Re: [PATCH 0/7] btrfs-progs: cmds/tune: add set/clear features

[Qu Wenruo <wqu@suse.com>]

On 2023/10/14 05:20, David Sterba wrote:
> On Tue, Sep 05, 2023 at 03:51:42PM +0800, Qu Wenruo wrote:
>> This is the first step to convert btrfstune functionality to "btrfs
>> tune" subcommand group.
>>
>> For now only binary features, aka set and clear, is supported,
>> thus uuid and csum change is not yet implemented.
>> (Both need their own subcommand groups other than set/clear groups)
> 
> There are the easy on/off features that can be added first but you also
> added the block-group-tree _conversion_. That's a different category and
> IMHO requires a separate command so we can add options to check or reset
> the unfinished state. And we also have the the conversion 'to' and
> 'from'.
> 
> My current list of 1st level command groups is:
> 
> - enable - for the simple on/off features (on)
> - disable - dtto, (off)
> - convert-to - for the BGT, checksum
> - convert-from - subset where the back conversion like BGT may make sense

So your idea is, if an conversion is a long running one, and can be 
interrupted, then we need to go convert instead of simple on/off?

That makes sense, although my question is, does that makes any difference?

If we have an interrupted conversion, the only valid operation we can do 
is to finish the conversion. No rollback for most conversions.

Thus in the end, it's sill on/off, just with an extra interrupted 
status, but that status can only lead to the "on" state, thus it makes 
no difference to have an dedicated state for it.

Thanks,
Qu

> - analyze - go through the structures and identify features (all, subset)
> 
> We can add aliases like set for enable and clear for disable, the two
> conversion commands may not be necessary or even confusing when it's not
> clear which direction is the right one.
> 
> Actions:
> 
> - extref (on/off)
> - skinny-metadata (on/off)
> - no-holes (on)
> - seeding (on/off)
> - uuid rewrite (one time)
> - metadata_uuid (set value)
> - change checksum (convert-to)
> - currently there's the simple quota, this may change
> 
> This should give examples of all categories of actions we might have in
> the future.
> 
>> And even for set/clear, there is some changes to btrfstune:
>>
>> - Merge seed feature into set/clear
>>    To enable seeding, just go "btrfs tune set seed <device>".
>>
>> - All supported features can be checked by "list-all" feature
>>    Please note that, "btrfs tune set list-all" and
>>    "btrfs tune clear list-all" will have different output.
> 
> As the help test works, we would get that for free if all the
> implemented actions are also command names, i.e. 'btrfs tune convert-to'
> would list 'block-group-tree'.