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ps:刚不小把文章发《内核问题》版去了，在这个版找不到还以为被删了，小气了下~~
还是不会从blog导入文章，只好复制粘贴了，原文在my blog：http://blog.chinaunix.net/u3/94771/showart_1945422.html
基于NETLINK的内核与用户空间共享内存的实现 author:bripengandre Email:bripengandre@126.com 一、前言
前些日子，开发中用到了netlink来实现内核与用户空间共享内存，写点笔记与大家分享。因为我对这块也不了解，写出来的东西一定存在很多错误，请大家批评指正~
内核与用户空间共享内存的关键是，用户空间必须得知共享内存的起始地址，这就要求内核空间应该有一种通信机制来通知用户空间。已经有Godbach版主等人用proc文件系统实现了（可以google '共享内存 内核 用户空间'）,很显然任何内核空间与用户空间的通信方法都可资利用。本文主要讲基于NETLINK机制的实现。
二、NETLINK简介
netlink在linux的内核与用户空间通信中用得很多（但具体例子我举不出，因为我不清楚~~请google之），其最大优势是接口与网络编程中的socket相似，且内核要主动发信息给用户空间很方便。
但通过实践，我发现netlink通信机制的最大弊病在于其在各内核版本中接口变化太大，让人难以适从（可从后文列出的源码中的kernel_receive的声明窥一斑）。
既然涉及到内核与用户空间两个空间，就应该在两个空间各有一套接口。用户空间的接口很简单，与一般的socket接口相似，内核空间则稍先复杂，但简单的应用只需简单地了解即可：首先也是建立描述符，建立描述符时会注册一个回调函数（源码中的kernel_receive即是），然后当用户空间有消息发过来时，我们的函数将被调用，显然在这个函数里我们可做相应的处理；当内核要主动发消息给用户进程时，直接调用一个类send函数即可（netlink_unicast系列函数）。当然这个过程中，有很多结构体变量需要填充。具体用法请google，我差不多忘光了~。
三、基于netlink的共享内存
这里的共享内存是指内核与用户空间，而不是通常的用户进程间的。
大概流程如下。
内核：__get_free__pages分配连续的物理内存页（貌似返回的其实是虚拟地址）-->SetPageReserved每一页（每一页都需这个操作，参见源码）-->如果用户空间通过netlink要求获取共享内存的起始物理地址，将__get_free__pages返回的地址__pa下发给用户空间。
用户空间：open "/dev/shm"（一个读写物理内存的设备，具体请google"linux读写物理内存"）-->发netlink消息给内核，得到共享内存的起始物理地址-->mmap上步得到的物理地址。
四、源码说明
正如二中提到的，netlink接口在各版本中接口变化很大，本人懒惰及时间紧，只实验了比较新的内核2.6.25，源码如需移植到老版本上，需要一些改动，敬请原谅。
另外，由于本源码是从一个比较大的程序里抠出来的，所以命名什么的可能有点怪异~
源码包括shm_k.c（内核模块）和用户空间程序（shm_u.c）两部分。shm_k.c模块的工作是：分配8KB内存供共享，并把前几十个字节置为“hello, use share memory withnetlink"字样。shm_u.c工作是：读取共享内存的前几十个字节，将内容输出在stdout上。
特别说明：该程序只适用于2.6.25左右的新版本！用__get_free_pages分配连续内存时，宜先用get_order获取页数，然后需将各页都SetPageReserved下，同样地，释放内存时，需要对每一页调用ClearPageReserved。
我成功用该程序分配了4MB共享内存，运行还比较稳定。因为linux内核的默认设置，一般情况下用get_free_pages只能分配到4MB内存左右，如需增大，可能需改相应的参数并重新编译内核。
五、运行结果
我是在mpc8377上运行的，全过程如下（有少许编辑，如dmesg信息只列出新增的）。
-sh-2.05b# insmod shm_k.ko
-sh-2.05b# dmesg
SHM_TEST: linux version:00020619
SHM_TEST: init_netlink ok.
SHM_TEST: size=00002000, page_cnt=2
SHM_TEST: __get_free_pages ok.
SHM_TEST: init_mem_pool ok.
-sh-2.05b# ./shm_u
SHM_TEST: 24, errno=0.Success, 0defe000, 00002000
the first 30 bytes of shm are: hello, use share memory with netlink
-sh-2.05b# dmesg
SHM_TEST: begin kernel_receive
SHM_TEST: receiv TA_GET_SHM_INFO
SHM_TEST: nlk_get_mem_addr ok
-sh-2.05b# rmmod shm_k
-sh-2.05b# dmesg
SHM_TEST: ta_exit ok.
-sh-2.05b#
六、内核源码
1、common.h（内核与用户空间都用到的头文件）- #ifndef _COMMON_H_
- #define _COMMON_H_
- /* protocol type */
- #define SHM_NETLINK 30
- /* message type */
- #define SHM_GET_SHM_INFO 1
- /* you can add othe message type here */
- #define SHM_WITH_NETLINK "hello, use share memory with netlink"
- typedef struct _nlk_msg
- {
- union _data
- {
- struct _shm_info
- {
- uint32_t mem_addr;
- uint32_t mem_size;
- }shm_info;
-
- /* you can add other content here */
- }data;
- }nlk_msg_t;
- #endif /* _COMMON_H_ */
- #include <linux/init.h>
- #include <linux/module.h>
- #include <linux/version.h>
- #include <linux/types.h>
- #include <linux/skbuff.h>
- #include <linux/netlink.h>
- #include <net/sock.h>
- #include <linux/spinlock.h>
- #include "common.h"
- #define SHM_TEST_DEBUG
- #ifdef SHM_TEST_DEBUG
- #define SHM_DBG(args...) printk(KERN_DEBUG "SHM_TEST: " args)
- #else
- #define SHM_DBG(args...)
- #endif
- #define SHM_ERR(args...) printk(KERN_ERR "SHM_TEST: " args)
- static struct _glb_para
- {
- struct _shm_para
- {
- uint32_t mem_addr; /* memory starting address */
- uint32_t mem_size; /* memory size */
- uint32_t page_cnt; /* memory page count*/
- uint16_t order;
- uint8_t mem_init_flag; /* 0, init failed; 1, init successful */
- }shm_para;
-
- struct sock *nlfd; /* netlink descriptor */
- uint32_t pid; /* user-space process's pid */
- rwlock_t lock;
- }glb_para;
- static void init_glb_para(void);
- static int init_netlink(void);
- static void kernel_receive(struct sk_buff* __skb);
- static int nlk_get_mem_addr(struct nlmsghdr *pnhdr);
- static void clean_netlink(void);
- static int init_shm(void);
- static void clean_shm(void);
- static int __init init_shm_test(void);
- static void clean_shm_test(void);
- static void init_glb_para(void)
- {
- memset(&glb_para, 0, sizeof(glb_para));
- }
- static int init_netlink(void)
- {
- rwlock_init(&glb_para.lock);
- SHM_DBG("linux version:%08x\n", LINUX_VERSION_CODE);
- #if(LINUX_VERSION_CODE < KERNEL_VERSION(2,6,18))
- glb_para.nlfd = netlink_kernel_create(SHM_NETLINK, kernel_receive);
- #elif(LINUX_VERSION_CODE < KERNEL_VERSION(2,6,24))
- glb_para.nlfd = netlink_kernel_create(SHM_NETLINK, 0, kernel_receive, THIS_MODULE));
- #else
- glb_para.nlfd = netlink_kernel_create(&init_net, SHM_NETLINK, 0, kernel_receive, NULL, THIS_MODULE);
- #endif
-
- if(glb_para.nlfd == NULL)
- {
- SHM_ERR("init_netlink::netlink_kernel_create error\n";);
- return (-1);
- }
-
- return (0);
- }
- static void kernel_receive(struct sk_buff* __skb)
- {
- struct sk_buff *skb;
- struct nlmsghdr *nlh = NULL;
- int invalid;
-
- SHM_DBG("begin kernel_receive\n";);
- skb = skb_get(__skb);
- invalid = 0;
- if(skb->len >= sizeof(struct nlmsghdr))
- {
- nlh = (struct nlmsghdr *)skb->data;
- if((nlh->nlmsg_len >= sizeof(struct nlmsghdr))
- && (skb->len >= nlh->nlmsg_len))
- {
- switch(nlh->nlmsg_type)
- {
- case SHM_GET_SHM_INFO:
- SHM_DBG("receiv TA_GET_SHM_INFO\n";);
- nlk_get_mem_addr(nlh);
- break;
- default:
- break;
- }
- }
- }
- kfree_skb(skb);
- }
- static int nlk_get_mem_addr(struct nlmsghdr *pnhdr)
- {
- int ret, size;
- unsigned char *old_tail;
- struct sk_buff *skb;
- struct nlmsghdr *nlh;
- struct _nlk_msg *p;
-
-
- glb_para.pid = pnhdr->nlmsg_pid; /* get the user-space process's pid */
-
- size = NLMSG_SPACE(sizeof(struct _nlk_msg)); /* compute the needed memory size */
- if( (skb = alloc_skb(size, GFP_ATOMIC)) == NULL) /* allocate memory */
- {
- SHM_DBG("nlk_hello_test::alloc_skb error.\n";);
- return (-1);
- }
-
- old_tail = skb->tail;
- nlh = NLMSG_PUT(skb, 0, 0, SHM_GET_SHM_INFO, size-sizeof(struct nlmsghdr)); /* put netlink message structure into memory */
-
- p = NLMSG_DATA(nlh); /* get netlink message body pointer */
- p->data.shm_info.mem_addr = __pa(glb_para.shm_para.mem_addr); /*__pa:convert virtual address to physical address, which needed by/dev/mem */
- p->data.shm_info.mem_size = glb_para.shm_para.mem_size;
-
- nlh->nlmsg_len = skb->tail - old_tail;
- NETLINK_CB(skb).pid = 0; /* from kernel */
- NETLINK_CB(skb).dst_group = 0;
- read_lock_bh(&glb_para.lock);
- ret = netlink_unicast(glb_para.nlfd, skb, glb_para.pid, MSG_DONTWAIT); /* send message to user-space process */
- read_unlock_bh(&glb_para.lock);
- SHM_DBG("nlk_get_mem_addr ok.\n";);
- return (ret);
-
- nlmsg_failure:
- SHM_DBG("nlmsg_failure\n";);
- if(skb)
- {
- kfree_skb(skb);
- }
- return (-1);
- }
- static void clean_netlink(void)
- {
- if(glb_para.nlfd != NULL)
- {
- sock_release(glb_para.nlfd->sk_socket);
- }
- }
- static int init_shm(void)
- {
- int i;
- char *p;
- uint32_t page_addr;
-
- glb_para.shm_para.order = get_order(1024*8); /* allocate 8kB */
- glb_para.shm_para.mem_addr = __get_free_pages(GFP_KERNEL, glb_para.shm_para.order);
- if(glb_para.shm_para.mem_addr == 0)
- {
- SHM_ERR("init_mem_pool::__get_free_pages error.\n";);
- glb_para.shm_para.mem_init_flag = 0;
- return (-1);
- }
- else
- {
- glb_para.shm_para.page_cnt = (1<<glb_para.shm_para.order);
- glb_para.shm_para.mem_size = glb_para.shm_para.page_cnt*PAGE_SIZE;
- glb_para.shm_para.mem_init_flag = 1;
- page_addr = glb_para.shm_para.mem_addr;
- SHM_DBG("size=%08x, page_cnt=%d\n", glb_para.shm_para.mem_size, glb_para.shm_para.page_cnt);
- for(i = 0; i < glb_para.shm_para.page_cnt; i++)
- {
- SetPageReserved(virt_to_page(page_addr)); /* reserved for used */
- page_addr += PAGE_SIZE;
- }
-
- p = (char *)glb_para.shm_para.mem_addr;
- strcpy(p, SHM_WITH_NETLINK); /* write */
- SHM_DBG("__get_free_pages ok.\n";);
- }
-
- return (0);
- }
- static void clean_shm(void)
- {
- int i;
- uint32_t page_addr;
-
- if(glb_para.shm_para.mem_init_flag == 1)
- {
- page_addr = glb_para.shm_para.mem_addr;
- for(i = 0; i < glb_para.shm_para.page_cnt; i++)
- {
- ClearPageReserved(virt_to_page(page_addr));
- page_addr += PAGE_SIZE;
- }
- free_pages(glb_para.shm_para.mem_addr, glb_para.shm_para.order);
- }
- }
- static int __init init_shm_test(void)
- {
- init_glb_para();
- if(init_netlink() < 0)
- {
- SHM_ERR("init_shm_test::init_netlink error.\n";);
- return (-1);
- }
- SHM_DBG("init_netlink ok.\n";);
-
- if(init_shm() < 0)
- {
- SHM_ERR("init_shm_test::init_mem_pool error.\n");
- clean_shm_test();
- return (-1);
- }
- SHM_DBG("init_mem_pool ok.\n");
-
- return (0);
- }
- static void clean_shm_test(void)
- {
- clean_shm();
- clean_netlink();
-
- SHM_DBG("ta_exit ok.\n");
- }
- module_init(init_shm_test);
- module_exit(clean_shm_test);
- MODULE_LICENSE("GPL");
- MODULE_AUTHOR("bripengandre (bripengandre@126.com)");
- MODULE_DESCRIPTION("Memory Share between user-space and kernel-space with netlink.");
- #include <stdio.h>
- #include <sys/socket.h>
- #include <arpa/inet.h>
- #include <linux/netlink.h>
- #include <stdlib.h>
- #include <string.h>
- #include <errno.h>
- #include <sys/types.h>
- #include <unistd.h>
- #include <fcntl.h>
- #include <sys/mman.h>
- #include "common.h"
- /* netlink */
- #define MAX_SEND_BUF_SIZE 2500
- #define MAX_RECV_BUF_SIZE 2500
- #define SHM_TEST_DEBUG
- #ifdef SHM_TEST_DEBUG
- #define SHM_DBG(args...) fprintf(stderr, "SHM_TEST: " args)
- #else
- #define SHM_DBG(args...)
- #endif
- #define SHM_ERR(args...) fprintf(stderr, "SHM_TEST: " args)
- struct _glb_para
- {
- struct _shm_para
- {
- uint32_t mem_addr;
- uint32_t mem_size;
- }shm_para;
-
- int nlk_fd;
- char send_buf[MAX_SEND_BUF_SIZE];
- char recv_buf[MAX_RECV_BUF_SIZE];
- }glb_para;
- static void init_glb_para(void);
- static int create_nlk_connect(void);
- static int nlk_get_shm_info(void);
- static int init_mem_pool(void);
- int main(int argc ,char *argv[])
- {
- char *p;
-
- init_glb_para();
- if(create_nlk_connect() < 0)
- {
- SHM_ERR("main::create_nlk_connect error.\n");
- return (1);
- }
-
- if(nlk_get_shm_info() < 0)
- {
- SHM_ERR("main::nlk_get_shm_info error.\n");
- return (1);
- }
-
- init_mem_pool();
- /* printf the first 30 bytes */
- p = (char *)glb_para.shm_para.mem_addr;
- p[strlen(SHM_WITH_NETLINK)] = '\0';
- printf("the first 30 bytes of shm are: %s\n", p);
-
- return (0);
- }
- static void init_glb_para(void)
- {
- memset(&glb_para, 0, sizeof(glb_para));
- }
- static int create_nlk_connect(void)
- {
- int sockfd;
- struct sockaddr_nl local;
-
- sockfd = socket(PF_NETLINK, SOCK_RAW, SHM_NETLINK);
- if(sockfd < 0)
- {
- SHM_ERR("create_nlk_connect::socket error:%s\n", strerror(errno));
- return (-1);
- }
- memset(&local, 0, sizeof(local));
- local.nl_family = AF_NETLINK;
- local.nl_pid = getpid();
- local.nl_groups = 0;
- if(bind(sockfd, (struct sockaddr*)&local, sizeof(local)) != 0)
- {
- SHM_ERR("create_nlk_connect::bind error: %s\n", strerror(errno));
- return -1;
- }
-
- glb_para.nlk_fd = sockfd;
-
- return (sockfd);
- }
- static int nlk_get_shm_info(void)
- {
- struct nlmsghdr *nlh;
- struct _nlk_msg *p;
- struct sockaddr_nl kpeer;
- int recv_len, kpeerlen;
-
- memset(&kpeer, 0, sizeof(kpeer));
- kpeer.nl_family = AF_NETLINK;
- kpeer.nl_pid = 0;
- kpeer.nl_groups = 0;
-
- memset(glb_para.send_buf, 0, sizeof(glb_para.send_buf));
- nlh = (struct nlmsghdr *)glb_para.send_buf;
- nlh->nlmsg_len = NLMSG_SPACE(0);
- nlh->nlmsg_flags = 0;
- nlh->nlmsg_type = SHM_GET_SHM_INFO;
- nlh->nlmsg_pid = getpid();
- sendto(glb_para.nlk_fd, nlh, nlh->nlmsg_len, 0, (struct sockaddr*)&kpeer, sizeof(kpeer));
- memset(glb_para.send_buf, 0, sizeof(glb_para.send_buf));
- kpeerlen = sizeof(struct sockaddr_nl);
- recv_len = recvfrom(glb_para.nlk_fd, glb_para.recv_buf,sizeof(glb_para.recv_buf), 0, (struct sockaddr*)&kpeer,&kpeerlen);
- p = NLMSG_DATA((struct nlmsghdr *) glb_para.recv_buf);
- SHM_DBG("%d, errno=%d.%s, %08x, %08x\n", recv_len, errno,strerror(errno),p->data.shm_info.mem_addr, p->data.shm_info.mem_size);
- glb_para.shm_para.mem_addr = p->data.shm_info.mem_addr;
- glb_para.shm_para.mem_size = p->data.shm_info.mem_size;
- return (0);
- }
- static int init_mem_pool(void)
- {
- int map_fd;
- void *map_addr;
-
- map_fd = open("/dev/mem", O_RDWR);
- if(map_fd < 0)
- {
- SHM_ERR("init_mem_pool::open %s error: %s\n", "/dev/mem", strerror(errno));
- return (-1);
- }
-
- map_addr = mmap(0, glb_para.shm_para.mem_size, PROT_READ|PROT_WRITE, MAP_SHARED, map_fd, glb_para.shm_para.mem_addr);
- if(map_addr == NULL)
- {
- SHM_ERR("init_mem_pool::mmap error: %s\n", strerror(errno));
- return (-1);
- }
- glb_para.shm_para.mem_addr = (uint32_t)map_addr;
- return (0);
- }
4、Makefile
#PREFIX = powerpc-e300c3-linux-gnu-
CC ?= $(PREFIX)gcc
KERNELDIR ?= /lib/modules/`uname -r`/build
all: modules app
obj-m:= shm_k.o
module-objs := shm_k.c
modules:
make -C $(KERNELDIR) M=`pwd` modules
app: shm_u.o
$(CC) -o shm_u shm_u.c
clean:
rm -rf *.o Module.symvers modules.order shm_u shm_k.ko shm_k.mod.c .tmp_versions .shm_k.*
[ 本帖最后由 bripengandre 于 2009-5-27 10:26 编辑 ] |
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发表于 2009-05-26 21:24
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