid(pup->up_pid))
			return SYSERR;
		if (pcount(pdg->dg_xport) <= 0) {
			pup->up_pid = getpid();
			if (recvtim(DG_TIME) == TIMEOUT) {
				pup->up_pid = BADPID;
				return TIMEOUT;
			}
		}
	}
	pep = (struct ep *) preceive(pdg->dg_xport);

	/* copy data into user's buffer & set length */

	pip = (struct ip *)pep->ep_data;
	pudp = (struct udp *)pip->ip_data;
	datalen = pudp->u_len - U_HLEN;
	if (pdg->dg_mode & DG_NMODE) {
		if (datalen+XGHLEN > len) {
			freebuf(pep);
			return SYSERR;
		}
		pxg->xg_fip = pip->ip_src;
		pxg->xg_fport = pudp->u_src;
		pxg->xg_lport = pdg->dg_lport;
		memcpy(pxg->xg_data, pudp->u_data, datalen);
	} else {
		if (datalen > len)
			datalen = len;
		memcpy(pxg, pudp->u_data, datalen);
	}
	freebuf(pep);
	return datalen;
}