linux-ext4 - Re: [PATCH v3 2/3] fs: record I_DIRTY_TIME even if inode already has I_DIRTY

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Date:   Fri, 12 Aug 2022 11:12:27 -0700
From:   Eric Biggers <ebiggers@...nel.org>
To:     Lukas Czerner <lczerner@...hat.com>
Cc:     linux-ext4@...r.kernel.org, tytso@....edu, jlayton@...nel.org,
        jack@...e.cz, linux-fsdevel@...r.kernel.org, david@...morbit.com,
        Christoph Hellwig <hch@...radead.org>
Subject: Re: [PATCH v3 2/3] fs: record I_DIRTY_TIME even if inode already has
 I_DIRTY_INODE

On Fri, Aug 12, 2022 at 02:37:26PM +0200, Lukas Czerner wrote:
> diff --git a/Documentation/filesystems/vfs.rst b/Documentation/filesystems/vfs.rst
> index 6cd6953e175b..5d72b6ba4e63 100644
> --- a/Documentation/filesystems/vfs.rst
> +++ b/Documentation/filesystems/vfs.rst
> @@ -274,6 +274,8 @@ or bottom half).
>  	This is specifically for the inode itself being marked dirty,
>  	not its data.  If the update needs to be persisted by fdatasync(),
>  	then I_DIRTY_DATASYNC will be set in the flags argument.
> +	If the inode has dirty timestamp and lazytime is enabled
> +	I_DIRTY_TIME will be set in the flags.

The new sentence is not always true, since with this patch if
__mark_inode_dirty(I_DIRTY_INODE) is called twice on an inode that has
I_DIRTY_TIME, the second call will no longer include I_DIRTY_TIME -- even though
the inode still has dirty timestamps.  Please be super clear about what the
flags actually mean -- I'm still struggling to understand this patch...

- Eric