Am Mi., 18. Juni 2025 um 22:53 Uhr schrieb Christian Brauner
<brauner@xxxxxxxxxx>:
>
> * Add a callback to struct stashed_operations so it's possible to
> implement custom behavior for pidfs and allow for it to return errors.
>
> * Teach stashed_dentry_get() to handle error pointers.
>
> Signed-off-by: Christian Brauner <brauner@xxxxxxxxxx>
Reviewed-by: Alexander Mikhalitsyn <aleksandr.mikhalitsyn@xxxxxxxxxxxxx>
> ---
> fs/internal.h | 3 +++
> fs/libfs.c | 27 ++++++++++++++++++++-------
> 2 files changed, 23 insertions(+), 7 deletions(-)
>
> diff --git a/fs/internal.h b/fs/internal.h
> index 393f6c5c24f6..22ba066d1dba 100644
> --- a/fs/internal.h
> +++ b/fs/internal.h
> @@ -322,12 +322,15 @@ struct mnt_idmap *alloc_mnt_idmap(struct user_namespace *mnt_userns);
> struct mnt_idmap *mnt_idmap_get(struct mnt_idmap *idmap);
> void mnt_idmap_put(struct mnt_idmap *idmap);
> struct stashed_operations {
> + struct dentry *(*stash_dentry)(struct dentry **stashed,
> + struct dentry *dentry);
> void (*put_data)(void *data);
> int (*init_inode)(struct inode *inode, void *data);
> };
> int path_from_stashed(struct dentry **stashed, struct vfsmount *mnt, void *data,
> struct path *path);
> void stashed_dentry_prune(struct dentry *dentry);
> +struct dentry *stash_dentry(struct dentry **stashed, struct dentry *dentry);
> struct dentry *stashed_dentry_get(struct dentry **stashed);
> /**
> * path_mounted - check whether path is mounted
> diff --git a/fs/libfs.c b/fs/libfs.c
> index 9ea0ecc325a8..3541e22c87b5 100644
> --- a/fs/libfs.c
> +++ b/fs/libfs.c
> @@ -2128,6 +2128,8 @@ struct dentry *stashed_dentry_get(struct dentry **stashed)
> dentry = rcu_dereference(*stashed);
> if (!dentry)
> return NULL;
> + if (IS_ERR(dentry))
> + return dentry;
> if (!lockref_get_not_dead(&dentry->d_lockref))
> return NULL;
> return dentry;
> @@ -2176,8 +2178,7 @@ static struct dentry *prepare_anon_dentry(struct dentry **stashed,
> return dentry;
> }
>
> -static struct dentry *stash_dentry(struct dentry **stashed,
> - struct dentry *dentry)
> +struct dentry *stash_dentry(struct dentry **stashed, struct dentry *dentry)
> {
> guard(rcu)();
> for (;;) {
> @@ -2218,12 +2219,15 @@ static struct dentry *stash_dentry(struct dentry **stashed,
> int path_from_stashed(struct dentry **stashed, struct vfsmount *mnt, void *data,
> struct path *path)
> {
> - struct dentry *dentry;
> + struct dentry *dentry, *res;
> const struct stashed_operations *sops = mnt->mnt_sb->s_fs_info;
>
> /* See if dentry can be reused. */
> - path->dentry = stashed_dentry_get(stashed);
> - if (path->dentry) {
> + res = stashed_dentry_get(stashed);
> + if (IS_ERR(res))
> + return PTR_ERR(res);
> + if (res) {
> + path->dentry = res;
> sops->put_data(data);
> goto out_path;
> }
> @@ -2234,8 +2238,17 @@ int path_from_stashed(struct dentry **stashed, struct vfsmount *mnt, void *data,
> return PTR_ERR(dentry);
>
> /* Added a new dentry. @data is now owned by the filesystem. */
> - path->dentry = stash_dentry(stashed, dentry);
> - if (path->dentry != dentry)
> + if (sops->stash_dentry)
> + res = sops->stash_dentry(stashed, dentry);
> + else
> + res = stash_dentry(stashed, dentry);
> + if (IS_ERR(res)) {
> + dput(dentry);
> + return PTR_ERR(res);
> + }
> + path->dentry = res;
> + /* A dentry was reused. */
> + if (res != dentry)
> dput(dentry);
>
> out_path:
>
> --
> 2.47.2
>
