Description: The patch creates a new sysfs entry framework for nbd. The
single existing sysfs entry for nbd (pid) now uses the framework.

From: Paul Clements <paul.clements@steeleye.com>
Signed-off-by: Paul Clements <paul.clements@steeleye.com>
---

 drivers/block/nbd.c |   87 ++++++++++++++++++++++++++++++++++++++--------------
 include/linux/nbd.h |    1 
 2 files changed, 66 insertions(+), 22 deletions(-)

diff --git a/drivers/block/nbd.c b/drivers/block/nbd.c
index e6fc716..23f3619 100644
--- a/drivers/block/nbd.c
+++ b/drivers/block/nbd.c
@@ -383,39 +383,17 @@ harderror:
 	return NULL;
 }
 
-static ssize_t pid_show(struct device *dev,
-			struct device_attribute *attr, char *buf)
-{
-	struct gendisk *disk = dev_to_disk(dev);
-
-	return sprintf(buf, "%ld\n",
-		(long) ((struct nbd_device *)disk->private_data)->pid);
-}
-
-static struct device_attribute pid_attr = {
-	.attr = { .name = "pid", .mode = S_IRUGO},
-	.show = pid_show,
-};
-
 static int nbd_do_it(struct nbd_device *lo)
 {
 	struct request *req;
-	int ret;
 
 	BUG_ON(lo->magic != LO_MAGIC);
 
 	lo->pid = current->pid;
-	ret = sysfs_create_file(&disk_to_dev(lo->disk)->kobj, &pid_attr.attr);
-	if (ret) {
-		printk(KERN_ERR "nbd: sysfs_create_file failed!");
-		lo->pid = 0;
-		return ret;
-	}
 
 	while ((req = nbd_read_stat(lo)) != NULL)
 		nbd_end_request(req);
 
-	sysfs_remove_file(&disk_to_dev(lo->disk)->kobj, &pid_attr.attr);
 	lo->pid = 0;
 	return 0;
 }
@@ -735,6 +713,67 @@ static const struct block_device_operations nbd_fops =
  *  (Just smiley confuses emacs :-)
  */
 
+struct nbd_sysfs_entry {
+	struct attribute attr;
+	ssize_t (*show)(struct nbd_device *, char *);
+	ssize_t (*store)(struct nbd_device *, const char *, size_t);
+};
+
+static ssize_t pid_show(struct nbd_device *lo, char *page)
+{
+	return sprintf(page, "%ld\n", (long)lo->pid);
+}
+
+static struct nbd_sysfs_entry nbd_pid =
+__ATTR(pid, S_IRUGO, pid_show, NULL);
+
+static struct attribute *nbd_default_attrs[] = {
+	&nbd_pid.attr,
+	NULL,
+};
+
+static ssize_t
+nbd_attr_show(struct kobject *kobj, struct attribute *attr, char *page)
+{
+	struct nbd_sysfs_entry *entry = container_of(attr, struct nbd_sysfs_entry, attr);
+	struct nbd_device *lo = container_of(kobj, struct nbd_device, kobj);
+	ssize_t rv;
+
+	if (!entry->show)
+		return -EIO;
+	rv = entry->show(lo, page);
+	return rv;
+}
+
+static ssize_t
+nbd_attr_store(struct kobject *kobj, struct attribute *attr,
+	      const char *page, size_t length)
+{
+	struct nbd_sysfs_entry *entry = container_of(attr, struct nbd_sysfs_entry, attr);
+	struct nbd_device *lo = container_of(kobj, struct nbd_device, kobj);
+	ssize_t rv;
+
+	if (!entry->store)
+		return -EIO;
+	if (!capable(CAP_SYS_ADMIN))
+		return -EACCES;
+	mutex_lock(&lo->tx_lock);
+	rv = entry->store(lo, page, length);
+	mutex_unlock(&lo->tx_lock);
+
+	return rv;
+}
+
+static const struct sysfs_ops nbd_sysfs_ops = {
+	.show   = nbd_attr_show,
+	.store  = nbd_attr_store,
+};
+
+static struct kobj_type nbd_ktype = {
+	.sysfs_ops      = &nbd_sysfs_ops,
+	.default_attrs  = nbd_default_attrs,
+};
+
 static int __init nbd_init(void)
 {
 	int err = -ENOMEM;
@@ -786,6 +825,7 @@ static int __init nbd_init(void)
 	dprintk(DBG_INIT, "nbd: debugflags=0x%x\n", debugflags);
 
 	for (i = 0; i < nbds_max; i++) {
+		int error;
 		struct gendisk *disk = nbd_dev[i].disk;
 		nbd_dev[i].file = NULL;
 		nbd_dev[i].magic = LO_MAGIC;
@@ -805,6 +845,8 @@ static int __init nbd_init(void)
 		sprintf(disk->disk_name, "nbd%d", i);
 		set_capacity(disk, 0);
 		add_disk(disk);
+		error = kobject_init_and_add(&nbd_dev[i].kobj, &nbd_ktype,
+				&disk_to_dev(disk)->kobj, "%s", "nbd");
 	}
 
 	return 0;
@@ -828,6 +870,7 @@ static void __exit nbd_cleanup(void)
 			blk_cleanup_queue(disk->queue);
 			put_disk(disk);
 		}
+		kobject_del(&nbd_dev[i].kobj);
 	}
 	unregister_blkdev(NBD_MAJOR, "nbd");
 	kfree(nbd_dev);
diff --git a/include/linux/nbd.h b/include/linux/nbd.h
index d146ca1..c795e28 100644
--- a/include/linux/nbd.h
+++ b/include/linux/nbd.h
@@ -68,6 +68,7 @@ struct nbd_device {
 	u64 bytesize;
 	pid_t pid; /* pid of nbd-client, if attached */
 	int xmit_timeout;
+	struct kobject kobj;
 };
 
 #endif