linux-ext4 - Re: [PATCH v4 6/9] xfs: switch to multigrain timestamps

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Message-ID: <20240708184739.GP612460@frogsfrogsfrogs>
Date: Mon, 8 Jul 2024 11:47:39 -0700
From: "Darrick J. Wong" <djwong@...nel.org>
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>,
	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>, kernel-team@...com,
	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 v4 6/9] xfs: switch to multigrain timestamps

On Mon, Jul 08, 2024 at 11:53:39AM -0400, Jeff Layton wrote:
> Enable multigrain timestamps, which should ensure that there is an
> apparent change to the timestamp whenever it has been written after
> being actively observed via getattr.
> 
> Also, anytime the mtime changes, the ctime must also change, and those
> are now the only two options for xfs_trans_ichgtime. Have that function
> unconditionally bump the ctime, and ASSERT that XFS_ICHGTIME_CHG is
> always set.
> 
> Finally, stop setting STATX_CHANGE_COOKIE in getattr, since the ctime
> should give us better semantics now.
> 
> Signed-off-by: Jeff Layton <jlayton@...nel.org>
> ---
>  fs/xfs/libxfs/xfs_trans_inode.c |  6 +++---
>  fs/xfs/xfs_iops.c               | 10 +++-------
>  fs/xfs/xfs_super.c              |  2 +-
>  3 files changed, 7 insertions(+), 11 deletions(-)
> 
> diff --git a/fs/xfs/libxfs/xfs_trans_inode.c b/fs/xfs/libxfs/xfs_trans_inode.c
> index 69fc5b981352..1f3639bbf5f0 100644
> --- a/fs/xfs/libxfs/xfs_trans_inode.c
> +++ b/fs/xfs/libxfs/xfs_trans_inode.c
> @@ -62,12 +62,12 @@ xfs_trans_ichgtime(
>  	ASSERT(tp);
>  	xfs_assert_ilocked(ip, XFS_ILOCK_EXCL);
>  
> -	tv = current_time(inode);
> +	/* If the mtime changes, then ctime must also change */
> +	ASSERT(flags & XFS_ICHGTIME_CHG);
>  
> +	tv = inode_set_ctime_current(inode);
>  	if (flags & XFS_ICHGTIME_MOD)
>  		inode_set_mtime_to_ts(inode, tv);
> -	if (flags & XFS_ICHGTIME_CHG)
> -		inode_set_ctime_to_ts(inode, tv);
>  	if (flags & XFS_ICHGTIME_CREATE)
>  		ip->i_crtime = tv;
>  }
> diff --git a/fs/xfs/xfs_iops.c b/fs/xfs/xfs_iops.c
> index a00dcbc77e12..d25872f818fa 100644
> --- a/fs/xfs/xfs_iops.c
> +++ b/fs/xfs/xfs_iops.c
> @@ -592,8 +592,9 @@ xfs_vn_getattr(
>  	stat->gid = vfsgid_into_kgid(vfsgid);
>  	stat->ino = ip->i_ino;
>  	stat->atime = inode_get_atime(inode);
> -	stat->mtime = inode_get_mtime(inode);
> -	stat->ctime = inode_get_ctime(inode);
> +
> +	fill_mg_cmtime(stat, request_mask, inode);

Sooo... for setting up a commit-range operation[1], XFS_IOC_START_COMMIT
could populate its freshness data by calling:

	struct kstat dummy;

	fill_mg_ctime(&dummy, STATX_CTIME | STATX_MTIME, inode);

and then using dummy.[cm]time to populate the freshness data that it
gives to userspace, right?  Having set QUERIED, a write to the file
immediately afterwards will cause a (tiny) increase in ctime_nsec which
will cause the XFS_IOC_COMMIT_RANGE to reject the commit[2].  Right?

--D

[1] https://lore.kernel.org/linux-xfs/20240227174649.GL6184@frogsfrogsfrogs/
[2] https://git.kernel.org/pub/scm/linux/kernel/git/djwong/xfs-linux.git/commit/?h=atomic-file-commits&id=0520d89c2698874c1f56ddf52ec4b8a3595baa14

> +
>  	stat->blocks = XFS_FSB_TO_BB(mp, ip->i_nblocks + ip->i_delayed_blks);
>  
>  	if (xfs_has_v3inodes(mp)) {
> @@ -603,11 +604,6 @@ xfs_vn_getattr(
>  		}
>  	}
>  
> -	if ((request_mask & STATX_CHANGE_COOKIE) && IS_I_VERSION(inode)) {
> -		stat->change_cookie = inode_query_iversion(inode);
> -		stat->result_mask |= STATX_CHANGE_COOKIE;
> -	}
> -
>  	/*
>  	 * Note: If you add another clause to set an attribute flag, please
>  	 * update attributes_mask below.
> diff --git a/fs/xfs/xfs_super.c b/fs/xfs/xfs_super.c
> index 27e9f749c4c7..210481b03fdb 100644
> --- a/fs/xfs/xfs_super.c
> +++ b/fs/xfs/xfs_super.c
> @@ -2052,7 +2052,7 @@ static struct file_system_type xfs_fs_type = {
>  	.init_fs_context	= xfs_init_fs_context,
>  	.parameters		= xfs_fs_parameters,
>  	.kill_sb		= xfs_kill_sb,
> -	.fs_flags		= FS_REQUIRES_DEV | FS_ALLOW_IDMAP,
> +	.fs_flags		= FS_REQUIRES_DEV | FS_ALLOW_IDMAP | FS_MGTIME,
>  };
>  MODULE_ALIAS_FS("xfs");
>  
> 
> -- 
> 2.45.2
> 
>