Re: [PATCH v2 5/5] ftrace: Add comments to ftrace_hash_move() and friends

[Mark Rutland <mark.rutland@arm.com>]

On Wed, Jun 05, 2024 at 02:03:39PM -0400, Steven Rostedt wrote:
> From: "Steven Rostedt (Google)" <rostedt@goodmis.org>
> 
> Describe what ftrace_hash_move() does and add some more comments to some
> other functions to make it easier to understand.
> 
> Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>

Acked-by: Mark Rutland <mark.rutland@arm.com>

Mark.

> ---
>  kernel/trace/ftrace.c | 24 +++++++++++++++++++++++-
>  1 file changed, 23 insertions(+), 1 deletion(-)
> 
> diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c
> index 83f23f8fc26d..ae1603e771c5 100644
> --- a/kernel/trace/ftrace.c
> +++ b/kernel/trace/ftrace.c
> @@ -169,6 +169,7 @@ static inline void ftrace_ops_init(struct ftrace_ops *ops)
>  #endif
>  }
>  
> +/* Call this function for when a callback filters on set_ftrace_pid */
>  static void ftrace_pid_func(unsigned long ip, unsigned long parent_ip,
>  			    struct ftrace_ops *op, struct ftrace_regs *fregs)
>  {
> @@ -1317,7 +1318,7 @@ static struct ftrace_hash *alloc_ftrace_hash(int size_bits)
>  	return hash;
>  }
>  
> -
> +/* Used to save filters on functions for modules not loaded yet */
>  static int ftrace_add_mod(struct trace_array *tr,
>  			  const char *func, const char *module,
>  			  int enable)
> @@ -1429,6 +1430,7 @@ static struct ftrace_hash *__move_hash(struct ftrace_hash *src, int size)
>  	return new_hash;
>  }
>  
> +/* Move the @src entries to a newly allocated hash */
>  static struct ftrace_hash *
>  __ftrace_hash_move(struct ftrace_hash *src)
>  {
> @@ -1443,6 +1445,26 @@ __ftrace_hash_move(struct ftrace_hash *src)
>  	return __move_hash(src, size);
>  }
>  
> +/**
> + * ftrace_hash_move - move a new hash to a filter and do updates
> + * @ops: The ops with the hash that @dst points to
> + * @enable: True if for the filter hash, false for the notrace hash
> + * @dst: Points to the @ops hash that should be updated
> + * @src: The hash to update @dst with
> + *
> + * This is called when an ftrace_ops hash is being updated and the
> + * the kernel needs to reflect this. Note, this only updates the kernel
> + * function callbacks if the @ops is enabled (not to be confused with
> + * @enable above). If the @ops is enabled, its hash determines what
> + * callbacks get called. This function gets called when the @ops hash
> + * is updated and it requires new callbacks.
> + *
> + * On success the elements of @src is moved to @dst, and @dst is updated
> + * properly, as well as the functions determined by the @ops hashes
> + * are now calling the @ops callback function.
> + *
> + * Regardless of return type, @src should be freed with free_ftrace_hash().
> + */
>  static int
>  ftrace_hash_move(struct ftrace_ops *ops, int enable,
>  		 struct ftrace_hash **dst, struct ftrace_hash *src)
> -- 
> 2.43.0
> 
>