165 строки
4.2 KiB
C
165 строки
4.2 KiB
C
/*
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* INET An implementation of the TCP/IP protocol suite for the LINUX
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* operating system. INET is implemented using the BSD Socket
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* interface as the means of communication with the user level.
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*
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* IP/TCP/UDP checksumming routines
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*
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* Authors: Jorge Cwik, <jorge@laser.satlink.net>
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* Arnt Gulbrandsen, <agulbra@nvg.unit.no>
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* Tom May, <ftom@netcom.com>
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* Andreas Schwab, <schwab@issan.informatik.uni-dortmund.de>
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* Lots of code moved from tcp.c and ip.c; see those files
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* for more names.
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*
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* 03/02/96 Jes Sorensen, Andreas Schwab, Roman Hodek:
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* Fixed some nasty bugs, causing some horrible crashes.
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* A: At some points, the sum (%0) was used as
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* length-counter instead of the length counter
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* (%1). Thanks to Roman Hodek for pointing this out.
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* B: GCC seems to mess up if one uses too many
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* data-registers to hold input values and one tries to
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* specify d0 and d1 as scratch registers. Letting gcc choose these
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* registers itself solves the problem.
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*
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* This program is free software; you can redistribute it and/or
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* modify it under the terms of the GNU General Public License
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* as published by the Free Software Foundation; either version
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* 2 of the License, or (at your option) any later version.
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*/
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/* Revised by Kenneth Albanowski for m68knommu. Basic problem: unaligned access kills, so most
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of the assembly has to go. */
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#include <net/checksum.h>
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#include <linux/module.h>
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static inline unsigned short from32to16(unsigned long x)
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{
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/* add up 16-bit and 16-bit for 16+c bit */
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x = (x & 0xffff) + (x >> 16);
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/* add up carry.. */
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x = (x & 0xffff) + (x >> 16);
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return x;
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}
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static unsigned long do_csum(const unsigned char * buff, int len)
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{
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int odd, count;
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unsigned long result = 0;
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if (len <= 0)
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goto out;
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odd = 1 & (unsigned long) buff;
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if (odd) {
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result = *buff;
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len--;
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buff++;
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}
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count = len >> 1; /* nr of 16-bit words.. */
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if (count) {
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if (2 & (unsigned long) buff) {
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result += *(unsigned short *) buff;
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count--;
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len -= 2;
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buff += 2;
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}
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count >>= 1; /* nr of 32-bit words.. */
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if (count) {
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unsigned long carry = 0;
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do {
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unsigned long w = *(unsigned long *) buff;
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count--;
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buff += 4;
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result += carry;
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result += w;
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carry = (w > result);
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} while (count);
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result += carry;
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result = (result & 0xffff) + (result >> 16);
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}
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if (len & 2) {
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result += *(unsigned short *) buff;
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buff += 2;
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}
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}
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if (len & 1)
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result += (*buff << 8);
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result = from32to16(result);
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if (odd)
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result = ((result >> 8) & 0xff) | ((result & 0xff) << 8);
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out:
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return result;
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}
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/*
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* This is a version of ip_compute_csum() optimized for IP headers,
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* which always checksum on 4 octet boundaries.
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*/
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__sum16 ip_fast_csum(const void *iph, unsigned int ihl)
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{
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return (__force __sum16)~do_csum(iph,ihl*4);
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}
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/*
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* computes the checksum of a memory block at buff, length len,
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* and adds in "sum" (32-bit)
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*
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* returns a 32-bit number suitable for feeding into itself
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* or csum_tcpudp_magic
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*
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* this function must be called with even lengths, except
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* for the last fragment, which may be odd
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*
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* it's best to have buff aligned on a 32-bit boundary
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*/
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/*
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* Egads... That thing apparently assumes that *all* checksums it ever sees will
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* be folded. Very likely a bug.
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*/
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__wsum csum_partial(const void *buff, int len, __wsum sum)
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{
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unsigned int result = do_csum(buff, len);
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/* add in old sum, and carry.. */
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result += (__force u32)sum;
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/* 16+c bits -> 16 bits */
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result = (result & 0xffff) + (result >> 16);
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return (__force __wsum)result;
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}
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EXPORT_SYMBOL(csum_partial);
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/*
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* this routine is used for miscellaneous IP-like checksums, mainly
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* in icmp.c
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*/
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__sum16 ip_compute_csum(const void *buff, int len)
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{
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return (__force __sum16)~do_csum(buff,len);
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}
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/*
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* copy from fs while checksumming, otherwise like csum_partial
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*/
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__wsum
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csum_partial_copy_from_user(const void __user *src, void *dst, int len,
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__wsum sum, int *csum_err)
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{
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if (csum_err) *csum_err = 0;
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memcpy(dst, (__force const void *)src, len);
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return csum_partial(dst, len, sum);
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}
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/*
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* copy from ds while checksumming, otherwise like csum_partial
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*/
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__wsum
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csum_partial_copy_nocheck(const void *src, void *dst, int len, __wsum sum)
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{
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memcpy(dst, src, len);
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return csum_partial(dst, len, sum);
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}
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