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Date:   Thu, 6 Jul 2023 08:19:00 +0900
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Subject: Re: [PATCH v2 08/92] fs: new helper: simple_rename_timestamp
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References: <20230705185812.579118-1-jlayton@kernel.org>
 <20230705185812.579118-3-jlayton@kernel.org>
From:   Damien Le Moal <dlemoal@kernel.org>
Organization: Western Digital Research
In-Reply-To: <20230705185812.579118-3-jlayton@kernel.org>
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Precedence: bulk

On 7/6/23 03:58, Jeff Layton wrote:
> A rename potentially involves updating 4 different inode timestamps. Add
> a function that handles the details sanely, and convert the libfs.c
> callers to use it.
> 
> Signed-off-by: Jeff Layton <jlayton@kernel.org>
> ---
>  fs/libfs.c         | 36 +++++++++++++++++++++++++++---------
>  include/linux/fs.h |  2 ++
>  2 files changed, 29 insertions(+), 9 deletions(-)
> 
> diff --git a/fs/libfs.c b/fs/libfs.c
> index a7e56baf8bbd..9ee79668c909 100644
> --- a/fs/libfs.c
> +++ b/fs/libfs.c
> @@ -692,6 +692,31 @@ int simple_rmdir(struct inode *dir, struct dentry *dentry)
>  }
>  EXPORT_SYMBOL(simple_rmdir);
>  
> +/**
> + * simple_rename_timestamp - update the various inode timestamps for rename
> + * @old_dir: old parent directory
> + * @old_dentry: dentry that is being renamed
> + * @new_dir: new parent directory
> + * @new_dentry: target for rename
> + *
> + * POSIX mandates that the old and new parent directories have their ctime and
> + * mtime updated, and that inodes of @old_dentry and @new_dentry (if any), have
> + * their ctime updated.
> + */
> +void simple_rename_timestamp(struct inode *old_dir, struct dentry *old_dentry,
> +			     struct inode *new_dir, struct dentry *new_dentry)
> +{
> +	struct inode *newino = d_inode(new_dentry);
> +
> +	old_dir->i_mtime = inode_set_ctime_current(old_dir);
> +	if (new_dir != old_dir)
> +		new_dir->i_mtime = inode_set_ctime_current(new_dir);
> +	inode_set_ctime_current(d_inode(old_dentry));
> +	if (newino)
> +		inode_set_ctime_current(newino);
> +}
> +EXPORT_SYMBOL_GPL(simple_rename_timestamp);
> +
>  int simple_rename_exchange(struct inode *old_dir, struct dentry *old_dentry,
>  			   struct inode *new_dir, struct dentry *new_dentry)
>  {
> @@ -707,11 +732,7 @@ int simple_rename_exchange(struct inode *old_dir, struct dentry *old_dentry,
>  			inc_nlink(old_dir);
>  		}
>  	}
> -	old_dir->i_ctime = old_dir->i_mtime =
> -	new_dir->i_ctime = new_dir->i_mtime =
> -	d_inode(old_dentry)->i_ctime =
> -	d_inode(new_dentry)->i_ctime = current_time(old_dir);
> -
> +	simple_rename_timestamp(old_dir, old_dentry, new_dir, new_dentry);

This is somewhat changing the current behavior: before the patch, the mtime and
ctime of old_dir, new_dir and the inodes associated with the dentries are always
equal. But given that simple_rename_timestamp() calls inode_set_ctime_current()
4 times, the times could potentially be different.

I am not sure if that is an issue, but it seems that calling
inode_set_ctime_current() once, recording the "now" time it sets and using that
value to set all times may be more efficient and preserve the existing behavior.

>  	return 0;
>  }
>  EXPORT_SYMBOL_GPL(simple_rename_exchange);
> @@ -720,7 +741,6 @@ int simple_rename(struct mnt_idmap *idmap, struct inode *old_dir,
>  		  struct dentry *old_dentry, struct inode *new_dir,
>  		  struct dentry *new_dentry, unsigned int flags)
>  {
> -	struct inode *inode = d_inode(old_dentry);
>  	int they_are_dirs = d_is_dir(old_dentry);
>  
>  	if (flags & ~(RENAME_NOREPLACE | RENAME_EXCHANGE))
> @@ -743,9 +763,7 @@ int simple_rename(struct mnt_idmap *idmap, struct inode *old_dir,
>  		inc_nlink(new_dir);
>  	}
>  
> -	old_dir->i_ctime = old_dir->i_mtime = new_dir->i_ctime =
> -		new_dir->i_mtime = inode->i_ctime = current_time(old_dir);
> -
> +	simple_rename_timestamp(old_dir, old_dentry, new_dir, new_dentry);
>  	return 0;
>  }
>  EXPORT_SYMBOL(simple_rename);
> diff --git a/include/linux/fs.h b/include/linux/fs.h
> index bdfbd11a5811..14e38bd900f1 100644
> --- a/include/linux/fs.h
> +++ b/include/linux/fs.h
> @@ -2979,6 +2979,8 @@ extern int simple_open(struct inode *inode, struct file *file);
>  extern int simple_link(struct dentry *, struct inode *, struct dentry *);
>  extern int simple_unlink(struct inode *, struct dentry *);
>  extern int simple_rmdir(struct inode *, struct dentry *);
> +void simple_rename_timestamp(struct inode *old_dir, struct dentry *old_dentry,
> +			     struct inode *new_dir, struct dentry *new_dentry);
>  extern int simple_rename_exchange(struct inode *old_dir, struct dentry *old_dentry,
>  				  struct inode *new_dir, struct dentry *new_dentry);
>  extern int simple_rename(struct mnt_idmap *, struct inode *,

-- 
Damien Le Moal
Western Digital Research