PMDK libpmemobj 例程1 读写持久化内存

版权声明： https://blog.csdn.net/qccz123456/article/details/81877218

(1) write and read the persistent memory
Key :
PMEMobjpool pmemobj_create() // 创建持久化内存池
PMEMobjpool pmemobj_open() // 打开已创建的持久化内存池
PMEMoid pmemobj_root() // 得到持久化内存池的根节点
pmemobj_direct() // 得到根节点的指针
pmemobj_persist() // 将单变量进行持久化存储
pmemobj_memcpy_persist() // 将数组等变量进行持久化存储
pmemobj_close() // 关闭内存池

write the persistent memory

#include <stdio.h>
#include <string.h>
#include <libpmemobj.h>

#define LAYOUT_NAME "intro_1"
#define MAX_BUF_LEN 10

struct my_root {
    size_t len;
    char buf[MAX_BUF_LEN];
};

int main(int argc, char *argv[])
{
    if (argc != 2) {
        printf("usage: %s file-name\n", argv[0]);
        return 1;
    }
    // 创建持久化的内存池
    PMEMobjpool *pop = pmemobj_create(argv[1], LAYOUT_NAME, PMEMOBJ_MIN_POOL, 0666);
    if (pop == NULL) {
        perror("pmemobj_create");
        return 1;
    }
    // 从内存池中得到对应数据结构的根节点，并得到该根节点的指针
    PMEMoid root = pmemobj_root(pop, sizeof(struct my_root));
    struct my_root *rootp = pmemobj_direct(root);

    char buf[MAX_BUF_LEN] = {0};
    if (scanf("%9s", buf) == EOF) {
        fprintf(stderr, "EOF\n");
        return 1;
    }
    // 将数据写入根节点对应的地址，以实现持久化:
    // 此处 rootp->len 变量采用 pmemobj_persist() 持久化，
    // 而数组 rootp->buf 采用 pmemobj_memcpy_persist 持久化
    rootp->len = strlen(buf);
    pmemobj_persist(pop, &rootp->len, sizeof(rootp->len));
    pmemobj_memcpy_persist(pop, rootp->buf, buf, rootp->len);

    pmemobj_close(pop);

    return 0;
}

read the persistent memory

#include <stdio.h>
#include <string.h>
#include <libpmemobj.h>

#define LAYOUT_NAME "intro_1"
#define MAX_BUF_LEN 10

struct my_root {
    size_t len;
    char buf[MAX_BUF_LEN];
};

int main(int argc, char *argv[])
{   
    if (argc != 2) {
        printf("usage: %s file-name\n", argv[0]);
        return 1;
    }
    // 打开对应已完成持久化的文件
    PMEMobjpool *pop = pmemobj_open(argv[1], LAYOUT_NAME);
    if (pop == NULL) {
        perror("pmemobj_open");
        return 1;
    }
    // 从内存池中得到对应数据结构的根节点，并得到该根节点的指针
    PMEMoid root = pmemobj_root(pop, sizeof(struct my_root));
    struct my_root *rootp = pmemobj_direct(root);

    if (rootp->len == strlen(rootp->buf))
        printf("%s\n", rootp->buf);

    pmemobj_close(pop);

    return 0;
}

运行结果如下，此处需要存下rootp->len，是因为防止rootp->buf刷入持久化设备的不一致性，导致数据的不完成，可通过len来判断数据是否完整：

$ ./writer pmem.001
qazxswedc
$ ls
pmem.001  reader  writer
$ ./reader pmem.001 
qazxswedc

写入的pmem.001文件，还可以通过pmempool命令查看数据，依据struct my_root的数据结构，前64字节size_t存储的是len，而后10字节存储数据：

$ pmempool info -d pmem.001 -o
Part file:
path                     : /home/eagle/pmdk/pmdk/src/examples/libpmemobj/string_store/pmem.001
type                     : regular file
size                     : 8388608

POOL Header:
Signature                : PMEMOBJ
Major                    : 4
Mandatory features       : 0x0
Not mandatory features   : 0x0
Forced RO                : 0x0
Pool set UUID            : b5edcde7-6e9b-4331-8e05-a046a060fef5
UUID                     : 174b0bc8-9e32-4be1-884f-d2312949ff2d
Previous part UUID       : 174b0bc8-9e32-4be1-884f-d2312949ff2d
Next part UUID           : 174b0bc8-9e32-4be1-884f-d2312949ff2d
Previous replica UUID    : 174b0bc8-9e32-4be1-884f-d2312949ff2d
Next replica UUID        : 174b0bc8-9e32-4be1-884f-d2312949ff2d
Creation Time            : Mon Aug 20 2018 21:24:10
Alignment Descriptor     : 0x000007f737777310[OK]
Class                    : 64
Data                     : 2's complement, little endian
Machine                  : AMD X86-64
Last shutdown            : clean
Checksum                 : 0x8105f1bce574bcad [OK]

PMEM OBJ Header:
Layout                   : intro_1
Lanes offset             : 0x2000
Number of lanes          : 1024
Heap offset              : 0x302000
Heap size                : 5234688
Checksum                 : 0x7aedc89172d611d8 [OK]
Root offset              : 0x3c0550

Root object:
Offset                   : 0x00000000003c0550
Size                     : 24
003c0550  09 00 00 00 00 00 00 00  71 61 7a 78 73 77 65 64  |........qazxswed|
003c0560  63 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  |c...............|
003c0570  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  |................|
*
003c05c0  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  |................|
------------------------------------------------------------------------------

参考文献：http://pmem.io/2015/06/13/accessing-pmem.html

（1）只能 pmemobj_persist(&root->u64var, 8); 而不能 pmemobj_persist(&root->u64var, 12);
only 8 bytes of memory can be written in an atomic way