Re: [PATCH 2/4] btrfs: detect uninitialized btrfs_root::anon_dev for user visible subvolumes

[Josef Bacik <josef@toxicpanda.com>]

On 6/17/20 7:31 AM, David Sterba wrote:
> On Wed, Jun 17, 2020 at 07:49:33AM +0800, Qu Wenruo wrote:
>>>>> Can we handle stat->dev not having a device set?  Or will this blow up
>>>>> in other ways?  Thanks,
>>>>
>>>> We can handle it without any problem, just users get confused.
>>>>
>>>> As a common practice, we use different bdev as a namespace for different
>>>> subvolumes.
>>>> Without a valid bdev, some user space tools may not be able to
>>>> distinguish inodes in different subvolumes.
>>>>
>>>
>>> Alright that's fine then.  But I feel like stat is one of those things
>>> that'll flood the console, can we put this somewhere else that's going
>>> to be hit less? Thanks,
>>
>> Unfortunately, stat() is the only user of btrfs_root::anon_dev.
>>
>> While fortunately, the logical is pretty simple, even without the safe
>> net we can understand the lifespan pretty well.
>>
>> I'm fine to drop this patch if you're concerned about the possible
>> warning flood, as the benefit is really not that much.
> 
> It could be a developer-only warning but if there's a root with a bad
> anon_dev, a simple 'ls -l' would flood the log for sure.
> 

We'll know in btrfs_init_fs_root() when get_anon_bdev() fails right?  Can't we 
just complain then?  That seems less spammy.  Thanks,

Josef