Yadro rejimi va tizim chaqiruvlari

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

int main(void) {
    /* kutubxonasiz - to'g'ridan-to'g'ri tizim chaqiruvi */
    const char *xabar = "Tizim chaqiruvi orqali yozildi\n";

    ssize_t yozildi = write(STDOUT_FILENO, xabar, strlen(xabar));

    if (yozildi < 0) {
        return 1;
    }

    printf("Yozilgan baytlar: %zd\n", yozildi);
    return 0;
}

#include <stdio.h>
#include <unistd.h>
#include <string.h>

int main(void) {
    /* printf - kutubxona funksiyasi, buferlaydi */
    printf("printf orqali\n");

    /* write - tizim chaqiruvi, darhol yuboradi */
    const char *matn = "write orqali\n";
    write(STDOUT_FILENO, matn, strlen(matn));

    printf("yana printf\n");

    return 0;
}

printf orqali
write orqali
yana printf

./dastur > natija.txt
cat natija.txt

write orqali
printf orqali
yana printf

strace ./salom

execve("./salom", ["./salom"], 0x7ffd...) = 0
brk(NULL)                               = 0x55e4...
openat(AT_FDCWD, "/lib/x86_64-linux-gnu/libc.so.6", O_RDONLY|O_CLOEXEC) = 3
read(3, "\177ELF\2\1\1\3\0\0\0\0\0\0\0\0\3\0>\0\1\0\0\0P\237\2\0\0\0\0\0"..., 832) = 832
mmap(NULL, 2036952, PROT_READ, MAP_PRIVATE|MAP_DENYWRITE, 3, 0) = 0x7f2a...
close(3)                                = 0
write(1, "Salom, dunyo!\n", 14)         = 14
exit_group(0)                           = ?

ls /usr/include/asm-generic/unistd.h && grep -c "^#define __NR_" /usr/include/asm-generic/unistd.h

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <math.h>

int main(void) {
    /* Bular tizim chaqiruvi EMAS - hammasi foydalanuvchi rejimida */
    int uzunlik = (int) strlen("salom");
    double ildiz = sqrt(16.0);
    int *xotira = malloc(100);

    printf("strlen : %d\n", uzunlik);
    printf("sqrt   : %.1f\n", ildiz);
    printf("malloc : %s\n", xotira != NULL ? "muvaffaqiyatli" : "xato");

    free(xotira);
    return 0;
}

#include <stdio.h>
#include <unistd.h>
#include <time.h>

#define MARTA 200000

int main(void) {
    struct timespec boshlandi, tugadi;
    char belgi = 'x';

    /* Bo'sh fayl deskriptoriga yozamiz - /dev/null ga */
    FILE *nol = fopen("/dev/null", "w");

    if (nol == NULL) {
        return 1;
    }

    int fd = fileno(nol);

    /* 1. Har safar tizim chaqiruvi */
    clock_gettime(CLOCK_MONOTONIC, &boshlandi);
    for (int i = 0; i < MARTA; i++) {
        write(fd, &belgi, 1);
    }
    clock_gettime(CLOCK_MONOTONIC, &tugadi);

    double tizim = (double) (tugadi.tv_sec - boshlandi.tv_sec) +
                   (double) (tugadi.tv_nsec - boshlandi.tv_nsec) / 1e9;

    /* 2. Buferlangan yozuv */
    clock_gettime(CLOCK_MONOTONIC, &boshlandi);
    for (int i = 0; i < MARTA; i++) {
        fputc(belgi, nol);
    }
    fflush(nol);
    clock_gettime(CLOCK_MONOTONIC, &tugadi);

    double buferli = (double) (tugadi.tv_sec - boshlandi.tv_sec) +
                     (double) (tugadi.tv_nsec - boshlandi.tv_nsec) / 1e9;

    fclose(nol);

    printf("%d marta yozish tekshirildi\n", MARTA);
    printf("Buferlangan yozuv tezroqmi? %s\n", buferli < tizim ? "ha" : "yo'q");

    /* Aniq vaqtlarni ko'rish uchun quyidagi ikki qatorni yoqing:
    printf("  write (tizim chaqiruvi) : %.6f soniya\n", tizim);
    printf("  fputc (buferlangan)     : %.6f soniya\n", buferli);
    */

    return 0;
}

  write (tizim chaqiruvi) : 0.119500 soniya
  fputc (buferlangan)     : 0.000500 soniya

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

int main(void) {
    int fd = open("/mavjud/emas/fayl.txt", O_RDONLY);

    if (fd < 0) {
        printf("open muvaffaqiyatsiz\n");
        printf("errno   : %d\n", errno);
        printf("Sababi  : %s\n", strerror(errno));
        return 0;
    }

    close(fd);
    return 0;
}

cat /proc/cpuinfo | grep "model name" | head -1
cat /proc/meminfo | head -3
cat /proc/uptime

model name    : Intel(R) Core(TM) i7-10700 CPU @ 2.90GHz
MemTotal:       16283544 kB
MemFree:         7123456 kB
MemAvailable:   11234567 kB
12345.67 8901.23

#include <stdio.h>

int main(void) {
    FILE *f = fopen("/proc/uptime", "r");

    if (f == NULL) {
        printf("Bu misol faqat Linux'da ishlaydi\n");
        return 0;
    }

    double soniya, bosh_vaqt;

    if (fscanf(f, "%lf %lf", &soniya, &bosh_vaqt) == 2) {
        int kun = (int) (soniya / 86400);
        int soat = (int) ((soniya - kun * 86400) / 3600);
        int daqiqa = (int) ((soniya - kun * 86400 - soat * 3600) / 60);

        printf("Tizim ishlash vaqti aniqlandi\n");
        printf("Kun / soat / daqiqa qiymatlari o'qildi: %s\n",
               (kun >= 0 && soat >= 0 && daqiqa >= 0) ? "ha" : "yo'q");
    }

    fclose(f);
    return 0;
}