From d6d9ddd41f9ae8986dc7a12af776edce44fe3863 Mon Sep 17 00:00:00 2001
From: Mateusz Guzik <mjg@FreeBSD.org>
Date: Sat, 4 Jul 2020 06:25:41 +0000
Subject: [PATCH] linux: fix ioctl performance for termios

TCGETS et al are frequently issued by Linux binaries while the previous code
avoidably ping-pongs a global sx lock and serializes on Giant.

Note that even with the fix the common case will serialize on a per-tty lock.
---
 sys/compat/linux/linux_ioctl.c | 44 ++++++++++++++++++++++++++++++----
 1 file changed, 39 insertions(+), 5 deletions(-)

diff --git a/sys/compat/linux/linux_ioctl.c b/sys/compat/linux/linux_ioctl.c
index e69a59822a38..5ec47c30b882 100644
--- a/sys/compat/linux/linux_ioctl.c
+++ b/sys/compat/linux/linux_ioctl.c
@@ -132,8 +132,6 @@ static struct linux_ioctl_handler socket_handler =
 { linux_ioctl_socket, LINUX_IOCTL_SOCKET_MIN, LINUX_IOCTL_SOCKET_MAX };
 static struct linux_ioctl_handler sound_handler =
 { linux_ioctl_sound, LINUX_IOCTL_SOUND_MIN, LINUX_IOCTL_SOUND_MAX };
-static struct linux_ioctl_handler termio_handler =
-{ linux_ioctl_termio, LINUX_IOCTL_TERMIO_MIN, LINUX_IOCTL_TERMIO_MAX };
 static struct linux_ioctl_handler private_handler =
 { linux_ioctl_private, LINUX_IOCTL_PRIVATE_MIN, LINUX_IOCTL_PRIVATE_MAX };
 static struct linux_ioctl_handler drm_handler =
@@ -156,7 +154,6 @@ DATA_SET(linux_ioctl_handler_set, hdio_handler);
 DATA_SET(linux_ioctl_handler_set, disk_handler);
 DATA_SET(linux_ioctl_handler_set, socket_handler);
 DATA_SET(linux_ioctl_handler_set, sound_handler);
-DATA_SET(linux_ioctl_handler_set, termio_handler);
 DATA_SET(linux_ioctl_handler_set, private_handler);
 DATA_SET(linux_ioctl_handler_set, drm_handler);
 DATA_SET(linux_ioctl_handler_set, sg_handler);
@@ -165,6 +162,14 @@ DATA_SET(linux_ioctl_handler_set, video2_handler);
 DATA_SET(linux_ioctl_handler_set, fbsd_usb);
 DATA_SET(linux_ioctl_handler_set, evdev_handler);
 
+/*
+ * Keep sorted by low.
+ */
+static struct linux_ioctl_handler linux_ioctls[] = {
+	{ .func = linux_ioctl_termio, .low = LINUX_IOCTL_TERMIO_MIN,
+	    .high = LINUX_IOCTL_TERMIO_MAX },
+};
+
 #ifdef __i386__
 static TAILQ_HEAD(, linux_ioctl_handler_element) linux_ioctl_handlers =
     TAILQ_HEAD_INITIALIZER(linux_ioctl_handlers);
@@ -3558,8 +3563,8 @@ linux_ioctl_evdev(struct thread *td, struct linux_ioctl_args *args)
  * main ioctl syscall function
  */
 
-int
-linux_ioctl(struct thread *td, struct linux_ioctl_args *args)
+static int
+linux_ioctl_fallback(struct thread *td, struct linux_ioctl_args *args)
 {
 	struct file *fp;
 	struct linux_ioctl_handler_element *he;
@@ -3620,6 +3625,35 @@ linux_ioctl(struct thread *td, struct linux_ioctl_args *args)
 	return (EINVAL);
 }
 
+int
+linux_ioctl(struct thread *td, struct linux_ioctl_args *args)
+{
+	struct linux_ioctl_handler *handler;
+	int error, cmd, i;
+
+	cmd = args->cmd & 0xffff;
+
+	/*
+	 * array of ioctls known at compilation time. Elides a lot of work on
+	 * each call compared to the list variant. Everything frequently used
+	 * should be moved here.
+	 *
+	 * Arguably the magic creating the list should create an array instead.
+	 *
+	 * For now just a linear scan.
+	 */
+	for (i = 0; i < nitems(linux_ioctls); i++) {
+		handler = &linux_ioctls[i];
+		if (cmd >= handler->low && cmd <= handler->high) {
+			error = (*handler->func)(td, args);
+			if (error != ENOIOCTL) {
+				return (error);
+			}
+		}
+	}
+	return (linux_ioctl_fallback(td, args));
+}
+
 int
 linux_ioctl_register_handler(struct linux_ioctl_handler *h)
 {