Webscale writes!

webscale.c

#include <fcntl.h>
#include <stdio.h>
#include <string.h>
#include <sys/mman.h>
#include <sys/time.h>

#define SAMPLES 10000

int
main()
{
    void* dest = NULL;
    size_t len = 1024;
    size_t pos = 0;
    int prot = PROT_READ | PROT_WRITE;
    int flags = MAP_FILE | MAP_PRIVATE;
    
    unsigned char* buf[1024];
    ssize_t bread;
    // Unfortunately mmaping /dev/null fails. :(
    //int fd = open("/dev/null", O_RDWR);
    int fd = open("foo", O_RDWR | O_CREAT, S_IRUSR | S_IWUSR);

    int count;
    unsigned long samples[SAMPLES];
    double rate;
    struct timeval before;
    struct timeval after;
    int i;

    if(fd < 0) {
        perror("foo");
        fprintf(stderr, "Failed to open webscale portal.\n");
        goto done;
    }

    if(ftruncate(fd, len) != 0) {
        fprintf(stderr, "Failed to initialize webscale portal.\n");
        goto done;
    }

    dest = mmap(NULL, len, prot, flags, fd, 0);
    if(dest == NULL) {
        fprintf(stderr, "Failed to map webscale portal.\n");
        goto done;
    }

    fprintf(stderr, "Webscale writes!\n");
    count = 0;
    do {
        gettimeofday(&before, NULL);
        bread = fread(buf, 1, 1024, stdin);
        if(pos + bread > len) {
            memcpy(dest+pos, buf, len-pos);
            pos = (len-pos);
            memcpy(dest, buf+pos, bread-pos);
        } else if(bread > 0) {
            memcpy(dest+pos, buf, bread);
            pos += bread;
        }
        gettimeofday(&after, NULL);
        count = (count + 1) % SAMPLES;
        samples[count] = (after.tv_sec * 1000000 + after.tv_usec) -
                            (before.tv_sec * 1000000 + before.tv_usec);
        rate = 0.0;
        for(i = 0; i < SAMPLES; i++) {
            rate += (double) samples[i] / 1000000.0;
        }
        rate = (SAMPLES * 1024.0) / rate;
        rate /= (1024.0 * 1024.0);
        if(count == 0) {
            fprintf(stderr, "                  \r%0.2f Mib/s", rate);
        }
    } while(bread > 0);

done:
    if(fd >= 0) close(fd);
    fprintf(stderr, "\n");
}