Linux开发心得总结13 - Linux内存管理和分析vmalloc使用的地址范围

static inline void mem_mapping_linear(void)

{

unsigned long pageoffset, sectionNumber;

/*4GB虚拟地址映射到相应的物理地址上，均不能缓存*/

for (sectionNumber = 0; sectionNumber < 4096; sectionNumber++)

{

pageoffset = (sectionNumber << 20);

*(mmu_tlb_base + (pageoffset >> 20)) = pageoffset | MMU_SECDESC;

//mmu_tlb_base为存放页表的首地址,tlb是转换旁路缓存，是转换表的Cache

}

/*使能DRAM的区域可缓存*/

/*SDRAM物理地址0x30000000-0x33ffffff，DRAM_BASE=0x30000000，DRAM_SIZE=64M*/

for (pageoffset = DRAM_BASE; pageoffset < (DRAM_BASE + DRAM_SIZE); pageoffset += SZ_1M)

{

*(mmu_tlb_base + (pageoffset >> 20)) = pageoffset | MMU_SECDESC | MMU_CACHEEABLE;

}

}

caddr_t mmap(caddr_t addr, size_t len, int prot, int flags, int fd, off_t offset);

/*

**参数fd为文件描述符，

**len是映射到用户空间的字节数，它从被映射文件开头offset开始算起

**prot指定访问权限，PROT_READ（可读）、PROT_WRITE（可写）、PROT_EXEC（可执行）、PROT_NONE（不可访问）

**参数addr指定文件应被映射到用户空间的起始地址，一般为NULL，这样起始地址的任务将由内核完成，而函数返回值就是映射到用户空间的地址

*/

1、在进程的虚拟空间查找一块VMA

2、将这块VMA进行映射到设备地址空间，如果file_operations定义了mmap()操作，则调用它

3、将这个VMA插入到进程的VMA链表中

static int

fb_mmap(struct file *file, struct vm_area_struct * vma)

{

int fbidx = iminor(file->f_path.dentry->d_inode);

struct fb_info *info = registered_fb[fbidx];

struct fb_ops *fb = info->fbops;

unsigned long off;

unsigned long start;

u32 len;

if (vma->vm_pgoff > (~0UL >> PAGE_SHIFT))

return -EINVAL;

off = vma->vm_pgoff << PAGE_SHIFT;

if (!fb)

return -ENODEV;

if (fb->fb_mmap) {

int res;

lock_kernel();

res = fb->fb_mmap(info, vma);

unlock_kernel();

return res;

}

lock_kernel();

/* frame buffer memory */

start = info->fix.smem_start;

len = PAGE_ALIGN((start & ~PAGE_MASK) + info->fix.smem_len);

if (off >= len) {

/* memory mapped io */

off -= len;

if (info->var.accel_flags) {

unlock_kernel();

return -EINVAL;

}

start = info->fix.mmio_start;

len = PAGE_ALIGN((start & ~PAGE_MASK) + info->fix.mmio_len);

}

unlock_kernel();

start &= PAGE_MASK;

if ((vma->vm_end - vma->vm_start + off) > len)

return -EINVAL;

off += start;

vma->vm_pgoff = off >> PAGE_SHIFT;

/* This is an IO map - tell maydump to skip this VMA */

vma->vm_flags |= VM_IO | VM_RESERVED;

fb_pgprotect(file, vma, off);

if (io_remap_pfn_range(vma, vma->vm_start, off >> PAGE_SHIFT,

vma->vm_end - vma->vm_start, vma->vm_page_prot))

return -EAGAIN;

return 0;

}

/*

**这段代码的核心是io_remap_pfn_range(vma, vma->vm_start, off >> PAGE_SHIFT, vma->vm_end - vma->vm_start, vma->vm_page_prot))

**其中vma->vm_start就是用户内存映射开始处的虚拟地址

**vma->vm_end - vma->vm_start是映射的虚拟地址范围

**而off >> PAGE_SHIFT是虚拟地址应该映射到的物理地址off的页帧号，实际上就是物理地址off右移了PAGE_SHIFT位：

off = vma->vm_pgoff << PAGE_SHIFT;

start = info->fix.smem_start;//smem_start是显存的起始物理地址

start &= PAGE_MASK;

off += start;

**从上述过程可以看出，将显存的物理地址的页帧号映射到用户空间的虚拟地址上

**mmap必须以PAGE_SIZE为单位进行映射，实际上内存只能以页为单位进行映射，如果非PAGE_SIZE整数倍的地址范围，要先进行页对齐，强行以PAGE_SIZE的倍数大小进行映射

*/

/*内核模块加载函数*/

int __init kmalloc_map_init(void)

{

//申请设备号，添加cdev结构体

buffer = kmalloc(BUFFER_SIZE, GFP_KERNEL);

for (page = virt_to_page(buffer); page < virt_to_page(buffer + BUFFER_SIZE); page++)

{

mem_map_reserve(page);//置页为保留，virt_to_page()将内核虚拟地址转化为页

}

}

/*mmap()函数*/

static int kmalloc_map_mmap(struct file *filp, struct vm_area_struct *vma)

{

unsigned long page, pos;

unsigned long start = (unsigned long)vma->vm_start;

unsigned long size = (unsigned long)(vma->vm_end - vma->vm_start);

if (size > BUFFER_SIZE)

{

return - EINVAL;

}

pos = (unsigned long)buffer;

/*映射buffer中的所有页*/

while (size > 0)

{

page = virt_to_phys((void *)pos);

if (remap_page_range(start, page, PAGE_SIZE, PAGE_SHARED))

return - EAGAIN;

start += PAGE_SIZE;

pos += PAGE_SIZE;

size -= PAGE_SIZE;

}

/*

**可否用io_remap_pfn_range(vma, vma->vm_start, virt_to_phys((void *)buffer) >> PAGE_SHIFT, vma->vm_end - vma->vm_start, PAGE_SHARED)来替代remap_page_range？

**在Linux kernel 2.6.27中，已经找不到remap_page_range的实现，见Linux kernel change log: Changes remap_page_range to remap_pfn_range for 2.6.10 and above kernels

*/

return 0;

}