proc: add proc_splice_unmountable()

Add a tiny procfs helper to splice a dentry that cannot be mounted upon.

Link: https://lore.kernel.org/r/20240806-work-procfs-v1-3-fb04e1d09f0c@kernel.org
Reviewed-by: Josef Bacik <josef@toxicpanda.com>
Signed-off-by: Christian Brauner <brauner@kernel.org>

diff --git a/fs/proc/internal.h b/fs/proc/internal.h
index a8a8576d8592e660fc88652ac973e972ab99996e..9e3f25e4c188ae18d36876c7ba93c3c4cf818959 100644 (file)
--- a/fs/proc/internal.h
+++ b/fs/proc/internal.h
@@ -349,3 +349,16 @@ static inline void pde_force_lookup(struct proc_dir_entry *pde)
        /* /proc/net/ entries can be changed under us by setns(CLONE_NEWNET) */
        pde->proc_dops = &proc_net_dentry_ops;
 }
+
+/*
+ * Add a new procfs dentry that can't serve as a mountpoint. That should
+ * encompass anything that is ephemeral and can just disappear while the
+ * process is still around.
+ */
+static inline struct dentry *proc_splice_unmountable(struct inode *inode,
+               struct dentry *dentry, const struct dentry_operations *d_ops)
+{
+       d_set_d_op(dentry, d_ops);
+       dont_mount(dentry);
+       return d_splice_alias(inode, dentry);
+}