Aim Wang

2024/04/18

[C] chek cpu endian

#include <stdint.h>

static uint8_t is_little_endian(void)
{
    uint16_t value = 0x0001;
    uint8_t *byte_ptr = (uint8_t *)&value;
    return (*byte_ptr == 0x01); // If the system is little endian, the least significant byte is 0x01.
}

2024/04/09

[C] Create a folder even if the parent folder does not exist.

static int my_dirname(char *path) {
    char *p = strrchr(path, '/');
    if (p == NULL || p == path) {
        return -1;
    }
    *p = '\0';
    return 0;
}

static int my_mkdir(char *path) {
    struct  stat    st;
    char            p[128];
    char            l[128];

    mkdir(path, 0775);
    while ((stat(path, &st) != 0)) {
        memset(p, 0, 128);
        memcpy(p, path, strlen(path));
        if (0 != my_dirname(p)) {
            return (-1);
        }
        while ((stat(p, &st) != 0)) {
            memset(l, 0, 128);
            memcpy(l, p, strlen(p));  // save the last not exist parent path.
            if (0 != my_dirname(p)) {
                return (-1);
            }
        }
        mkdir(l, 0775);
        if (stat(l, &st) != 0) {
            return (-1);
        }
        mkdir(path, 0775);
    }
    return (0);
}

2023/06/20

Use tc and netem to simulate network delay, jitter and packet loss.

netem relies on kernel module:
CONFIG_IFB
CONFIG_NET_SCHED
CONFIG_NET_SCH_NETEM.

tc qdisc add dev br-lan root handle 1: htb

This will create a root qdisc on the br-lan interface for htb

tc class add dev br-lan parent 1: classid 1:1 htb rate 1000mbit
tc qdisc add dev br-lan parent 1:1 netem delay 100ms 10ms
tc filter add dev br-lan parent 1:0 protocol ip u32 match ip sport 5101 0xffff flowid 1:1

Create a class 1:1 under 1: of br-lan and set the speed limit to 1000bps.
For class 1:1 set its netem to delay 100ms and jitter 10ms.
Direct the packet with src port 5101 of the br-lan interface to class 1:1.

tc class add dev br-lan parent 1: classid 1:2 htb rate 1000mbit
tc qdisc add dev br-lan parent 1:2 netem loss 0% duplicate 0% delay 30ms 20ms
tc filter add dev br-lan parent 1:0 protocol ip u32 match ip sport 5001 0xffff flowid 1:2

Create a class 1:2 under 1: of br-lan and set the speed limit to 1000bps.
For class 1:2 set its netem to loss 0%, duplicate 0%, delay 30ms and jitter 20ms.
Direct the packet with src port 5001 of the br-lan interface to class 1:2.

2023/04/21

[C] 16進制字串與 byte 陣列戶轉

Convert between hex string and byte array.

以空間換取時間, 盡量減少計算跟比較.

static uint8_t HEX_VALUE[256] = {
//  x0 x1 x2 x3 x4 x5 x6 x7   x8 x9 xA xB xC xD xE xF
     0, 0, 0, 0, 0, 0, 0, 0,   0, 0, 0, 0, 0, 0, 0, 0,  // 0x
     0, 0, 0, 0, 0, 0, 0, 0,   0, 0, 0, 0, 0, 0, 0, 0,  // 1x
     0, 0, 0, 0, 0, 0, 0, 0,   0, 0, 0, 0, 0, 0, 0, 0,  // 2x
     0, 1, 2, 3, 4, 5, 6, 7,   8, 9, 0, 0, 0, 0, 0, 0,  // 3x
     0,10,11,12,13,14,15, 0,   0, 0, 0, 0, 0, 0, 0, 0,  // 4x
     0, 0, 0, 0, 0, 0, 0, 0,   0, 0, 0, 0, 0, 0, 0, 0,  // 5x
     0,10,11,12,13,14,15, 0,   0, 0, 0, 0, 0, 0, 0, 0,  // 6x
     0, 0, 0, 0, 0, 0, 0, 0,   0, 0, 0, 0, 0, 0, 0, 0,  // 7x
     0, 0, 0, 0, 0, 0, 0, 0,   0, 0, 0, 0, 0, 0, 0, 0,  // 8x
     0, 0, 0, 0, 0, 0, 0, 0,   0, 0, 0, 0, 0, 0, 0, 0,  // 9x
     0, 0, 0, 0, 0, 0, 0, 0,   0, 0, 0, 0, 0, 0, 0, 0,  // Ax
     0, 0, 0, 0, 0, 0, 0, 0,   0, 0, 0, 0, 0, 0, 0, 0,  // Bx
     0, 0, 0, 0, 0, 0, 0, 0,   0, 0, 0, 0, 0, 0, 0, 0,  // Cx
     0, 0, 0, 0, 0, 0, 0, 0,   0, 0, 0, 0, 0, 0, 0, 0,  // Dx
     0, 0, 0, 0, 0, 0, 0, 0,   0, 0, 0, 0, 0, 0, 0, 0,  // Ex
     0, 0, 0, 0, 0, 0, 0, 0,   0, 0, 0, 0, 0, 0, 0, 0   // Fx
};

static uint8_t HEX_CHAR[16] = {
    '0', '1', '2', '3', '4', '5', '6', '7', '8', '9', 'a', 'b', 'c', 'd', 'e', 'f'
};

void bytes2hex(uint8_t* src, char* dest, uint8_t srcsize) {
    uint8_t flag;
    uint8_t pos;

    flag = 0;
    pos = 0;
    while (srcsize--) {
        if (flag || src[srcsize]) {
            dest[pos++] = HEX_CHAR[src[srcsize]>>4];
            dest[pos++] = HEX_CHAR[src[srcsize]&0xf];
        }
    }
}

void hex2bytes(char *src, uint8_t* dest, uint8_t destsize) {
    uint8_t     len;
    uint8_t     pos;
    uint8_t     hilo;
    uint8_t     byte;
    uint8_t     lohi[2];
    char       *cptr;

    len = strlen(src);
    if (len > (destsize* 2)) {
        return;
    }
    cptr = src + len;
    pos = 0;
    ++len;
    while (len) {
        memset(lohi, 0, 2);
        hilo = 2;
        while (hilo-- && --len) {
            lohi[hilo] = HEX_VALUE[*--cptr];
        }
        dest[pos++] = lohi[1] | (lohi[0] << 4);
    }

    return;
}

2023/03/16

Docker 筆記

列出所有 container

docker ps -a

啟動即停止 container

docker start container_id/name

docker stop container_id/name

刪除 container

docker rm container_id/name

在目前路徑執行 container 指令 (通常用於編譯)

docker --workdir $PWD container_id/name command

--------------------------------------------------------------------------------

docker --help

Usage: docker [OPTIONS] COMMAND

A self-sufficient runtime for containers

Options:
--config string Location of client config files (default "/home/jwang/.docker")
-D, --debug Enable debug mode
-H, --host list Daemon socket(s) to connect to
-l, --log-level string Set the logging level ("debug"|"info"|"warn"|"error"|"fatal") (default "info")
--tls Use TLS; implied by --tlsverify
--tlscacert string Trust certs signed only by this CA (default "/home/jwang/.docker/ca.pem")
--tlscert string Path to TLS certificate file (default "/home/jwang/.docker/cert.pem")
--tlskey string Path to TLS key file (default "/home/jwang/.docker/key.pem")
--tlsverify Use TLS and verify the remote
-v, --version Print version information and quit

Management Commands:
builder Manage builds
config Manage Docker configs
container Manage containers
engine Manage the docker engine
image Manage images
network Manage networks
node Manage Swarm nodes
plugin Manage plugins
secret Manage Docker secrets
service Manage services
stack Manage Docker stacks
swarm Manage Swarm
system Manage Docker
trust Manage trust on Docker images
volume Manage volumes

Commands:
attach Attach local standard input, output, and error streams to a running container
build Build an image from a Dockerfile
commit Create a new image from a container's changes
cp Copy files/folders between a container and the local filesystem
create Create a new container
diff Inspect changes to files or directories on a container's filesystem
events Get real time events from the server
exec Run a command in a running container
export Export a container's filesystem as a tar archive
history Show the history of an image
images List images
import Import the contents from a tarball to create a filesystem image
info Display system-wide information
inspect Return low-level information on Docker objects
kill Kill one or more running containers
load Load an image from a tar archive or STDIN
login Log in to a Docker registry
logout Log out from a Docker registry
logs Fetch the logs of a container
pause Pause all processes within one or more containers
port List port mappings or a specific mapping for the container
ps List containers
pull Pull an image or a repository from a registry
push Push an image or a repository to a registry
rename Rename a container
restart Restart one or more containers
rm Remove one or more containers
rmi Remove one or more images
run Run a command in a new container
save Save one or more images to a tar archive (streamed to STDOUT by default)
search Search the Docker Hub for images
start Start one or more stopped containers
stats Display a live stream of container(s) resource usage statistics
stop Stop one or more running containers
tag Create a tag TARGET_IMAGE that refers to SOURCE_IMAGE
top Display the running processes of a container
unpause Unpause all processes within one or more containers
update Update configuration of one or more containers
version Show the Docker version information
wait Block until one or more containers stop, then print their exit codes

Run 'docker COMMAND --help' for more information on a command.