btrfs: add comments for device counts in struct btrfs_fs_devices

A bug was was checking a wrong device count before we delete the struct
btrfs_fs_devices in btrfs_rm_device(). To avoid future confusion and
easy reference add a comment about the various device counts that we have
in the struct btrfs_fs_devices.

Signed-off-by: Anand Jain <anand.jain@oracle.com>
Signed-off-by: David Sterba <dsterba@suse.com>

diff --git a/fs/btrfs/volumes.h b/fs/btrfs/volumes.h
index 49322a4..874406f 100644 (file)
--- a/fs/btrfs/volumes.h
+++ b/fs/btrfs/volumes.h
@@ -236,11 +236,30 @@ struct btrfs_fs_devices {
        bool fsid_change;
        struct list_head fs_list;
 
+       /*
+        * Number of devices under this fsid including missing and
+        * replace-target device and excludes seed devices.
+        */
        u64 num_devices;
+
+       /*
+        * The number of devices that successfully opened, including
+        * replace-target, excludes seed devices.
+        */
        u64 open_devices;
+
+       /* The number of devices that are under the chunk allocation list. */
        u64 rw_devices;
+
+       /* Count of missing devices under this fsid excluding seed device. */
        u64 missing_devices;
        u64 total_rw_bytes;
+
+       /*
+        * Count of devices from btrfs_super_block::num_devices for this fsid,
+        * which includes the seed device, excludes the transient replace-target
+        * device.
+        */
        u64 total_devices;
 
        /* Highest generation number of seen devices */