Ticket #18733: mmap_private_mprotect.cpp

#include <errno.h>
#include <fcntl.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/mman.h>
#include <unistd.h>
#include <OS.h>

int
main()
{
    // This file should be larger than available RAM.
    const char* fileName = "/tmp/mmap-test-file";

    printf("opening file...\n");
    int fd = open(fileName, O_RDONLY);
    if (fd < 0) {
        fprintf(stderr, "Failed to open \"%s\": %s\n", fileName,
            strerror(errno));
        exit(1);
    }

    off_t fsize = lseek(fd, 0, SEEK_END);
    fprintf(stderr, "File size: %" B_PRIuSIZE "\n", fsize);

    // map
    printf("mapping file...\n");
    void* address = mmap(NULL, fsize, PROT_READ, MAP_PRIVATE, fd, 0);
    if (address == MAP_FAILED) {
        fprintf(stderr, "Failed to map the file: %s\n", strerror(errno));
        exit(1);
    }

    // remap writable (should fail, not enough memory)
    if (mprotect(address, fsize, PROT_WRITE) >= 0) {
        fprintf(stderr, "Unexpected success on mprotect!");
        exit(1);
    }

    // remap just one part writable (should work)
    if (mprotect(address, B_PAGE_SIZE, PROT_READ | PROT_WRITE) < 0) {
        fprintf(stderr, "Failed to protect first page: %s\n", strerror(errno));
        exit(1);
    }
    if (mprotect(address, B_PAGE_SIZE, PROT_READ) < 0) {
        fprintf(stderr, "Failed to unprotect page: %s\n", strerror(errno));
        exit(1);
    }
    if (mprotect(address, B_PAGE_SIZE * 10, PROT_READ | PROT_WRITE) < 0) {
        fprintf(stderr, "Failed to protect multiple pages: %s\n", strerror(errno));
        exit(1);
    }

    return 0;
}