进程地址空间 - 辅助函数分析
内存区操作函数分析
find_vmd
1431 /* Look up the first VMA which satisfies addr < vm_end, NULL if none. */
1432 struct vm_area_struct * find_vma(struct mm_struct * mm, unsigned long addr)
1433 {
1434 struct vm_area_struct *vma = NULL;
1435
1436 if (mm) {
1437 /* Check the cache first. */
1438 /* (Cache hit rate is typically around 35%.) */
1439 vma = mm->mmap_cache;
1440 if (!(vma && vma->vm_end > addr && vma->vm_start <= addr)) {
1441 struct rb_node * rb_node;
1442
1443 rb_node = mm->mm_rb.rb_node;
1444 vma = NULL;
1445
1446 while (rb_node) {
1447 struct vm_area_struct * vma_tmp;
1448
1449 vma_tmp = rb_entry(rb_node,
1450 struct vm_area_struct, vm_rb);
1451
1452 if (vma_tmp->vm_end > addr) {
1453 vma = vma_tmp;
1454 if (vma_tmp->vm_start <= addr)
1455 break;
1456 rb_node = rb_node->rb_left;
1457 } else
1458 rb_node = rb_node->rb_right;
1459 }
1460 if (vma)
1461 mm->mmap_cache = vma;
1462 }
1463 }
1464 return vma;
1465 }
find_vma用来在内存区查找第一个结束地址在addr之后的vma，
1439 根据局部性原理，内核首先检查上次处理的区域是否包含本次所需的地址，即mmap_cache包含住这个地址，如果成立，那么直接从1464返回。
1441～1463 不包含在mmap_cache中，那么我们从红黑树的根节点开始，进行查找.
1446 ~ 1459 红黑树的查找很简单，如果节点的结束地址大于addr并且开始地址小于addr，那么说明已经找到，退出循环；否则在进入不同的树分支。
1460~1461 用找到的vma更新mmap_cache
find_vma_intersection
1073 /* Look up the first VMA which intersects the interval start_addr..end_addr-1,
1074 NULL if none. Assume start_addr < end_addr. */
1075 static inline struct vm_area_struct * find_vma_intersection(struct mm_struct * mm, unsigned long start_addr, unsigned long end_addr)
1076 {
1077 struct vm_area_struct * vma = find_vma(mm,start_addr);
1078
1079 if (vma && end_addr <= vma->vm_start)
1080 vma = NULL;
1081 return vma;
1082 }
这个函数的作用是找到一个VMA，使得这个vma完全包含start_addr和end_addr定义的空间。
get_unmapped_area
1407 unsigned long
1408 get_unmapped_area(struct file *file, unsigned long addr, unsigned long len,
1409 unsigned long pgoff, unsigned long flags)
1410 {
1411 unsigned long (*get_area)(struct file *, unsigned long,
1412 unsigned long, unsigned long, unsigned long);
1413
1414 get_area = current->mm->get_unmapped_area;
1415 if (file && file->f_op && file->f_op->get_unmapped_area)
1416 get_area = file->f_op->get_unmapped_area;
1417 addr = get_area(file, addr, len, pgoff, flags);
1418 if (IS_ERR_VALUE(addr))
1419 return addr;
1420
1421 if (addr > TASK_SIZE - len)
1422 return -ENOMEM;
1423 if (addr & ~PAGE_MASK)
1424 return -EINVAL;
1425
1426 return addr;
1427 }