From b07fa8c110cc16d58b41c1cc2bc4492486faef5b Mon Sep 17 00:00:00 2001
From: Jason Volk <jason@zemos.net>
Date: Sun, 19 Mar 2023 18:34:43 -0700
Subject: [PATCH] ircd::net: Add interface for native_non_blocking(); mitigate
 unconditional ioctl.

---
 include/ircd/net/sock_opts.h |  3 +++
 ircd/net.cc                  | 37 ++++++++++++++++++++++++++++++++++--
 ircd/net_listener.cc         |  5 +++++
 3 files changed, 43 insertions(+), 2 deletions(-)

diff --git a/include/ircd/net/sock_opts.h b/include/ircd/net/sock_opts.h
index 69675e783..2fda9802b 100644
--- a/include/ircd/net/sock_opts.h
+++ b/include/ircd/net/sock_opts.h
@@ -14,8 +14,10 @@
 namespace ircd::net
 {
 	struct sock_opts;
+	IRCD_OVERLOAD(system);
 
 	bool v6only(const socket &);
+	bool blocking(const socket &, system_t);
 	bool blocking(const socket &);
 	bool nopush(const socket &);
 	bool nodelay(const socket &);
@@ -30,6 +32,7 @@ namespace ircd::net
 
 	// returns true if supported, false if unsupported; failures will throw.
 	bool v6only(socket &, const bool);
+	bool blocking(socket &, const bool, system_t);
 	bool blocking(socket &, const bool);
 	bool nopush(socket &, const bool);
 	bool nodelay(socket &, const bool);
diff --git a/ircd/net.cc b/ircd/net.cc
index 011677886..98db29df8 100644
--- a/ircd/net.cc
+++ b/ircd/net.cc
@@ -1114,8 +1114,11 @@ ircd::net::nopush(socket &socket,
 /// Toggles the behavior of non-async asio calls.
 ///
 /// This option affects very little in practice and only sets a flag in
-/// userspace in asio, not an actual ioctl(). Specifically:
+/// userspace in asio, not an actual ioctl(2) (XXX this is not true anymore,
+/// sd.non_blocking() and sd.native_non_blocking() both seem to ioctl(2)).
+/// See below the deprecated section.
 ///
+/// ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~
 /// * All sockets are already set by asio to FIONBIO=1 no matter what, thus
 /// nothing really blocks the event loop ever by default unless you try hard.
 ///
@@ -1134,13 +1137,35 @@ ircd::net::nopush(socket &socket,
 /// in this project there is never a reason to ever set this to true,
 /// however, sockets do get constructed by asio in blocking mode by default
 /// so we mostly use this function to set it to non-blocking.
+/// ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~
 ///
+/// The kern argument has been added to decide between native_non_blocking()
+/// (when kern=true) or non_blocking() (when kern=false). These both set
+/// different flags in asio but they both result in the same ioctl(FIONBIO)
+/// probably due to third-party libraries flipping FIONBIO outside of asio's
+/// knowledge and naive users complaining too much to the maintainer.
+///
+/// To deal with this we have added a query to the sd.non_blocking() getter
+/// which AT LEAST FOR NOW only reads asio's flags without a syscall and
+/// won't call the sd.non_blocking() setter if it's superfluous.
 bool
 ircd::net::blocking(socket &socket,
                     const bool b)
 {
 	ip::tcp::socket &sd(socket);
-	sd.non_blocking(!b);
+	if(likely(sd.non_blocking() == b))
+		sd.non_blocking(!b);
+
+	return true;
+}
+
+bool
+ircd::net::blocking(socket &socket,
+                    const bool b,
+                    system_t)
+{
+	ip::tcp::socket &sd(socket);
+	sd.native_non_blocking(!b);
 	return true;
 }
 
@@ -1292,6 +1317,14 @@ ircd::net::blocking(const socket &socket)
 	return !sd.non_blocking();
 }
 
+bool
+ircd::net::blocking(const socket &socket,
+                    system_t)
+{
+	const ip::tcp::socket &sd(socket);
+	return !sd.native_non_blocking();
+}
+
 bool
 ircd::net::v6only(const socket &socket)
 {
diff --git a/ircd/net_listener.cc b/ircd/net_listener.cc
index 828f6c340..bf2f54605 100644
--- a/ircd/net_listener.cc
+++ b/ircd/net_listener.cc
@@ -1070,8 +1070,13 @@ ircd::net::acceptor::accepted(const std::shared_ptr<socket> &sock)
 	assert(bool(cb));
 	assert(bool(sock));
 
+	#if !defined(BSD_BASED_OS)
 	// Toggles the behavior of non-async functions; see func comment
+	// This is not needed on BSD because the socket inherits the listener's
+	// non-blocking disposition.
 	blocking(*sock, false);
+	#endif
+
 	cb(*this, sock);
 }