Linux 内核 内存管理内存映射相关数据结构 ② ( vm_area_struct 结构体成员分析 | vm_mm 成员 | vm_page_prot 成员 | vm_flags 成员 )

Posted 2022-04-15 韩曙亮

文章目录

• 一、vm_area_struct 结构体成员分析
• • 1、vm_mm 成员
  • 2、vm_page_prot 成员
  • 3、vm_flags 成员
• 二、vm_area_struct 结构体完整源码

在之前的博客 【Linux 内核 内存管理】虚拟地址空间布局架构 ⑦ ( vm_area_struct 结构体成员分析 | vm_start | vm_end | vm_next | vm_prev |vm_rb) 中 , 分析了 vm_start vm_end vm_next vm_prev vm_rb 这 $5$ 个结构体成员的含义 , 下面继续分析剩余结构体成员的含义 ;

一、vm_area_struct 结构体成员分析

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1、vm_mm 成员

struct mm_struct *vm_mm 成员的作用是 指向 " 内存描述符 " mm_struct 结构体 , 这是该 " 虚拟内存区域 " vm_area_struct 所属的 " 进程的用户虚拟地址空间 " mm_struct 内存描述符结构体 ;

vm_area_struct 结构体 是 " 虚拟内存区域 " ;

mm_struct 结构体 是 " 进程的用户虚拟地址空间 " , 又称为 " 内存描述符 " ;

	struct mm_struct *vm_mm;	/* The address space we belong to. */

2、vm_page_prot 成员

pgprot_t vm_page_prot 成员是 控制访问权限 的 " 保护位 " ,

	pgprot_t vm_page_prot;		/* Access permissions of this VMA. */

3、vm_flags 成员

unsigned long vm_flags 表示 虚拟内存 的 标志 ;

	unsigned long vm_flags;		/* Flags, see mm.h. */

虚拟内存 相关的标志位定义在 linux-4.12\\include\\linux\\mm.h#159 位置

上述 unsigned long vm_flags 可设置的标志位有 VM_READ VM_WRITE VM_EXEC VM_SHARED 等 ;

/*
 * vm_flags in vm_area_struct, see mm_types.h.
 * When changing, update also include/trace/events/mmflags.h
 */
#define VM_NONE		0x00000000

#define VM_READ		0x00000001	/* currently active flags */
#define VM_WRITE	0x00000002
#define VM_EXEC		0x00000004
#define VM_SHARED	0x00000008

二、vm_area_struct 结构体完整源码

---

vm_area_struct 结构体完整源码 :

/*
 * This struct defines a memory VMM memory area. There is one of these
 * per VM-area/task.  A VM area is any part of the process virtual memory
 * space that has a special rule for the page-fault handlers (ie a shared
 * library, the executable area etc).
 */
struct vm_area_struct 
	/* The first cache line has the info for VMA tree walking. */

	unsigned long vm_start;		/* Our start address within vm_mm. */
	unsigned long vm_end;		/* The first byte after our end address
					   within vm_mm. */

	/* linked list of VM areas per task, sorted by address */
	struct vm_area_struct *vm_next, *vm_prev;

	struct rb_node vm_rb;

	/*
	 * Largest free memory gap in bytes to the left of this VMA.
	 * Either between this VMA and vma->vm_prev, or between one of the
	 * VMAs below us in the VMA rbtree and its ->vm_prev. This helps
	 * get_unmapped_area find a free area of the right size.
	 */
	unsigned long rb_subtree_gap;

	/* Second cache line starts here. */

	struct mm_struct *vm_mm;	/* The address space we belong to. */
	pgprot_t vm_page_prot;		/* Access permissions of this VMA. */
	unsigned long vm_flags;		/* Flags, see mm.h. */

	/*
	 * For areas with an address space and backing store,
	 * linkage into the address_space->i_mmap interval tree.
	 */
	struct 
		struct rb_node rb;
		unsigned long rb_subtree_last;
	 shared;

	/*
	 * A file's MAP_PRIVATE vma can be in both i_mmap tree and anon_vma
	 * list, after a COW of one of the file pages.	A MAP_SHARED vma
	 * can only be in the i_mmap tree.  An anonymous MAP_PRIVATE, stack
	 * or brk vma (with NULL file) can only be in an anon_vma list.
	 */
	struct list_head anon_vma_chain; /* Serialized by mmap_sem &
					  * page_table_lock */
	struct anon_vma *anon_vma;	/* Serialized by page_table_lock */

	/* Function pointers to deal with this struct. */
	const struct vm_operations_struct *vm_ops;

	/* Information about our backing store: */
	unsigned long vm_pgoff;		/* Offset (within vm_file) in PAGE_SIZE
					   units */
	struct file * vm_file;		/* File we map to (can be NULL). */
	void * vm_private_data;		/* was vm_pte (shared mem) */

#ifndef CONFIG_MMU
	struct vm_region *vm_region;	/* NOMMU mapping region */
#endif
#ifdef CONFIG_NUMA
	struct mempolicy *vm_policy;	/* NUMA policy for the VMA */
#endif
	struct vm_userfaultfd_ctx vm_userfaultfd_ctx;
;