patch sysfs-add-sys-dev-char-block-to-lookup-sysfs-path-by-major-minor.patch added to gregkh-2.6 tree

patch sysfs-add-sys-dev-char-block-to-lookup-sysfs-path-by-major-minor.patch added to gregkh-2.6 tree

[gregkh]

This is a note to let you know that I've just added the patch titled

     Subject: sysfs: add /sys/dev/{char,block} to lookup sysfs path by major:minor

to my gregkh-2.6 tree.  Its filename is

     sysfs-add-sys-dev-char-block-to-lookup-sysfs-path-by-major-minor.patch

This tree can be found at 
    http://www.kernel.org/pub/linux/kernel/people/gregkh/gregkh-2.6/patches/


>From dan.j.williams@intel.com Mon Apr 21 10:51:11 2008
From: Dan Williams <dan.j.williams@intel.com>
Date: Mon, 21 Apr 2008 10:51:07 -0700
Subject: sysfs: add /sys/dev/{char,block} to lookup sysfs path by major:minor
To: Greg KH <greg@kroah.com>, Andrew Morton <akpm@linux-foundation.org>
Cc: linux-kernel <linux-kernel@vger.kernel.org>
Message-ID: <1208800267.26479.3.camel@dwillia2-linux.ch.intel.com>

From: Dan Williams <dan.j.williams@intel.com>

Why?:
There are occasions where userspace would like to access sysfs
attributes for a device but it may not know how sysfs has named the
device or the path.  For example what is the sysfs path for
/dev/disk/by-id/ata-ST3160827AS_5MT004CK?  With this change a call to
stat(2) returns the major:minor then userspace can see that
/sys/dev/block/8:32 links to /sys/block/sdc.

What are the alternatives?:
1/ Add an ioctl to return the path: Doable, but sysfs is meant to reduce
   the need to proliferate ioctl interfaces into the kernel, so this
   seems counter productive.

2/ Use udev to create these symlinks: Also doable, but it adds a
   udev dependency to utilities that might be running in a limited
   environment like an initramfs.

3/ Do a full-tree search of sysfs.

[kay.sievers@vrfy.org: fix duplicate registrations]
[kay.sievers@vrfy.org: cleanup suggestions]

Cc: Neil Brown <neilb@suse.de>
Cc: Tejun Heo <htejun@gmail.com>
Cc: Kay Sievers <kay.sievers@vrfy.org>
Cc: SL Baur <steve@xemacs.org>
Acked-by: Kay Sievers <kay.sievers@vrfy.org>
Acked-by: Mark Lord <lkml@rtr.ca>
Acked-by: H. Peter Anvin <hpa@zytor.com>
Signed-off-by: Dan Williams <dan.j.williams@intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

---
 Documentation/ABI/testing/sysfs-dev |   20 ++++++++
 Documentation/filesystems/sysfs.txt |    6 ++
 block/genhd.c                       |    5 +-
 drivers/base/class.c                |    4 +
 drivers/base/core.c                 |   83 +++++++++++++++++++++++++++++++++++-
 drivers/usb/core/devio.c            |    5 ++
 include/linux/device.h              |    3 +
 7 files changed, 124 insertions(+), 2 deletions(-)

--- a/block/genhd.c
+++ b/block/genhd.c
@@ -360,7 +360,10 @@ static struct kobject *base_probe(dev_t 
 
 static int __init genhd_device_init(void)
 {
-	int error = class_register(&block_class);
+	int error;
+
+	block_class.dev_kobj = sysfs_dev_block_kobj;
+	error = class_register(&block_class);
 	if (unlikely(error))
 		return error;
 	bdev_map = kobj_map_init(base_probe, &block_class_lock);
--- /dev/null
+++ b/Documentation/ABI/testing/sysfs-dev
@@ -0,0 +1,20 @@
+What:		/sys/dev
+Date:		April 2008
+KernelVersion:	2.6.26
+Contact:	Dan Williams <dan.j.williams@intel.com>
+Description:	The /sys/dev tree provides a method to look up the sysfs
+		path for a device using the information returned from
+		stat(2).  There are two directories, 'block' and 'char',
+		beneath /sys/dev containing symbolic links with names of
+		the form "<major>:<minor>".  These links point to the
+		corresponding sysfs path for the given device.
+
+		Example:
+		$ readlink /sys/dev/block/8:32
+		../../block/sdc
+
+		Entries in /sys/dev/char and /sys/dev/block will be
+		dynamically created and destroyed as devices enter and
+		leave the system.
+
+Users:		mdadm <linux-raid@vger.kernel.org>
--- a/Documentation/filesystems/sysfs.txt
+++ b/Documentation/filesystems/sysfs.txt
@@ -248,6 +248,7 @@ The top level sysfs directory looks like
 block/
 bus/
 class/
+dev/
 devices/
 firmware/
 net/
@@ -274,6 +275,11 @@ fs/ contains a directory for some filesy
 filesystem wanting to export attributes must create its own hierarchy
 below fs/ (see ./fuse.txt for an example).
 
+dev/ contains two directories char/ and block/. Inside these two
+directories there are symlinks named <major>:<minor>.  These symlinks
+point to the sysfs directory for the given device.  /sys/dev provides a
+quick way to lookup the sysfs interface for a device from the result of
+a stat(2) operation.
 
 More information can driver-model specific features can be found in
 Documentation/driver-model/. 
--- a/drivers/base/class.c
+++ b/drivers/base/class.c
@@ -149,6 +149,10 @@ int class_register(struct class *cls)
 	if (error)
 		return error;
 
+	/* set the default /sys/dev directory for devices of this class */
+	if (!cls->dev_kobj)
+		cls->dev_kobj = sysfs_dev_char_kobj;
+
 #if defined(CONFIG_SYSFS_DEPRECATED) && defined(CONFIG_BLOCK)
 	/* let the block class directory show up in the root of sysfs */
 	if (cls != &block_class)
--- a/drivers/base/core.c
+++ b/drivers/base/core.c
@@ -27,6 +27,9 @@
 
 int (*platform_notify)(struct device *dev) = NULL;
 int (*platform_notify_remove)(struct device *dev) = NULL;
+static struct kobject *dev_kobj;
+struct kobject *sysfs_dev_char_kobj;
+struct kobject *sysfs_dev_block_kobj;
 
 #ifdef CONFIG_BLOCK
 static inline int device_is_not_partition(struct device *dev)
@@ -761,6 +764,54 @@ static void device_remove_class_symlinks
 }
 
 /**
+ * device_to_dev_kobj - select a /sys/dev/ directory for the device
+ * @dev: device
+ *
+ * By default we select char/ for new entries.  Setting class->dev_obj
+ * to NULL prevents an entry from being created.  class->dev_kobj must
+ * be set (or cleared) before any devices are registered to the class
+ * otherwise device_create_sys_dev_entry() and
+ * device_remove_sys_dev_entry() will disagree about the the presence
+ * of the link.
+ */
+static struct kobject *device_to_dev_kobj(struct device *dev)
+{
+	struct kobject *kobj;
+
+	if (dev->class)
+		kobj = dev->class->dev_kobj;
+	else
+		kobj = sysfs_dev_char_kobj;
+
+	return kobj;
+}
+
+static int device_create_sys_dev_entry(struct device *dev)
+{
+	struct kobject *kobj = device_to_dev_kobj(dev);
+	int error = 0;
+	char devt_str[15];
+
+	if (kobj) {
+		format_dev_t(devt_str, dev->devt);
+		error = sysfs_create_link(kobj, &dev->kobj, devt_str);
+	}
+
+	return error;
+}
+
+static void device_remove_sys_dev_entry(struct device *dev)
+{
+	struct kobject *kobj = device_to_dev_kobj(dev);
+	char devt_str[15];
+
+	if (kobj) {
+		format_dev_t(devt_str, dev->devt);
+		sysfs_remove_link(kobj, devt_str);
+	}
+}
+
+/**
  * device_add - add device to device hierarchy.
  * @dev: device.
  *
@@ -810,6 +861,10 @@ int device_add(struct device *dev)
 		error = device_create_file(dev, &devt_attr);
 		if (error)
 			goto ueventattrError;
+
+		error = device_create_sys_dev_entry(dev);
+		if (error)
+			goto devtattrError;
 	}
 
 	error = device_add_class_symlinks(dev);
@@ -854,6 +909,9 @@ int device_add(struct device *dev)
 	device_remove_class_symlinks(dev);
  SymlinkError:
 	if (MAJOR(dev->devt))
+		device_remove_sys_dev_entry(dev);
+ devtattrError:
+	if (MAJOR(dev->devt))
 		device_remove_file(dev, &devt_attr);
  ueventattrError:
 	device_remove_file(dev, &uevent_attr);
@@ -929,8 +987,10 @@ void device_del(struct device *dev)
 	device_pm_remove(dev);
 	if (parent)
 		klist_del(&dev->knode_parent);
-	if (MAJOR(dev->devt))
+	if (MAJOR(dev->devt)) {
+		device_remove_sys_dev_entry(dev);
 		device_remove_file(dev, &devt_attr);
+	}
 	if (dev->class) {
 		device_remove_class_symlinks(dev);
 
@@ -1055,7 +1115,25 @@ int __init devices_init(void)
 	devices_kset = kset_create_and_add("devices", &device_uevent_ops, NULL);
 	if (!devices_kset)
 		return -ENOMEM;
+	dev_kobj = kobject_create_and_add("dev", NULL);
+	if (!dev_kobj)
+		goto dev_kobj_err;
+	sysfs_dev_block_kobj = kobject_create_and_add("block", dev_kobj);
+	if (!sysfs_dev_block_kobj)
+		goto block_kobj_err;
+	sysfs_dev_char_kobj = kobject_create_and_add("char", dev_kobj);
+	if (!sysfs_dev_char_kobj)
+		goto char_kobj_err;
+
 	return 0;
+
+ char_kobj_err:
+	kobject_put(sysfs_dev_block_kobj);
+ block_kobj_err:
+	kobject_put(dev_kobj);
+ dev_kobj_err:
+	kset_unregister(devices_kset);
+	return -ENOMEM;
 }
 
 EXPORT_SYMBOL_GPL(device_for_each_child);
@@ -1351,4 +1429,7 @@ void device_shutdown(void)
 			dev->driver->shutdown(dev);
 		}
 	}
+	kobject_put(sysfs_dev_char_kobj);
+	kobject_put(sysfs_dev_block_kobj);
+	kobject_put(dev_kobj);
 }
--- a/drivers/usb/core/devio.c
+++ b/drivers/usb/core/devio.c
@@ -1748,6 +1748,11 @@ int __init usb_devio_init(void)
 		usb_classdev_class = NULL;
 		goto out;
 	}
+	/* devices of this class shadow the major:minor of their parent
+	 * device, so clear ->dev_kobj to prevent adding duplicate entries
+	 * to /sys/dev
+	 */
+	usb_classdev_class->dev_kobj = NULL;
 
 	usb_register_notify(&usbdev_nb);
 #endif
--- a/include/linux/device.h
+++ b/include/linux/device.h
@@ -194,6 +194,7 @@ struct class {
 	struct semaphore	sem; /* locks children, devices, interfaces */
 	struct class_attribute		*class_attrs;
 	struct device_attribute		*dev_attrs;
+	struct kobject			*dev_kobj;
 
 	int (*dev_uevent)(struct device *dev, struct kobj_uevent_env *env);
 
@@ -206,6 +207,8 @@ struct class {
 	struct pm_ops *pm;
 };
 
+extern struct kobject *sysfs_dev_block_kobj;
+extern struct kobject *sysfs_dev_char_kobj;
 extern int __must_check class_register(struct class *class);
 extern void class_unregister(struct class *class);
 extern int class_for_each_device(struct class *class, void *data,


Patches currently in gregkh-2.6 which might be from dan.j.williams@intel.com are

driver-core/sysfs-add-sys-dev-char-block-to-lookup-sysfs-path-by-major-minor.patch

Re: patch sysfs-add-sys-dev-char-block-to-lookup-sysfs-path-by-major-minor.patch added to gregkh-2.6 tree

[SL Baur]

On 4/28/08, gregkh@suse.de <gregkh@suse.de> wrote:
>
>  This is a note to let you know that I've just added the patch titled
>
>      Subject: sysfs: add /sys/dev/{char,block} to lookup sysfs path by major:minor
>
>  to my gregkh-2.6 tree.  Its filename is
>
>      sysfs-add-sys-dev-char-block-to-lookup-sysfs-path-by-major-minor.patch

>  +       char devt_str[15];
>  +
>  +       if (kobj) {
>  +               format_dev_t(devt_str, dev->devt);

This part is ugly, but is not the fault of the patch.  The ill-
considered interface for `format_dev_t' is something that probably
noone wants to fix.

Otherwise, still OK with me.

Reviewed-by: SL Baur <steve@xemacs.org>

(Is Reviewed-by not sticky?)

-sb

Re: patch sysfs-add-sys-dev-char-block-to-lookup-sysfs-path-by-major-minor.pat ch added to gregkh-2.6 tree

[Greg KH]

On Tue, Apr 29, 2008 at 12:48:11AM -0700, SL Baur wrote:
> On 4/28/08, gregkh@suse.de <gregkh@suse.de> wrote:
> >
> >  This is a note to let you know that I've just added the patch titled
> >
> >      Subject: sysfs: add /sys/dev/{char,block} to lookup sysfs path by major:minor
> >
> >  to my gregkh-2.6 tree.  Its filename is
> >
> >      sysfs-add-sys-dev-char-block-to-lookup-sysfs-path-by-major-minor.patch
> 
> >  +       char devt_str[15];
> >  +
> >  +       if (kobj) {
> >  +               format_dev_t(devt_str, dev->devt);
> 
> This part is ugly, but is not the fault of the patch.  The ill-
> considered interface for `format_dev_t' is something that probably
> noone wants to fix.

Why not?  Patches are always welcome, it's not like that function is
used in that many different places, should be a simple change...

> Otherwise, still OK with me.
> 
> Reviewed-by: SL Baur <steve@xemacs.org>
> 
> (Is Reviewed-by not sticky?)

Yes, it is, I'll add it to my version of the patch.

thanks,

greg k-h

Re: What to do about the 2TB limit on HDIO_GETGEO ?

[Dan Williams]

Subject: sysfs: add /sys/dev/{char,block} to lookup sysfs path by major:minor

From: Dan Williams <dan.j.williams@intel.com>

Why?:
There are occasions where userspace would like to access sysfs
attributes for a device but it may not know how sysfs has named the
device or the path.  For example what is the sysfs path for
/dev/disk/by-id/ata-ST3160827AS_5MT004CK?  With this change a call to
stat(2) returns the major:minor then userspace can see that
/sys/dev/block/8:32 links to /sys/block/sdc.

What are the alternatives?:
1/ Add an ioctl to return the path: Doable, but sysfs is meant to reduce
   the need to proliferate ioctl interfaces into the kernel, so this
   seems counter productive.

2/ Use udev to create these symlinks: Also doable, but it adds a
   udev dependency to utilities that might be running in a limited
   environment like an initramfs.

3/ Do a full-tree search of sysfs.

Cc: NeilBrown <neilb@suse.de>
Cc: Tejun Heo <htejun@gmail.com>
Cc: Kay Sievers <kay.sievers@vrfy.org>
Cc: Greg KH <gregkh@suse.de>
Acked-by: Mark Lord <lkml@rtr.ca>
Acked-by: H. Peter Anvin <hpa@zytor.com>
Reviewed-by: SL Baur <steve@xemacs.org>
Signed-off-by: Dan Williams <dan.j.williams@intel.com>
---

Andrew here is an updated patch with some presumptive acked-by's from Mark and hpa.

* fixed up ENOMEM handling in devices_init()
* added a short blurb in Documentation/filesystems/sysfs.txt
* dropped the size of the buffer passed to format_dev_t a bit

 Documentation/filesystems/sysfs.txt |    6 +++++
 drivers/base/core.c                 |   46 ++++++++++++++++++++++++++++++++++-
 2 files changed, 51 insertions(+), 1 deletions(-)


diff --git a/Documentation/filesystems/sysfs.txt b/Documentation/filesystems/sysfs.txt
index 7f27b8f..9e9c348 100644
--- a/Documentation/filesystems/sysfs.txt
+++ b/Documentation/filesystems/sysfs.txt
@@ -248,6 +248,7 @@ The top level sysfs directory looks like:
 block/
 bus/
 class/
+dev/
 devices/
 firmware/
 net/
@@ -274,6 +275,11 @@ fs/ contains a directory for some filesystems.  Currently each
 filesystem wanting to export attributes must create its own hierarchy
 below fs/ (see ./fuse.txt for an example).
 
+dev/ contains two directories char/ and block/. Inside these two
+directories there are symlinks named <major>:<minor>.  These symlinks
+point to the sysfs directory for the given device.  /sys/dev provides a
+quick way to lookup the sysfs interface for a device from the result of
+a stat(2) operation.
 
 More information can driver-model specific features can be found in
 Documentation/driver-model/. 
diff --git a/drivers/base/core.c b/drivers/base/core.c
index 24198ad..ba21118 100644
--- a/drivers/base/core.c
+++ b/drivers/base/core.c
@@ -27,6 +27,9 @@
 
 int (*platform_notify)(struct device *dev) = NULL;
 int (*platform_notify_remove)(struct device *dev) = NULL;
+static struct kobject *dev_kobj;
+static struct kobject *char_kobj;
+static struct kobject *block_kobj;
 
 #ifdef CONFIG_BLOCK
 static inline int device_is_not_partition(struct device *dev)
@@ -759,6 +762,11 @@ static void device_remove_class_symlinks(struct device *dev)
 	sysfs_remove_link(&dev->kobj, "subsystem");
 }
 
+static struct kobject *device_to_dev_kobj(struct device *dev)
+{
+	return dev->class == &block_class ? block_kobj : char_kobj;
+}
+
 /**
  * device_add - add device to device hierarchy.
  * @dev: device.
@@ -775,6 +783,7 @@ int device_add(struct device *dev)
 	struct device *parent = NULL;
 	struct class_interface *class_intf;
 	int error;
+	char devt_str[15];
 
 	dev = get_device(dev);
 	if (!dev || !strlen(dev->bus_id)) {
@@ -806,9 +815,16 @@ int device_add(struct device *dev)
 		goto attrError;
 
 	if (MAJOR(dev->devt)) {
+		struct kobject *kobj = device_to_dev_kobj(dev);
+
 		error = device_create_file(dev, &devt_attr);
 		if (error)
 			goto ueventattrError;
+
+		format_dev_t(devt_str, dev->devt);
+		error = sysfs_create_link(kobj, &dev->kobj, devt_str);
+		if (error)
+			goto devtattrError;
 	}
 
 	error = device_add_class_symlinks(dev);
@@ -854,6 +870,9 @@ int device_add(struct device *dev)
 	device_remove_class_symlinks(dev);
  SymlinkError:
 	if (MAJOR(dev->devt))
+		sysfs_remove_link(device_to_dev_kobj(dev), devt_str);
+ devtattrError:
+	if (MAJOR(dev->devt))
 		device_remove_file(dev, &devt_attr);
  ueventattrError:
 	device_remove_file(dev, &uevent_attr);
@@ -925,12 +944,16 @@ void device_del(struct device *dev)
 {
 	struct device *parent = dev->parent;
 	struct class_interface *class_intf;
+	char devt_str[15];
 
 	device_pm_remove(dev);
 	if (parent)
 		klist_del(&dev->knode_parent);
-	if (MAJOR(dev->devt))
+	if (MAJOR(dev->devt)) {
+		format_dev_t(devt_str, dev->devt);
+		sysfs_remove_link(device_to_dev_kobj(dev), devt_str);
 		device_remove_file(dev, &devt_attr);
+	}
 	if (dev->class) {
 		device_remove_class_symlinks(dev);
 
@@ -1055,7 +1078,25 @@ int __init devices_init(void)
 	devices_kset = kset_create_and_add("devices", &device_uevent_ops, NULL);
 	if (!devices_kset)
 		return -ENOMEM;
+	dev_kobj = kobject_create_and_add("dev", NULL);
+	if (!dev_kobj)
+		goto dev_kobj_err;
+	block_kobj = kobject_create_and_add("block", dev_kobj);
+	if (!block_kobj)
+		goto block_kobj_err;
+	char_kobj = kobject_create_and_add("char", dev_kobj);
+	if (!char_kobj)
+		goto char_kobj_err;
+
 	return 0;
+
+ char_kobj_err:
+	kobject_put(block_kobj);
+ block_kobj_err:
+	kobject_put(dev_kobj);
+ dev_kobj_err:
+	kset_unregister(devices_kset);
+	return -ENOMEM;
 }
 
 EXPORT_SYMBOL_GPL(device_for_each_child);
@@ -1380,4 +1421,7 @@ void device_shutdown(void)
 			dev->driver->shutdown(dev);
 		}
 	}
+	kobject_put(char_kobj);
+	kobject_put(block_kobj);
+	kobject_put(dev_kobj);
 }

patch sysfs-add-sys-dev-char-block-to-lookup-sysfs-path-by-major-minor.patch added to gregkh-2.6 tree

[gregkh]

This is a note to let you know that I've just added the patch titled

     Subject: sysfs: add /sys/dev/{char,block} to lookup sysfs path by major:minor

to my gregkh-2.6 tree.  Its filename is

     sysfs-add-sys-dev-char-block-to-lookup-sysfs-path-by-major-minor.patch

This tree can be found at 
    http://www.kernel.org/pub/linux/kernel/people/gregkh/gregkh-2.6/patches/


>From dan.j.williams@intel.com  Wed Apr 16 13:49:38 2008
From: Dan Williams <dan.j.williams@intel.com>
Date: Tue, 15 Apr 2008 16:43:15 -0700
Subject: sysfs: add /sys/dev/{char,block} to lookup sysfs path by major:minor
To: Andrew Morton <akpm@linux-foundation.org>
Cc: James Bottomley <James.Bottomley@HansenPartnership.com>, Kay Sievers <kay.sievers@vrfy.org>, Tejun Heo <htejun@gmail.com>, Mark Lord <lkml@rtr.ca>, Greg KH <gregkh@suse.de>, Jens Axboe <axboe@kernel.dk>, Jeff Garzik <jgarzik@pobox.com>, Linus Torvalds <torvalds@linux-foundation.org>, Linux Kernel <linux-kernel@vger.kernel.org>, IDE/ATA development list <linux-ide@vger.kernel.org>, linux-scsi <linux-scsi@vger.kernel.org>, "H. Peter Anvin" <hpa@zytor.com>
Message-ID: <1208302995.21877.12.camel@dwillia2-linux.ch.intel.com>


From: Dan Williams <dan.j.williams@intel.com>

Why?:
There are occasions where userspace would like to access sysfs
attributes for a device but it may not know how sysfs has named the
device or the path.  For example what is the sysfs path for
/dev/disk/by-id/ata-ST3160827AS_5MT004CK?  With this change a call to
stat(2) returns the major:minor then userspace can see that
/sys/dev/block/8:32 links to /sys/block/sdc.

What are the alternatives?:
1/ Add an ioctl to return the path: Doable, but sysfs is meant to reduce
   the need to proliferate ioctl interfaces into the kernel, so this
   seems counter productive.

2/ Use udev to create these symlinks: Also doable, but it adds a
   udev dependency to utilities that might be running in a limited
   environment like an initramfs.

3/ Do a full-tree search of sysfs.

Cc: Neil Brown <neilb@suse.de>
Cc: Tejun Heo <htejun@gmail.com>
Cc: Kay Sievers <kay.sievers@vrfy.org>
Cc: Greg KH <gregkh@suse.de>
Acked-by: Mark Lord <lkml@rtr.ca>
Acked-by: H. Peter Anvin <hpa@zytor.com>
Reviewed-by: SL Baur <steve@xemacs.org>
Signed-off-by: Dan Williams <dan.j.williams@intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

---
 Documentation/filesystems/sysfs.txt |    6 ++++
 drivers/base/core.c                 |   46 +++++++++++++++++++++++++++++++++++-
 2 files changed, 51 insertions(+), 1 deletion(-)

--- a/Documentation/filesystems/sysfs.txt
+++ b/Documentation/filesystems/sysfs.txt
@@ -248,6 +248,7 @@ The top level sysfs directory looks like
 block/
 bus/
 class/
+dev/
 devices/
 firmware/
 net/
@@ -274,6 +275,11 @@ fs/ contains a directory for some filesy
 filesystem wanting to export attributes must create its own hierarchy
 below fs/ (see ./fuse.txt for an example).
 
+dev/ contains two directories char/ and block/. Inside these two
+directories there are symlinks named <major>:<minor>.  These symlinks
+point to the sysfs directory for the given device.  /sys/dev provides a
+quick way to lookup the sysfs interface for a device from the result of
+a stat(2) operation.
 
 More information can driver-model specific features can be found in
 Documentation/driver-model/. 
--- a/drivers/base/core.c
+++ b/drivers/base/core.c
@@ -27,6 +27,9 @@
 
 int (*platform_notify)(struct device *dev) = NULL;
 int (*platform_notify_remove)(struct device *dev) = NULL;
+static struct kobject *dev_kobj;
+static struct kobject *char_kobj;
+static struct kobject *block_kobj;
 
 #ifdef CONFIG_BLOCK
 static inline int device_is_not_partition(struct device *dev)
@@ -760,6 +763,11 @@ static void device_remove_class_symlinks
 	sysfs_remove_link(&dev->kobj, "subsystem");
 }
 
+static struct kobject *device_to_dev_kobj(struct device *dev)
+{
+	return dev->class == &block_class ? block_kobj : char_kobj;
+}
+
 /**
  * device_add - add device to device hierarchy.
  * @dev: device.
@@ -776,6 +784,7 @@ int device_add(struct device *dev)
 	struct device *parent = NULL;
 	struct class_interface *class_intf;
 	int error;
+	char devt_str[15];
 
 	dev = get_device(dev);
 	if (!dev || !strlen(dev->bus_id)) {
@@ -807,9 +816,16 @@ int device_add(struct device *dev)
 		goto attrError;
 
 	if (MAJOR(dev->devt)) {
+		struct kobject *kobj = device_to_dev_kobj(dev);
+
 		error = device_create_file(dev, &devt_attr);
 		if (error)
 			goto ueventattrError;
+
+		format_dev_t(devt_str, dev->devt);
+		error = sysfs_create_link(kobj, &dev->kobj, devt_str);
+		if (error)
+			goto devtattrError;
 	}
 
 	error = device_add_class_symlinks(dev);
@@ -854,6 +870,9 @@ int device_add(struct device *dev)
 	device_remove_class_symlinks(dev);
  SymlinkError:
 	if (MAJOR(dev->devt))
+		sysfs_remove_link(device_to_dev_kobj(dev), devt_str);
+ devtattrError:
+	if (MAJOR(dev->devt))
 		device_remove_file(dev, &devt_attr);
  ueventattrError:
 	device_remove_file(dev, &uevent_attr);
@@ -925,12 +944,16 @@ void device_del(struct device *dev)
 {
 	struct device *parent = dev->parent;
 	struct class_interface *class_intf;
+	char devt_str[15];
 
 	device_pm_remove(dev);
 	if (parent)
 		klist_del(&dev->knode_parent);
-	if (MAJOR(dev->devt))
+	if (MAJOR(dev->devt)) {
+		format_dev_t(devt_str, dev->devt);
+		sysfs_remove_link(device_to_dev_kobj(dev), devt_str);
 		device_remove_file(dev, &devt_attr);
+	}
 	if (dev->class) {
 		device_remove_class_symlinks(dev);
 
@@ -1055,7 +1078,25 @@ int __init devices_init(void)
 	devices_kset = kset_create_and_add("devices", &device_uevent_ops, NULL);
 	if (!devices_kset)
 		return -ENOMEM;
+	dev_kobj = kobject_create_and_add("dev", NULL);
+	if (!dev_kobj)
+		goto dev_kobj_err;
+	block_kobj = kobject_create_and_add("block", dev_kobj);
+	if (!block_kobj)
+		goto block_kobj_err;
+	char_kobj = kobject_create_and_add("char", dev_kobj);
+	if (!char_kobj)
+		goto char_kobj_err;
+
 	return 0;
+
+ char_kobj_err:
+	kobject_put(block_kobj);
+ block_kobj_err:
+	kobject_put(dev_kobj);
+ dev_kobj_err:
+	kset_unregister(devices_kset);
+	return -ENOMEM;
 }
 
 EXPORT_SYMBOL_GPL(device_for_each_child);
@@ -1351,4 +1392,7 @@ void device_shutdown(void)
 			dev->driver->shutdown(dev);
 		}
 	}
+	kobject_put(char_kobj);
+	kobject_put(block_kobj);
+	kobject_put(dev_kobj);
 }


Patches currently in gregkh-2.6 which might be from dan.j.williams@intel.com are

driver-core/sysfs-refill-attribute-buffer-when-reading-from-offset-0.patch
driver-core/sysfs-add-sys-dev-char-block-to-lookup-sysfs-path-by-major-minor.patch