From 3e10eca0c4ec631798979f725d636e1d6fc44399 Mon Sep 17 00:00:00 2001 From: LP07 Date: Mon, 23 Nov 2020 11:06:25 +0800 Subject: [PATCH] add a new blog --- content/blog/2020/mem_manage/index.md | 272 ++++++++++++++++++++++++++ 1 file changed, 272 insertions(+) create mode 100644 content/blog/2020/mem_manage/index.md diff --git a/content/blog/2020/mem_manage/index.md b/content/blog/2020/mem_manage/index.md new file mode 100644 index 0000000..e593195 --- /dev/null +++ b/content/blog/2020/mem_manage/index.md @@ -0,0 +1,272 @@ +--- +title: "虚拟内存管理实例" +date: 2020-11-23T10:42:47+08:00 +author: "admin001—梁鹏转" +keywords: ["内存管理"] +categories : ["走进内核"] +banner : "img/blogimg/linux_wechat.png" +summary : "本文是关于虚拟内存管理的一个实例，通过我们写入的字符来调用不同的处理函数，打印不同的信息" +--- + +关于虚拟内存管理的基本内容参看相关内容，在此不再赘述，在理论的基础上，设计出合理的实验可以强化对理论的理解和应用能力 。 + +**实验内容**：在proc 文件系统下，建立一个文件，每次向这个文件写人字符时，调用相应的虚拟内存处理函数 + +```c +/* +mtest_dump_vma_list（）：打印出当前进程的各个VMA，这个功能我们简称"listvma" +mtest_find_vma()： 找出某个虚地址所在的VMA，这个功能我们简称“findvma" +my_follow_page( )：根据页表，求出某个虚地址所在的物理页面，这个功能我们简称"findpage" +mtest_write_val(), 在某个地址写上具体数据，这个功能我们简称“writeval". +*/ +#include +#include +#include +#include +#include +#include +#include +#include +#include +#include +MODULE_LICENSE("GPL"); +/* +@如何编写代码查看自己的进程到底有哪些虚拟区？ +*/ +static void mtest_dump_vma_list(void) +{ +struct mm_struct *mm = current->mm; +struct vm_area_struct *vma; +printk("The current process is %s\n",current->comm); +printk("mtest_dump_vma_list\n"); +down_read(&mm->mmap_sem); +for (vma = mm->mmap;vma; vma = vma->vm_next) { +printk("VMA 0x%lx-0x%lx ", +vma->vm_start, vma->vm_end); +if (vma->vm_flags & VM_WRITE) +printk("WRITE "); +if (vma->vm_flags & VM_READ) +printk("READ "); +if (vma->vm_flags & VM_EXEC) +printk("EXEC "); +printk("\n"); +} +up_read(&mm->mmap_sem); +} +/* +@如果知道某个虚地址，比如，0x8049000, +又如何找到这个地址所在VMA是哪个？ +*/ +static void mtest_find_vma(unsigned long addr) +{ +struct vm_area_struct *vma; +struct mm_struct *mm = current->mm; +printk("mtest_find_vma\n"); +down_read(&mm->mmap_sem); +vma = find_vma(mm, addr); +if (vma && addr >= vma->vm_start) { +printk("found vma 0x%lx-0x%lx flag %lx for addr 0x%lx\n", +vma->vm_start, vma->vm_end, vma->vm_flags, addr); +} else { +printk("no vma found for %lx\n", addr); +} +up_read(&mm->mmap_sem); +} +/* +@一个物理页在内核中用struct page来描述。 +给定一个虚存区VMA和一个虚地址addr， +找出这个地址所在的物理页面page. +*/ +static struct page * +my_follow_page(struct vm_area_struct *vma, unsigned long addr) +{ +pud_t *pud; +pmd_t *pmd; +pgd_t *pgd; +pte_t *pte; +spinlock_t *ptl; +struct page *page = NULL; +struct mm_struct *mm = vma->vm_mm; +pgd = pgd_offset(mm, addr); +if (pgd_none(*pgd) || unlikely(pgd_bad(*pgd))) { +goto out; +} +pud = pud_offset(pgd, addr); +if (pud_none(*pud) || unlikely(pud_bad(*pud))) +goto out; +pmd = pmd_offset(pud, addr); +if (pmd_none(*pmd) || unlikely(pmd_bad(*pmd))) { +goto out; +} +pte = pte_offset_map_lock(mm, pmd, addr, &ptl); +if (!pte) +goto out; +if (!pte_present(*pte)) +goto unlock; +page = pfn_to_page(pte_pfn(*pte)); +if (!page) +goto unlock; +get_page(page); +unlock: +pte_unmap_unlock(pte, ptl); +out: +return page; +} +/* +@ 根据页表，求出某个虚地址所在的物理页面， +这个功能我们简称"findpage" +*/ +static void mtest_find_page(unsigned long addr) +{ +struct vm_area_struct *vma; +struct mm_struct *mm = current->mm; +unsigned long kernel_addr; +struct page *page; +printk("mtest_write_val\n"); +down_read(&mm->mmap_sem); +vma = find_vma(mm, addr); +page = my_follow_page(vma, addr); +if (!page) +{ +printk("page not found for 0x%lx\n", addr); +goto out; +} +printk("page found for 0x%lx\n", addr); +kernel_addr = (unsigned long)page_address(page); +kernel_addr += (addr&~PAGE_MASK); +printk("find 0x%lx to kernel address 0x%lx\n", addr, kernel_addr); +out: +up_read(&mm->mmap_sem); +} +/* +@你是否有这样的想法， +给某个地址写入自己所想写的数据？ +*/ +static void +mtest_write_val(unsigned long addr, unsigned long val) +{ +struct vm_area_struct *vma; +struct mm_struct *mm = current->mm; +struct page *page; +unsigned long kernel_addr; +printk("mtest_write_val\n"); +down_read(&mm->mmap_sem); +vma = find_vma(mm, addr); +if (vma && addr >= vma->vm_start && (addr + sizeof(val)) < vma->vm_end) { +if (!(vma->vm_flags & VM_WRITE)) { +printk("vma is not writable for 0x%lx\n", addr); +goto out; +} +page = my_follow_page(vma, addr); +if (!page) { +printk("page not found for 0x%lx\n", addr); +goto out; +} +kernel_addr = (unsigned long)page_address(page); +kernel_addr += (addr&~PAGE_MASK); +printk("write 0x%lx to address 0x%lx\n", val, kernel_addr); +*(unsigned long *)kernel_addr = val; +put_page(page); +} else { +printk("no vma found for %lx\n", addr); +} +out: +up_read(&mm->mmap_sem); +} +static ssize_t +mtest_write(struct file *file, const char __user * buffer, +size_t count, loff_t * data) +{ +printk("mtest_write ........... \n"); +char buf[128]; +unsigned long val, val2; +if (count > sizeof(buf)) +return -EINVAL; +if (copy_from_user(buf, buffer, count)) +return -EINVAL; +if (memcmp(buf, "listvma", 7) == 0) +mtest_dump_vma_list(); +else if (memcmp(buf, "findvma", 7) == 0) { +if (sscanf(buf + 7, "%lx", &val) == 1) { +mtest_find_vma(val); +} +} +else if (memcmp(buf, "findpage", 8) == 0) { +if (sscanf(buf + 8, "%lx", &val) == 1) { +mtest_find_page(val); +//my_follow_page(vma, addr); +} +} +else if (memcmp(buf, "writeval", 8) == 0) { +if (sscanf(buf + 8, "%lx %lx", &val, &val2) == 2) { +mtest_write_val(val, val2); +} +} +return count; +} +static struct +file_operations proc_mtest_operations = { +.write = mtest_write +}; +static struct proc_dir_entry *mtest_proc_entry; +//整个操作我们以模块的形式实现，因此，模块的初始化和退出函数如下： +static int __init +mtest_init(void) +{ +mtest_proc_entry = create_proc_entry("mtest", 0777, NULL); +if (mtest_proc_entry == NULL) { +printk("Error creating proc entry\n"); +return -1; +} +printk("create the filename mtest mtest_init sucess \n"); +mtest_proc_entry->proc_fops = &proc_mtest_operations; +return 0; +} +static void +__exit mtest_exit(void) +{ +printk("exit the module......mtest_exit \n"); +remove_proc_entry("mtest", NULL); +} +MODULE_LICENSE("GPL"); +MODULE_DESCRIPTION("mtest"); +MODULE_AUTHOR("Zou Nan hai"); +module_init(mtest_init); +module_exit(mtest_exit); +``` + +下面为Makefile + +```c +obj-m := mm.o +# KDIR is the location of the kernel source. The current standard is +# to link to the associated source tree from the directory containing +# the compiled modules. +KDIR := /lib/modules/$(shell uname -r)/build +# PWD is the current working directory and the location of our module +# source files. +PWD := $(shell pwd) +# default is the default make target. The rule here says to run make +# with a working directory of the directory containing the kernel +# source and compile only the modules in the PWD (local) directory. +default: +$(MAKE) -C $(KDIR) M=$(PWD) modules +clean: +rm -rf *.o *.ko *.mod.c +``` + +下面为测试用例 + +```c +[root@HBIDS proc]# echo "listvma" > mtest +[root@HBIDS proc]# echo "listvma" > mtest +[root@HBIDS proc]# echo "findvma0xb7f2b001" > mtest +[root@HBIDS proc]# echo "findpage0xb7f2b001" > mtest +[root@HBIDS proc]# echo "writeval0xb7f2b001 123456" > mtest +打印结果为 +The current process is bash +mtest_dump_vma_list +VMA 0x8048000-0x80dc000 READ EXEC VMA 0x80dc000-0x80e2000 WRITE READ EXEC VMA 0x80e2000-0x811e000 WRITE READ EXEC VMA 0x42000000-0x4212e000 READ EXEC VMA 0x4212e000-0x42131000 WRITE READ EXEC VMA 0x42131000-0x42133000 WRITE READ EXEC VMA 0xb7d00000-0xb7f00000 READ EXEC VMA 0xb7f00000-0xb7f0b000 READ EXEC VMA 0xb7f0b000-0xb7f0c000 WRITE READ EXEC VMA 0xb7f0c000-0xb7f0d000 WRITE READ EXEC VMA 0xb7f0d000-0xb7f0f000 READ EXEC VMA 0xb7f0f000-0xb7f10000 WRITE READ EXEC VMA 0xb7f10000-0xb7f13000 READ EXEC VMA 0xb7f13000-0xb7f14000 WRITE READ EXEC VMA 0xb7f2b000-0xb7f31000 READ EXEC VMA 0xb7f31000-0xb7f32000 WRITE READ EXEC VMA 0xb7f32000-0xb7f47000 READ EXEC VMA 0xb7f47000-0xb7f48000 WRITE READ EXEC VMA 0xbfd31000-0xbfd47000 WRITE READ EXEC mtest_write ........... mtest_find_vma found vma 0xb7f47000-0xb7f48000 flag 100877 for addr 0xb7f47001 mtest_write ........... mtest_write_val page found for 0xb7f47001 find 0xb7f47001 to kernel address 0xc8c4e001 mtest_write ........... mtest_write_val write 0x1234 to address 0xc8c4e001 +``` + +后记：这个程序是去年八月份发表在我的博客上的，当时分为三篇发表。也许因为新博客搬家的缘故找不到了。最近的教学中需要这个例子，于是在网上去搜，幸好有网友收藏并进行了整理，在此贴出，以让大家对抽象的虚存管理有代码级的理解。 \ No newline at end of file -- Gitee