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Fix thinko when deciding whether to disable TCP's Nagle algorithm

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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").
This commit is contained in:
Sergio Durigan Junior
2018-08-03 18:04:38 -04:00
parent 4aae6e5abd
commit 425699f52d
2 changed files with 7 additions and 1 deletions
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6
gdb/ChangeLog
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@@ -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.

2
gdb/ser-tcp.c
View File

@@ -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;