From ce97f9355fda46bd7ca887271772977c024e5489 Mon Sep 17 00:00:00 2001 From: Christian Hesse Date: Mon, 5 May 2014 20:55:42 +0200 Subject: add some comments --- dyndhcpd.c | 35 +++++++++++++++++++++++++++++++++-- 1 file changed, 33 insertions(+), 2 deletions(-) diff --git a/dyndhcpd.c b/dyndhcpd.c index e7b7bf9..20f043f 100644 --- a/dyndhcpd.c +++ b/dyndhcpd.c @@ -67,7 +67,9 @@ int main(int argc, char ** argv) { struct sockaddr_in * s4; struct in_addr * v_host, * v_mask; struct in_addr s_broadcast, s_netaddress, s_minhost, s_maxhost; - char c_address[INET_ADDRSTRLEN], c_netmask[INET_ADDRSTRLEN], c_netaddress[INET_ADDRSTRLEN], c_broadcast[INET_ADDRSTRLEN], c_minhost[INET_ADDRSTRLEN], c_maxhost[INET_ADDRSTRLEN]; + char c_address[INET_ADDRSTRLEN], c_netmask[INET_ADDRSTRLEN], + c_netaddress[INET_ADDRSTRLEN], c_broadcast[INET_ADDRSTRLEN], + c_minhost[INET_ADDRSTRLEN], c_maxhost[INET_ADDRSTRLEN]; char * interface = NULL; char hostname[254]; @@ -81,6 +83,7 @@ int main(int argc, char ** argv) { printf("Starting dyndhcpd/" VERSION " (compiled: " __DATE__ ", " __TIME__ ")\n"); + /* get command line options */ for (i = 1; i < argc; i++) { switch ((int)argv[i][0]) { case '-': @@ -106,11 +109,13 @@ int main(int argc, char ** argv) { } } + /* bail if we are not root */ if (getuid() > 0) { fprintf(stderr, "You need to be root!\n"); goto out; } + /* get the domainname */ gethostname(hostname, 254); hp = gethostbyname(hostname); if ((domainname = strchr(hp->h_name, '.')) != NULL) @@ -120,17 +125,21 @@ int main(int argc, char ** argv) { domainname = FALLBACKDOMAIN; } + /* give an error if we do not have an interface */ if (interface == NULL) { fprintf(stderr, "No interface given!\n"); return EXIT_FAILURE; } + /* initialize ifaddr */ if (getifaddrs(&ifaddr) == -1) { fprintf(stderr, "getifaddrs() failed.\n"); return EXIT_FAILURE; } + /* to find the correct interface */ for (ifa = ifaddr; ifa != NULL; ifa = ifa->ifa_next) { + /* next iteration if requirements do not match */ if (strcmp(interface, ifa->ifa_name) != 0) continue; if (ifa->ifa_addr == NULL) @@ -149,33 +158,42 @@ int main(int argc, char ** argv) { if (!(ifa->ifa_flags & IFF_RUNNING)) fprintf(stderr, "Warning: Interface %s is not connected.\n", interface); + /* get variables in place for address */ s4 = (struct sockaddr_in *)ifa->ifa_addr; v_host = &s4->sin_addr; + /* convert address from binary to text form */ if (!inet_ntop(ifa->ifa_addr->sa_family, v_host, c_address, INET_ADDRSTRLEN)) fprintf(stderr, "%s: inet_ntop failed!\n", ifa->ifa_name); + /* get variables in place for netmask */ s4 = (struct sockaddr_in *)ifa->ifa_netmask; v_mask = &s4->sin_addr; + /* convert netmask from binary to text form */ if (!inet_ntop(ifa->ifa_netmask->sa_family, v_mask, c_netmask, INET_ADDRSTRLEN)) fprintf(stderr, "%s: inet_ntop failed!\n", ifa->ifa_name); + /* calculate broadcast and net address */ s_broadcast.s_addr = v_host->s_addr |~ v_mask->s_addr; s_netaddress.s_addr = v_host->s_addr & v_mask->s_addr; + /* check if subnet has enough addresses */ if (ntohl(s_broadcast.s_addr) - ntohl(s_netaddress.s_addr) < 2) { fprintf(stderr, "We do not have addresses to serve, need a netmask with 30 bit minimum.\n"); goto out; } + /* calculate min and max host */ s_minhost.s_addr = htonl(ntohl(s_netaddress.s_addr) + 1); s_maxhost.s_addr = htonl(ntohl(s_broadcast.s_addr) - 1); + /* convert missing addresses from binary to text form */ if (inet_ntop(AF_INET, &s_broadcast, c_broadcast, INET_ADDRSTRLEN) != NULL && inet_ntop(AF_INET, &s_netaddress, c_netaddress, INET_ADDRSTRLEN) != NULL && inet_ntop(AF_INET, &s_minhost, c_minhost, INET_ADDRSTRLEN) != NULL && inet_ntop(AF_INET, &s_maxhost, c_maxhost, INET_ADDRSTRLEN) != NULL) { + /* print information */ printf("Interface: %s\n" "Domain: %s\n" "Host Address: %s\n" @@ -185,15 +203,18 @@ int main(int argc, char ** argv) { "Hosts: %s - %s\n", interface, domainname, c_address, c_netaddress, c_broadcast, c_netmask, c_minhost, c_maxhost); - /* read the template */ + /* open the template for reading */ if ((configfile = fopen(CONFIG_TEMPLATE, "r")) == NULL) { fprintf(stderr, "Failed opening config template for reading.\n"); goto out; } + + /* seek to the and so we know the file size */ fseek(configfile, 0, SEEK_END); fsize = ftell(configfile); fseek(configfile, 0, SEEK_SET); + /* allocate memory and read file */ config = malloc(fsize + 1); if ((fread(config, fsize, 1, configfile)) != 1) { fprintf(stderr, "Failed reading config template.\n"); @@ -202,6 +223,7 @@ int main(int argc, char ** argv) { fclose(configfile); config[fsize] = 0; + /* replace strings with real values */ if ((config = str_replace(config, "__INTERFACE__", interface)) == NULL) goto out; if ((config = str_replace(config, "__VERSION__", VERSION)) == NULL) @@ -221,28 +243,37 @@ int main(int argc, char ** argv) { if ((config = str_replace(config, "__MAXHOST__", c_maxhost)) == NULL) goto out; + /* get new filename and open file for writing */ filename = malloc(strlen(CONFIG_OUTPUT) + strlen(interface) + 1); sprintf(filename, CONFIG_OUTPUT, interface); if ((configfile = fopen(filename, "w")) == NULL) { fprintf(stderr, "Failed opening config file for writing.\n"); goto out; } + + /* actually write the final configuration to file and close it */ fputs(config, configfile); fclose(configfile); + /* execute dhcp daemon, replace the current process + * dyndhcpd is cleared from memory here and code below is not execuded if + * everything goes well */ execlp("/usr/bin/dhcpd", "dhcpd", "-f", "-d", "-q", "-4", "-cf", filename, interface, NULL); rc = EXIT_SUCCESS; goto out; } else { + /* failed to convert addresses from binary to string */ fprintf(stderr, "Failed converting number to string\n"); goto out; } } + /* we did not find an interface to work with */ fprintf(stderr, "Interface not found, link down or no address.\n"); out: + /* free memory */ if (filename != NULL) free(filename); if (config != NULL) -- cgit v1.2.3-70-g09d2