Re: [PATCH 3/6] kernel-shark: Add KS_DEFINE_PLUGIN_CONTEXT macro

[Steven Rostedt <rostedt@goodmis.org>]

On Wed,  6 Jan 2021 18:11:17 +0200
"Yordan Karadzhov (VMware)" <y.karadz@gmail.com> wrote:

> When we implement a KernelShark plugins, we often need a way to define
> a structure that can hold context data that is visible only inside the
> plugin and that has specific values for each data stream. The tricky
> part here is that the total number of data streams and the IDs of the
> active streams are dynamic quantities that can change as the user adds
> or removes data streams. The macro defines an interface of functions
> that will be useful for the plugin developer, helping to directly use
> context objects, without caring for the complications due to the dynamic
> configuration of active data streams.
> ---
>  src/libkshark-plugin.h    | 43 +++++++++++++++++++++++++++++++++++++++
>  tests/libkshark-tests.cpp | 32 +++++++++++++++++++++++++++++
>  2 files changed, 75 insertions(+)
> 
> diff --git a/src/libkshark-plugin.h b/src/libkshark-plugin.h
> index f3c724f..e58d658 100644
> --- a/src/libkshark-plugin.h
> +++ b/src/libkshark-plugin.h
> @@ -360,6 +360,49 @@ int kshark_handle_all_dpis(struct kshark_data_stream *stream,
>  	}								\
>  }									\
>  
> +/** General purpose macro defining methods for adding plugin context. */
> +#define KS_DEFINE_PLUGIN_CONTEXT(type)					\

When macros like this are done in Linux, it is common to add a "prefix"
argument, and name all the variables and functions created by it with that
prefix.

#define KS_DEFINE_PLUGIN_CONTEXT(prefix, type) \
 static type **prefix##_context_handler; \
 [..]
 static inline type *prefix##_init(int sd) \
 [..]

This would allow this macro to be used more than once in a file.

It's up to you if you want to do it that way.

-- Steve

> +static type **__context_handler;					\
> +static ssize_t __n_streams = -1;					\
> +static bool ok;								\
> +static inline type *__init(int sd)					\
> +{									\
> +	type *obj;							\
> +	if (__n_streams < 0 && sd < KS_DEFAULT_NUM_STREAMS) {		\
> +		__context_handler =					\
> +			(type **) calloc(KS_DEFAULT_NUM_STREAMS,	\
> +					 sizeof(*__context_handler));	\
> +		if (!__context_handler)					\
> +			return NULL;					\
> +		__n_streams = KS_DEFAULT_NUM_STREAMS;			\
> +	} else if (sd >= __n_streams) {					\
> +		KS_DOUBLE_SIZE(type *, __context_handler,		\
> +			       &__n_streams, &ok)			\
> +		if (!ok)						\
> +			return NULL;					\
> +	}								\
> +	assert(__context_handler[sd] == NULL);				\
> +	obj = (type *) calloc(1, sizeof(*obj));				\
> +	__context_handler[sd] = obj;					\
> +	return obj;							\
> +}									\
> +static inline void __close(int sd)					\
> +{									\
> +	if (sd < 0) {							\
> +		free(__context_handler);				\
> +		__n_streams = -1;					\
> +		return;							\
> +	}								\
> +	free(__context_handler[sd]);					\
> +	__context_handler[sd] = NULL;					\
> +}									\
> +static inline type *__get_context(int sd)				\
> +{									\
> +	if (sd < 0 || sd >= __n_streams)				\
> +		return NULL;						\
> +	return __context_handler[sd];					\
> +}									\
> +
>  #ifdef __cplusplus
>  }
>  #endif // __cplusplus