linux-ext4 - Re: exclude bitmap update

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Date:	Wed, 22 Jun 2011 15:04:01 +0300
From:	Amir Goldstein <amir73il@...il.com>
To:	Yongqiang Yang <xiaoqiangnk@...il.com>
Cc:	Andreas Dilger <adilger@...ger.ca>, Theodore Tso <tytso@....edu>,
	Ext4 Developers List <linux-ext4@...r.kernel.org>
Subject: Re: exclude bitmap update

On Wed, Jun 22, 2011 at 2:17 PM, Yongqiang Yang <xiaoqiangnk@...il.com> wrote:
> Hi Amir,
>
> Now the resize's input is a struct which determines blockbitmap ,
> inode bitmap and inode tables, then the kernel add groups.
>
> What we want to do is as follows.
>
> We need to remove IOC_EXTEND_GROUP and IOC_GROUP_ADD, and add

We do not remove them. we leave them to support resize with old
e2fsprogs version
when new features are not enabled (exclude_bitmap, big_alloc)

> IOC_RESIZE,  the input of which is a 64 bit argument which indicates
> the nr. of blocks we want to add.

The argument is new nr. of blocks, just like in EXT4_IOC_GROUP_EXTEND,
not the nr. of blocks we want to add.

>
> Then the kernel will extend original last group and add groups and
> allocate bitmaps and inode tables for new groups.

Correct, and init them if needed (no uninit_bg, first flex_bg group,
last partial group).

>
> Am I right?  I am right, I am willing to propose a design to you.  If
> you think it is no problem, I will do the code work.
>

Please do the code work.

> If I am right, resize in userspace will be simpler.
>

Yes, it will. very simple.
The only thing you need to do in userspace is check for online resize
support in the kernel,
like mke2fs does for lazy_itable_init:

        if (access("/sys/fs/ext4/features/lazy_itable_init", R_OK) == 0)
                lazy_itable_init = 1;

We can either just create the /sys/fs/ext4/features/online_resize entry in
ext4_feat_attrs array with:
EXT4_INFO_ATTR(online_resize);
to indicate the new ioctl is implemented by the kernel.

Or we can export the specific features which are supported by online
resize with:
EXT4_RO_ATTR(online_resize);
and an online_resize_show() function.

Then, for example, if Andreas's group will add support for online resize with
64bit and meta_bg features, they could use this interface to advertise the
new resize capabilities to userspace.

Maybe somebody has a better suggestion or maybe we should just
let the ioctl return ENOTSUP, like today, with unsupported features for resize.

Cheers,
Amir.

> Thank you,
> Yongqiang.
>
> On Tue, Jun 21, 2011 at 12:06 AM, Amir Goldstein <amir73il@...il.com> wrote:
>> Hi,
>>
>> A quick update from todays' ext4 conf call.
>> Ted says we should allow to add exclude bitmap by tune2fs.
>> And he says new resize ioctl should be just passing to the kernel the
>> new 64bit size
>> and let the kernel do all the bitmap allocation logic.
>> So it simplifies the patch to resize2fs and adds another
>> exclude bitmap patch to the kernel.
>>
>> I will send a detailed design to the list later on.
>> As usual, please let me know if you want to continue this task
>> or to hand it over to me.
>>
>> Thanks,
>> Amir.
>>
>
>
>
> --
> Best Wishes
> Yongqiang Yang
>
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