Question

I need to convert a string “00:11:22:33:44:55” to an uint8_t[6] representing a mac.
I tried on my own, read somewhere char can be casted to uint8_t, but I’m kinda exhausted to try on my own. 🙁

Maybe there is a function in the kernel which does what I want.

If not, here is my code, what do I do wrong?

char * cleaned_mac =NULL;
char * extractMac(unsigned char * shared_user_buffer, size_t offset) {
    char * buffer = kmalloc(17, GFP_KERNEL);
    cleaned_mac = kmalloc(13, GFP_KERNEL);
    int i = 0;
    strncpy(buffer, shared_user_buffer + offset, 17);
    printk("BUFFER [%s]\n", buffer);
    while (*buffer && i < 12) {
        if (isxdigit(*buffer)) {
            printk("BUFFER [%c]\n", *buffer);
            cleaned_mac[i] = *buffer;
            printk("CLEANED BUFFER [%c]\n", *cleaned_mac);
            i++;
        }
        ++buffer;
    }
    cleaned_mac[12]=0x00;
    printk("CLEANED BUFFER [%s]\n", cleaned_mac);
    return cleaned_mac;
}

calling it like:

uint8_t * mac;
mac = extractMac(shared_user_buffer, strlen(tmq_server_prefix));
printk(KERN_DEBUG "MAC[%s]\n", mac);

printk(KERN_DEBUG "MAC[%02x:%02x:%02x:%02x:%02x:%02x]\n", mac[0], mac[1], mac[2], mac[3], mac[4], mac[5]);

so when I give “08:00:27:19:1f:02” in the function the result is:

Oct 13 17:41:28 client2 kernel: [ 1953.179271] CLEANED BUFFER [080027191f02]
Oct 13 17:41:28 client2 kernel: [ 1953.179273] MAC[080027191f02]
Oct 13 17:41:28 client2 kernel: [ 1953.179276] MAC[30:38:30:30:32:37]

So 08 became 30 and 38 ? Why is that?

Solution inspired from Dave (thank you):

uint8_t * cleaned_mac = NULL;
uint8_t * extractMac(unsigned char * shared_user_buffer, size_t offset) {
    char *c;
    char * buffer = kmalloc(17, GFP_KERNEL);
    int p = 0;
    const char * sep = ":";
    cleaned_mac = kmalloc(ETH_ALEN * sizeof(uint8_t), GFP_KERNEL);
    strncpy(buffer, shared_user_buffer + offset, 17);

    while ((c = strsep(&buffer, sep))) {
        cleaned_mac[p++] = simple_strtol(c, NULL, 16);
    }
    return cleaned_mac;
}

Usage then:

uint8_t *  mac;
mac = extractMac(shared_user_buffer, strlen(tmq_server_prefix));
        printk(KERN_DEBUG "---------------MAC [%02x:%02x:%02x:%02x:%02x:%02x]\n",
                mac[0], mac[1], mac[2], mac[3], mac[4], mac[5]);

Answer 1

Tokenize the string, and call strtol on each result

char *c;
int p = 0;
for(c=strtok(buffer, ",");c;c=strtok(NULL, ","))
     mac[p++] = strtol(c, NULL, 16);