Re: [RFC PATCH] Revert "btrfs: allow mounting btrfs subvolumes with different ro/rw options"

[Tobias Geerinckx-Rice <tobias.geerinckx.rice@gmail.com>]

On 3 July 2014 10:33, Qu Wenruo <quwenruo@cn.fujitsu.com> wrote:
> Oh, sorry for my confusing words.

And I probably should have waited for my frustration with my mail
client/device/public transport to subside before panicking^Creplying.

I use a combination of ro & rw (not insanely nested) subvolumes on a
few pseudo-embedded home/office servers and would like to keep that
arrangement working if possible. I'm also aware that it doesn't
protect against all possible bugs.

> To make it clear, when mentioning 'the whole disk(or partition whatever)' I mean the FS_TREE.
> (Of course not the default subvolume)
>
> The problem is that, even you mount a subvolume ro, you can still change contents in the subvolume
> through its rw parent subvolume.
> And if a subvolume can still be modified, the ro mount lose it meaning.

That makes so much more sense than my original reading, which was
weird and wrong and implied strange subvol-5-only magic. Sorry!

> So we need special rules to prevent such things.

Not that it matters, but: agreed.

   Tobias