linux-kernel - Re: [PATCH v6 05/15] ubifs: Rename whiteout atomically

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Date:   Mon, 10 Jan 2022 21:58:09 +0100 (CET)
From:   Richard Weinberger <richard@....at>
To:     chengzhihao1 <chengzhihao1@...wei.com>
Cc:     Miquel Raynal <miquel.raynal@...tlin.com>,
        Vignesh Raghavendra <vigneshr@...com>,
        mcoquelin stm32 <mcoquelin.stm32@...il.com>,
        kirill shutemov <kirill.shutemov@...ux.intel.com>,
        Sascha Hauer <s.hauer@...gutronix.de>,
        linux-mtd <linux-mtd@...ts.infradead.org>,
        linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v6 05/15] ubifs: Rename whiteout atomically

----- Ursprüngliche Mail -----
>> The whiteout inode is clean after creation from create_whiteout(), and
>> it can't be marked dirty until ubifs_jnl_rename() finished. So, I think
>> there is no chance for whiteout being written on disk. Then,
>> 'ubifs_assert(c, !whiteout_ui->dirty)' never fails in ubifs_jnl_rename()
>> during my local stress tests. You may add some delay executions after
>> whiteout creation to make sure that whiteout won't be written back
>> before ubifs_jnl_rename().
> 
> From UBIFS point of view I fully agree with you. I'm just a little puzzled why
> other filesystems use the tmpfile approach. My fear is that VFS can do things
> to the inode we don't have in mind right now.

After digging a bit into XFS I'm sure your approach is okay.
So, UBIFS can do a whiteout without help of tmpfiles. :-)

Thanks,
//richard