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export symbols for lguest as a module
lguest does some fairly lowlevel things to support a host, which normal modules don't need:
math_state_restore:
When the guest triggers a Device Not Available fault, we need
to be able to restore the FPU
1. 1037 /*
2. 1038 * 'math_state_restore()' saves the current math information in the
3. 1039 * old math state array, and gets the new ones from the current task
4. 1040 *
5. 1041 * Careful.. There are problems with IBM-designed IRQ13 behaviour.
6. 1042 * Don't touch unless you *really* know how it works.
7. 1043 *
8. 1044 * Must be called with kernel preemption disabled (in this case,
9. 1045 * local interrupts are disabled at the call-site in entry.S).
10. 1046 */
11. 1047 asmlinkage void math_state_restore(void)
12. 1048 {
13. 1049 struct thread_info *thread = current_thread_info();
14. 1050 struct task_struct *tsk = thread->task;
15. 1051
16. 1052 clts(); /* Allow maths ops (or we recurse) */
17. 1053 if (!tsk_used_math(tsk))
18. 1054 init_fpu(tsk);
19. 1055 restore_fpu(tsk);
20. 1056 thread->status |= TS_USEDFPU; /* So we fnsave on switch_to() */
21. 1057 tsk->fpu_counter++;
22. 1058 }
23. 1059 EXPORT_SYMBOL_GPL(math_state_restore);
24.
当模块被装载时,它被动态链接到内核.像用户空间的动态库一样,只有把函数导出才能 被调用. 在内核中, 导出内核函数使用这两个声明： called EXPORT_ SYMBOL() 和 EXPORT_SYMBOL_GPL().导出内核的符号表后被看作还是导出的内核的接口，有时，也称为内核的API.(详细请看《Linux kernel Development》Second Edition第16章第7小节)
__put_task_struct:
We need to hold a reference to another task for inter-guest I/O, and put_task_struct() is an inline function which calls __put_task_struct.
1. 116 void __put_task_struct(struct task_struct *tsk)
2. 117 {
3. 118 WARN_ON(!(tsk->exit_state & (EXIT_DEAD | EXIT_ZOMBIE)));
4. 119 WARN_ON(atomic_read(&tsk->usage));
5. 120 WARN_ON(tsk == current);
6. 121
7. 122 security_task_free(tsk);
8. 123 free_uid(tsk->user);
9. 124 put_group_info(tsk->group_info);
10. 125 delayacct_tsk_free(tsk);
11. 126
12. 127 if (!profile_handoff_task(tsk))
13. 128 free_task(tsk);
14. 129 }
15. 130 EXPORT_SYMBOL_GPL(__put_task_struct);
16.
access_process_vm:
We need to access another task for inter-guest I/O.
1. 2816 /*
2. 2817 * Access another process' address space.
3. 2818 * Source/target buffer must be kernel space,
4. 2819 * Do not walk the page table directly, use get_user_pages
5. 2820 */
6. 2821 int access_process_vm(struct task_struct *tsk, unsigned long addr, void *buf, int len, int write)
7. 2822 {
8. 2823 struct mm_struct *mm;
9. 2824 struct vm_area_struct *vma;
10. 2825 struct page *page;
11. 2826 void *old_buf = buf;
12. 2827
13. 2828 mm = get_task_mm(tsk);
14. 2829 if (!mm)
15. 2830 return 0;
16. 2831
17. 2832 down_read(&mm->mmap_sem);
18. 2833 /* ignore errors, just check how much was sucessfully transfered */
19. 2834 while (len) {
20. 2835 int bytes, ret, offset;
21. 2836 void *maddr;
22. 2837
23. 2838 ret = get_user_pages(tsk, mm, addr, 1,
24. 2839 write, 1, &page, &vma);
25. 2840 if (ret <= 0)
26. 2841 break;
27. 2842
28. 2843 bytes = len;
29. 2844 offset = addr & (PAGE_SIZE-1);
30. 2845 if (bytes > PAGE_SIZE-offset)
31. 2846 bytes = PAGE_SIZE-offset;
32. 2847
33. 2848 maddr = kmap(page);
34. 2849 if (write) {
35. 2850 copy_to_user_page(vma, page, addr,
36. 2851 maddr + offset, buf, bytes);
37. 2852 set_page_dirty_lock(page);
38. 2853 } else {
39. 2854 copy_from_user_page(vma, page, addr,
40. 2855 buf, maddr + offset, bytes);
41. 2856 }
42. 2857 kunmap(page);
43. 2858 page_cache_release(page);
44. 2859 len -= bytes;
45. 2860 buf += bytes;
46. 2861 addr += bytes;
47. 2862 }
48. 2863 up_read(&mm->mmap_sem);
49. 2864 mmput(mm);
50. 2865
51. 2866 return buf - old_buf;
52. 2867 }
53. 2868 EXPORT_SYMBOL_GPL(access_process_vm);
54.
map_vm_area & __get_vm_area:
We need to map the switcher shim (ie. monitor) at 0xFFC01000.
1. /*
2. * each page frame allocated to the noncontiguous memory area is now associated with * a linear address included in the interval of contiguous linear addresses.
3. */
4. 148 int map_vm_area(struct vm_struct *area, pgprot_t prot, struct page ***pages)
5. 149 {
6. 150 pgd_t *pgd;
7. 151 unsigned long next;
8. 152 unsigned long addr = (unsigned long) area->addr;
9. 153 unsigned long end = addr + area->size - PAGE_SIZE;
10. 154 int err;
11. 155
12. 156 BUG_ON(addr >= end);
13. 157 pgd = pgd_offset_k(addr);
14. 158 do {
15. 159 next = pgd_addr_end(addr, end);
16. 160 err = vmap_pud_range(pgd, addr, next, prot, pages);
17. 161 if (err)
18. 162 break;
19. 163 } while (pgd++, addr = next, addr != end);
20. 164 flush_cache_vmap((unsigned long) area->addr, end);
21. 165 return err;
22. 166 }
23. 167 EXPORT_SYMBOL_GPL(map_vm_area);
24. 241 struct vm_struct *__get_vm_area(unsigned long size, unsigned long flags,
25. 242 unsigned long start, unsigned long end)
26. 243 {
27. 244 return __get_vm_area_node(size, flags, start, end, -1, GFP_KERNEL);
28. 245 }
29. 246 EXPORT_SYMBOL_GPL(__get_vm_area);
30.
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