[PATCH RFC v2] btrfs: add sysfs layout to show volume info

[Anand Jain <anand.jain@oracle.com>]

From: Anand Jain <Anand.Jain@oracle.com>

Not yet ready for integration, but for review and testing of the new sysfs layout
which is currently under /sys/fs/btrfs/by_fsid

This patch makes btrfs_fs_devices and btrfs_device information readable
from sysfs. This uses the sysfs group visible entry point to mark
certain attributes visible/hidden depending the FS state (mount/unmounted).

The new layout is as shown below.

/sys/fs/btrfs/by_fsid*
	./7b047f4d-c2ce-4f22-94a3-68c09057f1bf*
		status
		fsid*
		missing_devices
		num_devices*
		open_devices
		opened*
		rotating
		rw_devices
		seeding
		total_devices*
		total_rw_bytes
		./e6701882-220a-4416-98ac-a99f095bddcc*
			active_pending
			bdev
			bytes_used
			can_discard
			devid*
			dev_root_fsid
			devstats_valid
			dev_totalbytes
			generation*
			in_fs_metadata
			io_align
			io_width
			missing
			name*
			nobarriers
			replace_tgtdev
			sector_size
			total_bytes
			type
			uuid*
			writeable

(* indicates that attribute will be visible even when device is
unmounted but registered with btrfs kernel)

The old kobject <fsid> will be merged into this new 'by_fsid' kobject,
so that older attributes under <fsid> and newer attributed under by_fsid
will be merged together as well.

v2: added support for device add/delete/replace
    rebase on the latest integration branch

Signed-off-by: Anand Jain <anand.jain@oracle.com>
---
 fs/btrfs/dev-replace.c |   7 +
 fs/btrfs/super.c       |  15 ++
 fs/btrfs/sysfs.c       | 383 +++++++++++++++++++++++++++++++++++++++++++++++++
 fs/btrfs/sysfs.h       |   6 +
 fs/btrfs/volumes.c     |  42 ++++++
 fs/btrfs/volumes.h     |   6 +
 6 files changed, 459 insertions(+)

diff --git a/fs/btrfs/dev-replace.c b/fs/btrfs/dev-replace.c
index 715a115..31ce3a9 100644
--- a/fs/btrfs/dev-replace.c
+++ b/fs/btrfs/dev-replace.c
@@ -474,6 +474,7 @@ static int btrfs_dev_replace_finishing(struct btrfs_fs_info *fs_info,
 	u8 uuid_tmp[BTRFS_UUID_SIZE];
 	struct btrfs_trans_handle *trans;
 	int ret = 0;
+	char uuid_buf[BTRFS_UUID_UNPARSED_SIZE];
 
 	/* don't allow cancel or unmount to disturb the finishing procedure */
 	mutex_lock(&dev_replace->lock_finishing_cancel_unmount);
@@ -595,7 +596,13 @@ static int btrfs_dev_replace_finishing(struct btrfs_fs_info *fs_info,
 	/* replace the sysfs entry */
 	btrfs_kobj_rm_device(fs_info, src_device);
 	btrfs_kobj_add_device(fs_info, tgt_device);
+	btrfs_destroy_dev_sysfs(src_device);
 	btrfs_rm_dev_replace_free_srcdev(fs_info, src_device);
+	snprintf(uuid_buf, BTRFS_UUID_UNPARSED_SIZE, "%pU",
+						tgt_device->uuid);
+	if (kobject_rename(&tgt_device->dev_kobj, uuid_buf))
+		printk(KERN_ERR "BTRFS: sysfs uuid %s rename error\n",
+							uuid_buf);
 
 	/* write back the superblocks */
 	trans = btrfs_start_transaction(root, 0);
diff --git a/fs/btrfs/super.c b/fs/btrfs/super.c
index 017d92d..918eb9d 100644
--- a/fs/btrfs/super.c
+++ b/fs/btrfs/super.c
@@ -1389,6 +1389,11 @@ static struct dentry *btrfs_mount(struct file_system_type *fs_type, int flags,
 		goto error_sec_opts;
 	}
 
+	error = btrfs_update_by_fsid_sysfs_group(fs_devices);
+	if (error)
+		btrfs_warn(fs_info, "sysfs update error during mount: %d",
+			error);
+
 	return root;
 
 error_close_devices:
@@ -1885,8 +1890,18 @@ static int btrfs_statfs(struct dentry *dentry, struct kstatfs *buf)
 static void btrfs_kill_super(struct super_block *sb)
 {
 	struct btrfs_fs_info *fs_info = btrfs_sb(sb);
+	struct btrfs_fs_devices *fs_devs = fs_info->fs_devices;
+	int error;
+
+	set_bit(BTRFS_FS_DEVS_UNMOUNTING, &fs_devs->flags);
+	error = btrfs_update_by_fsid_sysfs_group(fs_devs);
+	if (error)
+		btrfs_warn(fs_info, "sysfs update error during unmount: %d",
+			error);
+
 	kill_anon_super(sb);
 	free_fs_info(fs_info);
+	clear_bit(BTRFS_FS_DEVS_UNMOUNTING, &fs_devs->flags);
 }
 
 static struct file_system_type btrfs_fs_type = {
diff --git a/fs/btrfs/sysfs.c b/fs/btrfs/sysfs.c
index 92db3f6..b658812 100644
--- a/fs/btrfs/sysfs.c
+++ b/fs/btrfs/sysfs.c
@@ -25,6 +25,7 @@
 #include <linux/bug.h>
 #include <linux/genhd.h>
 #include <linux/debugfs.h>
+#include <linux/rcustring.h>
 
 #include "ctree.h"
 #include "disk-io.h"
@@ -32,6 +33,18 @@
 #include "sysfs.h"
 #include "volumes.h"
 
+struct kobject *by_fsid;
+static ssize_t btrfs_dev_attr_show(struct kobject *kobj,
+				       struct kobj_attribute *a, char *buf);
+static ssize_t btrfs_dev_attr_store(struct kobject *kobj,
+					struct kobj_attribute *a,
+					const char *buf, size_t count);
+static ssize_t btrfs_fs_devs_attr_show(struct kobject *kobj,
+				       struct kobj_attribute *a, char *buf);
+static ssize_t btrfs_fs_devs_attr_store(struct kobject *kobj,
+					struct kobj_attribute *a,
+					const char *buf, size_t count);
+
 static inline struct btrfs_fs_info *to_fs_info(struct kobject *kobj);
 
 static u64 get_features(struct btrfs_fs_info *fs_info,
@@ -738,13 +751,383 @@ int btrfs_init_sysfs(void)
 	init_feature_attrs();
 	ret = sysfs_create_group(&btrfs_kset->kobj, &btrfs_feature_attr_group);
 
+	by_fsid = kobject_create_and_add("by_fsid", &btrfs_kset->kobj);
+
 	return ret;
 }
 
 void btrfs_exit_sysfs(void)
 {
+	kobject_put(by_fsid);
 	sysfs_remove_group(&btrfs_kset->kobj, &btrfs_feature_attr_group);
 	kset_unregister(btrfs_kset);
 	debugfs_remove_recursive(btrfs_debugfs_root_dentry);
 }
 
+
+/******* Add support for by_fsid *******/
+static ssize_t btrfs_show_uuid(u8 *valptr, char *buf)
+{
+	return snprintf(buf, PAGE_SIZE, "%pU\n", valptr);
+}
+
+static ssize_t btrfs_show_str(char *strptr, char *buf)
+{
+	return snprintf(buf, PAGE_SIZE, "%s\n", strptr);
+}
+
+static ssize_t btrfs_show_u(uint val, char *buf)
+{
+	return snprintf(buf, PAGE_SIZE, "%u\n", val);
+}
+
+static ssize_t btrfs_show_d(int val, char *buf)
+{
+	return snprintf(buf, PAGE_SIZE, "%d\n", val);
+}
+
+static void release_by_fsid_kobj(struct kobject *kobj)
+{
+
+}
+
+struct kobj_type btrfs_by_fsid_ktype = {
+	.sysfs_ops = &kobj_sysfs_ops,
+	.release = release_by_fsid_kobj,
+};
+
+struct btrfs_fs_devs_attr {
+	struct kobj_attribute kobj_attr;
+};
+
+#define to_btrfs_fs_devices(_kobj) container_of(_kobj, struct btrfs_fs_devices, fs_devs_kobj)
+
+#define BTRFS_FS_DEV_ATTR(_name)\
+	static struct btrfs_fs_devs_attr btrfs_fs_devs_attr_##_name = {\
+		.kobj_attr = __INIT_KOBJ_ATTR(_name, S_IRUGO,\
+					btrfs_fs_devs_attr_show,\
+					btrfs_fs_devs_attr_store),\
+	}
+
+BTRFS_FS_DEV_ATTR(fsid);
+BTRFS_FS_DEV_ATTR(num_devices);
+BTRFS_FS_DEV_ATTR(open_devices);
+BTRFS_FS_DEV_ATTR(rw_devices);
+BTRFS_FS_DEV_ATTR(missing_devices);
+BTRFS_FS_DEV_ATTR(total_rw_bytes);
+BTRFS_FS_DEV_ATTR(total_devices);
+BTRFS_FS_DEV_ATTR(opened);
+BTRFS_FS_DEV_ATTR(seeding);
+BTRFS_FS_DEV_ATTR(rotating);
+
+#define BTRFS_FS_DEV_ATTR_PTR(_name) (&btrfs_fs_devs_attr_##_name.kobj_attr.attr)
+
+static struct attribute *btrfs_fs_devs_attrs[] = {
+	BTRFS_FS_DEV_ATTR_PTR(fsid),
+	BTRFS_FS_DEV_ATTR_PTR(num_devices),
+	BTRFS_FS_DEV_ATTR_PTR(open_devices),
+	BTRFS_FS_DEV_ATTR_PTR(rw_devices),
+	BTRFS_FS_DEV_ATTR_PTR(missing_devices),
+	BTRFS_FS_DEV_ATTR_PTR(total_rw_bytes),
+	BTRFS_FS_DEV_ATTR_PTR(total_devices),
+	BTRFS_FS_DEV_ATTR_PTR(opened),
+	BTRFS_FS_DEV_ATTR_PTR(seeding),
+	BTRFS_FS_DEV_ATTR_PTR(rotating),
+	NULL
+};
+
+#define BTRFS_FS_DEVS_GET_ATTR_UUID(attr, name, valprt, buf)\
+	if (attr == BTRFS_FS_DEV_ATTR_PTR(name))\
+		return btrfs_show_uuid(valprt, buf)
+#define BTRFS_FS_DEVS_GET_ATTR_STR(attr, name, strprt, buf)\
+	if (attr == BTRFS_FS_DEV_ATTR_PTR(name))\
+		return btrfs_show_str(strprt, buf)
+#define BTRFS_FS_DEVS_GET_ATTR_U64(attr, name, valprt, buf)\
+	if (attr == BTRFS_FS_DEV_ATTR_PTR(name))\
+		return btrfs_show_u64(valprt, NULL, buf)
+#define BTRFS_FS_DEVS_GET_ATTR_U(attr, name, val, buf)\
+	if (attr == BTRFS_FS_DEV_ATTR_PTR(name))\
+		return btrfs_show_u(val, buf)
+#define BTRFS_FS_DEVS_GET_ATTR_D(attr, name, val, buf)\
+	if (attr == BTRFS_FS_DEV_ATTR_PTR(name))\
+		return btrfs_show_d(val, buf)
+
+static ssize_t btrfs_fs_devs_attr_show(struct kobject *kobj,
+				       struct kobj_attribute *a, char *buf)
+{
+	struct btrfs_fs_devices *fs_devs = to_btrfs_fs_devices(kobj);
+
+	BTRFS_FS_DEVS_GET_ATTR_UUID(&a->attr, fsid, fs_devs->fsid, buf);
+	BTRFS_FS_DEVS_GET_ATTR_U64(&a->attr, num_devices, &fs_devs->num_devices, buf);
+	BTRFS_FS_DEVS_GET_ATTR_U64(&a->attr, open_devices, &fs_devs->open_devices, buf);
+	BTRFS_FS_DEVS_GET_ATTR_U64(&a->attr, rw_devices, &fs_devs->rw_devices, buf);
+	BTRFS_FS_DEVS_GET_ATTR_U64(&a->attr, missing_devices, &fs_devs->missing_devices, buf);
+	BTRFS_FS_DEVS_GET_ATTR_U64(&a->attr, total_rw_bytes, &fs_devs->total_rw_bytes, buf);
+	BTRFS_FS_DEVS_GET_ATTR_U64(&a->attr, total_devices, &fs_devs->total_devices, buf);
+	BTRFS_FS_DEVS_GET_ATTR_D(&a->attr, opened, fs_devs->opened, buf);
+	BTRFS_FS_DEVS_GET_ATTR_D(&a->attr, seeding, fs_devs->seeding, buf);
+	BTRFS_FS_DEVS_GET_ATTR_D(&a->attr, rotating, fs_devs->rotating, buf);
+
+	return 0;
+}
+
+static ssize_t btrfs_fs_devs_attr_store(struct kobject *kobj,
+					struct kobj_attribute *a,
+					const char *buf, size_t count)
+{
+	/*
+	 * we might need some of the parameter to be writable
+	 * but as of now just deny all
+	 */
+	return -EPERM;
+}
+
+
+static umode_t btrfs_fs_devs_attr_visible(struct kobject *kobj,
+				     struct attribute *attr, int unused)
+{
+	struct btrfs_fs_devices *fs_devs = to_btrfs_fs_devices(kobj);
+
+	/* if device is mounted then all is visible */
+	if (fs_devs->opened &&
+		!(test_bit(BTRFS_FS_DEVS_UNMOUNTING, &fs_devs->flags)))
+		return attr->mode|S_IWUSR;
+
+	/* when device is unmounted(ing) show only following set*/
+	if (attr == BTRFS_FS_DEV_ATTR_PTR(num_devices))
+		return attr->mode|S_IWUSR;
+	else if (attr == BTRFS_FS_DEV_ATTR_PTR(total_devices))
+		return attr->mode|S_IWUSR;
+	else if (attr == BTRFS_FS_DEV_ATTR_PTR(opened))
+		return attr->mode|S_IWUSR;
+	else if (attr == BTRFS_FS_DEV_ATTR_PTR(fsid))
+		return attr->mode|S_IWUSR;
+
+	return 0;
+}
+
+static const struct attribute_group btrfs_fs_devs_attr_group = {
+	.attrs = btrfs_fs_devs_attrs,
+	.is_visible = btrfs_fs_devs_attr_visible,
+};
+
+int btrfs_create_fs_devs_sysfs(struct btrfs_fs_devices *fs_devs)
+{
+	int rc;
+
+	rc = kobject_init_and_add(&fs_devs->fs_devs_kobj, &btrfs_by_fsid_ktype,
+			by_fsid, "%pU", fs_devs->fsid);
+
+	rc = sysfs_create_group(&fs_devs->fs_devs_kobj, &btrfs_fs_devs_attr_group);
+	return rc;
+}
+
+int btrfs_update_fs_devs_sysfs(struct btrfs_fs_devices *fs_devs)
+{
+	int rc;
+
+	rc = sysfs_update_group(&fs_devs->fs_devs_kobj, &btrfs_fs_devs_attr_group);
+
+	return rc;
+}
+
+/**** Do the same for the btrfs_device ****/
+
+static void release_btrfs_dev_kobj(struct kobject *kobj)
+{
+
+}
+
+struct kobj_type btrfs_dev_ktype = {
+	.sysfs_ops = &kobj_sysfs_ops,
+	.release = release_btrfs_dev_kobj,
+};
+
+struct btrfs_dev_attr {
+	struct kobj_attribute kobj_attr;
+};
+
+#define to_btrfs_device(_kobj) container_of(_kobj, struct btrfs_device, dev_kobj)
+
+#define BTRFS_DEV_ATTR(_name)\
+	static struct btrfs_dev_attr btrfs_dev_attr_##_name = {\
+		.kobj_attr = __INIT_KOBJ_ATTR(_name, S_IRUGO,\
+					btrfs_dev_attr_show,\
+					btrfs_dev_attr_store),\
+	}
+
+BTRFS_DEV_ATTR(uuid);
+BTRFS_DEV_ATTR(name);
+BTRFS_DEV_ATTR(devid);
+BTRFS_DEV_ATTR(dev_root_fsid);
+BTRFS_DEV_ATTR(generation);
+BTRFS_DEV_ATTR(total_bytes);
+BTRFS_DEV_ATTR(dev_totalbytes);
+BTRFS_DEV_ATTR(bytes_used);
+BTRFS_DEV_ATTR(type);
+BTRFS_DEV_ATTR(io_align);
+BTRFS_DEV_ATTR(io_width);
+BTRFS_DEV_ATTR(sector_size);
+BTRFS_DEV_ATTR(writeable);
+BTRFS_DEV_ATTR(in_fs_metadata);
+BTRFS_DEV_ATTR(missing);
+BTRFS_DEV_ATTR(can_discard);
+BTRFS_DEV_ATTR(replace_tgtdev);
+BTRFS_DEV_ATTR(active_pending);
+BTRFS_DEV_ATTR(nobarriers);
+BTRFS_DEV_ATTR(devstats_valid);
+BTRFS_DEV_ATTR(bdev);
+
+#define BTRFS_DEV_ATTR_PTR(_name) (&btrfs_dev_attr_##_name.kobj_attr.attr)
+
+static struct attribute *btrfs_dev_attrs[] = {
+	BTRFS_DEV_ATTR_PTR(uuid),
+	BTRFS_DEV_ATTR_PTR(name),
+	BTRFS_DEV_ATTR_PTR(devid),
+	BTRFS_DEV_ATTR_PTR(dev_root_fsid),
+	BTRFS_DEV_ATTR_PTR(generation),
+	BTRFS_DEV_ATTR_PTR(total_bytes),
+	BTRFS_DEV_ATTR_PTR(dev_totalbytes),
+	BTRFS_DEV_ATTR_PTR(bytes_used),
+	BTRFS_DEV_ATTR_PTR(type),
+	BTRFS_DEV_ATTR_PTR(io_align),
+	BTRFS_DEV_ATTR_PTR(io_width),
+	BTRFS_DEV_ATTR_PTR(sector_size),
+	BTRFS_DEV_ATTR_PTR(writeable),
+	BTRFS_DEV_ATTR_PTR(in_fs_metadata),
+	BTRFS_DEV_ATTR_PTR(missing),
+	BTRFS_DEV_ATTR_PTR(can_discard),
+	BTRFS_DEV_ATTR_PTR(replace_tgtdev),
+	BTRFS_DEV_ATTR_PTR(active_pending),
+	BTRFS_DEV_ATTR_PTR(nobarriers),
+	BTRFS_DEV_ATTR_PTR(devstats_valid),
+	BTRFS_DEV_ATTR_PTR(bdev),
+	NULL
+};
+
+#define BTRFS_DEV_GET_ATTR_UUID(attr, name, valprt, buf)\
+	if (attr == BTRFS_DEV_ATTR_PTR(name))\
+		return btrfs_show_uuid(valprt, buf)
+#define BTRFS_DEV_GET_ATTR_STR(attr, name, strprt, buf)\
+	if (attr == BTRFS_DEV_ATTR_PTR(name))\
+		return btrfs_show_str(strprt, buf)
+#define BTRFS_DEV_GET_ATTR_U64(attr, name, valprt, buf)\
+	if (attr == BTRFS_DEV_ATTR_PTR(name))\
+		return btrfs_show_u64(valprt, NULL, buf)
+#define BTRFS_DEV_GET_ATTR_U(attr, name, val, buf)\
+	if (attr == BTRFS_DEV_ATTR_PTR(name))\
+		return btrfs_show_u(val, buf)
+#define BTRFS_DEV_GET_ATTR_D(attr, name, val, buf)\
+	if (attr == BTRFS_DEV_ATTR_PTR(name))\
+		return btrfs_show_d(val, buf)
+#define BTRFS_DEV_CHECK_ATTR(attr, name)\
+		attr == BTRFS_DEV_ATTR_PTR(name)
+
+static ssize_t btrfs_dev_attr_show(struct kobject *kobj,
+				       struct kobj_attribute *a, char *buf)
+{
+	struct btrfs_device *dev = to_btrfs_device(kobj);
+
+	/* Todo: handle the missing device case */
+	BTRFS_DEV_GET_ATTR_STR(&a->attr, name, rcu_string_dereference(dev->name), buf);
+	BTRFS_DEV_GET_ATTR_UUID(&a->attr, uuid, dev->uuid, buf);
+	BTRFS_DEV_GET_ATTR_U64(&a->attr, devid, &dev->devid, buf);
+	BTRFS_DEV_GET_ATTR_UUID(&a->attr, dev_root_fsid, dev->dev_root->fs_info->fsid, buf);
+	BTRFS_DEV_GET_ATTR_U64(&a->attr, generation, &dev->generation, buf);
+	BTRFS_DEV_GET_ATTR_U64(&a->attr, total_bytes, &dev->total_bytes, buf);
+	BTRFS_DEV_GET_ATTR_U64(&a->attr, dev_totalbytes, &dev->disk_total_bytes, buf);
+	BTRFS_DEV_GET_ATTR_U64(&a->attr, bytes_used, &dev->bytes_used, buf);
+	BTRFS_DEV_GET_ATTR_U64(&a->attr, type, &dev->type, buf);
+	BTRFS_DEV_GET_ATTR_U(&a->attr, io_align, dev->io_align, buf);
+	BTRFS_DEV_GET_ATTR_U(&a->attr, sector_size, dev->sector_size, buf);
+	BTRFS_DEV_GET_ATTR_D(&a->attr, writeable, dev->writeable, buf);
+	BTRFS_DEV_GET_ATTR_D(&a->attr, in_fs_metadata, dev->in_fs_metadata, buf);
+	BTRFS_DEV_GET_ATTR_D(&a->attr, missing, dev->missing, buf);
+	BTRFS_DEV_GET_ATTR_D(&a->attr, can_discard, dev->can_discard, buf);
+	BTRFS_DEV_GET_ATTR_D(&a->attr, replace_tgtdev, dev->is_tgtdev_for_dev_replace, buf);
+	BTRFS_DEV_GET_ATTR_D(&a->attr, active_pending, dev->running_pending, buf);
+	BTRFS_DEV_GET_ATTR_D(&a->attr, nobarriers, dev->nobarriers, buf);
+	BTRFS_DEV_GET_ATTR_D(&a->attr, devstats_valid, dev->dev_stats_valid, buf);
+	BTRFS_DEV_GET_ATTR_STR(&a->attr, bdev, dev->bdev ? "not_null":"null", buf);
+
+	return 0;
+}
+
+static ssize_t btrfs_dev_attr_store(struct kobject *kobj,
+					struct kobj_attribute *a,
+					const char *buf, size_t count)
+{
+	/*
+	 * we might need some of the parameter to be writable
+	 * but as of now just deny all
+	 */
+	return -EPERM;
+}
+
+static umode_t btrfs_dev_attr_visible(struct kobject *kobj,
+				     struct attribute *attr, int unused)
+{
+	struct btrfs_fs_devices *fs_devs = to_btrfs_device(kobj)->fs_devices;
+
+	/* if device is mounted then all is visible */
+	if (fs_devs->opened &&
+		!(test_bit(BTRFS_FS_DEVS_UNMOUNTING, &fs_devs->flags)))
+		return attr->mode|S_IWUSR;
+
+	/* when device is unmounted  only the below attributes are visible */
+	if (attr == BTRFS_DEV_ATTR_PTR(uuid))
+		return attr->mode|S_IWUSR;
+	if (attr == BTRFS_DEV_ATTR_PTR(name))
+		return attr->mode|S_IWUSR;
+	else if (attr == BTRFS_DEV_ATTR_PTR(devid))
+		return attr->mode|S_IWUSR;
+	else if (attr == BTRFS_DEV_ATTR_PTR(generation))
+		return attr->mode|S_IWUSR;
+
+	return 0;
+}
+
+static const struct attribute_group btrfs_dev_attr_group = {
+	.attrs = btrfs_dev_attrs,
+	.is_visible = btrfs_dev_attr_visible,
+};
+
+void btrfs_destroy_dev_sysfs(struct btrfs_device *dev)
+{
+	sysfs_remove_group(&dev->dev_kobj, &btrfs_dev_attr_group);
+	kobject_del(&dev->dev_kobj);
+	kobject_put(&dev->dev_kobj);
+}
+
+int btrfs_create_dev_sysfs(struct btrfs_device *dev)
+{
+	int rc;
+
+	rc = kobject_init_and_add(&dev->dev_kobj, &btrfs_by_fsid_ktype,
+			&dev->fs_devices->fs_devs_kobj, "%pU", dev->uuid);
+
+	rc = sysfs_create_group(&dev->dev_kobj, &btrfs_dev_attr_group);
+	if (rc)
+		kobject_put(&dev->dev_kobj);
+
+	return rc;
+
+}
+
+int btrfs_update_dev_sysfs(struct btrfs_device *dev)
+{
+	int rc;
+
+	rc = sysfs_update_group(&dev->dev_kobj, &btrfs_dev_attr_group);
+
+	return rc;
+}
+
+void btrfs_migrate_dev_kobj(struct kobject *src, struct kobject *dst)
+{
+	struct btrfs_device *dev = to_btrfs_device(src);
+	btrfs_destroy_dev_sysfs(dev);
+
+	dev = to_btrfs_device(dst);
+	btrfs_create_dev_sysfs(dev);
+}
diff --git a/fs/btrfs/sysfs.h b/fs/btrfs/sysfs.h
index f7dd298..9b03f9a 100644
--- a/fs/btrfs/sysfs.h
+++ b/fs/btrfs/sysfs.h
@@ -74,4 +74,10 @@ int btrfs_kobj_add_device(struct btrfs_fs_info *fs_info,
 		struct btrfs_device *one_device);
 int btrfs_kobj_rm_device(struct btrfs_fs_info *fs_info,
                 struct btrfs_device *one_device);
+int btrfs_create_fs_devs_sysfs(struct btrfs_fs_devices *fs_devices);
+int btrfs_create_dev_sysfs(struct btrfs_device *dev);
+int btrfs_update_fs_devs_sysfs(struct btrfs_fs_devices *fs_devs);
+int btrfs_update_dev_sysfs(struct btrfs_device *dev);
+void btrfs_destroy_dev_sysfs(struct btrfs_device *dev);
+void btrfs_migrate_dev_kobj(struct kobject *src, struct kobject *dst);
 #endif /* _BTRFS_SYSFS_H_ */
diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c
index d13b253..2f9ea3a 100644
--- a/fs/btrfs/volumes.c
+++ b/fs/btrfs/volumes.c
@@ -53,6 +53,11 @@ static void btrfs_dev_stat_print_on_load(struct btrfs_device *device);
 DEFINE_MUTEX(uuid_mutex);
 static LIST_HEAD(fs_uuids);
 
+struct list_head *btrfs_get_fs_uuids(void)
+{
+	return &fs_uuids;
+}
+
 static void lock_chunks(struct btrfs_root *root)
 {
 	mutex_lock(&root->fs_info->chunk_mutex);
@@ -478,6 +483,9 @@ static noinline int device_list_add(const char *path,
 
 		list_add(&fs_devices->list, &fs_uuids);
 
+		if (btrfs_create_fs_devs_sysfs(fs_devices))
+			printk(KERN_ERR "BTRFS: create fs_devices sysfs entry failed\n");
+
 		device = NULL;
 	} else {
 		device = __find_device(&fs_devices->devices, devid,
@@ -509,6 +517,9 @@ static noinline int device_list_add(const char *path,
 
 		ret = 1;
 		device->fs_devices = fs_devices;
+
+		if (btrfs_create_dev_sysfs(device))
+			printk(KERN_ERR "BTRFS: create btrfs_dev sysfs entry failed\n");
 	} else if (!device->name || strcmp(device->name->str, path)) {
 		/*
 		 * When FS is already mounted.
@@ -741,6 +752,16 @@ static int __btrfs_close_devices(struct btrfs_fs_devices *fs_devices)
 		list_replace_rcu(&device->dev_list, &new_device->dev_list);
 		new_device->fs_devices = device->fs_devices;
 
+		/*
+		 * Todo:
+		 * its bit ugly that btrfs_device is being deleted and recreated
+		 * for which we need to delete the sysfs kobject and create it
+		 * again. which means if users cwd is this sysfs dir, then it
+		 * would be staled. - need to avoid deleting btrfs_device when
+		 * closing.
+		 */
+		btrfs_migrate_dev_kobj(&device->dev_kobj, &new_device->dev_kobj);
+
 		call_rcu(&device->rcu, free_device);
 	}
 	mutex_unlock(&fs_devices->device_list_mutex);
@@ -1703,6 +1724,7 @@ int btrfs_rm_device(struct btrfs_root *root, char *device_path)
 		/* remove sysfs entry */
 		btrfs_kobj_rm_device(root->fs_info, device);
 	}
+	btrfs_destroy_dev_sysfs(device);
 
 	call_rcu(&device->rcu, free_device);
 
@@ -2207,6 +2229,9 @@ int btrfs_init_new_device(struct btrfs_root *root, char *device_path)
 
 	/* add sysfs device entry */
 	btrfs_kobj_add_device(root->fs_info, device);
+	/* add the kobject for the new by_fsid layout */
+	if (btrfs_create_dev_sysfs(device))
+		printk(KERN_ERR "BTRFS: create btrfs_dev sysfs entry failed\n");
 
 	/*
 	 * we've got more storage, clear any full flags on the space
@@ -2381,6 +2406,10 @@ int btrfs_init_dev_replace_tgtdev(struct btrfs_root *root, char *device_path,
 	list_add(&device->dev_list, &fs_info->fs_devices->devices);
 	fs_info->fs_devices->num_devices++;
 	fs_info->fs_devices->open_devices++;
+
+	if (btrfs_create_dev_sysfs(device))
+		printk(KERN_ERR "BTRFS: sysfs dev create failed for transit device\n");
+
 	mutex_unlock(&root->fs_info->fs_devices->device_list_mutex);
 
 	*device_out = device;
@@ -6691,3 +6720,16 @@ void btrfs_update_commit_device_bytes_used(struct btrfs_root *root,
 	}
 	unlock_chunks(root);
 }
+
+int btrfs_update_by_fsid_sysfs_group(struct btrfs_fs_devices *fs_devs)
+{
+	int rc;
+	struct btrfs_device *dev;
+
+	rc = btrfs_update_fs_devs_sysfs(fs_devs);
+
+	list_for_each_entry(dev, &fs_devs->devices, dev_list)
+		rc = btrfs_update_dev_sysfs(dev);
+
+	return rc;
+}
diff --git a/fs/btrfs/volumes.h b/fs/btrfs/volumes.h
index 6e04f27..bada662 100644
--- a/fs/btrfs/volumes.h
+++ b/fs/btrfs/volumes.h
@@ -28,6 +28,8 @@ extern struct mutex uuid_mutex;
 
 #define BTRFS_STRIPE_LEN	(64 * 1024)
 
+#define BTRFS_FS_DEVS_UNMOUNTING	(1ULL << 0)
+
 struct buffer_head;
 struct btrfs_pending_bios {
 	struct bio *head;
@@ -150,6 +152,7 @@ struct btrfs_device {
 	/* Counter to record the change of device stats */
 	atomic_t dev_stats_ccnt;
 	atomic_t dev_stat_values[BTRFS_DEV_STAT_VALUES_MAX];
+	struct kobject dev_kobj;
 };
 
 /*
@@ -253,6 +256,8 @@ struct btrfs_fs_devices {
 	 * nonrot flag set
 	 */
 	int rotating;
+	struct kobject fs_devs_kobj;
+	unsigned long flags;
 };
 
 #define BTRFS_BIO_INLINE_CSUM_SIZE	64
@@ -523,4 +528,5 @@ static inline void btrfs_dev_stat_reset(struct btrfs_device *dev,
 void btrfs_update_commit_device_size(struct btrfs_fs_info *fs_info);
 void btrfs_update_commit_device_bytes_used(struct btrfs_root *root,
 					struct btrfs_transaction *transaction);
+int btrfs_update_by_fsid_sysfs_group(struct btrfs_fs_devices *fs_devs);
 #endif
-- 
1.9.1