Re: [PATCH v4 1/2] btrfs: Introduce new mount option backuproot to replace recovery

["Austin S. Hemmelgarn" <ahferroin7@gmail.com>]

On 2015-12-22 07:30, Holger Hoffstätte wrote:
> On Tue, Dec 22, 2015 at 3:16 AM, Qu Wenruo <quwenruo@cn.fujitsu.com> wrote:
>> Current "recovery" mount option will only try to use backup root.
>> However the word "recovery" is too generic and may be confusing for some
>> users.
>>
>> Here introduce a new and more specific mount option, "backuproot" to
>> replace "recovery" mount option.
>> "Recovery" will be kept for compatibility reason, but will be
>> deprecated.
>
> I agree that this makes much more sense from a user's perspective, so +1.
>
> But why not go all the way: try backuproot automatically when the
> initial mount fails,
> log the fallback and simply deprecate/ignore the option?
>
> Either this works - in which case there is no need to involve a human,
> which may not
> even exist - or it does not. If it does not, things are hosed anyway
> and we can fail
> properly.
I have seen cases where mounting -o ro,recovery didn't work, but restore 
did, so there are cases where data is recoverable but this mount option 
won't work.
>
> Any reasons not to do this?
I'm not 100% certain, but I think that there is a chance if it doesn't 
work that it will make things worse.  That, and TBH, it really should be 
the administrator's choice; personally, if I come across a filesystem on 
one of my systems that needs this, then I'm nuking the filesystem and 
restoring from backup, because I don't trust that the rest of the 
filesystem isn't broken.  It's also consistent with other filesystems 
(at least ext4 requires an option to force using a backup superblock). 
Perhaps we could add a module parameter that specifies whether or not to 
automatically try this?