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Reply-To: kreijack@inwind.it
Subject: Re: [PATCH] VFS/BTRFS/NFSD: provide more unique inode number for
 btrfs export
To:     NeilBrown <neilb@suse.de>
Cc:     Roman Mamedov <rm@romanrm.net>,
        Christoph Hellwig <hch@infradead.org>,
        Josef Bacik <josef@toxicpanda.com>,
        "J. Bruce Fields" <bfields@fieldses.org>,
        Chuck Lever <chuck.lever@oracle.com>, Chris Mason <clm@fb.com>,
        David Sterba <dsterba@suse.com>,
        Alexander Viro <viro@zeniv.linux.org.uk>,
        linux-fsdevel@vger.kernel.org, linux-nfs@vger.kernel.org,
        linux-btrfs@vger.kernel.org
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 <162906443866.1695.6446438554332029261@noble.neil.brown.name>
From:   Goffredo Baroncelli <kreijack@inwind.it>
Message-ID: <d8d67284-8d53-ed97-f387-81b27d17fdde@inwind.it>
Date:   Tue, 17 Aug 2021 21:34:21 +0200
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On 8/15/21 11:53 PM, NeilBrown wrote:
> On Mon, 16 Aug 2021, kreijack@inwind.it wrote:
>> On 8/15/21 9:35 PM, Roman Mamedov wrote:
>>> On Sun, 15 Aug 2021 09:39:08 +0200
>>> Goffredo Baroncelli <kreijack@libero.it> wrote:
>>>
>>>> I am sure that it was discussed already but I was unable to find any track
>>>> of this discussion. But if the problem is the collision between the inode
>>>> number of different subvolume in the nfd export, is it simpler if the export
>>>> is truncated to the subvolume boundary ? It would be more coherent with the
>>>> current behavior of vfs+nfsd.
>>>
>>> See this bugreport thread which started it all:
>>> https://www.spinics.net/lists/linux-btrfs/msg111172.html
>>>
>>> In there the reporting user replied that it is strongly not feasible for them
>>> to export each individual snapshot.
>>
>> Thanks for pointing that.
>>
>> However looking at the 'exports' man page, it seems that NFS has already an
>> option to cover these cases: 'crossmnt'.
>>
>> If NFSd detects a "child" filesystem (i.e. a filesystem mounted inside an already
>> exported one) and the "parent" filesystem is marked as 'crossmnt',  the client mount
>> the parent AND the child filesystem with two separate mounts, so there is not problem of inode collision.
> 
> As you acknowledged, you haven't read the whole back-story.  Maybe you
> should.
> 
> https://lore.kernel.org/linux-nfs/20210613115313.BC59.409509F4@e16-tech.com/
> https://lore.kernel.org/linux-nfs/162848123483.25823.15844774651164477866.stgit@noble.brown/
> https://lore.kernel.org/linux-btrfs/162742539595.32498.13687924366155737575.stgit@noble.brown/
> 
> The flow of conversation does sometimes jump between threads.
> 
> I'm very happy to respond you questions after you've absorbed all that.

Hi Neil,

I read the other threads. And I still have the opinion that the nfsd crossmnt behavior should be a good solution for the btrfs subvolumes.
> 
> NeilBrown
> 


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