mkudp.c

实现一个网卡到内存空间的零拷贝程序

/*
 *  mkudp.c
 *  Joris van Rantwijk, May 2001.
 */

#include <linux/socket.h>
#include <linux/in.h>
#include <linux/ip.h>
#include <linux/udp.h>
#include "mkudp.h"


#ifdef __i386__

/* i386 assembler version from asm-i386/checksum.h */

/*
 *	This is a version of ip_compute_csum() optimized for IP headers,
 *	which always checksum on 4 octet boundaries.
 *
 *	By Jorge Cwik <[e-mail]>, adapted for linux by
 *	Arnt Gulbrandsen.
 */
static unsigned short ip_fast_csum(unsigned char * iph,
					  unsigned int ihl) {
	unsigned int sum;

	__asm__ __volatile__("
	    movl (%1), %0
	    subl $4, %2
	    jbe 2f
	    addl 4(%1), %0
	    adcl 8(%1), %0
	    adcl 12(%1), %0
1:	    adcl 16(%1), %0
	    lea 4(%1), %1
	    decl %2
	    jne	1b
	    adcl $0, %0
	    movl %0, %2
	    shrl $16, %0
	    addw %w2, %w0
	    adcl $0, %0
	    notl %0
2:
	    "
	/* Since the input registers which are loaded with iph and ipl
	   are modified, we must also specify them as outputs, or gcc
	   will assume they contain their original values. */
	: "=r" (sum), "=r" (iph), "=r" (ihl)
	: "1" (iph), "2" (ihl));
	return(sum);
}

#endif

#ifdef __ppc__

static unsigned short ip_fast_csum(unsigned char * iph, unsigned int ihl)
{
	unsigned int sum, dummy;

	__asm__ __volatile__ ("
/*
 * ip_fast_csum(buf, len) -- Optimized for IP header
 * len is in words and is always >= 5.
 */
	lwz	%0,0(%1)
	lwzu	%3,4(%1)
	addic.	%2,%2,-2
	addc	%0,%0,%3
	mtctr	%2
	ble-	2f
1:	lwzu	%2,4(%1)
	adde	%0,%0,%2
	bdnz	1b
	addze	%0,%0		/* add in final carry */
	rlwinm	%1,%0,16,0,31	/* fold two halves together */
	add	%0,%0,%1
	not	%0,%0
	srwi	%0,%0,16
2:	"
	: "=r" (sum), "=r" (iph), "=r" (ihl), "=r" (dummy)
	: "1" (iph), "2" (ihl) );

	return sum;
}
#if 0
/*
 * Compute checksum of TCP or UDP pseudo-header:
 *   csum_tcpudp_magic(saddr, daddr, len, proto, sum)
 */	
_GLOBAL(csum_tcpudp_magic)
	rlwimi	r5,r6,16,0,15	/* put proto in upper half of len */
	addc	r0,r3,r4	/* add 4 32-bit words together */
	adde	r0,r0,r5
	adde	r0,r0,r7
	addze	r0,r0		/* add in final carry */
	rlwinm	r3,r0,16,0,31	/* fold two halves together */
	add	r3,r0,r3
	not	r3,r3
	srwi	r3,r3,16
	blr

/*
 * computes the checksum of a memory block at buff, length len,
 * and adds in "sum" (32-bit)
 *
 * csum_partial(buff, len, sum)
 */
_GLOBAL(csum_partial)
	addic	r0,r5,0
	subi	r3,r3,4
	srwi.	r6,r4,2
	beq	3f		/* if we're doing < 4 bytes */
	andi.	r5,r3,2		/* Align buffer to longword boundary */
	beq+	1f
	lhz	r5,4(r3)	/* do 2 bytes to get aligned */
	addi	r3,r3,2
	subi	r4,r4,2
	addc	r0,r0,r5
	srwi.	r6,r4,2		/* # words to do */
	beq	3f
1:	mtctr	r6
2:	lwzu	r5,4(r3)	/* the bdnz has zero overhead, so it should */
	adde	r0,r0,r5	/* be unnecessary to unroll this loop */
	bdnz	2b
	andi.	r4,r4,3
3:	cmpi	0,r4,2
	blt+	4f
	lhz	r5,4(r3)
	addi	r3,r3,2
	subi	r4,r4,2
	adde	r0,r0,r5
4:	cmpi	0,r4,1
	bne+	5f
	lbz	r5,4(r3)
	slwi	r5,r5,8		/* Upper byte of word */
	adde	r0,r0,r5
5:	addze	r3,r0		/* add in final carry */
	blr
#endif
#endif

#if 0

/* generic C version */

static inline unsigned short
ip_fast_csum(unsigned char * iph, unsigned int ihl)
{
	unsigned short *ip = (unsigned short *) iph;
	unsigned long sum = 0;
	int i;

	for (i = 0; i < 2*ihl; i++)
		sum += ip[i];

	sum = (sum & 0x0000ffff) + (sum >> 16);
	sum = (sum & 0x0000ffff) + (sum >> 16);

	return ~sum;
}

#endif

/*
 *  Construct the IP and UDP headers for an UDP/IP datagram.
 *  packetbuf points to the start of the resulting packet with
 *  exactly UPD_IP_HEADER_LEN bytes room to put the header, followed
 *  by dlen bytes of application data.
 *  Fragmentation is not supported, the datagram must fit in a single packet.
 *  UDP checksumming is not supported.
 */
void build_udp_ip_header(unsigned char *packetbuf, unsigned int dlen,
                         const struct sockaddr_in *saddr,
                         const struct sockaddr_in *daddr)
{
	struct iphdr *iph = (struct iphdr *) packetbuf;
	struct udphdr *uh = (struct udphdr *) (packetbuf + IP_HEADER_LEN);
	static int ip_ident_hack = 1;

	/* Build IP header */
	iph->version = 4;
	iph->ihl = 5;
	iph->tos = 0;
	iph->tot_len = htons(dlen + UDP_IP_HEADER_LEN);
	iph->id = htons(ip_ident_hack++); /* Ugly */
	iph->frag_off = 0;
	iph->ttl = IP_DEFAULT_TTL;
	iph->protocol = IPPROTO_UDP;
	iph->saddr = saddr->sin_addr.s_addr;
	iph->daddr = daddr->sin_addr.s_addr;
	iph->check = 0;
	iph->check = ip_fast_csum((unsigned char *)iph, iph->ihl);

	/* Build UPD header */
	uh->source = saddr->sin_port;
	uh->dest = daddr->sin_port;
	uh->len = htons(dlen + sizeof(struct udphdr));
	uh->check = 0;
}

/* end */