[PATCH v4] btrfs: sysfs, add devid/dev_state kobject and attribute

Anand Jain
2020-01-06T11:39:16Z

New sysfs attributes
in_fs_metadata missing replace_target writeable
are added under a new kobject
UUID/devinfo/<devid>

These attributes reflects the state of the device from the kernel
fed by %btrfs_device::dev_state.
These attributes are born during mount and goes along with the dynamic
nature of the device add and delete, otherwise these attribute and kobject
gets deleted at unmount.

Sample output:
pwd
/sys/fs/btrfs/6e1961f1-5918-4ecc-a22f-948897b409f7/devinfo/1/
ls
in_fs_metadata missing replace_target writeable
cat missing
0

The output from these attributes are 0 or 1. 0 indicates unset and 1
indicates set.

As of now these attributes are readonly.

It is observed that the device delete thread and sysfs read thread will
not race because the delete thread calls sysfs kobject_put() which in turn
waits for existing sysfs read to complete.

Signed-off-by: Anand Jain <anand.jain@oracle.com>
---
v4:
after patch
[PATCH v5 2/2] btrfs: reset device back to allocation state when removing
in misc-next, the device::devid_kobj remains stale, fix it by using
release.

v3:
Use optional groupid devid in BTRFS_ATTR(), it was blank in v2.

V2:
Make the devinfo attribute to carry one parameter, so now
instead of dev_state attribute, we create in_fs_metadata,
writeable, missing and replace_target attributes.

fs/btrfs/sysfs.c | 142 ++++++++++++++++++++++++++++++++++++++++++++---------
fs/btrfs/volumes.h | 3 ++
2 files changed, 122 insertions(+), 23 deletions(-)

diff --git a/fs/btrfs/sysfs.c b/fs/btrfs/sysfs.c
index 834f712ed60c..18dac99188ce 100644
--- a/fs/btrfs/sysfs.c
+++ b/fs/btrfs/sysfs.c
@@ -978,29 +978,116 @@ int btrfs_sysfs_remove_devices_attr(struct btrfs_fs_devices *fs_devices,
if (!fs_devices->devices_kobj)
return -EINVAL;

- if (one_device && one_device->bdev) {
- disk = one_device->bdev->bd_part;
- disk_kobj = &part_to_dev(disk)->kobj;
+ if (one_device) {
+ if (one_device->bdev) {
+ disk = one_device->bdev->bd_part;
+ disk_kobj = &part_to_dev(disk)->kobj;
+ sysfs_remove_link(fs_devices->devices_kobj, disk_kobj->name);
+ }

- sysfs_remove_link(fs_devices->devices_kobj, disk_kobj->name);
- }
+ kobject_del(&one_device->devid_kobj);
+ kobject_put(&one_device->devid_kobj);
+
+ wait_for_completion(&one_device->kobj_unregister);

- if (one_device)
return 0;
+ }

- list_for_each_entry(one_device,
- &fs_devices->devices, dev_list) {
- if (!one_device->bdev)
- continue;
- disk = one_device->bdev->bd_part;
- disk_kobj = &part_to_dev(disk)->kobj;
+ list_for_each_entry(one_device, &fs_devices->devices, dev_list) {
+
+ if (one_device->bdev) {
+ disk = one_device->bdev->bd_part;
+ disk_kobj = &part_to_dev(disk)->kobj;
+ sysfs_remove_link(fs_devices->devices_kobj, disk_kobj->name);
+ }
+ kobject_del(&one_device->devid_kobj);
+ kobject_put(&one_device->devid_kobj);

- sysfs_remove_link(fs_devices->devices_kobj, disk_kobj->name);
+ wait_for_completion(&one_device->kobj_unregister);
}

return 0;
}

+static ssize_t btrfs_sysfs_writeable_show(struct kobject *kobj,
+ struct kobj_attribute *a, char *buf)
+{
+ int val;
+ struct btrfs_device *device = container_of(kobj, struct btrfs_device,
+ devid_kobj);
+
+ val = test_bit(BTRFS_DEV_STATE_WRITEABLE, &device->dev_state) ? 1 : 0;
+
+ return snprintf(buf, PAGE_SIZE, "%d\n", val);
+}
+BTRFS_ATTR(devid, writeable, btrfs_sysfs_writeable_show);
+
+static ssize_t btrfs_sysfs_in_fs_metadata_show(struct kobject *kobj,
+ struct kobj_attribute *a,
+ char *buf)
+{
+ int val;
+ struct btrfs_device *device = container_of(kobj, struct btrfs_device,
+ devid_kobj);
+
+ val = test_bit(BTRFS_DEV_STATE_IN_FS_METADATA,
+ &device->dev_state) ? 1 : 0;
+
+ return snprintf(buf, PAGE_SIZE, "%d\n", val);
+}
+BTRFS_ATTR(devid, in_fs_metadata, btrfs_sysfs_in_fs_metadata_show);
+
+static ssize_t btrfs_sysfs_missing_show(struct kobject *kobj,
+ struct kobj_attribute *a, char *buf)
+{
+ int val;
+ struct btrfs_device *device = container_of(kobj, struct btrfs_device,
+ devid_kobj);
+
+ val = test_bit(BTRFS_DEV_STATE_MISSING, &device->dev_state) ? 1 : 0;
+
+ return snprintf(buf, PAGE_SIZE, "%d\n", val);
+}
+BTRFS_ATTR(devid, missing, btrfs_sysfs_missing_show);
+
+static ssize_t btrfs_sysfs_replace_target_show(struct kobject *kobj,
+ struct kobj_attribute *a,
+ char *buf)
+{
+ int val;
+ struct btrfs_device *device = container_of(kobj, struct btrfs_device,
+ devid_kobj);
+
+ val = test_bit(BTRFS_DEV_STATE_REPLACE_TGT, &device->dev_state) ? 1 : 0;
+
+ return snprintf(buf, PAGE_SIZE, "%d\n", val);
+}
+BTRFS_ATTR(devid, replace_target, btrfs_sysfs_replace_target_show);
+
+static struct attribute *devid_attrs[] = {
+ BTRFS_ATTR_PTR(devid, writeable),
+ BTRFS_ATTR_PTR(devid, in_fs_metadata),
+ BTRFS_ATTR_PTR(devid, missing),
+ BTRFS_ATTR_PTR(devid, replace_target),
+ NULL
+};
+ATTRIBUTE_GROUPS(devid);
+
+static void btrfs_release_devid_kobj(struct kobject *kobj)
+{
+ struct btrfs_device *device = container_of(kobj, struct btrfs_device,
+ devid_kobj);
+
+ memset(&device->devid_kobj, 0, sizeof(struct kobject));
+ complete(&device->kobj_unregister);
+}
+
+static struct kobj_type devid_ktype = {
+ .sysfs_ops = &kobj_sysfs_ops,
+ .default_groups = devid_groups,
+ .release = btrfs_release_devid_kobj,
+};
+
int btrfs_sysfs_add_devices_attr(struct btrfs_fs_devices *fs_devices,
struct btrfs_device *one_device)
{
@@ -1008,22 +1095,31 @@ int btrfs_sysfs_add_devices_attr(struct btrfs_fs_devices *fs_devices,
struct btrfs_device *dev;

list_for_each_entry(dev, &fs_devices->devices, dev_list) {
- struct hd_struct *disk;
- struct kobject *disk_kobj;
-
- if (!dev->bdev)
- continue;

if (one_device && one_device != dev)
continue;

- disk = dev->bdev->bd_part;
- disk_kobj = &part_to_dev(disk)->kobj;
+ if (dev->bdev) {
+ struct hd_struct *disk;
+ struct kobject *disk_kobj;
+
+ disk = dev->bdev->bd_part;
+ disk_kobj = &part_to_dev(disk)->kobj;

- error = sysfs_create_link(fs_devices->devices_kobj,
- disk_kobj, disk_kobj->name);
- if (error)
+ error = sysfs_create_link(fs_devices->devices_kobj,
+ disk_kobj, disk_kobj->name);
+ if (error)
+ break;
+ }
+
+ init_completion(&dev->kobj_unregister);
+ error = kobject_init_and_add(&dev->devid_kobj, &devid_ktype,
+ fs_devices->devinfo_kobj, "%llu",
+ dev->devid);
+ if (error) {
+ kobject_put(&dev->devid_kobj);
break;
+ }
}

return error;
diff --git a/fs/btrfs/volumes.h b/fs/btrfs/volumes.h
index 38f2e8437b68..da9c6e1b843a 100644
--- a/fs/btrfs/volumes.h
+++ b/fs/btrfs/volumes.h
@@ -138,6 +138,9 @@ struct btrfs_device {
atomic_t dev_stat_values[BTRFS_DEV_STAT_VALUES_MAX];

struct extent_io_tree alloc_state;
+
+ struct completion kobj_unregister;
+ struct kobject devid_kobj;
};

/*
--
1.8.3.1