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1. Òý×Ó
int a;
int size = 8;
Èç¹ûÈÃaΪ(size =8)µÄÕûÊý±¶±íʾ³É¶þ½øÖÆÓ¦ÊÇʲôÑù×ÓÄØ£¿ÄǾÍÊÇÈÃÕâ¸öÊý±íʾ³É¶þ½øÖÆÊ±µÄ×îºóÈýλΪ0.
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11111111 11111111 11111111 11111000
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#define alignment_down(a, size) (a & (~(size-1)) )
#define alignment_up(a, size) ((a+size-1) & (~ (size-1)))
ÀýÈç:
a=0, size=8, Ôòalignment_down(a,size)=0, alignment_up(a,size)=0.
a=6, size=8, Ôòalignment_down(a,size)=0, alignment_up(a,size)=8.
a=8, size=8, Ôòalignment_down(a,size)=8, alignment_up(a,size)=8.
a=14, size=8, Ôòalignment_down(a,size)=8, alignment_up(a,size)=16.
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2. ÔÚlinuxÖеÄÓ¦ÓÃ
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Àý£±£ºµ±·ÖÅ䵨ַaddrʱ, Òª½«¸ÃµØÖ·ÒÔsizeΪ±¶Êý¶ÔÆë, ¶øÇÒÒªµÃµ½ÊDZÈaddr´óµÄÖµ, ÔòʹÓÃ_ALIGNºê£º
/* align addr on a size boundary - adjust address up if needed -- Cort */
#define _ALIGN(addr,size) (((addr)+(size)-1)&(~((size)-1)))
Àý2£ºÓëÒ³Ãæ¶ÔÆëÏà¹ØµÄºê
#define PAGE_SIZE 4096
#define PAGE_MASK (~(PAGE_SIZE-1))
/* to align the pointer to the (next) page boundary */
#define PAGE_ALIGN(addr) (((addr)+PAGE_SIZE-1) & PAGE_MASK)
Àý3£ºÓëskb·ÖÅäʱ¶ÔÆëÏà¹ØµÄºê
#define SKB_DATA_ALIGN(X)
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Áù¡¢ À©Õ¹µÄmatch
6.1 do_matchº¯Êý ip_tables.c
do_matchͨ¹ýIPT_MATCH_ITERATEºêÀ´µ÷ÓÃ,
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7.1 ipt_targetºÍipt_entry_target½á¹¹ ip_tables.h
ipt_targetºÍipt_match½á¹¹ÀàËÆ£º
struct ipt_target
{
struct list_head list;
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