static?inline?void?mem_mapping_linear(void)
{
??unsigned?long?pageoffset,?sectionNumber;
??/*4GB虛擬地址映射到相應的物理地址上，均不能緩存*/
??for?(sectionNumber?=?0;?sectionNumber?<?4096;?sectionNumber++)
??{
????pageoffset?=?(sectionNumber?<<?20);
????*(mmu_tlb_base?+?(pageoffset?>>?20))?=?pageoffset?|?MMU_SECDESC;
????//mmu_tlb_base為存放頁表的首地址,tlb是轉換旁路緩存，是轉換表的Cache
??}
??/*使能DRAM的區域可緩存*/
??/*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);

/*

**參數fd為文件描述符，

**len是映射到用戶空間的字節數，它從被映射文件開頭offset開始算起

**prot指定訪問權限，PROT_READ（可讀）、PROT_WRITE（可寫）、PROT_EXEC（可執行）、PROT_NONE（不可訪問）

**參數addr指定文件應被映射到用戶空間的起始地址，一般為NULL，這樣起始地址的任務將由內核完成，而函數返回值就是映射到用戶空間的地址

*/

1、在進程的虛擬空間查找一塊VMA

2、將這塊VMA進行映射到設備地址空間，如果file_operations定義了mmap()操作，則調用它

3、將這個VMA插入到進程的VMA鏈表中

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;
}

/*

**這段代碼的核心是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就是用戶內存映射開始處的虛擬地址
**vma->vm_end - vma->vm_start是映射的虛擬地址范圍
**而off >> PAGE_SHIFT是虛擬地址應該映射到的物理地址off的頁幀號，實際上就是物理地址off右移了PAGE_SHIFT位：
off = vma->vm_pgoff << PAGE_SHIFT;
start = info->fix.smem_start;//smem_start是顯存的起始物理地址
start &= PAGE_MASK;
off += start;
**從上述過程可以看出，將顯存的物理地址的頁幀號映射到用戶空間的虛擬地址上

**mmap必須以PAGE_SIZE為單位進行映射，實際上內存只能以頁為單位進行映射，如果非PAGE_SIZE整數倍的地址范圍，要先進行頁對齊，強行以PAGE_SIZE的倍數大小進行映射

*/

/*內核模塊加載函數*/
int?__init kmalloc_map_init(void)
{
????//申請設備號，添加cdev結構體
????buffer?=?kmalloc(BUFFER_SIZE,?GFP_KERNEL);
????for?(page?=?virt_to_page(buffer);?page?<?virt_to_page(buffer?+?BUFFER_SIZE);?page++)
????{
????????mem_map_reserve(page);//置頁為保留，virt_to_page()將內核虛擬地址轉化為頁
????}
}
/*mmap()函數*/
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中的所有頁*/
????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)來替代remap_page_range？

**在Linux kernel 2.6.27中，已經找不到remap_page_range的實現，見Linux kernel change log:?Changes remap_page_range to remap_pfn_range for 2.6.10 and above kernels

*/
????return?0;
}