[ltt-dev] [BABELTRACE RFC PATCH] Add mmap trace reading

[Mathieu Desnoyers]

* Julien Desfossez (julien.desfossez at polymtl.ca) wrote:
> This set of functions allows a client to open a trace that is not stored
> on tracefiles but instead is in memory.
> Since the parameters required for such an operation are really different
> than typical traces, we define the open_mmap_trace function.
> This patch also introduces the mmap_subbuf_info structure that
> represents a list of FDs readable by mmap.

Is "mmap_subbuf_info" the name you want here ? I would think more in
terms of a linked-list of mmap_stream ?

Mathieu

> 
> Signed-off-by: Julien Desfossez <julien.desfossez at polymtl.ca>
> ---
>  formats/ctf/ctf.c           |  158 +++++++++++++++++++++++++++++++++++++++++++
>  include/babeltrace/format.h |   13 ++++
>  2 files changed, 171 insertions(+), 0 deletions(-)
> 
> diff --git a/formats/ctf/ctf.c b/formats/ctf/ctf.c
> index f9f9e47..81152a2 100644
> --- a/formats/ctf/ctf.c
> +++ b/formats/ctf/ctf.c
> @@ -59,6 +59,12 @@ struct trace_descriptor *ctf_open_trace(const char *path, int flags,
>  		void (*move_pos_slow)(struct ctf_stream_pos *pos, size_t offset,
>  			int whence), FILE *metadata_fp);
>  static
> +struct trace_descriptor *ctf_open_mmap_trace(
> +		struct mmap_subbuf_info_list *mmap_list,
> +		void (*move_pos_slow)(struct ctf_stream_pos *pos, size_t offset, int whence),
> +		FILE *metadata_fp);
> +
> +static
>  void ctf_close_trace(struct trace_descriptor *descriptor);
>  
>  static
> @@ -88,6 +94,7 @@ rw_dispatch write_dispatch_table[] = {
>  static
>  struct format ctf_format = {
>  	.open_trace = ctf_open_trace,
> +	.open_mmap_trace = ctf_open_mmap_trace,
>  	.close_trace = ctf_close_trace,
>  };
>  
> @@ -1256,6 +1263,157 @@ error:
>  	return NULL;
>  }
>  
> +
> +void ctf_init_mmap_pos(struct ctf_stream_pos *pos,
> +		struct mmap_subbuf_info *mmap_info)
> +{
> +	pos->mmap_offset = 0;
> +	pos->packet_size = 0;
> +	pos->content_size = 0;
> +	pos->content_size_loc = NULL;
> +	pos->fd = mmap_info->fd;
> +	pos->base = 0;
> +	pos->offset = 0;
> +	pos->dummy = false;
> +	pos->cur_index = 0;
> +	pos->packet_index = NULL;
> +	pos->prot = PROT_READ;
> +	pos->flags = MAP_PRIVATE;
> +	pos->parent.rw_table = read_dispatch_table;
> +	pos->parent.event_cb = ctf_read_event;
> +}
> +
> +/* FIXME : function name, not really index */
> +static
> +int create_stream_mmap_packet_index(struct ctf_trace *td,
> +		struct ctf_file_stream *file_stream)
> +{
> +	struct ctf_stream_class *stream;
> +	uint64_t stream_id = 0;
> +	int ret;
> +
> +	file_stream->parent.stream_id = stream_id;
> +	if (stream_id >= td->streams->len) {
> +		fprintf(stdout, "[error] Stream %" PRIu64 " is not declared "
> +				"in metadata.\n", stream_id);
> +		ret = -EINVAL;
> +		goto end;
> +	}
> +	stream = g_ptr_array_index(td->streams, stream_id);
> +	if (!stream) {
> +		fprintf(stdout, "[error] Stream %" PRIu64 " is not declared "
> +				"in metadata.\n", stream_id);
> +		ret = -EINVAL;
> +		goto end;
> +	}
> +	file_stream->parent.stream_class = stream;
> +	ret = create_stream_definitions(td, &file_stream->parent);
> +
> +end:
> +	return ret;
> +}
> +
> +static
> +int ctf_open_mmap_stream_read(struct ctf_trace *td,
> +		struct mmap_subbuf_info *mmap_info,
> +		void (*move_pos_slow)(struct ctf_stream_pos *pos, size_t offset,
> +			int whence))
> +{
> +	int ret;
> +	struct ctf_file_stream *file_stream;
> +
> +	file_stream = g_new0(struct ctf_file_stream, 1);
> +	ctf_init_mmap_pos(&file_stream->pos, mmap_info);
> +
> +	file_stream->pos.move_pos_slow = move_pos_slow;
> +
> +	ret = create_trace_definitions(td, &file_stream->parent);
> +	if (ret) {
> +		goto error_def;
> +	}
> +
> +	ret = create_stream_mmap_packet_index(td, file_stream);
> +	if (ret)
> +		goto error_index;
> +
> +	/* Add stream file to stream class */
> +	g_ptr_array_add(file_stream->parent.stream_class->streams,
> +			&file_stream->parent);
> +	return 0;
> +
> +error_index:
> +	if (file_stream->parent.trace_packet_header)
> +		definition_unref(&file_stream->parent.trace_packet_header->p);
> +error_def:
> +	g_free(file_stream);
> +	return ret;
> +}
> +
> +int ctf_open_mmap_trace_read(struct ctf_trace *td,
> +		struct mmap_subbuf_info_list *mmap_list,
> +		void (*move_pos_slow)(struct ctf_stream_pos *pos, size_t offset,
> +			int whence),
> +		FILE *metadata_fp)
> +{
> +	int ret;
> +	struct mmap_subbuf_info *mmap_info;
> +
> +	ret = ctf_open_trace_metadata_read(td, ctf_move_pos_slow, metadata_fp);
> +	if (ret) {
> +		goto error;
> +	}
> +
> +	/*
> +	 * for each stream, try to open, check magic number, and get the stream ID
> +	 * to add to the right location in the stream array.
> +	 */
> +	cds_list_for_each_entry(mmap_info, &mmap_list->head, list) {
> +		ret = ctf_open_mmap_stream_read(td, mmap_info, move_pos_slow);
> +		if (ret) {
> +			fprintf(stdout, "[error] Open file mmap stream error.\n");
> +			goto error;
> +		}
> +	}
> +
> +	return 0;
> +
> +error:
> +	return ret;
> +}
> +
> +static
> +struct trace_descriptor *ctf_open_mmap_trace(
> +		struct mmap_subbuf_info_list *mmap_list,
> +		void (*move_pos_slow)(struct ctf_stream_pos *pos, size_t offset, int whence),
> +		FILE *metadata_fp)
> +{
> +	struct ctf_trace *td;
> +	int ret;
> +
> +	td = g_new0(struct ctf_trace, 1);
> +
> +	if (!metadata_fp) {
> +		fprintf(stderr, "[error] No metadata file pointer associated, "
> +				"required for mmap parsing\n");
> +		goto error;
> +	}
> +
> +	if (!move_pos_slow) {
> +		fprintf(stderr, "[error] move_pos_slow function undefined.\n");
> +		goto error;
> +	}
> +
> +	ret = ctf_open_mmap_trace_read(td, mmap_list, move_pos_slow, metadata_fp);
> +	if (ret)
> +		goto error;
> +
> +	return &td->parent;
> +error:
> +	g_free(td);
> +	return NULL;
> +}
> +
> +
>  static
>  void ctf_close_file_stream(struct ctf_file_stream *file_stream)
>  {
> diff --git a/include/babeltrace/format.h b/include/babeltrace/format.h
> index 5b2f694..f54b253 100644
> --- a/include/babeltrace/format.h
> +++ b/include/babeltrace/format.h
> @@ -31,12 +31,25 @@
>  struct trace_descriptor {
>  };
>  
> +struct mmap_subbuf_info {
> +	int fd;
> +	struct cds_list_head list;
> +};
> +
> +struct mmap_subbuf_info_list {
> +	struct cds_list_head head;
> +};
> +
>  struct format {
>  	GQuark name;
>  
>  	struct trace_descriptor *(*open_trace)(const char *path, int flags,
>  			void (*move_pos_slow)(struct ctf_stream_pos *pos, size_t offset,
>  				int whence), FILE *metadata_fp);
> +	struct trace_descriptor *(*open_mmap_trace)(
> +			struct mmap_subbuf_info_list *mmap_list,
> +			void (*move_pos_slow)(struct ctf_stream_pos *pos, size_t offset,
> +				int whence), FILE *metadata_fp);
>  	void (*close_trace)(struct trace_descriptor *descriptor);
>  };
>  
> -- 
> 1.7.5.4
> 

-- 
Mathieu Desnoyers
Operating System Efficiency R&D Consultant
EfficiOS Inc.
http://www.efficios.com