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