From 425699f52d8fb875c2197b202b9e05bdc09d0115 Mon Sep 17 00:00:00 2001 From: Sergio Durigan Junior Date: Fri, 3 Aug 2018 18:04:38 -0400 Subject: [PATCH] Fix thinko when deciding whether to disable TCP's Nagle algorithm This patch fixes a thinko that happened when I was implementing the IPv6 support on GDB/gdbserver. On certain situations, it is necessary to disable TCP's Nagle algorithm (NODELAY). For obvious reasons, this only applies when we are dealing with a TCP connection. While implementing the IPv6 patch, I noticed that the net_open function (on gdb/ser-tcp.c) kept a flag indicating whether the connection type was UDP or TCP. I eliminated that flag, and started using the 'struct addrinfo *' related to the successful connection directly. However, I made a mistake: if (success_ainfo->ai_socktype == IPPROTO_TCP) ^^^^^^^^^^^ { /* Disable Nagle algorithm. Needed in some cases. */ int tmp = 1; setsockopt (scb->fd, IPPROTO_TCP, TCP_NODELAY, (char *) &tmp, sizeof (tmp)); } The 'ai_socktype' field specifies the socket type (SOCK_STREAM or SOCK_DGRAM), and not the protocol. This test was always failing, and the Nagle algorithm was never being disabled. The obvious fix is to use the 'ai_protocol' field. This is what this patch does. Huge "thank you" to Joel Brobecker who reported the regression (he was experiencing an unusual delay while debugging a bare-metal program running under QEMU) and helped me set up a proper reproducer for the bug. gdb/ChangeLog: 2018-08-03 Sergio Durigan Junior * ser-tcp.c (net_open): Fix thinko when deciding whether to disable TCP's Nagle algorithm (use "ai_protocol" instead of "ai_socktype"). --- gdb/ChangeLog | 6 ++++++ gdb/ser-tcp.c | 2 +- 2 files changed, 7 insertions(+), 1 deletion(-) diff --git a/gdb/ChangeLog b/gdb/ChangeLog index 227e3ff74f6..43594561d50 100644 --- a/gdb/ChangeLog +++ b/gdb/ChangeLog @@ -1,3 +1,9 @@ +2018-08-03 Sergio Durigan Junior + + * ser-tcp.c (net_open): Fix thinko when deciding whether to + disable TCP's Nagle algorithm (use "ai_protocol" instead of + "ai_socktype"). + 2018-08-02 Tom Tromey PR symtab/16842. diff --git a/gdb/ser-tcp.c b/gdb/ser-tcp.c index 618d2d931ac..bdfd55663b6 100644 --- a/gdb/ser-tcp.c +++ b/gdb/ser-tcp.c @@ -371,7 +371,7 @@ net_open (struct serial *scb, const char *name) ioctl (scb->fd, FIONBIO, &ioarg); - if (success_ainfo->ai_socktype == IPPROTO_TCP) + if (success_ainfo->ai_protocol == IPPROTO_TCP) { /* Disable Nagle algorithm. Needed in some cases. */ int tmp = 1; -- 2.30.2