On Fri, 2021-06-11 at 14:49 +0200, Miklos Szeredi wrote:
> 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?
Yes they are.
>
> You could just reduce that to a WARN_ON, or remove the conditions
> altogether then.
I was tempted to not use the check, a WARN_ON sounds better than
removing the check, I'll do that in a v7.
Thanks
Ian
