Ticket #4106: mmap_zero_test.cpp

#include <sys/mman.h>
#include <sys/stat.h>
#include <sys/types.h>

#include <errno.h>
#include <fcntl.h>
#include <stdio.h>
#include <string.h>


static const int skDataLen = 4096;
static const int skTruncatedLen = 3766;
    // just anything smaller than skDataLen, to leave a gap in the last page
static char testData[skDataLen];


int
main()
{
    int fileDes = open("mmap_zero_test.data", O_CREAT | O_RDWR | O_TRUNC);
    if (fileDes == -1) {
        fprintf(stderr, "unable to create test-file - errno=%x\n", errno);
        return 1;
    }

    memset(testData, 'x', skDataLen);

    ssize_t bytesWritten = write(fileDes, testData, skDataLen);
    if (bytesWritten < 0) {
        fprintf(stderr, "unable to write data - errno=%x\n", errno);
        return 1;
    }
    if (bytesWritten != skDataLen) {
        fprintf(stderr, "wrote only %d bytes instead of %d\n", bytesWritten,
            skDataLen);
        return 1;
    }

    int res = ftruncate(fileDes, skTruncatedLen);
    if (res == -1) {
        fprintf(stderr, "unable to set size of file - errno=%x\n", errno);
        return 1;
    }

    void* pa 
        = mmap(NULL, skTruncatedLen + 1, PROT_READ, MAP_PRIVATE, fileDes, 0);
    if (pa == NULL) {
        fprintf(stderr, "unable to mmap the file - errno=%x\n", errno);
        return 1;
    }
    
    int mappedStrLen = strlen((char*)pa);
    if (mappedStrLen != skTruncatedLen) {
        fprintf(stderr, "mapped string length is %d bytes instead of %d\n", 
            mappedStrLen, skTruncatedLen);
        return 1;
    }

    return 0;
}