On Fri, 2021-06-11 at 14:49 +0200, Miklos Szeredi wrote:

On Wed, 9 Jun 2021 at 10:50, Ian Kent [off-list ref] wrote:

quoted

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@themaw.net>
---
 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