[PATCH 4/6] btrfs: Introduce 2 more members to struct btrfs_fs_devices

[Nikolay Borisov]

In order to gracefully handle split-brain scenario which are very
unlikely, yet still possible while performing the FSID change I'm
gonna need two more pieces of information:
 1. The highes generation number among all devices registered to a
 particular btrfs_fs_devices

 2. A boolean flag whether a given btrfs_fs_devices was created by a
 device which had the FSID_CHANGING_V2 flag set.

This is a preparatory patch and just introduces the variables as well
as code which sets, their actual use is going to happen in a later
patch.

Signed-off-by: Nikolay Borisov <nbori...@suse.com>
---
 fs/btrfs/volumes.c | 9 ++++++++-
 fs/btrfs/volumes.h | 5 +++++
 2 files changed, 13 insertions(+), 1 deletion(-)

diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c
index bf0aa900f22c..c2b66d15e08d 100644
--- a/fs/btrfs/volumes.c
+++ b/fs/btrfs/volumes.c
@@ -785,6 +785,8 @@ static noinline struct btrfs_device *device_list_add(const 
char *path,
        u64 devid = btrfs_stack_device_id(&disk_super->dev_item);
        bool has_metadata_uuid = (btrfs_super_incompat_flags(disk_super) &
                BTRFS_FEATURE_INCOMPAT_METADATA_UUID);
+       bool fsid_change_in_progress = (btrfs_super_flags(disk_super) &
+                                       BTRFS_SUPER_FLAG_CHANGING_FSID_v2);
 
        if (has_metadata_uuid)
                fs_devices = find_fsid(disk_super->fsid, 
disk_super->metadata_uuid);
@@ -798,6 +800,8 @@ static noinline struct btrfs_device *device_list_add(const 
char *path,
                else
                        fs_devices = alloc_fs_devices(disk_super->fsid, NULL);
 
+               fs_devices->fsid_change = fsid_change_in_progress;
+
                if (IS_ERR(fs_devices))
                        return ERR_CAST(fs_devices);
 
@@ -904,8 +908,11 @@ static noinline struct btrfs_device *device_list_add(const 
char *path,
         * it back. We need it to pick the disk with largest generation
         * (as above).
         */
-       if (!fs_devices->opened)
+       if (!fs_devices->opened) {
                device->generation = found_transid;
+               fs_devices->latest_generation= max(found_transid,
+                                               fs_devices->latest_generation);
+       }
 
        fs_devices->total_devices = btrfs_super_num_devices(disk_super);
 
diff --git a/fs/btrfs/volumes.h b/fs/btrfs/volumes.h
index 04860497b33c..6b2a01c55426 100644
--- a/fs/btrfs/volumes.h
+++ b/fs/btrfs/volumes.h
@@ -211,6 +211,7 @@ BTRFS_DEVICE_GETSET_FUNCS(bytes_used);
 struct btrfs_fs_devices {
        u8 fsid[BTRFS_FSID_SIZE]; /* FS specific uuid */
        u8 metadata_uuid[BTRFS_FSID_SIZE];
+       bool fsid_change;
        struct list_head fs_list;
 
        u64 num_devices;
@@ -219,6 +220,10 @@ struct btrfs_fs_devices {
        u64 missing_devices;
        u64 total_rw_bytes;
        u64 total_devices;
+
+       /* Highest generation number of seen devices */
+       u64 latest_generation;
+
        struct block_device *latest_bdev;
 
        /* all of the devices in the FS, protected by a mutex
-- 
2.7.4