On Fri, Jun 02, 2017 at 02:53:56PM -0700, Shaohua Li wrote:
> From: Shaohua Li <shli@xxxxxx>
>
> Add an API to get kernfs node from inode number. We will need this to
> implement exportfs operations.
>
> To make the API lock free, kernfs node is freed in RCU context. And we
> depend on kernfs_node count/ino number to filter stale kernfs nodes.
>
> Signed-off-by: Shaohua Li <shli@xxxxxx>
> ---
> fs/kernfs/dir.c | 35 +++++++++++++++++++++++++++++++++++
> fs/kernfs/kernfs-internal.h | 2 ++
> fs/kernfs/mount.c | 4 +++-
> 3 files changed, 40 insertions(+), 1 deletion(-)
>
> diff --git a/fs/kernfs/dir.c b/fs/kernfs/dir.c
> index 8e8545a..4c86e4c 100644
> --- a/fs/kernfs/dir.c
> +++ b/fs/kernfs/dir.c
> @@ -643,6 +643,7 @@ static struct kernfs_node *__kernfs_new_node(struct kernfs_root *root,
> kn->ino = ret;
> kn->generation = atomic_inc_return(&root->next_generation);
>
> + /* set ino first. Above atomic_inc_return has a barrier */
> atomic_set(&kn->count, 1);
> atomic_set(&kn->active, KN_DEACTIVATED_BIAS);
> RB_CLEAR_NODE(&kn->rb);
> @@ -674,6 +675,40 @@ struct kernfs_node *kernfs_new_node(struct kernfs_node *parent,
> return kn;
> }
>
> +/*
> + * kernfs_get_node_by_ino - get kernfs_node from inode number
> + * @root: the kernfs root
> + * @ino: inode number
> + *
> + * RETURNS:
> + * NULL on failure. Return a kernfs node with reference counter incremented
> + */
Is the above supposed to be a valid kernel doc entry?
> +struct kernfs_node *kernfs_get_node_by_ino(struct kernfs_root *root,
> + unsigned int ino)
> +{
> + struct kernfs_node *kn;
> +
> + rcu_read_lock();
> + kn = idr_find(&root->ino_idr, ino);
> + if (!kn)
> + goto out;
> + /* kernfs_put removes the ino after count is 0 */
> + if (!atomic_inc_not_zero(&kn->count)) {
> + kn = NULL;
Why do yo need to set kn to NULL?
> + goto out;
> + }
> + /* If this node is reused, __kernfs_new_node sets ino before count */
> + if (kn->ino != ino)
> + goto out;
> + rcu_read_unlock();
> +
> + return kn;
> +out:
> + rcu_read_unlock();
> + kernfs_put(kn);
> + return NULL;
> +}
> +
> /**
> * kernfs_add_one - add kernfs_node to parent without warning
> * @kn: kernfs_node to be added
> diff --git a/fs/kernfs/kernfs-internal.h b/fs/kernfs/kernfs-internal.h
> index 2d5144a..3534cfe 100644
> --- a/fs/kernfs/kernfs-internal.h
> +++ b/fs/kernfs/kernfs-internal.h
> @@ -98,6 +98,8 @@ int kernfs_add_one(struct kernfs_node *kn);
> struct kernfs_node *kernfs_new_node(struct kernfs_node *parent,
> const char *name, umode_t mode,
> unsigned flags);
> +struct kernfs_node *kernfs_get_node_by_ino(struct kernfs_root *root,
> + unsigned int ino);
>
> /*
> * file.c
> diff --git a/fs/kernfs/mount.c b/fs/kernfs/mount.c
> index d5b149a..343dfeb 100644
> --- a/fs/kernfs/mount.c
> +++ b/fs/kernfs/mount.c
> @@ -332,5 +332,7 @@ void __init kernfs_init(void)
> {
> kernfs_node_cache = kmem_cache_create("kernfs_node_cache",
> sizeof(struct kernfs_node),
> - 0, SLAB_PANIC, NULL);
> + 0,
> + SLAB_PANIC | SLAB_TYPESAFE_BY_RCU,
> + NULL);
> }
> --
> 2.9.3
>
>
--
All the best,
Eduardo Valentin
