Re: [PATCH 0/4] btrfs: sysfs and unsupported temp-fsid features for clones

[Anand Jain <anand.jain@oracle.com>]

On 10/10/23 05:29, David Sterba wrote:
> On Mon, Oct 09, 2023 at 01:37:22PM +0530, Anand Jain wrote:
>>>> Can Guilherme send an RFC patch for feedback from others and
>>>> copy suggested-by. Because, I haven't found a compelling reason
>>>> for the restriction, except to improve the user experience.
>>
>> My comments about the superblock flag are above.
>>
>> User experiences are subjective, so we need others to comment;
>> an RFC will help.
> 
> A few things changed, the incompat bit was supposed to prevent
> accidentally duplicated fsids but with your recent changes this is safe.
> This would need to let Guilherme check if the A/B use case still works
> but this seems to be so as I'm reading the changelog.
> 


> In a controlled environment the incompat bit will not bring much value
> other than yet another sanity check preventing some user error, > but
> related only to the multiple devices.


Agreed. Anyway, the kernel would continue to fail the mount of the
duplicate-fsid for a multi-device filesystem.

And

    $ mkfs.btrfs -U <duplicate-fsid> /dev/sda1 /dev/sda2 ..

for a multi-device filesystem will also fail.

Therefore, the only avenue for the user to make a mistake is
by using dd to copy for a multi-device setup.

Thanks, Anand