当CONFIG_X86_PAT=y的情况下，无法mmap；当CONFIG_X86_PAT=n的情况下，同时CONFIG_STRICT_DEVMEM必须是n，否则无法mmap；总结：如果需要mmap，则必须CONFIG_X86_PAT=nCONFIG_STRICT_DEVMEM=n
之所以想写这篇帖子，是有两个方面原因。其一是内核版有一个关于《内核可以从线性地址直接计算物理地址，用来做什么呢？》的讨论，偶说计算出物理地址可以共享给用户空间读写。dreamice兄说能否说一下详细的应用。其二是alb*版主提到wheelz曾经写过这样一个例程，拜读了一把，发现在传递物理地址和内存大小上，wheelz的例程还有些不够灵活。alb*版主提到可以通过文件的方式实现动态的传递。因此，偶也写了这样一个例程，可以动态的将内核空间的物理地址和大小传给用户空间。整个内核模块，在模块插入时建立proc文件，分配内存。卸载模块的时候将用户空间写入的内容打印出来。以下是内核模块的代码和用户空间的测试代码。
QUOTE:
/*This program is used to allocate memory in kerneland pass the physical address to userspace through proc file.*/#include <linux/version.h>#include <linux/module.h>#include <linux/proc_fs.h>#include <linux/mm.h>#define PROC_MEMSHARE_DIR “memshare”#define PROC_MEMSHARE_PHYADDR “phymem_addr”#define PROC_MEMSHARE_SIZE “phymem_size”/*alloc one page. 4096 bytes*/#define PAGE_ORDER 0/*this value can get from PAGE_ORDER*/#define PAGES_NUMBER 1struct proc_dir_entry *proc_memshare_dir ;unsigned long kernel_memaddr = 0;unsigned long kernel_memsize= 0;static int proc_read_phymem_addr(char *page, char **start, off_t off, int count){ return sprintf(page, “%08lx/n”, __pa(kernel_memaddr));}static int proc_read_phymem_size(char *page, char **start, off_t off, int count){ return sprintf(page, “%lu/n”, kernel_memsize);}static int __init init(void){ /*build proc dir “memshare”and two proc files: phymem_addr, phymem_size in the dir*/ proc_memshare_dir = proc_mkdir(PROC_MEMSHARE_DIR, NULL); create_proc_info_entry(PROC_MEMSHARE_PHYADDR, 0, proc_memshare_dir, proc_read_phymem_addr); create_proc_info_entry(PROC_MEMSHARE_SIZE, 0, proc_memshare_dir, proc_read_phymem_size); /*alloc one page*/ kernel_memaddr =__get_free_pages(GFP_KERNEL, PAGE_ORDER); if(!kernel_memaddr) { printk(“Allocate memory failure!/n”); } else { SetPageReserved(virt_to_page(kernel_memaddr)); kernel_memsize = PAGES_NUMBER * PAGE_SIZE; printk(“Allocate memory success!. The phy mem addr=%08lx, size=%lu/n”, __pa(kernel_memaddr), kernel_memsize); } return 0;}static void __exit fini(void){ printk(“The content written by user is: %s/n”, (unsigned char *) kernel_memaddr); ClearPageReserved(virt_to_page(kernel_memaddr)); free_pages(kernel_memaddr, PAGE_ORDER); remove_proc_entry(PROC_MEMSHARE_PHYADDR, proc_memshare_dir); remove_proc_entry(PROC_MEMSHARE_SIZE, proc_memshare_dir); remove_proc_entry(PROC_MEMSHARE_DIR, NULL); return;}module_init(init);module_exit(fini);MODULE_LICENSE(“GPL”);MODULE_AUTHOR(“Godbach (nylzhaowei@163.com)”);MODULE_DESCRIPTION(“Kernel memory share module.”);
用户空间的测试代码：
QUOTE:
#include <stdio.h>#include <stdlib.h>#include <unistd.h>#include <string.h>#include <fcntl.h>#include <sys/stat.h>#include <sys/types.h>#include <sys/mman.h>int main(int argc, char* argv[]){ if(argc != 2) { printf(“Usage: %s string/n”, argv[0]); return 0; } unsigned long phymem_addr, phymem_size; char *map_addr; char s[256]; int fd; /*get the physical address of allocated memory in kernel*/ fd = open(“/proc/memshare/phymem_addr”, O_RDONLY); if(fd < 0) { printf(“cannot open file /proc/memshare/phymem_addr/n”); return 0; } read(fd, s, sizeof(s)); sscanf(s, “%lx”, &phymem_addr); close(fd); /*get the size of allocated memory in kernel*/ fd = open(“/proc/memshare/phymem_size”, O_RDONLY); if(fd < 0) { printf(“cannot open file /proc/memshare/phymem_size/n”); return 0; } read(fd, s, sizeof(s)); sscanf(s, “%lu”, &phymem_size); close(fd); printf(“phymem_addr=%lx, phymem_size=%lu/n”, phymem_addr, phymem_size); /*memory map*/ int map_fd = open(“/dev/mem”, O_RDWR); if(map_fd < 0) { printf(“cannot open file /dev/mem/n”); return 0; } map_addr = mmap(0, phymem_size, PROT_READ|PROT_WRITE, MAP_SHARED, map_fd, phymem_addr); strcpy(map_addr, argv[1]); munmap(map_addr, phymem_size); close(map_fd); return 0; }
测试的内核是2.6.25.以下是执行结果。
QUOTE:
debian:/home/km/memshare# insmod memshare_kernel.kodebian:/home/km/memshare# ./memshare_user ‘hello,world!’phymem_addr=e64e000, phymem_size=4096debian:/home/km/memshare# cat /proc/memshare/phymem_addr0e64e000debian:/home/km/memshare# cat /proc/memshare/phymem_size4096debian:/home/km/memshare# rmmod memshare_kerneldebian:/home/km/memshare# tail /var/log/messagesSep 27 18:14:24 debian kernel: [50527.567931] Allocate memory success!. The phy mem addr=0e64e000, size=4096Sep 27 18:15:31 debian kernel: [50592.570986] The content written by user is: hello,world!
仓促之间，有些地方处理的还是比较简单。希望高手多多指正。需要了解这方面实现的可以参考一下，共同学习。
梦想从来不会选择人，它是上天赋予每个人构建未来蓝图的神奇画笔。