On 2017年10月28日 01:37, David Sterba wrote:
> On Fri, Oct 27, 2017 at 03:29:28PM +0800, Qu Wenruo wrote:
>> This patchset adds quota support, which means the result fs will have
>> quota enabled by default, and its accounting is already consistent, no
>> manually rescan or quota enable is needed.
> 
> Great, thanks for working on that. I'm going to merge the preparatory
> patches next. I'm not sure about the command line option, we might want
> to design it in a similar way as -O/--features. As this is a runtime
> feature (unlike the on-disk format features), a new option will be
> needed, backed by some research what other mkfs.* tools use.

Well, checked xfs and ext4, they mostly co-operate with mount options
and mkfs options to handle optional feature like their quota.


But considering they have multiple options for journal/extra setting, it
won't be reasonable for mkfs.btrfs to have something like
"--runtime-features|-R"

If you're OK with that option name, I can use it to implement "-R quota".

> 
> The uuid_tree would at least use the btrfs_create_tree, but I don't
> think we'd need to create it only on request, so quotas will be the only
> option.
> 
>> 2) Fill quota root with basic skeleton
>>    Only 3 items are really needed
>>    a) global quota status item
>>    b) quota info for 0/5 qgroup
>>    c) quota limit for 0/5 qgroup
>>
>>    The content doesn't matter at all.
> 
> How would --rootdir and quotas behave in that case? A related question
> is what will be the semantics of rootdir+quotas+subvolume created at
> mkfs time.
> 
> We can certainly start with only quotas on the empty filesystem, but I'm
> sure somebody will ask for the wild combination at some point.

I'll add test case for quota with --rootdir in next update.

Thanks,
Qu

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