linux-kernel - Re: [PATCH v2 0/1] exfat: Add support for FS_IOC

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Message-ID: <aKQyrMX7xS5A8cv6@infradead.org>
Date: Tue, 19 Aug 2025 01:15:40 -0700
From: Christoph Hellwig <hch@...radead.org>
To: Ethan Ferguson <ethan.ferguson@...ier.com>
Cc: hch@...radead.org, linkinjeon@...nel.org, linux-fsdevel@...r.kernel.org,
	linux-kernel@...r.kernel.org, sj1557.seo@...sung.com,
	yuezhang.mo@...y.com
Subject: Re: [PATCH v2 0/1] exfat: Add support for FS_IOC_{GET,SET}FSLABEL

On Mon, Aug 18, 2025 at 01:49:11PM -0400, Ethan Ferguson wrote:
> That's fair. I took a look at how btrfs guards against this, it seems
> as if they use mnt_want_write_file to guard against bad writes, and
> only write to the in-memory superblock, and commit the transaction
> afterwards. However, this (during my testing with
> CONFIG_BLK_DEV_WRITE_MOUNTED both on and off) still results in an
> immediate disk flush.
> 
> My changes from this thread also seem to work with
> CONFIG_BLK_DEV_WRITE_MOUNTED both disabled and enabled.

What I meant to say is that we actually need your change to work with
CONFIG_BLK_DEV_WRITE_MOUNTED, as the current way in tunefs is broken,
even if that's something a few Linux file systems have historically
done.

> Maybe an alternative would be to only write to sbi->volume_label (with
> mutex guarding), and only flush to disk on exfat_put_super? And to use
> mnt_want_write_file as well.

I think your patch is fine as-is.  I've just been trying to give you
additional ammunition.