linux0.11内存管理——try_to_share()

0 推荐 00292 static int try_to_share(unsigned long address, struct task_struct * p) 00293 { 00294     unsigned long from; 00295     unsigned long to; 00296     unsigned long from_page; 00297     unsigned long to_page; 00298     unsigned long phys_addr; 00299 00300     from_page = to_page = ((address>>20) & 0xffc); 00301     from_page += ((p->start_code>>20) & 0xffc);                   //找到ｐ进程address所对应的页目录项 00302     to_page += ((current->start_code>>20) & 0xffc);　　//找到当前进程address所对应的页目录项　 00303 /* is there a page-directory at from? */ 00304     from = *(unsigned long *) from_page; 00305     if (!(from & 1)) 00306         return 0; 00307     from &= 0xfffff000; 00308     from_page = from + ((address>>10) & 0xffc); 00309     phys_addr = *(unsigned long *) from_page; 00310 /* is the page clean and present? */ 00311     if ((phys_addr & 0x41) != 0x01) 00312         return 0; 00313     phys_addr &= 0xfffff000; 00314     if (phys_addr >= HIGH_MEMORY || phys_addr < LOW_MEM) 00315         return 0; 00316     to = *(unsigned long *) to_page; 00317     if (!(to & 1)) { 00318         if ((to = get_free_page())) 00319             *(unsigned long *) to_page = to | 7; 00320         else 00321             oom(); 00322     } 00323     to &= 0xfffff000; 00324     to_page = to + ((address>>10) & 0xffc); 00325     if (1 & *(unsigned long *) to_page) 00326         panic("try_to_share: to_page already exists"); 00327 /* share them: write-protect */ 00328     *(unsigned long *) from_page &= ~2; 00329     *(unsigned long *) to_page = *(unsigned long *) from_page; 00330     invalidate(); 00331     phys_addr -= LOW_MEM; 00332     phys_addr >>= 12; 00333     mem_map[phys_addr]++; 00334     return 1; 00335 }