I've notice that polling for timestamp in socket's error queue from a thread that hasn't sended the packet results in not waking the polling thread when an event arrives. A simple proof of that is the following code. When compiled with SEND_IN_SAME_THREAD defined, the program will poll on the same thread it has sent the packet. Otherwise the waiter thread polls and the main thread send packets. Please first look in the two SEND_IN_SAME_THREAD preprocessor conditionals before check the rest of the code. Is this the expected behavior? Should I block waiting for packet to be sent while I could send more packets? kernel documentation about network timestamping (see section 1.3): https://www.kernel.org/doc/Documentation/networking/timestamping.txt kernel version: 4.12.14 glibc version: 2.24 /* * 10/11/2017 * polling for timestamp on socket's error queue */ #include <arpa/inet.h> /* hton*() */ #include <poll.h> /* poll() */ #include <pthread.h> /* pthread_*() */ #include <string.h> /* memset() */ #include <sys/types.h> /* socket() recv() */ #include <sys/socket.h> /* socket() recv() */ #include <unistd.h> /* close() */ #include <linux/net_tstamp.h> /* timestamp stuff */ #define PORT 8080 static int do_poll(int sfd) { struct pollfd pfd; /* prepare */ memset(&pfd, 0, sizeof(pfd)); pfd.fd = sfd; pfd.events = POLLERR; /* poll */ return poll(&pfd, 1, -1); } static void do_recv(int sfd) { char tmp; while (recv(sfd, &tmp, sizeof(tmp), MSG_ERRQUEUE) == sizeof(tmp)); } static void do_send(int sfd) { struct sockaddr_in saddr; char tmp = 'a'; /* prepare */ saddr.sin_family = AF_INET; saddr.sin_port = htons(PORT); saddr.sin_addr.s_addr = htonl(INADDR_LOOPBACK); sendto(sfd, &tmp, sizeof(tmp), 0, (struct sockaddr*) &saddr, sizeof(saddr)); sleep(1); } static void* waiter(void *data) { int sfd = *((int*) data); for (;;) { #ifdef SEND_IN_SAME_THREAD do_send(sfd); #endif do_poll(sfd); do_recv(sfd); } return NULL; } static int set_ts_opt(int sfd) { unsigned int opt; /* set timestamp option */ opt = SOF_TIMESTAMPING_SOFTWARE | SOF_TIMESTAMPING_TX_SCHED | SOF_TIMESTAMPING_OPT_CMSG; if (setsockopt(sfd, SOL_SOCKET, SO_TIMESTAMPING, (char*) &opt, sizeof(opt)) == -1) return -1; return 0; } static int open_socket(void) { int sfd; int tmp; /* open socket in non-blocking mode */ sfd = socket(AF_INET, SOCK_DGRAM|SOCK_NONBLOCK, 0); if (sfd == -1) return -1; tmp = set_ts_opt(sfd); if (tmp == -1) goto _go_close_socket; return sfd; _go_close_socket: close(sfd); return -1; } int main(int argc, char **argv) { pthread_t waiter_thread; int sfd; if ((sfd = open_socket()) == -1) return 1; /* create thread and wait for it to terminate */ pthread_create(&waiter_thread, NULL, waiter, &sfd); #ifndef SEND_IN_SAME_THREAD for (;;) do_send(sfd); #endif pthread_join(waiter_thread, NULL); return 0; } Cheers! -- Ricardo Biehl Pasquali _______________________________________________ Kernelnewbies mailing list Kernelnewbies@xxxxxxxxxxxxxxxxx https://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies
