On 2019/10/17 下午12:17, Anand Jain wrote:
> 
>  Depending on the size of the FS the convert may take longer, further
>  fatal error (power loss; pid kill) may leave the FS in a state where
>  the bg items are in both extent-tree and bg-tree.

That's why I'm using one transaction to convert them all.

So if the convert get interrutped, we're still safe.

Thanks,
Qu
> 
>  The lessons which lead to the implementation of metadata_uuid fsid
>  suggests, for conversions its better to use the btrfstune to only
>  flag the bg convert requirement and let the kernel handle of migration
>  of the bg items from the extent-tree to the bg-tree as and when the
>  bg-items are written.
> 
> Thanks, Anand
> 
> 
> On 10/8/19 12:49 PM, Qu Wenruo wrote:
>> Add a new option '-b' for btrfstune, to enable bg-tree feature for a
>> unmounted fs.
>>
>> This feature will convert all BLOCK_GROUP_ITEMs in extent tree to bg
>> tree, by reusing the existing btrfs_convert_to_bg_tree() function.
>>
>> Signed-off-by: Qu Wenruo <wqu@suse.com>
>> ---
>>   Documentation/btrfstune.asciidoc |  6 +++++
>>   btrfstune.c                      | 44 ++++++++++++++++++++++++++++++--
>>   2 files changed, 48 insertions(+), 2 deletions(-)
>>
>> diff --git a/Documentation/btrfstune.asciidoc
>> b/Documentation/btrfstune.asciidoc
>> index 1d6bc98deed8..ed54c2e1597f 100644
>> --- a/Documentation/btrfstune.asciidoc
>> +++ b/Documentation/btrfstune.asciidoc
>> @@ -26,6 +26,12 @@ means.  Please refer to the 'FILESYSTEM FEATURES'
>> in `btrfs`(5).
>>   OPTIONS
>>   -------
>>   +-b::
>> +(since kernel: 5.x)
>> ++
>> +enable bg-tree feature (faster mount time for large fs), enabled by mkfs
>> +feature 'bg-tree'.
>> +
>>   -f::
>>   Allow dangerous changes, e.g. clear the seeding flag or change fsid.
>> Make sure
>>   that you are aware of the dangers.
>> diff --git a/btrfstune.c b/btrfstune.c
>> index afa3aae35412..aa1ac568aef0 100644
>> --- a/btrfstune.c
>> +++ b/btrfstune.c
>> @@ -476,11 +476,39 @@ static void print_usage(void)
>>       printf("\t-m          change fsid in metadata_uuid to a random
>> UUID\n");
>>       printf("\t            (incompat change, more lightweight than
>> -u|-U)\n");
>>       printf("\t-M UUID     change fsid in metadata_uuid to UUID\n");
>> +    printf("\t-b          enable bg-tree feature (mkfs: bg-tree, for
>> faster mount time)\n");
>>       printf("  general:\n");
>>       printf("\t-f          allow dangerous operations, make sure that
>> you are aware of the dangers\n");
>>       printf("\t--help      print this help\n");
>>   }
>>   +static int convert_to_bg_tree(struct btrfs_fs_info *fs_info)
>> +{
>> +    struct btrfs_trans_handle *trans;
>> +    int ret;
>> +
>> +    trans = btrfs_start_transaction(fs_info->tree_root, 1);
>> +    if (IS_ERR(trans)) {
>> +        ret = PTR_ERR(trans);
>> +        errno = -ret;
>> +        error("failed to start transaction: %m");
>> +        return ret;
>> +    }
>> +    ret = btrfs_convert_to_bg_tree(trans);
>> +    if (ret < 0) {
>> +        errno = -ret;
>> +        error("failed to convert: %m");
>> +        btrfs_abort_transaction(trans, ret);
>> +        return ret;
>> +    }
>> +    ret = btrfs_commit_transaction(trans, fs_info->tree_root);
>> +    if (ret < 0) {
>> +        errno = -ret;
>> +        error("failed to commit transaction: %m");
>> +    }
>> +    return ret;
>> +}
>> +
>>   int BOX_MAIN(btrfstune)(int argc, char *argv[])
>>   {
>>       struct btrfs_root *root;
>> @@ -491,6 +519,7 @@ int BOX_MAIN(btrfstune)(int argc, char *argv[])
>>       u64 seeding_value = 0;
>>       int random_fsid = 0;
>>       int change_metadata_uuid = 0;
>> +    bool to_bg_tree = false;
>>       char *new_fsid_str = NULL;
>>       int ret;
>>       u64 super_flags = 0;
>> @@ -501,7 +530,7 @@ int BOX_MAIN(btrfstune)(int argc, char *argv[])
>>               { "help", no_argument, NULL, GETOPT_VAL_HELP},
>>               { NULL, 0, NULL, 0 }
>>           };
>> -        int c = getopt_long(argc, argv, "S:rxfuU:nmM:", long_options,
>> NULL);
>> +        int c = getopt_long(argc, argv, "S:rxfuU:nmM:b",
>> long_options, NULL);
>>             if (c < 0)
>>               break;
>> @@ -539,6 +568,9 @@ int BOX_MAIN(btrfstune)(int argc, char *argv[])
>>               ctree_flags |= OPEN_CTREE_IGNORE_FSID_MISMATCH;
>>               change_metadata_uuid = 1;
>>               break;
>> +        case 'b':
>> +            to_bg_tree = true;
>> +            break;
>>           case GETOPT_VAL_HELP:
>>           default:
>>               print_usage();
>> @@ -556,7 +588,7 @@ int BOX_MAIN(btrfstune)(int argc, char *argv[])
>>           return 1;
>>       }
>>       if (!super_flags && !seeding_flag && !(random_fsid ||
>> new_fsid_str) &&
>> -        !change_metadata_uuid) {
>> +        !change_metadata_uuid && !to_bg_tree) {
>>           error("at least one option should be specified");
>>           print_usage();
>>           return 1;
>> @@ -602,6 +634,14 @@ int BOX_MAIN(btrfstune)(int argc, char *argv[])
>>           return 1;
>>       }
>>   +    if (to_bg_tree) {
>> +        ret = convert_to_bg_tree(root->fs_info);
>> +        if (ret < 0) {
>> +            errno = -ret;
>> +            error("failed to convert to bg-tree feature: %m");
>> +            goto out;
>> +        }
>> +    }
>>       if (seeding_flag) {
>>           if (btrfs_fs_incompat(root->fs_info, METADATA_UUID)) {
>>               fprintf(stderr, "SEED flag cannot be changed on a
>> metadata-uuid changed fs\n");
>>
>