linux-kernel - Re: [PATCH v6 5/9] Documentation: add a new file documenting multigrain timestamps

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Message-ID: <20240717113132.dvzsczxjr67224bx@quack3>
Date: Wed, 17 Jul 2024 13:31:32 +0200
From: Jan Kara <jack@...e.cz>
To: Jeff Layton <jlayton@...nel.org>
Cc: Alexander Viro <viro@...iv.linux.org.uk>,
	Christian Brauner <brauner@...nel.org>, Jan Kara <jack@...e.cz>,
	Steven Rostedt <rostedt@...dmis.org>,
	Masami Hiramatsu <mhiramat@...nel.org>,
	Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
	Chandan Babu R <chandan.babu@...cle.com>,
	"Darrick J. Wong" <djwong@...nel.org>,
	Theodore Ts'o <tytso@....edu>,
	Andreas Dilger <adilger.kernel@...ger.ca>, Chris Mason <clm@...com>,
	Josef Bacik <josef@...icpanda.com>, David Sterba <dsterba@...e.com>,
	Hugh Dickins <hughd@...gle.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Jonathan Corbet <corbet@....net>,
	Dave Chinner <david@...morbit.com>, Andi Kleen <ak@...ux.intel.com>,
	Christoph Hellwig <hch@...radead.org>,
	Uros Bizjak <ubizjak@...il.com>,
	Kent Overstreet <kent.overstreet@...ux.dev>,
	Arnd Bergmann <arnd@...db.de>, Randy Dunlap <rdunlap@...radead.org>,
	linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-trace-kernel@...r.kernel.org, linux-xfs@...r.kernel.org,
	linux-ext4@...r.kernel.org, linux-btrfs@...r.kernel.org,
	linux-mm@...ck.org, linux-nfs@...r.kernel.org,
	linux-doc@...r.kernel.org
Subject: Re: [PATCH v6 5/9] Documentation: add a new file documenting
 multigrain timestamps

On Mon 15-07-24 08:48:56, Jeff Layton wrote:
> Add a high-level document that describes how multigrain timestamps work,
> rationale for them, and some info about implementation and tradeoffs.
> 
> Reviewed-by: Josef Bacik <josef@...icpanda.com>
> Signed-off-by: Jeff Layton <jlayton@...nel.org>

One comment below. With that fixed feel free to add:

Reviewed-by: Jan Kara <jack@...e.cz>

> +Implementation Notes
> +====================
> +Multigrain timestamps are intended for use by local filesystems that get
> +ctime values from the local clock. This is in contrast to network filesystems
> +and the like that just mirror timestamp values from a server.
> +
> +For most filesystems, it's sufficient to just set the FS_MGTIME flag in the
> +fstype->fs_flags in order to opt-in, providing the ctime is only ever set via
> +inode_set_ctime_current(). If the filesystem has a ->getattr routine that
> +doesn't call generic_fillattr, then you should have it call fill_mg_cmtime to
> +fill those values.

I think you should explicitely mention that ->setattr() implementation
needs to use setattr_copy() or otherwise mimic its behavior...

								Honza
-- 
Jan Kara <jack@...e.com>
SUSE Labs, CR