Re: [PATCH 2/3] btrfs: Introduce the single-dev feature

["Guilherme G. Piccoli" <gpiccoli@igalia.com>]

On 04/08/2023 05:27, Qu Wenruo wrote:
> [...] 
> My concern is still about the "virtual" fsid part.
> 
> If we go virtual fsid, there can be some unexpected problems.
> 
> E.g. the /sys/fs/btrfs/<uuid>/ entry would be the new virtual one.
> 
> And there may be some other problems like user space UUID detection of
> mounted fs, thus I'm not 100% sure if this is a good idea.
> 
> However I don't have any better solution either, so this may be the
> least worst solution for now.
> 
> Thanks,
> Qu

Hi Qu, thanks for your analysis!

I think the virtual/spoofed fsid part is not without problems but I
consider it to be less prone to unexpected issues than not.

It's based on the metadata_uuid code, which is stable and present in
btrfs for like 5 years. Also, we don't need to "corner-case" a lot of
stuff to use that, which would be needed if we went to the pure dup fsid
route. I tried that and it breaks in a lot of places, to which we
require a lot of if conditionals (I even discussed that briefly in the
last thread with you, about sysfs, remember?).

So, despite not perfect, I agree with you that seems to be the least
worse solution :)

Cheers,


Guilherme