> The difficulty in pipe mode is that information needs to be written > sequentially to the pipe. Meta data headers are usually generated > (and also expected) at the beginning of the file (or piped output). > To solve this problem, we introduce new synthetic record types, > one for each meta-data type. The approach is similar to what > is *ALREADY* used for BUILD_ID and TRACING_DATA.
The new headers need documentation in Documentation/perf.data-file-format.txt -Andi