Module Name: src
Committed By: ozaki-r
Date: Fri Dec 15 04:07:20 UTC 2017
Modified Files:
src/sys/net: if.h
Log Message:
Write a guideline for converting an interface to IFEF_MPSAFE
Requested by skrll@
To generate a diff of this commit:
cvs rdiff -u -r1.255 -r1.256 src/sys/net/if.h
Please note that diffs are not public domain; they are subject to the
copyright notices on the relevant files.
Modified files:
Index: src/sys/net/if.h
diff -u src/sys/net/if.h:1.255 src/sys/net/if.h:1.256
--- src/sys/net/if.h:1.255 Fri Dec 15 04:06:42 2017
+++ src/sys/net/if.h Fri Dec 15 04:07:20 2017
@@ -1,4 +1,4 @@
-/* $NetBSD: if.h,v 1.255 2017/12/15 04:06:42 ozaki-r Exp $ */
+/* $NetBSD: if.h,v 1.256 2017/12/15 04:07:20 ozaki-r Exp $ */
/*-
* Copyright (c) 1999, 2000, 2001 The NetBSD Foundation, Inc.
@@ -427,11 +427,33 @@ typedef struct ifnet {
#define IFEF_NO_LINK_STATE_CHANGE __BIT(1) /* doesn't use link state interrupts */
/*
- * The following if_XXX() handlers don't take KERNEL_LOCK if the interface
- * is set IFEF_MPSAFE:
- * - if_start
- * - if_output
- * - if_ioctl
+ * The guidelines for converting an interface to IFEF_MPSAFE are as follows
+ *
+ * Enabling IFEF_MPSAFE on an interface suppresses taking KERNEL_LOCK when
+ * calling the following handlers:
+ * - if_start
+ * - Note that if_transmit is always called without KERNEL_LOCK
+ * - if_output
+ * - if_ioctl
+ * - if_init
+ * - if_stop
+ *
+ * This means that an interface with IFEF_MPSAFE must make the above handlers
+ * MP-safe or take KERNEL_LOCK by itself inside handlers that aren't MP-safe
+ * yet.
+ *
+ * There are some additional restrictions to access member variables of struct
+ * ifnet:
+ * - if_flags
+ * - Must be updated with holding IFNET_LOCK
+ * - You cannot use the flag in Tx/Rx paths anymore because there is no
+ * synchronization on the flag except for IFNET_LOCK
+ * - if_watchdog and if_timer
+ * - The watchdog framework works only for non-IFEF_MPSAFE interfaces
+ * that rely on KERNEL_LOCK
+ * - Interfaces with IFEF_MPSAFE have to provide its own watchdog mechanism
+ * if needed
+ * - Keep if_watchdog NULL when calling if_attach
*/
#ifdef _KERNEL
