Skip to content

Instantly share code, notes, and snippets.

@jmoiron

jmoiron/shm_test.c

Created April 2, 2015 20:07
Show Gist options
  • Save jmoiron/ec5329d099dfcf9ce5e7 to your computer and use it in GitHub Desktop.
Save jmoiron/ec5329d099dfcf9ce5e7 to your computer and use it in GitHub Desktop.
Download ZIP

Revisions

  1. jmoiron created this gist Apr 2, 2015.
    109 changes: 109 additions & 0 deletions shm_test.c
    View file
    Original file line number Diff line number Diff line change
    @@ -0,0 +1,109 @@
    #include <stdbool.h>
    #include <stdio.h>
    #include <fcntl.h>
    #include <sys/stat.h>
    #include <sys/mman.h>

    void print_region(char *ptr, size_t len);

    // mark a few locations in a pointer
    void mark(char *ptr, size_t len) {
    int i;
    // do not mark position 0
    for (i=1; i<len; i++) {
    if (!(i%17)) {
    ptr[i] = 1;
    }
    if (!(i%23)) {
    ptr[i] = 2;
    }
    }
    }

    // check for the marks from mark
    bool check(char *ptr, size_t len) {
    int i;
    for (i=1; i<len; i++) {
    if (!(i%17) && (i%23)) {
    if (ptr[i] != 1) {
    return false;
    }
    } else if (!(i%23)) {
    if (ptr[i] != 2) {
    return false;
    }
    } else if (ptr[i] != 0) {
    return false;
    }
    }
    return true;
    }

    int main(int argc, char **argv) {
    int i;
    int fd, ok, max;
    char *ptr;

    shm_unlink("/test");

    // create new shm
    fd = shm_open("/test", O_CREAT|O_RDWR|O_TRUNC, 0);
    if (fd < 0) {
    perror("could not create shm_open fd");
    return;
    }

    // make shm 1k
    ok = ftruncate(fd, 1024);

    if (ok < 0) {
    perror("initial ftruncate");
    goto done;
    }

    ptr = (char *)mmap(NULL, 1024, PROT_READ|PROT_WRITE, MAP_SHARED, fd, 0);
    if (ptr == MAP_FAILED) {
    printf("fd: %d\n", fd);
    perror("map failed");
    goto done;
    }

    mark(ptr, 1024);
    if (!check(ptr, 1024)) {
    printf("region failed check");
    goto done;
    }

    max = 1024*1024;
    printf("checking from size=1024 to size=%d\n", max);
    for (i=2; i<=max/1024; i*=2) {
    int size=1024*i;

    ok = ftruncate(fd, size);
    if (ok < 0) {
    perror("second ftruncate");
    goto done;
    }

    ptr = (char *)mmap(NULL, size, PROT_READ|PROT_WRITE, MAP_SHARED, fd, 0);

    if (!check(ptr, size/2)) {
    printf("region failed check; mmap overwrote?");
    goto done;
    }

    if (check(ptr, size)) {
    printf("newly mapped region unexpectedly passed check");
    goto done;
    }

    mark(ptr, size);
    if (!check(ptr, size)) {
    printf("region failed check");
    goto done;
    }
    }

    done:
    shm_unlink("/test");
    }