LINUX 64位下運行32位程序加載和讀取大數據段共享內存

1. 查看當前機器共享內存
1073741824 = 1024 * 1024 * 1024
[root@six shm]# ipcs

------ Semaphore Arrays --------
key        semid      owner      perms      nsems
0x00000000 0          root       600        1
0x00000000 32769      root       600        1
0x00000000 65538      apache     600        1
0x00000000 98307      apache     600        1
0x00000000 131076     apache     600        1

------ Message Queues --------
key msqid owner perms used-bytes messages

共享內存無我們加載的數據，正常。

2 修改需要被加載的文件,指定文件任意位置(1G)修改爲隨機指定的內容
[root@six shm]# ./modifyfile bigdatafile.dat 1073741824 ABCD1234567890END
read content=ABCD1234567890END,17

3 把大文件bigdatafile.dat(1.11G)加載到共享內存,一個進程一次加載兩個,共加載3次
[root@six shm]# ./fileload mykey1 mykey2 bigdatafile.dat
Usage: mykey1 KeyFile
e.g. srcfile:bigdatafile.dat
Key generated by ftok: 0x64030017
shaddr:0xb0109000,length:1198011173
Usage: mykey2 KeyFile
e.g. srcfile:bigdatafile.dat
Key generated by ftok: 0x64030018
shaddr:0x68a85000,length:1198011173
[root@six shm]# ./fileload mykey3 mykey4 bigdatafile.dat
Usage: mykey3 KeyFile
e.g. srcfile:bigdatafile.dat
Key generated by ftok: 0x6403000d
shaddr:0xb0134000,length:1198011173
Usage: mykey4 KeyFile
e.g. srcfile:bigdatafile.dat
Key generated by ftok: 0x6403000e
shaddr:0x68ab0000,length:1198011173
[root@six shm]# ./fileload mykey5 mykey6 bigdatafile.dat
Usage: mykey5 KeyFile
e.g. srcfile:bigdatafile.dat
Key generated by ftok: 0x6403001b
shaddr:0xb014b000,length:1198011173
Usage: mykey6 KeyFile
e.g. srcfile:bigdatafile.dat
Key generated by ftok: 0x6403001c
shaddr:0x68ac7000,length:1198011173

4 加載完成，查看有 6.6G的共享內存申請
[root@six shm]# ipcs

------ Shared Memory Segments --------
key        shmid      owner      perms      bytes      nattch     status
0x00000000 0          gdm        600        393216     2          dest
0x00000000 32769      gdm        600        393216     2          dest
0x00000000 65538      gdm        600        393216     2          dest
0x64030017 589827     root       0          1198011173 0
0x64030018 622596     root       0          1198011173 0
0x6403000d 655365     root       0          1198011173 0
0x6403000e 688134     root       0          1198011173 0
0x6403001b 720903     root       0          1198011173 0
0x6403001c 753672     root       0          1198011173 0

------ Message Queues --------
key msqid owner perms used-bytes messages

5 根據設定偏移量多次組合讀取共享內存裏面的數據,驗證是否一致,結論：和修改的一致。
[root@six shm]# ./memread mykey1 mykey2 1073741824 15
Key generated by ftok: 0x64030017
buff:ABCD1234567890E
Key generated by ftok: 0x64030018
buff:ABCD1234567890E
[root@six shm]# ./memread mykey1 mykey2 1073741824 10
Key generated by ftok: 0x64030017
buff:ABCD123456
Key generated by ftok: 0x64030018
buff:ABCD123456
[root@six shm]# ./memread mykey1 mykey6 1073741824 17
Key generated by ftok: 0x64030017
buff:ABCD1234567890END
Key generated by ftok: 0x6403001c
buff:ABCD1234567890END
[root@six shm]# ./memread mykey1 mykey2 1073741827 14
Key generated by ftok: 0x64030017
buff:D1234567890END
Key generated by ftok: 0x64030018
buff:D1234567890END
[root@six shm]# ./memread mykey3 mykey5 1073741825 10
Key generated by ftok: 0x6403000d
buff:BCD1234567
Key generated by ftok: 0x6403001b
buff:BCD1234567

6 測試環境
測試程序在LINUX 32位開發機編譯完成,運行驗證在LINUX 64 上通過。

7. fileload.c 代碼
#include <stdio.h>
#include <sys/ipc.h>
#include <sys/shm.h>
#include <string.h>
#include <stdlib.h>
#define PROJ_ID 100

const char * loadfile(char *keyfile, char* srcfile)
{
     printf("Usage: %s KeyFile\n e.g. srcfile:%s\n", keyfile, srcfile);
     key_t key = ftok(keyfile, PROJ_ID);
     printf("Key generated by ftok: 0x%x\n",key);
     FILE * fp = fopen(srcfile,"rb");
     if(fp == NULL)
     {
          printf("open file fail\n");
          return NULL;
     }
     fseek(fp,0,SEEK_END);
     size_t length = ftell(fp);

     //get share memory
     int shmid = shmget(key,length,IPC_CREAT|IPC_EXCL);
     if(shmid < 0)
     {
         fclose(fp);
         perror("shmget fail");
         return NULL;
     }
     void *shmaddr = (char *)shmat(shmid,0,0);
     if(shmaddr == (char *)(-1))
     {
          fclose(fp);
          perror("shmat fail");
          return NULL;
     }
     #define LOADBUFF 1024 * 8
     fseek(fp,0,SEEK_SET);
     size_t count = length/LOADBUFF;
     size_t offset = 0,i = 0;
     for(i = 0;i < count;++i)
     {
         char buff[LOADBUFF] = {0};
         size_t onceread = 0;
         onceread = fread(buff,1,LOADBUFF,fp);
         if(onceread <= 0 )
         {
             if(ferror(fp) > 0)
             {
                 fclose(fp);
                 shmdt(shmaddr);
                 shmctl(shmid,IPC_RMID,0);
                 printf("fread fail,error\n");
                 return NULL;
             }
         }
         else
         {
             memcpy(shmaddr + offset,buff,onceread);
             offset += onceread;
         }
     }
     fclose(fp);

     printf("shaddr:%p,length:%u\n",shmaddr,length);
     /*
     if(0 > shmdt(shmaddr))
     {
         free(buff);
         perror("shmdt fail");
         return 5;
     }
     */
     return shmaddr;
}

int main(int argc, char* argv[])
{
    if (argc != 4 )
     {
        printf("Usage: %s KeyFile\n e.g. %s /tmp/mykeyfile\n", argv[0], argv[0]);
        return 0;
     }

     loadfile(argv[1],argv[3]);
     loadfile(argv[2],argv[3]);
    return 0;
}

8. modifyfile.c 代碼
#include <stdio.h>
#include <unistd.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <sys/ipc.h>
#include <sys/shm.h>
#include <string.h>
#include <stdlib.h>
#define PROJ_ID 100

const char * modifyfile(char *srcfile, size_t offset,char* content)
{
     int fp = open(srcfile,O_WRONLY);
     if(fp == -1)
     {
          perror("open file fail\n");
          return NULL;
     }
     size_t length = strlen(content);
     lseek(fp,offset,SEEK_SET);
     if(length != write(fp,content,length))
     {
          perror("modify fail");
          close(fp);
          return NULL;
     }
     close(fp);
     fp = open(srcfile,O_RDONLY);
     char buff[8192] = {0};
     lseek(fp,offset,SEEK_SET);
     length = read(fp,buff,length);
     printf("read content=%s,%u\n",buff,length);
     close(fp);
     return NULL;
}

int main(int argc, char* argv[])
{
    if (argc != 4 )
     {
        printf("Usage: %s KeyFile\n e.g. %s /tmp/mykeyfile\n", argv[0], argv[0]);
        return 0;
     }

     modifyfile(argv[1],atoi(argv[2]),argv[3]);
     return 0;
}

9. memread.c 代碼
#include <stdio.h>
#include <sys/ipc.h>
#include <sys/shm.h>
#include <string.h>
#include <stdlib.h>
#define PROJ_ID 100

int readsharememory(char *keyfile,size_t offset,size_t length)
{
     char buff[8192] = {0};
     if(sizeof(buff) < length)
     {
         printf("length too length\n");
         return 1;
     }
     key_t key = ftok(keyfile, PROJ_ID);
     printf("Key generated by ftok: 0x%x\n",key);

     int shmid = shmget(key,0,IPC_CREAT);
     if(shmid < 0)
     {
         perror("shmget fail");
         return 4;
     }

     char *shmaddr = (char *)shmat(shmid,0,SHM_RDONLY);
     if(shmaddr == (char *)(-1))
     {
          perror("shmat fail");
          return 5;
     }

     memcpy(buff,shmaddr + offset,length);
     if(0 > shmdt(shmaddr))
     {
         perror("shmdt fail");
         return 5;
     }

     printf("buff:%s\n",buff);
     return 0;
}

int main(int argc, char* argv[])
{
    if (argc != 5 )
     {
        printf("Usage: %s KeyFile\n e.g. %s /tmp/mykeyfile\n", argv[0], argv[0]);
        return 0;
     }
     readsharememory(argv[1],atoi(argv[3]),atoi(argv[4]));
     readsharememory(argv[2],atoi(argv[3]),atoi(argv[4]));
     return 0;
}

10. share_ctl.c 代碼，用於管理共享內存
#include <stdio.h>
#include <sys/ipc.h>
#include <sys/shm.h>
#include <string.h>
#include <stdlib.h>
#include <sys/types.h>
#include <unistd.h>

#define PROJ_ID 100

int delsharememory(char *keyfile)
{
     printf("Usage: %s KeyFile\n", keyfile);
     key_t key = ftok(keyfile, PROJ_ID);
     printf("Key generated by ftok: 0x%x\n",key);

     int shmid = shmget(key,0,IPC_CREAT);
     if(shmid < 0)
     {
         perror("shmget fail");
         return 4;
     }

     if(-1 == shmctl(shmid,IPC_RMID,0))
     {
          perror("shctl del fail");
          return 5;
     }

     return 0;
}

int getsharememory(char *keyfile)
{
     printf("Usage: %s KeyFile\n", keyfile);
     key_t key = ftok(keyfile, PROJ_ID);
     printf("Key generated by ftok: 0x%x\n",key);

     int shmid = shmget(key,0,IPC_CREAT);
     if(shmid < 0)
     {
         perror("shmget fail");
         return 4;
     }

     struct shmid_ds buf;
     if(-1 == shmctl(shmid,IPC_STAT,&buf))
     {
          perror("shctl del fail");
          return 5;
     }
     printf("shm_segsz =%d bytes\n", buf.shm_segsz);
     printf("parent pid=%d, shm_cpid = %d \n",getppid(),buf.shm_cpid);
     printf("chlid pid=%d, shm_lpid = %d \n",getpid(),buf.shm_lpid);

return 0;
}

int main(int argc, char* argv[])
{
    if (argc != 3 )
     {
        printf("Usage: %s KeyFile CMD(SHOW OR DEL)\n e.g. %s /tmp/mykeyfile\n", argv[0], argv[0]);
        return 0;
     }
     if(strcmp(argv[2],"SHOW") == 0)
     {
         getsharememory(argv[1]);
     }

     if(strcmp(argv[2],"DEL") == 0)
     {
        delsharememory(argv[1]);
     }
     return 0;
}

11. ftok.c 用於創建共享內存
#include <stdio.h>
#include <sys/ipc.h>
#define PROJ_ID 100

int main(int argc, char* argv[])
{
    if (argc !=2 )
     {
printf("Usage: %s KeyFile\n e.g. %s /tmp/mykeyfile\n", argv[0], argv[0]);
return 0;
     }
     printf("Key generated by ftok: 0x%x\n", ftok(argv[1], PROJ_ID));
     return 0;
}

12. 測試準備
創建6個key 文件
touch mykey1
touch mykey2
touch mykey3
touch mykey4
touch mykey5
touch mykey6
準備一個大數據文件(1G),名字命名爲 : bigdatafile.dat
就可以按上面的步驟測試了。

13. 結論，只要 32 位程序不突破4G的進程最大地址空間，可以掛接其他的任何文件，任何共享
內存區域，和mmap 類似。

14. 公共文件(shm_file.h)

#ifndef _C_LOADFILE_INCLUDE_H_
#define _C_LOADFILE_INCLUDE_H_

//根據文件名構造共享內存段,把文件內容加載到共享內存,返回共享內存首地址
const char * loadfile2shm(const char * filename);

//根據文件名獲取到共享內存首地址(只讀)
const char * getaddressbyname(const char * filename);

#endif

15. 公共文件(shm_file.c)

#include <assert.h>
#include <sys/ipc.h>
#include <sys/shm.h>
#include <string.h>
#include <stdlib.h>
#include <unistd.h>
#include <stdio.h>

#include "shm_file.h"

#define KEYSUFFIX ".key"
#define PROJ_ID 100
#define LOADBUFF 1024 * 8

const char * loadfile2shm(const char * filename)
{
assert(filename != NULL);

char *shmaddr = NULL;
char keyfile[255] = {0};
snprintf(keyfile,sizeof(keyfile) - 1,"%s%s",filename,KEYSUFFIX);
if(0 != access(keyfile,F_OK|R_OK) || 0 != access(filename,F_OK|R_OK))
{
  return shmaddr;
}
key_t key = -1;
if(-1 == (key = ftok(keyfile, PROJ_ID)))
{
  return shmaddr;
}

    FILE * fp = fopen(filename,"rb");
    if(fp == NULL)
    {
    return shmaddr;
    }
    fseek(fp,0,SEEK_END);
    size_t length = 0;
    if(0 >= (length = ftell(fp)))
    {
    fclose(fp);
        //perror("shmget fail");
        return shmaddr;
    }

    //get share memory
    int shmid = shmget(key,length,IPC_CREAT|IPC_EXCL|0600);
    if(shmid < 0)
    {
    fclose(fp);
        //perror("shmget fail");
        return shmaddr;
    }
    //寫打開,地址OS動態分配
    shmaddr = (char *)shmat(shmid,0,0);
    if(shmaddr == (char *)(-1))
    {
    fclose(fp);
        //perror("shmat fail");
        return shmaddr;
    }
    fseek(fp,0,SEEK_SET);

    size_t total = 0,offset = 0,i = 0;
    total = length/LOADBUFF + 1;
    for(i = 0;i < total;++i)
    {
    char buff[LOADBUFF] = {0};
        size_t onceread = 0;
        onceread = fread(buff,1,LOADBUFF,fp);
        if(onceread <= 0 )
        {
        if(ferror(fp) > 0)
            {
            fclose(fp);
                shmdt(shmaddr);
                shmctl(shmid,IPC_RMID,0);
                shmaddr = NULL;
                //printf("fread fail,error\n");
                return shmaddr;
            }
            else
            {
            //feof
            }
        }
        else
        {
            memcpy(shmaddr + offset,buff,onceread);
            offset += onceread;
        }
    }
    fclose(fp);
    return shmaddr;
}

const char * getaddressbyname(const char * filename)
{
assert(filename != NULL);

char *shmaddr = NULL;
char keyfile[255] = {0};
snprintf(keyfile,sizeof(keyfile) - 1,"%s%s",filename,KEYSUFFIX);
if(0 != access(keyfile,F_OK|R_OK))
{
  return shmaddr;
}
key_t key = -1;
if(-1 == (key = ftok(keyfile, PROJ_ID)))
{
  return shmaddr;
}

int shmid = shmget(key,0,IPC_CREAT);
    if(shmid < 0)
    {
    //perror("shmget fail");
    return shmaddr;
    }

    shmaddr = (char *)shmat(shmid,0,SHM_RDONLY);
    if(shmaddr == (char *)(-1))
    {
    //perror("shmat fail");
        return shmaddr;
    }

    return shmaddr;
}