Re: [PATCH 2/2] btrfs-progs: Deprecate unused super block member log_root_transid

[Nikolay Borisov <nborisov@suse.com>]

On 12.10.2018 11:46, Qu Wenruo wrote:
> 
> 
> On 2018/10/12 下午2:53, Nikolay Borisov wrote:
>>
>>
>> On 12.10.2018 09:42, Qu Wenruo wrote:
>>> The only user of it is "btrfs inspect dump-super".
>>>
>>> Signed-off-by: Qu Wenruo <wqu@suse.com>
>>> ---
>>>  cmds-inspect-dump-super.c | 4 ++--
>>>  ctree.h                   | 6 ++----
>>>  2 files changed, 4 insertions(+), 6 deletions(-)
>>>
>>> diff --git a/cmds-inspect-dump-super.c b/cmds-inspect-dump-super.c
>>> index e965267c5d96..3f33931ed9bc 100644
>>> --- a/cmds-inspect-dump-super.c
>>> +++ b/cmds-inspect-dump-super.c
>>> @@ -387,8 +387,8 @@ static void dump_superblock(struct btrfs_super_block *sb, int full)
>>>  	       (unsigned long long)btrfs_super_chunk_root_level(sb));
>>>  	printf("log_root\t\t%llu\n",
>>>  	       (unsigned long long)btrfs_super_log_root(sb));
>>> -	printf("log_root_transid\t%llu\n",
>>> -	       (unsigned long long)btrfs_super_log_root_transid(sb));
>>> +	printf("log_root_transid (deprecated)\t%llu\n",
>>> +	       le64_to_cpu(sb->__unused_log_root_transid));
>>
>> This should be entirely removed.
> 
> It looks OK to me.
> Just like the old leafsize.
> 
> And if we try to use this member again, even old progs could show it
> without problem.

But what is the point of having something which always shows 0 and is
essentially unused?

> 
> Thanks,
> Qu
> 
>>
>>>  	printf("log_root_level\t\t%llu\n",
>>>  	       (unsigned long long)btrfs_super_log_root_level(sb));
>>>  	printf("total_bytes\t\t%llu\n",
>>> diff --git a/ctree.h b/ctree.h
>>> index 4719962df67d..a314fdb102b0 100644
>>> --- a/ctree.h
>>> +++ b/ctree.h
>>> @@ -427,8 +427,8 @@ struct btrfs_super_block {
>>>  	__le64 chunk_root;
>>>  	__le64 log_root;
>>>  
>>> -	/* this will help find the new super based on the log root */
>>> -	__le64 log_root_transid;
>>> +	/* This member is never touched, should always be 0 */
>>> +	__le64 __unused_log_root_transid;
>>>  	__le64 total_bytes;
>>>  	__le64 bytes_used;
>>>  	__le64 root_dir_objectid;
>>> @@ -2203,8 +2203,6 @@ BTRFS_SETGET_STACK_FUNCS(super_chunk_root_level, struct btrfs_super_block,
>>>  			 chunk_root_level, 8);
>>>  BTRFS_SETGET_STACK_FUNCS(super_log_root, struct btrfs_super_block,
>>>  			 log_root, 64);
>>> -BTRFS_SETGET_STACK_FUNCS(super_log_root_transid, struct btrfs_super_block,
>>> -			 log_root_transid, 64);
>>>  BTRFS_SETGET_STACK_FUNCS(super_log_root_level, struct btrfs_super_block,
>>>  			 log_root_level, 8);
>>>  BTRFS_SETGET_STACK_FUNCS(super_total_bytes, struct btrfs_super_block,
>>>
>