[lttng-dev] [Patch LTTng-ust] RFC: Syntax changes to add support of other CTF metadata

[Geneviève Bastien]

For a more visual view of those changes than a txt patch, here it is:
https://github.com/tahini/lttng-ust/commit/0ac6d504222833b97cd8391d5bba81c013c0d066

On 12/05/2013 03:22 PM, Geneviève Bastien wrote:
> The CTF spec defines metadata types enumerations, structures and variants
> that are not yet available for use in tracepoints in LTTng-ust. This
> proposes the syntax for how those types could be defined and used.
>
> For now, it won't be possible to define them inline in a tracepoint. They
> will have to be named and defined outside the TRACEPOINT_EVENT macro and
> used in the tracepoint definition. It will make it easier for a first
> implementation. Once that is done, it won't be too difficult to add inline
> support.
>
> Signed-off-by: Geneviève Bastien <gbastien+lttng at versatic.net>
> ---
>   doc/man/lttng-ust.3 | 193 ++++++++++++++++++++++++++++++++++++++++++++++++++++
>   1 file changed, 193 insertions(+)
>
> diff --git a/doc/man/lttng-ust.3 b/doc/man/lttng-ust.3
> index 7624e88..c8229f2 100644
> --- a/doc/man/lttng-ust.3
> +++ b/doc/man/lttng-ust.3
> @@ -158,6 +158,39 @@ TRACEPOINT_EVENT(
>   		 */
>   		ctf_float(float, floatfield, floatarg)
>   		ctf_float(double, doublefield, doublearg)
> +
> +		/*
> +		 * ctf_enum: a field using a previously defined named enumeration
> +		 * args: (provider, enum name, field name, argument expression)
> +		 * The enumeration itself and its values must have been defined
> +		 * previously with the TRACEPOINT_ENUM macro, described below.
> +		 */
> +		ctf_enum(sample_component, enumeration_name, enumfield, enumarg)
> +
> +		/*
> +		 * ctf_struct: a field using a previously defined struct
> +		 * args: (provider, struct name, field name, [argument expression]*)
> +		 * The structure must have been previously defined with the
> +		 * TRACEPOINT_STRUCT macro, described below.
> +		 *
> +		 * The [argument expression]* part must correspond to the arguments
> +		 * defined in the TP_ARGS of the struct.
> +		 */
> +		ctf_struct(sample_component, structure_name, structfield, args...)
> +
> +		/*
> +		 * ctf_variant: a field using a previously defined variant
> +		 * args: (provider, variant name, field name, enum field name,
> +		              [argument expression]*)
> +		 *
> +		 * The [argument expression]* part must correspond to the arguments
> +		 * defined in the TP_ARGS of the variant.
> +		 *
> +		 * There must be a field in the same tracepoint named 'enumfield'
> +		 * defined with ctf_enum(...)
> +		 */
> +		ctf_variant(sample_component, variant_name, variantfield,
> +				enumfield, args...)
>   	)
>   )
>   
> @@ -165,6 +198,166 @@ There can be an arbitrary number of tracepoint providers within an
>   application, but they must each have their own provider name. Duplicate
>   provider names are not allowed.
>   
> +The CTF specification also supports some named basic and compound types that
> +can be defined inside a tracepoint provider and used as fields in the
> +tracepoint. This shows how to specify them and what they can be used for:
> +
> +The enumeration is a mapping between an integer and a string. It can be used
> +to have a more compact trace in cases where the possible values for a field are
> +limited:
> +
> +TRACEPOINT_ENUM(
> +	/*
> +	 * The provider name, as described in the TRACEPOINT_EVENT macro
> +	 */
> +	sample_component,
> +
> +	/*
> +	 * The name of this enumeration, that will be used when using this
> +	 * metadata type in tracepoint fields
> +	 */
> +	enumeration_name,
> +
> +	/*
> +	 * Integer type by which this enumeration will be represented.
> +	 * It can be: char, int, long or any variant on those
> +	 */
> +	type,
> +
> +	/*
> +	 * TP_ENUM_VALUES describe the values of this enumeration and what they
> +	 * map to.
> +	 */
> +	TP_ENUM_VALUES(
> +		/*
> +		 * Maps an integer with this string value. By default, enumerations
> +		 * start at 0 and increment 1 for each entry.
> +		 */
> +		ctf_enum_value(string_value)
> +
> +		/*
> +		 * Maps the string value to integers in the range 'start' to 'end'
> +		 * inclusively. If 'start' == 'end', then the string is mapped to
> +		 * a specific value.
> +		 */
> +		ctf_enum_range(start, end, string_value)
> +	)
> +)
> +
> +A structure allows to groupe fields together. They can be reused by different
> +tracepoints:
> +
> +TRACEPOINT_STRUCT(
> +	/*
> +	 * The provider name, as described in the TRACEPOINT_EVENT macro
> +	 */
> +	sample_component,
> +
> +	/*
> +	 * The name of this structure, that will be used when using this
> +	 * metadata type in tracepoint fields
> +	 */
> +	structure_name,
> +
> +	/*
> +	 * TP_ARGS macro contains the arguments passed for the structure
> +	 * it is in the following format
> +	 *	      TP_ARGS(type1, name1, type2, name2, ... type10,
> +				 name10)
> +	 * where there can be from zero to ten elements.
> +	 * typeN is the datatype, such as int, struct or double **.
> +	 * name is the variable name (in "int myInt" the name would be
> +	 * myint)
> +	 *	      TP_ARGS() is valid to mean no arguments
> +	 *	      TP_ARGS(void) is valid too
> +	 */
> +	TP_ARGS(int, anint, int, netint, long *, values,
> +		 char *, text, size_t, textlen,
> +		 double, doublearg, float, floatarg),
> +
> +	/*
> +	 * TP_FIELDS describes how to write the fields of the structure.
> +	 * You can put expressions in the "argument expression" area,
> +	 * typically using the input arguments from TP_ARGS.
> +	 *
> +	 * See TP_FIELDS macro in TRACEPOINT_EVENT for complete description
> +	 * of possible fields. A structure may not contain itself and there cannot
> +	 * be a cycle.
> +	 */
> +	TP_FIELDS(...)
> +)
> +
> +A variant is a selection between different types, given a
> +'tag'. It is linked with the value of an enumeration.
> +
> +TRACEPOINT_VARIANT(
> +	/*
> +	 * The provider name, as described in the TRACEPOINT_EVENT macro
> +	 */
> +	sample_component,
> +
> +	/*
> +	 * The name of this variant, that will be used when using this
> +	 * metadata type in tracepoint fields
> +	 */
> +	variant_name,
> +
> +	/*
> +	 * The name of the provider where the linked enumeration is defined
> +	 */
> +	enumeration_component,
> +
> +	/*
> +	 * The name of the enumeration, whose values will be linked to a field
> +	 * type
> +	 */
> +	enumeration_name,
> +
> +	/*
> +	 * TP_ARGS macro contains the arguments passed for the structure
> +	 * it is in the following format
> +	 *	      TP_ARGS(type1, name1, type2, name2, ... type10,
> +				 name10)
> +	 * where there can be from zero to ten elements.
> +	 * typeN is the datatype, such as int, struct or double **.
> +	 * name is the variable name (in "int myInt" the name would be
> +	 * myint)
> +	 *	      TP_ARGS() is valid to mean no arguments
> +	 *	      TP_ARGS(void) is valid too
> +	 */
> +	TP_ARGS(int, anint, int, netint, long *, values,
> +		 char *, text, size_t, textlen,
> +		 double, doublearg, float, floatarg),
> +
> +	/*
> +	 * TP_VARIANTS will describe what field will be linked to what value of
> +	 * the enumeration
> +	 */
> +	TP_VARIANTS(
> +		/*
> +		 * TP_VARIANT describes one mapping from an enum value to a field
> +		 */
> +		TP_VARIANT(
> +			/*
> +			 * The value of the enumeration field. This must correspond to one
> +			 * of the string_values defined in TP_ENUM_VALUES of the linked
> +			 * enumeration.
> +			 */
> +			enum_val,
> +
> +			/*
> +			 * This is the field that will be added to the tracepoint if the
> +			 * value of the enum is enum_val.
> +			 *
> +			 * See TP_FIELDS macro in TRACEPOINT_EVENT for complete description
> +			 * of possible fields. A variant may not contain itself and there cannot
> +			 * be a cycle.
> +			 */
> +			<tp_field_expr>
> +		)
> +	)
> +)
> +
>   .fi
>   
>   .SH "ASSIGNING LOGLEVEL TO EVENTS"