linux-ext4 - Re: mke2fs accepts block size not mentioned in its man page

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Date:   Thu, 8 Aug 2019 18:00:58 -0700
From:   "Darrick J. Wong" <darrick.wong@...cle.com>
To:     Qu Wenruo <quwenruo.btrfs@....com>
Cc:     linux-ext4@...r.kernel.org,
        "linux-btrfs@...r.kernel.org" <linux-btrfs@...r.kernel.org>
Subject: Re: mke2fs accepts block size not mentioned in its man page

On Fri, Jul 05, 2019 at 01:35:02PM +0800, Qu Wenruo wrote:
> Hi,
> 
> Just doing some tests on aarch64 with 64K page size.
> 
> Man page of mke2fs only mentions 3 valid block size: 1k, 2k, 4k.
> But in real world, we can pass 64K as block size for it without any problem:
> 
>   $mke2fs -F -t ext3 -b 65536 /dev/loop1
>   Warning: blocksize 65536 not usable on most systems.
>   mke2fs 1.45.2 (27-May-2019)
>   /dev/loop1 contains a btrfs file system
>   Discarding device blocks: done
>   Creating filesystem with 81920 64k blocks and 81920 inodes
>   Filesystem UUID: 311bb224-6d2d-44a7-9790-92c4878d6549
>   [...]
> 
> It's great to see mke2fs accepts 64K as nodesize, which allows
> btrfs-convert to work.
> (If blocksize is default to 4K or doesn't accept 64K page size,
> btrfs-convert can work but can't be mounted on system with 64K page size)
> 
> Shouldn't the man page mention all valid values?

You'd think so, but 64k blocks only works on machines with 64k pages,
so that's why it doesn't mention anything beyond the lowest common
denominator. :/

--D

> Thanks,
> Qu
>