why does pmem_is_pmem return false

[zaorangyang]

QUESTION: why does pmem_is_pmem return false

Details

I use the library named libpmem to handle AEP on the machine powered by centos7.2. Both pmem_is_pmem and pmem_map_file can't recongnize the device is a pmem device.

test code

/*
 * simple_copy.c
 *
 * usage: simple_copy src-file dst-file
 *
 * Reads 4k from src-file and writes it to dst-file.
 */

#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <stdio.h>
#include <errno.h>
#include <stdlib.h>
#ifndef _WIN32
#include <unistd.h>
#else
#include <io.h>
#endif
#include <string.h>
#include <libpmem.h>

/* Just copying 4K to pmem for this example */
#define BUF_LEN 4096

int
main(int argc, char *argv[])
{
    int srcfd;
    char buf[BUF_LEN];
    char *pmemaddr;
    size_t mapped_len;
    int is_pmem;
    int cc;

    if (argc != 3) {
        fprintf(stderr,
            "usage: %s src-file dst-file\n", argv[0]);
        exit(1);
    }

    /* open src-file */
    if ((srcfd = open(argv[1], O_RDONLY)) < 0) {
        perror(argv[1]);
        exit(1);
    }

    /* create a pmem file and memory map it */
    if ((pmemaddr = pmem_map_file(argv[2], BUF_LEN,
            PMEM_FILE_CREATE|PMEM_FILE_EXCL,
            0666, &mapped_len, &is_pmem)) == NULL) {
        perror("pmem_map_file");
        exit(1);
    }

        printf("IS_PMEM: %d\n", pmem_is_pmem(pmemaddr, BUF_LEN));

    /* read up to BUF_LEN from srcfd */
    if ((cc = read(srcfd, buf, BUF_LEN)) < 0) {
        pmem_unmap(pmemaddr, mapped_len);
        perror("read");
        exit(1);
    }

    /* write it to the pmem */
    if (is_pmem) {
        printf("Yes, it's pmem!\n");
        pmem_memcpy_persist(pmemaddr, buf, cc);
    } else {
        printf("No, it's not pmem!\n");
        memcpy(pmemaddr, buf, cc);
        pmem_msync(pmemaddr, cc);
    }

    close(srcfd);
    pmem_unmap(pmemaddr, mapped_len);

    exit(0);
}

result

[pbalcer]

libpmem requires that the underlying linux kernel supports MAP_SYNC for pmem_is_pmem to return true on fsdax.

[zaorangyang]

Thank you