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SubjectRe: [patch] kernel events layer
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Date
On Sat, 2004-07-24 at 01:11 -0700, Andrew Morton wrote:
> Robert Love <rml@ximian.com> wrote:
> >
> > + buffer = (char *) get_zeroed_page(gfp_mask);
>
> Why zeroed?

Paranoia over a buffer we send to user-space. But the skb is created
using only the 'len' bytes, so it should be safe. Switched to
alloc_page().

> > + if (!buffer)
> > + return -ENOMEM;
> > +
> > + snprintf(buffer, PAGE_SIZE, "From: %s\n", object);
> > + len = strlen(buffer);
> > + snprintf(buffer + len, PAGE_SIZE - len, "Signal: %s\n", signal);
> > + len = strlen(buffer);
>
> A single snprintf here would suit.

Doh!

Updated patch attached - also converts the 'type' value to an enum,
which is safer and something a debugger in user-space can resolve.

Robert Love


Kernel to user-space communication layer using netlink
Signed-off-by: Robert Love <rml@ximian.com>

arch/i386/kernel/cpu/mcheck/p4.c | 9 ++
include/linux/kevent.h | 39 ++++++++++
include/linux/netlink.h | 1
init/Kconfig | 14 +++
kernel/Makefile | 1
kernel/kevent.c | 141 +++++++++++++++++++++++++++++++++++++++
6 files changed, 204 insertions(+), 1 deletion(-)
diff -urN linux-2.6.8-rc2/arch/i386/kernel/cpu/mcheck/p4.c linux/arch/i386/kernel/cpu/mcheck/p4.c
--- linux-2.6.8-rc2/arch/i386/kernel/cpu/mcheck/p4.c 2004-06-16 01:19:37.000000000 -0400
+++ linux/arch/i386/kernel/cpu/mcheck/p4.c 2004-07-24 01:25:07.301870200 -0400
@@ -9,6 +9,7 @@
#include <linux/irq.h>
#include <linux/interrupt.h>
#include <linux/smp.h>
+#include <linux/kevent.h>

#include <asm/processor.h>
#include <asm/system.h>
@@ -59,9 +60,15 @@
if (l & 0x1) {
printk(KERN_EMERG "CPU%d: Temperature above threshold\n", cpu);
printk(KERN_EMERG "CPU%d: Running in modulated clock mode\n",
- cpu);
+ cpu);
+ send_kevent(KEVENT_GENERAL,
+ "/org/kernel/arch/kernel/cpu/temperature", "high",
+ "Cpu: %d\n", cpu);
} else {
printk(KERN_INFO "CPU%d: Temperature/speed normal\n", cpu);
+ send_kevent(KEVENT_GENERAL,
+ "/org/kernel/arch/kernel/cpu/temperature", "normal",
+ "Cpu: %d\n", cpu);
}
}

diff -urN linux-2.6.8-rc2/include/linux/kevent.h linux/include/linux/kevent.h
--- linux-2.6.8-rc2/include/linux/kevent.h 1969-12-31 19:00:00.000000000 -0500
+++ linux/include/linux/kevent.h 2004-07-24 01:31:33.077223432 -0400
@@ -0,0 +1,39 @@
+#ifndef _LINUX_KEVENT_H
+#define _LINUX_KEVENT_H
+
+#include <linux/config.h>
+
+/* kevent types - these are used as the multicast group */
+enum kevent {
+ KEVENT_GENERAL = 0,
+ KEVENT_STORAGE = 1,
+ KEVENT_POWER = 2,
+ KEVENT_FS = 3,
+ KEVENT_HOTPLUG = 4,
+};
+
+#ifdef CONFIG_KERNEL_EVENTS
+
+int send_kevent(enum kevent type, const char *object,
+ const char *signal, const char *fmt, ...);
+
+int send_kevent_atomic(enum kevent type, const char *object,
+ const char *signal, const char *fmt, ...);
+
+#else
+
+static inline int send_kevent(enum kevent type, const char *object,
+ const char *signal, const char *fmt, ...)
+{
+ return 0;
+}
+
+static inline int send_kevent_atomic(int type, const char *object,
+ const char *signal, const char *fmt, ...)
+{
+ return 0;
+}
+
+#endif /* ! CONFIG_KERNEL_EVENTS */
+
+#endif /* _LINUX_KEVENT_H */
diff -urN linux-2.6.8-rc2/include/linux/netlink.h linux/include/linux/netlink.h
--- linux-2.6.8-rc2/include/linux/netlink.h 2004-07-23 22:18:04.000000000 -0400
+++ linux/include/linux/netlink.h 2004-07-24 01:25:07.302870048 -0400
@@ -17,6 +17,7 @@
#define NETLINK_ROUTE6 11 /* af_inet6 route comm channel */
#define NETLINK_IP6_FW 13
#define NETLINK_DNRTMSG 14 /* DECnet routing messages */
+#define NETLINK_KEVENT 15 /* Kernel messages to userspace */
#define NETLINK_TAPBASE 16 /* 16 to 31 are ethertap */

#define MAX_LINKS 32
diff -urN linux-2.6.8-rc2/init/Kconfig linux/init/Kconfig
--- linux-2.6.8-rc2/init/Kconfig 2004-07-23 22:18:04.000000000 -0400
+++ linux/init/Kconfig 2004-07-24 01:25:07.302870048 -0400
@@ -160,6 +160,20 @@
logging of avc messages output). Does not do system-call
auditing without CONFIG_AUDITSYSCALL.

+config KERNEL_EVENTS
+ bool "Kernel Events Layer"
+ depends on NET
+ default y
+ help
+ This option enables the kernel events layer, which is a simple
+ mechanism for kernel-to-user communication over a netlink socket.
+ The goal of the kernel events layer is to provide a simple and
+ efficient logging, error, and events system. Specifically, code
+ is available to link the events into D-BUS. Say Y, unless you
+ are building a system requiring minimal memory consumption.
+
+ D-BUS is available at http://dbus.freedesktop.org/
+
config AUDITSYSCALL
bool "Enable system-call auditing support"
depends on AUDIT && (X86 || PPC64 || ARCH_S390 || IA64)
diff -urN linux-2.6.8-rc2/kernel/kevent.c linux/kernel/kevent.c
--- linux-2.6.8-rc2/kernel/kevent.c 1969-12-31 19:00:00.000000000 -0500
+++ linux/kernel/kevent.c 2004-07-24 01:31:38.561389712 -0400
@@ -0,0 +1,141 @@
+/*
+ * kernel/kevent.c - kernel event delivery over a netlink socket
+ *
+ * Copyright (C) 2004 Red Hat, Inc. All rights reserved.
+ *
+ * Licensed under the GNU GPL v2.
+ *
+ * Authors:
+ * Arjan van de Ven <arjanv@redhat.com>
+ * Kay Sievers <kay.sievers@vrfy.org>
+ * Robert Love <rml@novell.com>
+ */
+
+#include <linux/module.h>
+#include <linux/spinlock.h>
+#include <linux/socket.h>
+#include <linux/skbuff.h>
+#include <linux/netlink.h>
+#include <linux/string.h>
+#include <linux/kevent.h>
+#include <net/sock.h>
+
+/* There is one global netlink socket */
+static struct sock *kevent_sock = NULL;
+
+static void netlink_receive(struct sock *sk, int len)
+{
+ struct sk_buff *skb;
+
+ /* just drop them all */
+ while ((skb = skb_dequeue(&sk->sk_receive_queue)) != NULL)
+ kfree_skb(skb);
+}
+
+static int netlink_send(__u32 groups, int gfp_mask, const char *buffer, int len)
+{
+ struct sk_buff *skb;
+ char *data_start;
+
+ if (!kevent_sock)
+ return -EIO;
+
+ if (!buffer)
+ return -EINVAL;
+
+ if (len > PAGE_SIZE)
+ return -EINVAL;
+
+ skb = alloc_skb(len, gfp_mask);
+ if (!skb)
+ return -ENOMEM;
+ data_start = skb_put(skb, len);
+ memcpy(data_start, buffer, len);
+
+ return netlink_broadcast(kevent_sock, skb, 0, groups, gfp_mask);
+}
+
+static int do_send_kevent(enum kevent type, int gfp_mask, const char *object,
+ const char *signal, const char *fmt, va_list args)
+{
+ char *buffer;
+ int len;
+ int ret;
+
+ if (!object)
+ return -EINVAL;
+
+ if (!signal)
+ return -EINVAL;
+
+ if (strlen(object) > PAGE_SIZE)
+ return -EINVAL;
+
+ buffer = (char *) alloc_page(gfp_mask);
+ if (!buffer)
+ return -ENOMEM;
+
+ snprintf(buffer, PAGE_SIZE, "From: %s\nSignal: %s\n", object, signal);
+ len = strlen(buffer);
+
+ /* possible auxiliary data */
+ if (fmt)
+ len += vscnprintf(buffer+len, PAGE_SIZE-len-1, fmt, args);
+ buffer[len++] = '\0';
+
+ ret = netlink_send((1 << type), gfp_mask, buffer, len);
+ free_page((unsigned long) buffer);
+
+ return ret;
+}
+
+/**
+ * send_kevent - send a message to user-space via the kernel events layer
+ */
+int send_kevent(enum kevent type, const char *object,
+ const char *signal, const char *fmt, ...)
+{
+ va_list args;
+ int ret;
+
+ va_start(args, fmt);
+ ret = do_send_kevent(type, GFP_KERNEL, object, signal, fmt, args);
+ va_end(args);
+
+ return ret;
+}
+
+EXPORT_SYMBOL_GPL(send_kevent);
+
+/**
+ * send_kevent_atomic - send a message to user-space via the kernel events layer
+ */
+int send_kevent_atomic(enum kevent type, const char *object,
+ const char *signal, const char *fmt, ...)
+{
+ va_list args;
+ int ret;
+
+ va_start(args, fmt);
+ ret = do_send_kevent(type, GFP_ATOMIC, object, signal, fmt, args);
+ va_end(args);
+
+ return ret;
+}
+
+EXPORT_SYMBOL_GPL(send_kevent_atomic);
+
+static int kevent_init(void)
+{
+ kevent_sock = netlink_kernel_create(NETLINK_KEVENT, netlink_receive);
+
+ if (!kevent_sock) {
+ printk(KERN_ERR "kevent: "
+ "unable to create netlink socket; aborting\n");
+ return -ENODEV;
+ }
+
+ return 0;
+}
+
+module_init(kevent_init);
diff -urN linux-2.6.8-rc2/kernel/Makefile linux/kernel/Makefile
--- linux-2.6.8-rc2/kernel/Makefile 2004-07-23 22:18:04.000000000 -0400
+++ linux/kernel/Makefile 2004-07-24 01:25:07.303869896 -0400
@@ -23,6 +23,7 @@
obj-$(CONFIG_STOP_MACHINE) += stop_machine.o
obj-$(CONFIG_AUDIT) += audit.o
obj-$(CONFIG_AUDITSYSCALL) += auditsc.o
+obj-$(CONFIG_KERNEL_EVENTS) += kevent.o

ifneq ($(CONFIG_IA64),y)
# According to Alan Modra <alan@linuxcare.com.au>, the -fno-omit-frame-pointer is

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