Re: [PATCH v2 08/92] fs: new helper: simple_rename_timestamp

Damien Le Moal
2023-07-05T23:19:24Z

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