Re: export of SEQNUM to userspace

[Kay Sievers <kay.sievers@vrfy.org>]

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On Thu, Sep 02, 2004 at 10:10:06AM +0200, Greg KH wrote:
> On Thu, Sep 02, 2004 at 12:36:57AM +0200, Kay Sievers wrote:
> > On Tue, Aug 31, 2004 at 02:16:32PM -0400, Greg KH wrote:
> > > On Sun, Aug 29, 2004 at 10:35:23PM +0200, Kay Sievers wrote:
> > > > Hi Greg,
> > > > we want to init HAL with the last emitted hotplug SEQNUM from the
> > > > kernel. I think of a sysfs file we can read. It would solve the problem
> > > > of the initial timeout, like we have with udevd too (the very first
> > > > event is delayed).
> > > 
> > > Ok, that sounds reasonable.
> > > 
> > > > What is a proper place to live for this beast?
> > > 
> > > I'm getting a lot of requests for odd stuff like this in sysfs.  Things
> > > that are "kernel" specific, and aren't associated with any one place
> > > (things that would end up in /proc/sys/kernel if we didn't have sysfs.)
> > > 
> > > So, how about /sys/kernel?
> > 
> > Sounds good!
> > Who should create the kset (or in this case it's a subsystem) for this?
> 
> Hm, how about a new file in kernel/ ?

Something like this?

o /sys/kernel/hotplug_seqnum exports the current number
o lib/kobject.c's  sequence_num is renamed to hotplug_seqnum and
  exported by include/linux/kobject.h
o the source file ksysfs.c in kernel/ creates on init the
  sybsystem "/sys/kernel/" in sysfs

Thanks,
Kay

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--- ./dev/null	1970-01-01 01:00:00.000000000 +0100
+++ ./kernel/ksysfs.c	2004-09-03 01:51:38.101622646 +0200
@@ -0,0 +1,63 @@
+/*
+ * kernel/ksysfs.c - sysfs attributes in /sys/kernel, which
+ * 		     are not related to any other subsystem
+ *
+ * Copyright (C) 2004 Kay Sievers <kay.sievers@vrfy.org>
+ * 
+ * This file is release under the GPLv2
+ *
+ */
+
+#include <linux/config.h>
+#include <linux/kobject.h>
+#include <linux/string.h>
+#include <linux/sysfs.h>
+#include <linux/init.h>
+
+#define KERNEL_ATTR_RO(_name) \
+static struct subsys_attribute _name##_attr = {	\
+	.attr	= {				\
+		.name = __stringify(_name),	\
+		.mode = 0444,			\
+	},					\
+	.show	= _name##_show,			\
+}
+
+#define KERNEL_ATTR_RW(_name) \
+static struct subsys_attribute _name##_attr = {	\
+	.attr	= {				\
+		.name = __stringify(_name),	\
+		.mode = 0644,		\
+	},					\
+	.show	= _name##_show,			\
+	.store	= _name##_store,		\
+}
+
+static ssize_t hotplug_seqnum_show(struct subsystem * subsys, char * page)
+{
+	return sprintf(page, "%lu\n", hotplug_seqnum);
+}
+KERNEL_ATTR_RO(hotplug_seqnum);
+
+
+decl_subsys(kernel, NULL, NULL);
+
+static struct attribute * g[] = {
+	&hotplug_seqnum_attr.attr,
+	NULL
+};
+
+static struct attribute_group attr_group = {
+	.attrs = g,
+};
+
+static int __init ksysfs_init(void)
+{
+	int error = subsystem_register(&kernel_subsys);
+	if (!error)
+		error = sysfs_create_group(&kernel_subsys.kset.kobj,&attr_group);
+
+	return error;
+}
+
+core_initcall(ksysfs_init);
===== include/linux/kobject.h 1.31 vs edited =====
--- 1.31/include/linux/kobject.h	2004-09-02 01:24:31 +02:00
+++ edited/include/linux/kobject.h	2004-09-03 01:51:17 +02:00
@@ -26,6 +26,9 @@
 
 #define KOBJ_NAME_LEN	20
 
+/* counter to tag the hotplug event, also available through sysfs */
+extern unsigned long hotplug_seqnum;
+
 struct kobject {
 	char			* k_name;
 	char			name[KOBJ_NAME_LEN];
===== kernel/Makefile 1.42 vs edited =====
--- 1.42/kernel/Makefile	2004-08-31 09:55:12 +02:00
+++ edited/kernel/Makefile	2004-09-03 01:46:09 +02:00
@@ -7,7 +7,7 @@ obj-y     = sched.o fork.o exec_domain.o
 	    sysctl.o capability.o ptrace.o timer.o user.o \
 	    signal.o sys.o kmod.o workqueue.o pid.o \
 	    rcupdate.o intermodule.o extable.o params.o posix-timers.o \
-	    kthread.o
+	    kthread.o ksysfs.o
 
 obj-$(CONFIG_FUTEX) += futex.o
 obj-$(CONFIG_GENERIC_ISA_DMA) += dma.o
===== lib/kobject.c 1.45 vs edited =====
--- 1.45/lib/kobject.c	2004-08-25 21:30:25 +02:00
+++ edited/lib/kobject.c	2004-09-03 01:51:02 +02:00
@@ -122,7 +122,7 @@ char * kobject_get_path(struct kset *kse
 
 #define BUFFER_SIZE	1024	/* should be enough memory for the env */
 #define NUM_ENVP	32	/* number of env pointers */
-static unsigned long sequence_num;
+unsigned long hotplug_seqnum;
 static spinlock_t sequence_lock = SPIN_LOCK_UNLOCKED;
 
 static void kset_hotplug(const char *action, struct kset *kset,
@@ -178,7 +178,7 @@ static void kset_hotplug(const char *act
 	scratch += sprintf(scratch, "ACTION=%s", action) + 1;
 
 	spin_lock(&sequence_lock);
-	seq = sequence_num++;
+	seq = hotplug_seqnum++;
 	spin_unlock(&sequence_lock);
 
 	envp [i++] = scratch;