On Wed, 9 Jun 2021 at 10:50, Ian Kent <raven@xxxxxxxxxx> wrote:
>
> Add a revision counter to kernfs directory nodes so it can be used
> to detect if a directory node has changed during negative dentry
> revalidation.
>
> There's an assumption that sizeof(unsigned long) <= sizeof(pointer)
> on all architectures and as far as I know that assumption holds.
>
> So adding a revision counter to the struct kernfs_elem_dir variant of
> the kernfs_node type union won't increase the size of the kernfs_node
> struct. This is because struct kernfs_elem_dir is at least
> sizeof(pointer) smaller than the largest union variant. It's tempting
> to make the revision counter a u64 but that would increase the size of
> kernfs_node on archs where sizeof(pointer) is smaller than the revision
> counter.
>
> Signed-off-by: Ian Kent <raven@xxxxxxxxxx>
> ---
> fs/kernfs/dir.c | 2 ++
> fs/kernfs/kernfs-internal.h | 23 +++++++++++++++++++++++
> include/linux/kernfs.h | 5 +++++
> 3 files changed, 30 insertions(+)
>
> diff --git a/fs/kernfs/dir.c b/fs/kernfs/dir.c
> index 33166ec90a112..b3d1bc0f317d0 100644
> --- a/fs/kernfs/dir.c
> +++ b/fs/kernfs/dir.c
> @@ -372,6 +372,7 @@ static int kernfs_link_sibling(struct kernfs_node *kn)
> /* successfully added, account subdir number */
> if (kernfs_type(kn) == KERNFS_DIR)
> kn->parent->dir.subdirs++;
> + kernfs_inc_rev(kn->parent);
>
> return 0;
> }
> @@ -394,6 +395,7 @@ static bool kernfs_unlink_sibling(struct kernfs_node *kn)
>
> if (kernfs_type(kn) == KERNFS_DIR)
> kn->parent->dir.subdirs--;
> + kernfs_inc_rev(kn->parent);
>
> rb_erase(&kn->rb, &kn->parent->dir.children);
> RB_CLEAR_NODE(&kn->rb);
> diff --git a/fs/kernfs/kernfs-internal.h b/fs/kernfs/kernfs-internal.h
> index ccc3b44f6306f..b4e7579e04799 100644
> --- a/fs/kernfs/kernfs-internal.h
> +++ b/fs/kernfs/kernfs-internal.h
> @@ -81,6 +81,29 @@ static inline struct kernfs_node *kernfs_dentry_node(struct dentry *dentry)
> return d_inode(dentry)->i_private;
> }
>
> +static inline void kernfs_set_rev(struct kernfs_node *kn,
> + struct dentry *dentry)
> +{
> + if (kernfs_type(kn) == KERNFS_DIR)
> + dentry->d_time = kn->dir.rev;
> +}
> +
> +static inline void kernfs_inc_rev(struct kernfs_node *kn)
> +{
> + if (kernfs_type(kn) == KERNFS_DIR)
> + kn->dir.rev++;
> +}
> +
> +static inline bool kernfs_dir_changed(struct kernfs_node *kn,
> + struct dentry *dentry)
> +{
> + if (kernfs_type(kn) == KERNFS_DIR) {
Aren't these always be called on a KERNFS_DIR node?
You could just reduce that to a WARN_ON, or remove the conditions
altogether then.
Thanks,
Miklos
