dm: add name and uuid to sysfs

Implement simple read-only sysfs entry for device-mapper block device.

This patch adds a simple sysfs directory named "dm" under block device
properties and implements
	- name attribute (string containing mapped device name)
	- uuid attribute (string containing UUID, or empty string if not set)

The kobject is embedded in mapped_device struct, so no additional
memory allocation is needed for initializing sysfs entry.

During the processing of sysfs attribute we need to lock mapped device
which is done by a new function dm_get_from_kobj, which returns the md
associated with kobject and increases the usage count.

Each 'show attribute' function is responsible for its own locking.

Signed-off-by: Milan Broz <mbroz@redhat.com>
Signed-off-by: Alasdair G Kergon <agk@redhat.com>

4 files changed, 136 insertions, 2 deletions

diff --git a/drivers/md/Makefile b/drivers/md/Makefile
index 1c615804ea7..63f0ae94415 100644
--- a/drivers/md/Makefile
+++ b/drivers/md/Makefile
@@ -3,7 +3,7 @@
 #
 
 dm-mod-objs     := dm.o dm-table.o dm-target.o dm-linear.o dm-stripe.o \
-                   dm-ioctl.o dm-io.o dm-kcopyd.o
+                   dm-ioctl.o dm-io.o dm-kcopyd.o dm-sysfs.o
 dm-multipath-objs := dm-path-selector.o dm-mpath.o
 dm-snapshot-objs := dm-snap.o dm-exception-store.o
 dm-mirror-objs  := dm-raid1.o
diff --git a/drivers/md/dm-sysfs.c b/drivers/md/dm-sysfs.c
new file mode 100644
index 00000000000..a2a45e6c7c8
--- /dev/null
+++ b/drivers/md/dm-sysfs.c
@@ -0,0 +1,99 @@
+/*
+ * Copyright (C) 2008 Red Hat, Inc. All rights reserved.
+ *
+ * This file is released under the GPL.
+ */
+
+#include <linux/sysfs.h>
+#include <linux/dm-ioctl.h>
+#include "dm.h"
+
+struct dm_sysfs_attr {
+        struct attribute attr;
+        ssize_t (*show)(struct mapped_device *, char *);
+        ssize_t (*store)(struct mapped_device *, char *);
+};
+
+#define DM_ATTR_RO(_name) \
+struct dm_sysfs_attr dm_attr_##_name = \
+        __ATTR(_name, S_IRUGO, dm_attr_##_name##_show, NULL)
+
+static ssize_t dm_attr_show(struct kobject *kobj, struct attribute *attr,
+                            char *page)
+{
+        struct dm_sysfs_attr *dm_attr;
+        struct mapped_device *md;
+        ssize_t ret;
+
+        dm_attr = container_of(attr, struct dm_sysfs_attr, attr);
+        if (!dm_attr->show)
+                return -EIO;
+
+        md = dm_get_from_kobject(kobj);
+        if (!md)
+                return -EINVAL;
+
+        ret = dm_attr->show(md, page);
+        dm_put(md);
+
+        return ret;
+}
+
+static ssize_t dm_attr_name_show(struct mapped_device *md, char *buf)
+{
+        if (dm_copy_name_and_uuid(md, buf, NULL))
+                return -EIO;
+
+        strcat(buf, "\n");
+        return strlen(buf);
+}
+
+static ssize_t dm_attr_uuid_show(struct mapped_device *md, char *buf)
+{
+        if (dm_copy_name_and_uuid(md, NULL, buf))
+                return -EIO;
+
+        strcat(buf, "\n");
+        return strlen(buf);
+}
+
+static DM_ATTR_RO(name);
+static DM_ATTR_RO(uuid);
+
+static struct attribute *dm_attrs[] = {
+        &dm_attr_name.attr,
+        &dm_attr_uuid.attr,
+        NULL,
+};
+
+static struct sysfs_ops dm_sysfs_ops = {
+        .show   = dm_attr_show,
+};
+
+/*
+ * dm kobject is embedded in mapped_device structure
+ * no need to define release function here
+ */
+static struct kobj_type dm_ktype = {
+        .sysfs_ops      = &dm_sysfs_ops,
+        .default_attrs  = dm_attrs,
+};
+
+/*
+ * Initialize kobj
+ * because nobody using md yet, no need to call explicit dm_get/put
+ */
+int dm_sysfs_init(struct mapped_device *md)
+{
+        return kobject_init_and_add(dm_kobject(md), &dm_ktype,
+                                    &disk_to_dev(dm_disk(md))->kobj,
+                                    "%s", "dm");
+}
+
+/*
+ * Remove kobj, called after all references removed
+ */
+void dm_sysfs_exit(struct mapped_device *md)
+{
+        kobject_put(dm_kobject(md));
+}
diff --git a/drivers/md/dm.c b/drivers/md/dm.c
index 9f9aa64f733..51ba1db4b3e 100644
--- a/drivers/md/dm.c
+++ b/drivers/md/dm.c
@@ -1,6 +1,6 @@
 /*
  * Copyright (C) 2001, 2002 Sistina Software (UK) Limited.
- * Copyright (C) 2004-2006 Red Hat, Inc. All rights reserved.
+ * Copyright (C) 2004-2008 Red Hat, Inc. All rights reserved.
  *
  * This file is released under the GPL.
  */
@@ -167,6 +167,9 @@ struct mapped_device {
 
         /* forced geometry settings */
         struct hd_geometry geometry;
+
+        /* sysfs handle */
+        struct kobject kobj;
 };
 
 #define MIN_IOS 256
@@ -1285,6 +1288,8 @@ int dm_create(int minor, struct mapped_device **result)
         if (!md)
                 return -ENXIO;
 
+        dm_sysfs_init(md);
+
         *result = md;
         return 0;
 }
@@ -1360,6 +1365,7 @@ void dm_put(struct mapped_device *md)
                         dm_table_presuspend_targets(map);
                         dm_table_postsuspend_targets(map);
                 }
+                dm_sysfs_exit(md);
                 dm_table_put(map);
                 __unbind(md);
                 free_dev(md);
@@ -1699,6 +1705,27 @@ struct gendisk *dm_disk(struct mapped_device *md)
         return md->disk;
 }
 
+struct kobject *dm_kobject(struct mapped_device *md)
+{
+        return &md->kobj;
+}
+
+/*
+ * struct mapped_device should not be exported outside of dm.c
+ * so use this check to verify that kobj is part of md structure
+ */
+struct mapped_device *dm_get_from_kobject(struct kobject *kobj)
+{
+        struct mapped_device *md;
+
+        md = container_of(kobj, struct mapped_device, kobj);
+        if (&md->kobj != kobj)
+                return NULL;
+
+        dm_get(md);
+        return md;
+}
+
 int dm_suspended(struct mapped_device *md)
 {
         return test_bit(DMF_SUSPENDED, &md->flags);
diff --git a/drivers/md/dm.h b/drivers/md/dm.h
index bbbe9110f3b..20194e000c5 100644
--- a/drivers/md/dm.h
+++ b/drivers/md/dm.h
@@ -74,6 +74,14 @@ int dm_interface_init(void);
 void dm_interface_exit(void);
 
 /*
+ * sysfs interface
+ */
+int dm_sysfs_init(struct mapped_device *md);
+void dm_sysfs_exit(struct mapped_device *md);
+struct kobject *dm_kobject(struct mapped_device *md);
+struct mapped_device *dm_get_from_kobject(struct kobject *kobj);
+
+/*
  * Targets for linear and striped mappings
  */
 int dm_linear_init(void);