[binutils-gdb] Fix thinko when deciding whether to disable TCP's Nagle algorithm

[Sergio Durigan Junior]

https://sourceware.org/git/gitweb.cgi?p=binutils-gdb.git;h=425699f52d8fb875c2197b202b9e05bdc09d0115

commit 425699f52d8fb875c2197b202b9e05bdc09d0115
Author: Sergio Durigan Junior <sergiodj@redhat.com>
Date:   Fri Aug 3 18:04:38 2018 -0400

    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  <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").

Diff:
---
 gdb/ChangeLog | 6 ++++++
 gdb/ser-tcp.c | 2 +-
 2 files changed, 7 insertions(+), 1 deletion(-)

diff --git a/gdb/ChangeLog b/gdb/ChangeLog
index 227e3ff..4359456 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 618d2d9..bdfd556 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;