diff mbox

[obvious/pushed] Fix thinko when deciding whether to disable TCP's Nagle algorithm

Message ID 20180803221450.11838-1-sergiodj@redhat.com
State New, archived
Headers

Commit Message

Sergio Durigan Junior Aug. 3, 2018, 10:14 p.m. UTC 
  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  <sergiodj@redhat.com>

	* 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 mbox

Patch

diff --git a/gdb/ChangeLog b/gdb/ChangeLog
index 227e3ff74f..43594561d5 100644
--- a/gdb/ChangeLog
+++ b/gdb/ChangeLog
@@ -1,3 +1,9 @@ 
+2018-08-03  Sergio Durigan Junior  <sergiodj@redhat.com>
+
+	* 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  <tom@tromey.com>
 
 	PR symtab/16842.
diff --git a/gdb/ser-tcp.c b/gdb/ser-tcp.c
index 618d2d931a..bdfd55663b 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;