[PATCH 01/79] sysfs: add /sys/dev/{char,block} to lookup sysfs path by major:minor
From: Greg Kroah-Hartman
Date: Tue Jul 22 2008 - 01:21:47 EST
From: Dan Williams <dan.j.williams@xxxxxxxxx>
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@xxxxxxxx: fix duplicate registrations]
[kay.sievers@xxxxxxxx: cleanup suggestions]
Cc: Neil Brown <neilb@xxxxxxx>
Cc: Tejun Heo <htejun@xxxxxxxxx>
Acked-by: Kay Sievers <kay.sievers@xxxxxxxx>
Reviewed-by: SL Baur <steve@xxxxxxxxxx>
Acked-by: Kay Sievers <kay.sievers@xxxxxxxx>
Acked-by: Mark Lord <lkml@xxxxxx>
Acked-by: H. Peter Anvin <hpa@xxxxxxxxx>
Signed-off-by: Dan Williams <dan.j.williams@xxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxx>
---
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(-)
create mode 100644 Documentation/ABI/testing/sysfs-dev
diff --git a/Documentation/ABI/testing/sysfs-dev b/Documentation/ABI/testing/sysfs-dev
new file mode 100644
index 0000000..a9f2b8b
--- /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@xxxxxxxxx>
+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@xxxxxxxxxxxxxxx>
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/block/genhd.c b/block/genhd.c
index 9074f38..24e3fc9 100644
--- a/block/genhd.c
+++ b/block/genhd.c
@@ -370,7 +370,10 @@ static struct kobject *base_probe(dev_t devt, int *part, void *data)
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);
diff --git a/drivers/base/class.c b/drivers/base/class.c
index e085af0..71ce3ff 100644
--- a/drivers/base/class.c
+++ b/drivers/base/class.c
@@ -148,6 +148,10 @@ 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)
diff --git a/drivers/base/core.c b/drivers/base/core.c
index ee0a51a..be9aba4 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;
+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)
@@ -776,6 +779,54 @@ int dev_set_name(struct device *dev, const char *fmt, ...)
EXPORT_SYMBOL_GPL(dev_set_name);
/**
+ * 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.
*
@@ -829,6 +880,10 @@ 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);
@@ -873,6 +928,9 @@ 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);
@@ -948,8 +1006,10 @@ 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);
@@ -1074,7 +1134,25 @@ 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);
@@ -1447,4 +1525,7 @@ void device_shutdown(void)
dev->driver->shutdown(dev);
}
}
+ kobject_put(sysfs_dev_char_kobj);
+ kobject_put(sysfs_dev_block_kobj);
+ kobject_put(dev_kobj);
}
diff --git a/drivers/usb/core/devio.c b/drivers/usb/core/devio.c
index 54a350c..6fbc8f5 100644
--- a/drivers/usb/core/devio.c
+++ b/drivers/usb/core/devio.c
@@ -1792,6 +1792,11 @@ 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
diff --git a/include/linux/device.h b/include/linux/device.h
index f71a78d..e49aa74 100644
--- a/include/linux/device.h
+++ b/include/linux/device.h
@@ -193,6 +193,7 @@ 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);
@@ -205,6 +206,8 @@ 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,
--
1.5.6.3
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