The tracing ring-buffers can be stored on disk or sent to network without any copy via splice. However the later doesn't allow real time processing of the traces. A solution is to give userspace direct access to the ring-buffer pages via a mapping. An application can now become a consumer of the ring-buffer, in a similar fashion to what trace_pipe offers.
Support for this new feature in libtracefs can be found here: https://lore.kernel.org/all/20231228201100.78aae...@rorschach.local.home Vincent v9 -> v10: * Refactor rb_update_meta_page() * In-loop declaration for foreach_subbuf_page() * Check for cpu_buffer->mapped overflow v8 -> v9: * Fix the unlock path in ring_buffer_map() * Fix cpu_buffer cast with rb_work_rq->is_cpu_buffer * Rebase on linux-trace/for-next (3cb3091138ca0921c4569bcf7ffa062519639b6a) v7 -> v8: * Drop the subbufs renaming into bpages * Use subbuf as a name when relevant v6 -> v7: * Rebase onto lore.kernel.org/lkml/20231215175502.106587...@goodmis.org/ * Support for subbufs * Rename subbufs into bpages v5 -> v6: * Rebase on next-20230802. * (unsigned long) -> (void *) cast for virt_to_page(). * Add a wait for the GET_READER_PAGE ioctl. * Move writer fields update (overrun/pages_lost/entries/pages_touched) in the irq_work. * Rearrange id in struct buffer_page. * Rearrange the meta-page. * ring_buffer_meta_page -> trace_buffer_meta_page. * Add meta_struct_len into the meta-page. v4 -> v5: * Trivial rebase onto 6.5-rc3 (previously 6.4-rc3) v3 -> v4: * Add to the meta-page: - pages_lost / pages_read (allow to compute how full is the ring-buffer) - read (allow to compute how many entries can be read) - A reader_page struct. * Rename ring_buffer_meta_header -> ring_buffer_meta * Rename ring_buffer_get_reader_page -> ring_buffer_map_get_reader_page * Properly consume events on ring_buffer_map_get_reader_page() with rb_advance_reader(). v2 -> v3: * Remove data page list (for non-consuming read) ** Implies removing order > 0 meta-page * Add a new meta page field ->read * Rename ring_buffer_meta_page_header into ring_buffer_meta_header v1 -> v2: * Hide data_pages from the userspace struct * Fix META_PAGE_MAX_PAGES * Support for order > 0 meta-page * Add missing page->mapping. --- Vincent Donnefort (2): ring-buffer: Introducing ring-buffer mapping functions tracing: Allow user-space mapping of the ring-buffer include/linux/ring_buffer.h | 7 + include/uapi/linux/trace_mmap.h | 31 +++ kernel/trace/ring_buffer.c | 384 +++++++++++++++++++++++++++++++- kernel/trace/trace.c | 79 ++++++- 4 files changed, 497 insertions(+), 4 deletions(-) create mode 100644 include/uapi/linux/trace_mmap.h base-commit: 3cb3091138ca0921c4569bcf7ffa062519639b6a -- 2.43.0.472.g3155946c3a-goog
