Revert mount/umount uevent removal

This change reverts the 033b96fd commit
from Kay Sievers that removed the mount/umount uevents from the kernel.
Some older versions of HAL still depend on these events to detect when a
new device has been mounted.  These events are not correctly emitted,
and are broken by design, and so, should not be relied upon by any
future program.  Instead, the /proc/mounts file should be polled to
properly detect this kind of event.

A feature-removal-schedule.txt entry has been added, noting when this
interface will be removed from the kernel.
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

Documentation/feature-removal-schedule.txt

@@ -171,3 +171,12 @@ Why:	The ISA interface is faster and should be always available. The I2C
 	probing is also known to cause trouble in at least one case (see
 	bug #5889.)
 Who:	Jean Delvare <khali@linux-fr.org>
+
+---------------------------
+
+What:	mount/umount uevents
+When:	February 2007
+Why:	These events are not correct, and do not properly let userspace know
+	when a file system has been mounted or unmounted.  Userspace should
+	poll the /proc/mounts file instead to detect this properly.
+Who:	Greg Kroah-Hartman <gregkh@suse.de>

fs/super.c

@@ -666,6 +666,16 @@ static int test_bdev_super(struct super_block *s, void *data)
 	return (void *)s->s_bdev == data;
 }
 
+static void bdev_uevent(struct block_device *bdev, enum kobject_action action)
+{
+	if (bdev->bd_disk) {
+		if (bdev->bd_part)
+			kobject_uevent(&bdev->bd_part->kobj, action);
+		else
+			kobject_uevent(&bdev->bd_disk->kobj, action);
+	}
+}
+
 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))
@@ -707,8 +717,10 @@ struct super_block *get_sb_bdev(struct file_system_type *fs_type,
 			up_write(&s->s_umount);
 			deactivate_super(s);
 			s = ERR_PTR(error);
-		} else
+		} else {
 			s->s_flags |= MS_ACTIVE;
+			bdev_uevent(bdev, KOBJ_MOUNT);
+		}
 	}
 
 	return s;
@@ -724,6 +736,7 @@ void kill_block_super(struct super_block *sb)
 {
 	struct block_device *bdev = sb->s_bdev;
 
+	bdev_uevent(bdev, KOBJ_UMOUNT);
 	generic_shutdown_super(sb);
 	sync_blockdev(bdev);
 	close_bdev_excl(bdev);

include/linux/kobject.h

@@ -41,8 +41,10 @@ enum kobject_action {
 	KOBJ_ADD	= (__force kobject_action_t) 0x01,	/* exclusive to core */
 	KOBJ_REMOVE	= (__force kobject_action_t) 0x02,	/* exclusive to core */
 	KOBJ_CHANGE	= (__force kobject_action_t) 0x03,	/* device state change */
-	KOBJ_OFFLINE	= (__force kobject_action_t) 0x04,	/* device offline */
-	KOBJ_ONLINE	= (__force kobject_action_t) 0x05,	/* device online */
+	KOBJ_MOUNT	= (__force kobject_action_t) 0x04,	/* mount event for block devices (broken) */
+	KOBJ_UMOUNT	= (__force kobject_action_t) 0x05,	/* umount event for block devices (broken) */
+	KOBJ_OFFLINE	= (__force kobject_action_t) 0x06,	/* device offline */
+	KOBJ_ONLINE	= (__force kobject_action_t) 0x07,	/* device online */
 };
 
 struct kobject {

lib/kobject_uevent.c

@@ -38,6 +38,10 @@ static char *action_to_string(enum kobject_action action)
 		return "remove";
 	case KOBJ_CHANGE:
 		return "change";
+	case KOBJ_MOUNT:
+		return "mount";
+	case KOBJ_UMOUNT:
+		return "umount";
 	case KOBJ_OFFLINE:
 		return "offline";
 	case KOBJ_ONLINE: