Re: [PATCH v2 00/19] btrfs: add read-only support for subpage sector size

Qu Wenruo
2020-09-17T00:29:34Z

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On 2020/9/17 上午8:13, Neal Gompa wrote:
> On Wed, Sep 16, 2020 at 8:03 PM Qu Wenruo <wqu@suse.com> wrote:
>>
>>
>>
>> On 2020/9/17 上午12:18, Neal Gompa wrote:
>>> On Tue, Sep 15, 2020 at 1:36 AM Qu Wenruo <wqu@suse.com> wrote:
>>>>
>>>> Patches can be fetched from github:
>>>> https://github.com/adam900710/linux/tree/subpage
>>>>
>>>> Currently btrfs only allows to mount fs with sectorsize == PAGE_SIZE.
>>>>
>>>> That means, for 64K page size system, they can only use 64K sector size
>>>> fs.
>>>> This brings a big compatible problem for btrfs.
>>>>
>>>> This patch is going to slightly solve the problem by, allowing 64K
>>>> system to mount 4K sectorsize fs in read-only mode.
>>>>
>>>> The main objective here, is to remove the blockage in the code base, and
>>>> pave the road to full RW mount support.
>>>>
>>>
>>> Is there a reason we don't include a patch in here to just hardwire
>>> the block size to 4K going forward?
>>>
>>
>> Did you mean to make 4K sector size the hard requirement?
>>
>> That would make existing 64K sector size fs unable to be mounted then.
>>
>
> I mean, make the 64K variant a legacy one and force 4K for all new
> filesystems. That then simplifies this work to making it mountable and
> usable as a legacy filesystem format.

That's the plan.

But not for now, since currently the subpage support is only read-only.

>
> I guess that would be an incompat flag, no?

No need for incompat flag.

For older kernel they just can't mount subpage fs.

Thanks,
Qu

>
>
>
> --
> 真実はいつも一つ！/ Always, there's only one truth!
>

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