Hello João, On 1/15/22 13:23, João Sampaio wrote: > Hello, > > The manpage for TCP (`man 7 tcp`, [1]) reads, in the paragraphs about > `TCP_USER_TIMEOUT`: > > [1] https://man7.org/linux/man-pages/man7/tcp.7.html > > ``` > This option can be set during any state of a TCP > connection, but is effective only during the synchronized > states of a connection (ESTABLISHED, FIN-WAIT-1, FIN- > WAIT-2, CLOSE-WAIT, CLOSING, and LAST-ACK). > ``` > > When I read that, I understand that that option should only apply to > established TCP connections, and should not apply when trying to > establish a TCP connection. > > I wrote a simple program to test that: > > ``` > #include <netdb.h> > #include <stdio.h> > #include <stdlib.h> > #include <unistd.h> > #include <string.h> > #include <time.h> > #include <sys/socket.h> > #include <netinet/in.h> > #include <netinet/tcp.h> > > // We'll skip error-checking since this is just for testing purposes. > > void do_connect(int with_tcp_user_timeout) { > struct addrinfo hint; > struct addrinfo *ai; > int sock; > time_t start; > time_t end; > unsigned int timeout = 10000; > > memset(&hint, 0, sizeof(hint)); > hint.ai_family = AF_INET; > hint.ai_socktype = SOCK_STREAM; > hint.ai_protocol = IPPROTO_TCP; > getaddrinfo("10.0.42.16", "5432", &hint, &ai); > > sock = socket(ai->ai_family, ai->ai_socktype, ai->ai_protocol); > if (with_tcp_user_timeout) { > setsockopt( > sock, IPPROTO_TCP, TCP_USER_TIMEOUT, &timeout, > sizeof(timeout) > ); > } > > printf( > "Attempting to connect, with_user_tcp_timeout = %d... ", > with_tcp_user_timeout > ); > fflush(stdout); > > start = time(NULL); > connect(sock, ai->ai_addr, ai->ai_addrlen); > end = time(NULL); > printf("Done!\n"); > > freeaddrinfo(ai); > > printf( > "with_tcp_user_timeout = %d, took %ld seconds\n", > with_tcp_user_timeout, end - start > ); > } > > int main(void) { > // Let's connect with TCP_USER_TIMEOUT first for faster useful > // first data. > do_connect(1); > do_connect(0); > > exit(EXIT_SUCCESS); > } > ``` > > This program gives me the following output: > > ``` > $ gcc main.c -Wall -Wextra -Werror && ./a.out > Attempting to connect, with_user_tcp_timeout = 1... Done! > with_tcp_user_timeout = 1, took 10 seconds > Attempting to connect, with_user_tcp_timeout = 0... Done! > with_tcp_user_timeout = 0, took 130 seconds > ``` > > So it seems like that option does apply when trying to establish a > connection! This above output was obtained with Linux 5.15.8 and gcc > 9.3.0. > > Am I reading the manpage wrong, or is the manpage wrong? Or is this > just an "undocumented behavior" that shouldn't be relied on and can > be removed without warning in future releases? I never used TCP_USER_TIMEOUT, so can't answer. I added Jerry and David (and netdev@) to the thread, which I guess should know how to answer you better. Thanks, Alex -- Alejandro Colomar Linux man-pages maintainer; https://www.kernel.org/doc/man-pages/ http://www.alejandro-colomar.es/
