checksum.h

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#ifndef _I386_CHECKSUM_H
#define _I386_CHECKSUM_H


/*
 * computes the checksum of a memory block at buff, length len,
 * and adds in "sum" (32-bit)
 *
 * returns a 32-bit number suitable for feeding into itself
 * or csum_tcpudp_magic
 *
 * this function must be called with even lengths, except
 * for the last fragment, which may be odd
 *
 * it's best to have buff aligned on a 32-bit boundary
 */
asmlinkage unsigned int csum_partial(const unsigned char * buff, int len, unsigned int sum);

/*
 * the same as csum_partial, but copies from src while it
 * checksums, and handles user-space pointer exceptions correctly, when needed.
 *
 * here even more important to align src and dst on a 32-bit (or even
 * better 64-bit) boundary
 */

asmlinkage unsigned int csum_partial_copy_generic( const char *src, char *dst, int len, int sum,
						   int *src_err_ptr, int *dst_err_ptr);

/*
 *	Note: when you get a NULL pointer exception here this means someone
 *	passed in an incorrect kernel address to one of these functions. 
 *	
 *	If you use these functions directly please don't forget the 
 *	verify_area().
 */
static __inline__
unsigned int csum_partial_copy_nocheck ( const char *src, char *dst,
					int len, int sum)
{
	return csum_partial_copy_generic ( src, dst, len, sum, NULL, NULL);
}

static __inline__
unsigned int csum_partial_copy_from_user ( const char *src, char *dst,
						int len, int sum, int *err_ptr)
{
	return csum_partial_copy_generic ( src, dst, len, sum, err_ptr, NULL);
}

/*
 * These are the old (and unsafe) way of doing checksums, a warning message will be
 * printed if they are used and an exeption occurs.
 *
 * these functions should go away after some time.
 */

#define csum_partial_copy_fromuser csum_partial_copy
unsigned int csum_partial_copy( const char *src, char *dst, int len, int sum);

/*
 *	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 inline 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);
}

/*
 *	Fold a partial checksum
 */

static inline unsigned int csum_fold(unsigned int sum)
{
	__asm__("
		addl %1, %0
		adcl $0xffff, %0
		"
		: "=r" (sum)
		: "r" (sum << 16), "0" (sum & 0xffff0000)
	);
	return (~sum) >> 16;
}
 
static inline unsigned long csum_tcpudp_nofold(unsigned long saddr,
						   unsigned long daddr,
						   unsigned short len,
						   unsigned short proto,
						   unsigned int sum) 
{
    __asm__("
	addl %1, %0
	adcl %2, %0
	adcl %3, %0
	adcl $0, %0
	"
	: "=r" (sum)
	: "g" (daddr), "g"(saddr), "g"((ntohs(len)<<16)+proto*256), "0"(sum));
    return sum;
}

/*
 * computes the checksum of the TCP/UDP pseudo-header
 * returns a 16-bit checksum, already complemented
 */
static inline unsigned short int csum_tcpudp_magic(unsigned long saddr,
						   unsigned long daddr,
						   unsigned short len,
						   unsigned short proto,
						   unsigned int sum) 
{
	return csum_fold(csum_tcpudp_nofold(saddr,daddr,len,proto,sum));
}

/*
 * this routine is used for miscellaneous IP-like checksums, mainly
 * in icmp.c
 */

static inline unsigned short ip_compute_csum(unsigned char * buff, int len) {
    return csum_fold (csum_partial(buff, len, 0));
}

#define _HAVE_ARCH_IPV6_CSUM
static __inline__ unsigned short int csum_ipv6_magic(struct in6_addr *saddr,
						     struct in6_addr *daddr,
						     __u32 len,
						     unsigned short proto,
						     unsigned int sum) 
{
	__asm__("
		addl 0(%1), %0
		adcl 4(%1), %0
		adcl 8(%1), %0
		adcl 12(%1), %0
		adcl 0(%2), %0
		adcl 4(%2), %0
		adcl 8(%2), %0
		adcl 12(%2), %0
		adcl %3, %0
		adcl %4, %0
		adcl $0, %0
		"
		: "=&r" (sum)
		: "r" (saddr), "r" (daddr), 
		  "r"(htonl(len)), "r"(htonl(proto)), "0"(sum));

	return csum_fold(sum);
}

/* 
 *	Copy and checksum to user
 */
#define HAVE_CSUM_COPY_USER
static __inline__ unsigned int csum_and_copy_to_user (const char *src, char *dst,
				    int len, int sum, int *err_ptr)
{
	if (access_ok(VERIFY_WRITE, dst, len))
		return csum_partial_copy_generic(src, dst, len, sum, NULL, err_ptr);

	if (len)
		*err_ptr = -EFAULT;

	return -1; /* invalid checksum */
}

#endif