Specifications

This is the Title of the Book, eMatter Edition

460

Chapter 15: Memory Mapping and DMA

unsigned long kmap(struct page *page);

void kunmap(struct page *page);

kmap returns a kernel virtual address that is mapped to the given page, creating

the mapping if need be. kunmap deletes the mapping for the given page.

#include <linux/highmem.h>

#include <asm/kmap_types.h>

void *kmap_atomic(struct page *page, enum km_type type);

void kunmap_atomic(void *addr, enum km_type type);

The high-performance version of kmap; the resulting mappings can be held only by

atomic code. For drivers,

type should be KM_USER0, KM_USER1, KM_IRQ0, or KM_IRQ1.

struct vm_area_struct;

Structure describing a VMA.

Implementing mmap

int remap_pfn_range(struct vm_area_struct *vma, unsigned long virt_add,

unsigned long pfn, unsigned long size, pgprot_t prot);

int io_remap_page_range(struct vm_area_struct *vma, unsigned long virt_add,

unsigned long phys_add, unsigned long size, pgprot_t prot);

Functions that sit at the heart of mmap. They map size bytes of physical

addresses, starting at the page number indicated by

pfn to the virtual address

virt_add. The protection bits associated with the virtual space are specified in

prot. io_remap_page_range should be used when the target address is in I/O

memory space.

struct page *vmalloc_to_page(void *vmaddr);

Converts a kernel virtual address obtained from vmalloc to its corresponding

struct page pointer.

Implementing Direct I/O

int get_user_pages(struct task_struct *tsk, struct mm_struct *mm, unsigned

long start, int len, int write, int force, struct page **pages, struct

vm_area_struct **vmas);

Function that locks a user-space buffer into memory and returns the correspond-

ing

struct page pointers. The caller must hold mm->mmap_sem.

SetPageDirty(struct page *page);

Macro that marks the given page as “dirty” (modified) and in need of writing to

its backing store before it can be freed.

void page_cache_release(struct page *page);

Frees the given page from the page cache.

,ch15.13676 Page 460 Friday, January 21, 2005 11:04 AM