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>

1 files changed, 99 insertions, 0 deletions

diff --git a/drivers/md/dm-sysfs.c b/drivers/md/dm-sysfs.c
new file mode 100644
index 000000000000..a2a45e6c7c8b
--- /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));
+}