Re: [patch] kernel sysfs events layer

From: Kay Sievers
Date: Sun Sep 05 2004 - 21:07:39 EST

On Sun, Sep 05, 2004 at 02:18:14PM +0200, Kay Sievers wrote:
> On Sat, Sep 04, 2004 at 10:58:08PM -0400, Robert Love wrote:
> > On Sat, 2004-09-04 at 02:54 +0200, Greg KH wrote:
> >
> > > So, we're back to the original issue. Why is this kernel event system
> > > different from the hotplug system? I would argue there isn't one,
> > > becides the transport, as you seem to want everything that we currently
> > > provide in the current kobject_hotplug() call.
> > >
> > > But transports are important, I agree.
> > >
> > > How about you just add the ability to send hotplug calls across netlink?
> > > Make it so the kobject_hotplug() function does both the exec() call, and
> > > a netlink call (based on a config option for those people who like to
> > > configure such stuff.)
> >
> > This smells.
> >
> > Look, I agree that unifying the two ideas and transports as much as
> > possible is the right way to proceed. But the fact is, as you said,
> > transports _are_ important. And simply always sending out a hotplug
> > event _and_ a netlink event is silly and superfluous. We need to make
> > up our minds.
> >
> > I don't think anyone argues that netlink makes sense for these low
> > priority asynchronous events.
> >
> > I'd prefer to integrate the two approaches as much as possible, but keep
> > the two transports separate. Use hotplug for hotplug events as we do
> > now and use kevent, which is over netlink, for the new events we want to
> > add.
> >
> > Maybe always do the kevent from the hotplug, but definitely do not do
> > the hotplug from all kevents. It is redundant and extra overhead.
> >
> > Doing both simultaneous begs the question of why have both. Picking the
> > right tool for the job is, well, the right tool for the job.
>
> Yes, it doesn't make much sense to pipe the kevents through
> /sbin/hotplug, but I definitely want the hotplug-events over netlink,
> to get rid of the SEQNUM reorder nightmare and unpredictable delay of
> the execution of the /etc/hotplug.d/ helpers, we currently can't handle
> very well with HAL.
>
> I expect, that we need to have both transports (for hotplug), cause early
> boot is unable to react to netlink messages.
> The /sbin/hotplug can easily switched off, after some "advanced event daemon"
> is running by: "echo -n "" > /proc/sys/kernel/hotplug".
>
> What about moving the /sbin/hotplug execution from lib/kobject.c to
> kernel/kobj_notify.c and merge it with our netlink code? This would
> separate the "object-storage" from the "object-notification" which is
> nice. And we would have a single place to implement all kind of event
> transports.
> If anybody invents some other kind of transport it can go into
> kobj_notify.c. All transports can share some code and are highly
> configurable then.

I tried it! Here is a version that moves kobject_hotplug() event out of the
kobject core to the new "userspace event"-file kernel/kobject_uevent.c.

The /sbin/hotplug message is now just a special kind of userspace notification.
All hotplug messages are also send over netlink, with the whole hotplug
environment attached to the message. It looks like this on the wire:

recv(3, "add@/class/input/mouse2\0ACTION=add\0DEVPATH=/class/input/mouse2\0SEQNUM=768\0SUBSYSTEM=input\0", 1024, 0) = 90

All other events like the filesystem device claim/release are only sent
through the netlink interface by kobject_uevent().

Thanks,
Kay

diff -Nru a/fs/super.c b/fs/super.c
--- a/fs/super.c 2004-09-06 03:47:59 +02:00
+++ b/fs/super.c 2004-09-06 03:47:59 +02:00
@@ -35,6 +35,7 @@
#include <linux/vfs.h>
#include <linux/writeback.h> /* for the emergency remount stuff */
#include <linux/idr.h>
+#include <linux/kobject_uevent.h>
#include <asm/uaccess.h>


@@ -633,6 +634,16 @@
return (void *)s->s_bdev == data;
}

+static void bdev_claim_uevent(const char *action, struct block_device *bdev)
+{
+ if (bdev->bd_disk) {
+ if (bdev->bd_part)
+ kobject_uevent(action, &bdev->bd_part->kobj, NULL);
+ else
+ kobject_uevent(action, &bdev->bd_disk->kobj, NULL);
+ }
+}
+
struct super_block *get_sb_bdev(struct file_system_type *fs_type,
int flags, const char *dev_name, void *data,
int (*fill_super)(struct super_block *, void *, int))
@@ -675,8 +686,10 @@
up_write(&s->s_umount);
deactivate_super(s);
s = ERR_PTR(error);
- } else
+ } else {
s->s_flags |= MS_ACTIVE;
+ bdev_claim_uevent("claim", bdev);
+ }
}

return s;
@@ -691,6 +704,8 @@
void kill_block_super(struct super_block *sb)
{
struct block_device *bdev = sb->s_bdev;
+
+ bdev_claim_uevent("release", bdev);
generic_shutdown_super(sb);
set_blocksize(bdev, sb->s_old_blocksize);
close_bdev_excl(bdev);
diff -Nru a/include/linux/kobject.h b/include/linux/kobject.h
--- a/include/linux/kobject.h 2004-09-06 03:47:59 +02:00
+++ b/include/linux/kobject.h 2004-09-06 03:47:59 +02:00
@@ -61,7 +61,7 @@

extern void kobject_hotplug(const char *action, struct kobject *);

-extern char * kobject_get_path(struct kset *, struct kobject *, int);
+extern char * kobject_get_path(struct kobject *, int);

struct kobj_type {
void (*release)(struct kobject *);
diff -Nru a/include/linux/kobject_uevent.h b/include/linux/kobject_uevent.h
--- /dev/null Wed Dec 31 16:00:00 196900
+++ b/include/linux/kobject_uevent.h 2004-09-06 03:47:59 +02:00
@@ -0,0 +1,39 @@
+#ifndef _KOBJECT_UEVENT_H_
+#define _KOBJECT_UEVENT_H_
+
+#ifdef __KERNEL__
+
+#ifdef CONFIG_HOTPLUG
+/* counter to tag the hotplug event, read only except for the kobject uevent */
+extern u64 hotplug_seqnum;
+extern void kobject_hotplug(const char *action, struct kobject *kobj);
+#else
+static inline void kobject_hotplug(const char *action, struct kobject *kobj)
+{
+ return;
+}
+#endif
+
+
+#ifdef CONFIG_KOBJECT_UEVENT
+extern int kobject_uevent(const char *signal, struct kobject *kobj,
+ struct attribute *attr);
+
+extern int kobject_uevent_atomic(const char *signal, struct kobject *kobj,
+ struct attribute *attr);
+#else
+static inline int kobject_uevent(const char *signal, struct kobject *kobj,
+ struct attribute *attr)
+{
+ return 0;
+}
+
+static inline int kobject_uevent_atomic(const char *signal, struct kobject *kobj,
+ struct attribute *attr)
+{
+ return 0;
+}
+#endif
+
+#endif /* __KERNEL__ */
+#endif /* _KOBJECT_UEVENT_H_ */
diff -Nru a/include/linux/netlink.h b/include/linux/netlink.h
--- a/include/linux/netlink.h 2004-09-06 03:47:59 +02:00
+++ b/include/linux/netlink.h 2004-09-06 03:47:59 +02:00
@@ -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_KOBJECT_UEVENT 15 /* Kernel messages to userspace */
#define NETLINK_TAPBASE 16 /* 16 to 31 are ethertap */

#define MAX_LINKS 32
diff -Nru a/init/Kconfig b/init/Kconfig
--- a/init/Kconfig 2004-09-06 03:47:59 +02:00
+++ b/init/Kconfig 2004-09-06 03:47:59 +02:00
@@ -195,6 +195,22 @@
agent" (/sbin/hotplug) to load modules and set up software needed
to use devices as you hotplug them.

+config KOBJECT_UEVENT
+ bool "Kernel Userspace Events"
+ depends on NET && HOTPLUG
+ default y
+ help
+ This option enables the kernel userspace events layer, which is a
+ simple mechanism for kernel-to-user communication over a netlink
+ socket.
+ The goal of the kernel userspace events layer is to provide a simple
+ and efficient events system, that notifies userspace about kobject
+ state changes e.g. hotplug events, power state transitions or block
+ device claiming (mount/unmount).
+
+ Say Y, unless you are building a system requiring minimal memory
+ consumption.
+
config IKCONFIG
bool "Kernel .config support"
---help---
diff -Nru a/kernel/Makefile b/kernel/Makefile
--- a/kernel/Makefile 2004-09-06 03:47:59 +02:00
+++ b/kernel/Makefile 2004-09-06 03:47:59 +02:00
@@ -24,6 +24,7 @@
obj-$(CONFIG_AUDIT) += audit.o
obj-$(CONFIG_AUDITSYSCALL) += auditsc.o
obj-$(CONFIG_KPROBES) += kprobes.o
+obj-$(CONFIG_HOTPLUG) += kobject_uevent.o

ifneq ($(CONFIG_IA64),y)
# According to Alan Modra <alan@xxxxxxxxxxxxxxxx>, the -fno-omit-frame-pointer is
diff -Nru a/kernel/kobject_uevent.c b/kernel/kobject_uevent.c
--- /dev/null Wed Dec 31 16:00:00 196900
+++ b/kernel/kobject_uevent.c 2004-09-06 03:47:59 +02:00
@@ -0,0 +1,233 @@
+/*
+ * kernel/kobj_uevent.c - kernel userspace event delivery
+ *
+ * Copyright (C) 2004 Red Hat, Inc. All rights reserved.
+ * Copyright (C) 2004 Novell, Inc. All rights reserved.
+ *
+ * Licensed under the GNU GPL v2.
+ *
+ * Authors:
+ * Robert Love <rml@xxxxxxxxxx>
+ * Kay Sievers <kay.sievers@xxxxxxxx>
+ * Arjan van de Ven <arjanv@xxxxxxxxxx>
+ */
+
+#include <linux/spinlock.h>
+#include <linux/socket.h>
+#include <linux/skbuff.h>
+#include <linux/netlink.h>
+#include <linux/string.h>
+#include <linux/kobject.h>
+#include <linux/kobject_uevent.h>
+#include <net/sock.h>
+
+#ifdef CONFIG_HOTPLUG
+u64 hotplug_seqnum;
+static spinlock_t sequence_lock = SPIN_LOCK_UNLOCKED;
+#endif
+
+#ifdef CONFIG_KOBJECT_UEVENT
+static struct sock *uevent_sock = NULL;
+#endif
+
+static int send_uevent(const char *signal, const char *obj,
+ const void *buf, int buflen, int gfp_mask)
+{
+ struct sk_buff *skb;
+ char *pos;
+ int len;
+
+ if (!uevent_sock)
+ return -EIO;
+
+ len = strlen(signal) + 1;
+ len += strlen(obj) + 1;
+ len += buflen;
+
+ skb = alloc_skb(len, gfp_mask);
+ if (!skb)
+ return -ENOMEM;
+
+ pos = skb_put(skb, len);
+
+ pos += sprintf(pos, "%s@%s", signal, obj) + 1;
+ memcpy(pos, buf, buflen);
+
+ return netlink_broadcast(uevent_sock, skb, 0, 1, gfp_mask);
+}
+
+static int do_kobject_uevent(const char *signal, struct kobject *kobj,
+ struct attribute *attr, int gfp_mask)
+{
+ char *path;
+ char *attrpath;
+ int len;
+ int rc = -ENOMEM;
+
+ path = kobject_get_path(kobj, gfp_mask);
+ if (!path)
+ return -ENOMEM;
+
+ if (attr) {
+ len = strlen(path);
+ len += strlen(attr->name) + 2;
+ attrpath = kmalloc(len, gfp_mask);
+ if (!attrpath)
+ goto exit;
+ sprintf(attrpath, "%s/%s", path, attr->name);
+ rc = send_uevent(signal, attrpath, NULL, 0, gfp_mask);
+ kfree(attrpath);
+ } else {
+ rc = send_uevent(signal, path, NULL, 0, gfp_mask);
+ }
+
+exit:
+ kfree(path);
+ return rc;
+}
+
+int kobject_uevent(const char *signal, struct kobject *kobj,
+ struct attribute *attr)
+{
+ return do_kobject_uevent(signal, kobj, attr, GFP_KERNEL);
+}
+
+EXPORT_SYMBOL(kobject_uevent);
+
+int kobject_uevent_atomic(const char *signal, struct kobject *kobj,
+ struct attribute *attr)
+{
+ return do_kobject_uevent(signal, kobj, attr, GFP_ATOMIC);
+}
+
+EXPORT_SYMBOL(kobject_uevent_atomic);
+
+
+#define BUFFER_SIZE 1024 /* should be enough memory for the env */
+#define NUM_ENVP 32 /* number of env pointers */
+void kobject_hotplug(const char *action, struct kobject *kobj)
+{
+ char *argv [3];
+ char **envp = NULL;
+ char *buffer = NULL;
+ char *scratch;
+ int i = 0;
+ int retval;
+ char *kobj_path = NULL;
+ char *name = NULL;
+ u64 seq;
+ struct kobject * top_kobj = kobj;
+ struct kset * kset;
+
+ if (!top_kobj->kset && top_kobj->parent) {
+ do {
+ top_kobj = top_kobj->parent;
+ } while (!top_kobj->kset && top_kobj->parent);
+ }
+
+ if (top_kobj->kset && top_kobj->kset->hotplug_ops)
+ kset = top_kobj->kset;
+ else
+ return;
+
+ /* If the kset has a filter operation, call it.
+ Skip the event, if the filter returns zero. */
+ if (kset->hotplug_ops->filter) {
+ if (!kset->hotplug_ops->filter(kset, kobj))
+ return;
+ }
+
+ pr_debug ("%s\n", __FUNCTION__);
+
+ envp = kmalloc(NUM_ENVP * sizeof (char *), GFP_KERNEL);
+ if (!envp)
+ return;
+ memset (envp, 0x00, NUM_ENVP * sizeof (char *));
+
+ buffer = kmalloc(BUFFER_SIZE, GFP_KERNEL);
+ if (!buffer)
+ goto exit;
+
+ if (kset->hotplug_ops->name)
+ name = kset->hotplug_ops->name(kset, kobj);
+ if (name == NULL)
+ name = kset->kobj.name;
+
+ argv [0] = hotplug_path;
+ argv [1] = name;
+ argv [2] = NULL;
+
+ /* minimal command environment */
+ envp [i++] = "HOME=/";
+ envp [i++] = "PATH=/sbin:/bin:/usr/sbin:/usr/bin";
+
+ scratch = buffer;
+
+ envp [i++] = scratch;
+ scratch += sprintf(scratch, "ACTION=%s", action) + 1;
+
+ spin_lock(&sequence_lock);
+ seq = ++hotplug_seqnum;
+ spin_unlock(&sequence_lock);
+
+ kobj_path = kobject_get_path(kobj, GFP_KERNEL);
+ if (!kobj_path)
+ goto exit;
+
+ envp [i++] = scratch;
+ scratch += sprintf (scratch, "DEVPATH=%s", kobj_path) + 1;
+
+ envp [i++] = scratch;
+ scratch += sprintf(scratch, "SEQNUM=%lld", seq) + 1;
+
+ envp [i++] = scratch;
+ scratch += sprintf(scratch, "SUBSYSTEM=%s", name) + 1;
+
+ if (kset->hotplug_ops->hotplug) {
+ /* have the kset specific function add its stuff */
+ retval = kset->hotplug_ops->hotplug (kset, kobj,
+ &envp[i], NUM_ENVP - i, scratch,
+ BUFFER_SIZE - (scratch - buffer));
+ if (retval) {
+ pr_debug ("%s - hotplug() returned %d\n",
+ __FUNCTION__, retval);
+ goto exit;
+ }
+ }
+
+ pr_debug ("%s: %s %s %s %s %s %s %s\n", __FUNCTION__, argv[0], argv[1],
+ envp[0], envp[1], envp[2], envp[3], envp[4]);
+
+ send_uevent(action, kobj_path, buffer, scratch - buffer, GFP_KERNEL);
+
+ if (!hotplug_path[0])
+ goto exit;
+
+ retval = call_usermodehelper (argv[0], argv, envp, 0);
+ if (retval)
+ pr_debug ("%s - call_usermodehelper returned %d\n",
+ __FUNCTION__, retval);
+
+exit:
+ kfree(kobj_path);
+ kfree(buffer);
+ kfree(envp);
+ return;
+}
+
+EXPORT_SYMBOL(kobject_hotplug);
+
+static int __init kobject_uevent_init(void)
+{
+ uevent_sock = netlink_kernel_create(NETLINK_KOBJECT_UEVENT, NULL);
+
+ if (!uevent_sock) {
+ printk(KERN_ERR
+ "kobject_uevent: unable to create netlink socket!\n");
+ return -ENODEV;
+ }
+
+ return 0;
+}
+
+core_initcall(kobject_uevent_init);
diff -Nru a/lib/kobject.c b/lib/kobject.c
--- a/lib/kobject.c 2004-09-06 03:47:59 +02:00
+++ b/lib/kobject.c 2004-09-06 03:47:59 +02:00
@@ -13,6 +13,7 @@
#undef DEBUG

#include <linux/kobject.h>
+#include <linux/kobject_uevent.h>
#include <linux/string.h>
#include <linux/module.h>
#include <linux/stat.h>
@@ -63,7 +64,7 @@
return container_of(entry,struct kobject,entry);
}

-static int get_kobj_path_length(struct kset *kset, struct kobject *kobj)
+static int get_kobj_path_length(struct kobject *kobj)
{
int length = 1;
struct kobject * parent = kobj;
@@ -79,7 +80,7 @@
return length;
}

-static void fill_kobj_path(struct kset *kset, struct kobject *kobj, char *path, int length)
+static void fill_kobj_path(struct kobject *kobj, char *path, int length)
{
struct kobject * parent;

@@ -103,146 +104,21 @@
* @kobj: kobject in question, with which to build the path
* @gfp_mask: the allocation type used to allocate the path
*/
-char * kobject_get_path(struct kset *kset, struct kobject *kobj, int gfp_mask)
+char * kobject_get_path(struct kobject *kobj, int gfp_mask)
{
char *path;
int len;

- len = get_kobj_path_length(kset, kobj);
+ len = get_kobj_path_length(kobj);
path = kmalloc(len, gfp_mask);
if (!path)
return NULL;
memset(path, 0x00, len);
- fill_kobj_path(kset, kobj, path, len);
+ fill_kobj_path(kobj, path, len);

return path;
}

-#ifdef CONFIG_HOTPLUG
-
-#define BUFFER_SIZE 1024 /* should be enough memory for the env */
-#define NUM_ENVP 32 /* number of env pointers */
-static unsigned long sequence_num;
-static spinlock_t sequence_lock = SPIN_LOCK_UNLOCKED;
-
-static void kset_hotplug(const char *action, struct kset *kset,
- struct kobject *kobj)
-{
- char *argv [3];
- char **envp = NULL;
- char *buffer = NULL;
- char *scratch;
- int i = 0;
- int retval;
- char *kobj_path = NULL;
- char *name = NULL;
- unsigned long seq;
-
- /* If the kset has a filter operation, call it. If it returns
- failure, no hotplug event is required. */
- if (kset->hotplug_ops->filter) {
- if (!kset->hotplug_ops->filter(kset, kobj))
- return;
- }
-
- pr_debug ("%s\n", __FUNCTION__);
-
- if (!hotplug_path[0])
- return;
-
- envp = kmalloc(NUM_ENVP * sizeof (char *), GFP_KERNEL);
- if (!envp)
- return;
- memset (envp, 0x00, NUM_ENVP * sizeof (char *));
-
- buffer = kmalloc(BUFFER_SIZE, GFP_KERNEL);
- if (!buffer)
- goto exit;
-
- if (kset->hotplug_ops->name)
- name = kset->hotplug_ops->name(kset, kobj);
- if (name == NULL)
- name = kset->kobj.name;
-
- argv [0] = hotplug_path;
- argv [1] = name;
- argv [2] = NULL;
-
- /* minimal command environment */
- envp [i++] = "HOME=/";
- envp [i++] = "PATH=/sbin:/bin:/usr/sbin:/usr/bin";
-
- scratch = buffer;
-
- envp [i++] = scratch;
- scratch += sprintf(scratch, "ACTION=%s", action) + 1;
-
- spin_lock(&sequence_lock);
- seq = sequence_num++;
- spin_unlock(&sequence_lock);
-
- envp [i++] = scratch;
- scratch += sprintf(scratch, "SEQNUM=%ld", seq) + 1;
-
- kobj_path = kobject_get_path(kset, kobj, GFP_KERNEL);
- if (!kobj_path)
- goto exit;
-
- envp [i++] = scratch;
- scratch += sprintf (scratch, "DEVPATH=%s", kobj_path) + 1;
-
- if (kset->hotplug_ops->hotplug) {
- /* have the kset specific function add its stuff */
- retval = kset->hotplug_ops->hotplug (kset, kobj,
- &envp[i], NUM_ENVP - i, scratch,
- BUFFER_SIZE - (scratch - buffer));
- if (retval) {
- pr_debug ("%s - hotplug() returned %d\n",
- __FUNCTION__, retval);
- goto exit;
- }
- }
-
- pr_debug ("%s: %s %s %s %s %s %s %s\n", __FUNCTION__, argv[0], argv[1],
- envp[0], envp[1], envp[2], envp[3], envp[4]);
- retval = call_usermodehelper (argv[0], argv, envp, 0);
- if (retval)
- pr_debug ("%s - call_usermodehelper returned %d\n",
- __FUNCTION__, retval);
-
-exit:
- kfree(kobj_path);
- kfree(buffer);
- kfree(envp);
- return;
-}
-
-void kobject_hotplug(const char *action, struct kobject *kobj)
-{
- struct kobject * top_kobj = kobj;
-
- /* If this kobj does not belong to a kset,
- try to find a parent that does. */
- if (!top_kobj->kset && top_kobj->parent) {
- do {
- top_kobj = top_kobj->parent;
- } while (!top_kobj->kset && top_kobj->parent);
- }
-
- if (top_kobj->kset && top_kobj->kset->hotplug_ops)
- kset_hotplug(action, top_kobj->kset, kobj);
-}
-#else
-void kobject_hotplug(const char *action, struct kobject *kobj)
-{
- return;
-}
-#endif /* CONFIG_HOTPLUG */
-
-/**
- * kobject_init - initialize object.
- * @kobj: object in question.
- */
void kobject_init(struct kobject * kobj)
{
kref_init(&kobj->kref);
@@ -654,7 +530,6 @@
EXPORT_SYMBOL(kobject_add);
EXPORT_SYMBOL(kobject_del);
EXPORT_SYMBOL(kobject_rename);
-EXPORT_SYMBOL(kobject_hotplug);

EXPORT_SYMBOL(kset_register);
EXPORT_SYMBOL(kset_unregister);