/*
* linux/mm/vmalloc.c
*
* Copyright (C) 1993 Linus Torvalds
*/
#include <asm/system.h>
#include <linux/config.h>
#include <linux/signal.h>
#include <linux/sched.h>
#include <linux/head.h>
#include <linux/kernel.h>
#include <linux/errno.h>
#include <linux/types.h>
#include <linux/malloc.h>
#include <asm/segment.h>
//虚拟内存结构体定义
struct vm_struct {
unsigned long flags; //标志
void * addr; //地址
unsigned long size; //长度
struct vm_struct * next; //下一个指针
};
static struct vm_struct * vmlist = NULL;
/* Just any arbitrary offset to the start of the vmalloc VM area: the
* current 8MB value just means that there will be a 8MB "hole" after the
* physical memory until the kernel virtual memory starts. That means that
* any out-of-bounds memory accesses will hopefully be caught.
* The vmalloc() routines leaves a hole of 4kB between each vmalloced
* area for the same reason. ;)
*/
#define VMALLOC_OFFSET (8*1024*1024)
//设置页目录，实际上每个任务都知道其它任务的页目录
static inline void set_pgdir(unsigned long dindex, unsigned long value)
{
struct task_struct * p;
//取init任务
p = &init_task;
//每个任务中的指定索引设置为指定值
do {
((unsigned long *) p->tss.cr3)[dindex] = value;
p = p->next_task;
} while (p != &init_task);
}
//释放区域页面
static int free_area_pages(unsigned long dindex, unsigned long index, unsigned long nr)
{
unsigned long page, *pte;
//找到页表
if (!(PAGE_PRESENT & (page = swapper_pg_dir[dindex])))
return 0;
//
page &= PAGE_MASK;
//页表中索引
pte = index + (unsigned long *) page;
//遍历释放内存页
do {
unsigned long pg = *pte;
*pte = 0;
if (pg & PAGE_PRESENT)
free_page(pg);
pte++;
} while (--nr);
//指向页表
pte = (unsigned long *) page;
//页表中
for (nr = 0 ; nr < 1024 ; nr++, pte++)
if (*pte)
return 0;
//设置页目录表项
set_pgdir(dindex,0);
mem_map[MAP_NR(page)] = 1;
//释放页表所在页面
free_page(page);
//刷新
invalidate();
return 0;
}
//分配区域页面
static int alloc_area_pages(unsigned long dindex, unsigned long index, unsigned long nr)
{
unsigned long page, *pte;
//根据索引从页目录中找到页表
page = swapper_pg_dir[dindex];
//如果页面不存在
if (!page) {
//从核心内存中申请一页内存
page = get_free_page(GFP_KERNEL);
//如果申请不到，则退出
if (!page)
return -ENOMEM;
//如果能够获取到指定页面
if (swapper_pg_dir[dindex]) {
//则释放刚刚申请的页面
free_page(page);
//使用索引到的页面
page = swapper_pg_dir[dindex];
} else {
//设置页面属性
mem_map[MAP_NR(page)] = MAP_PAGE_RESERVED;
set_pgdir(dindex, page | PAGE_SHARED);
}
}
//已经获取到页面了
//页面边界对齐
page &= PAGE_MASK;
//指定内存
pte = index + (unsigned long *) page;
//从竞争中移除，设置为共享
*pte = PAGE_SHARED; /* remove a race with vfree() */
//循环申请内存，共计nr页
do {
//申请一页内存
unsigned long pg = get_free_page(GFP_KERNEL);
//申请失败，返回错误
if (!pg)
return -ENOMEM;
//申请成功，设置属性
*pte = pg | PAGE_SHARED;
pte++;
} while (--nr);
invalidate();
return 0;
}
//执行
static int do_area(void * addr, unsigned long size,
int (*area_fn)(unsigned long,unsigned long,unsigned long))
{
unsigned long nr, dindex, index;
//内存页数
nr = size >> PAGE_SHIFT;
//页目录索引
dindex = (TASK_SIZE + (unsigned long) addr) >> 22;
//页表索引
index = (((unsigned long) addr) >> PAGE_SHIFT) & (PTRS_PER_PAGE-1);
//遍历处理，执行area_fn功能
while (nr > 0) {
unsigned long i = PTRS_PER_PAGE - index;
if (i > nr)
i = nr;
nr -= i;
if (area_fn(dindex, index, i))
return -1;
index = 0;
dindex++;
}
return 0;
}
//释放虚拟内存
void vfree(void * addr)
{
struct vm_struct **p, *tmp;
if (!addr)
return;
if ((PAGE_SIZE-1) & (unsigned long) addr) {
printk("Trying to vfree() bad address (%p)\n", addr);
return;
}
for (p = &vmlist ; (tmp = *p) ; p = &tmp->next) {
if (tmp->addr == addr) {
*p = tmp->next;
do_area(tmp->addr, tmp->size, free_area_pages);
kfree(tmp);
return;
}
}
printk("Trying to vfree() nonexistent vm area (%p)\n", addr);
}
//分配虚拟内存
void * vmalloc(unsigned long size)
{
void * addr;
struct vm_struct **p, *tmp, *area;
size = PAGE_ALIGN(size);
if (!size || size > high_memory)
return NULL;
area = (struct vm_struct *) kmalloc(sizeof(*area), GFP_KERNEL);
if (!area)
return NULL;
addr = (void *) ((high_memory + VMALLOC_OFFSET) & ~(VMALLOC_OFFSET-1));
area->size = size + PAGE_SIZE;
area->next = NULL;
for (p = &vmlist; (tmp = *p) ; p = &tmp->next) {
if (size + (unsigned long) addr < (unsigned long) tmp->addr)
break;
addr = (void *) (tmp->size + (unsigned long) tmp->addr);
}
area->addr = addr;
area->next = *p;
*p = area;
if (do_area(addr, size, alloc_area_pages)) {
vfree(addr);
return NULL;
}
return addr;
}
//读取
int vread(char *buf, char *addr, int count)
{
struct vm_struct **p, *tmp;
char *vaddr, *buf_start = buf;
int n;
for (p = &vmlist; (tmp = *p) ; p = &tmp->next) {
vaddr = (char *) tmp->addr;
while (addr < vaddr) {
if (count == 0)
goto finished;
put_fs_byte('\0', buf++), addr++, count--;
}
n = tmp->size - PAGE_SIZE;
if (addr > vaddr)
n -= addr - vaddr;
while (--n >= 0) {
if (count == 0)
goto finished;
put_fs_byte(*addr++, buf++), count--;
}
}
finished:
return buf - buf_start;
}
mm/vmalloc.c
