Hi Beau,
Thanks for updating. This series looks good to me.
Acked-by: Masami Hiramatsu <mhiramat@xxxxxxxxxx>
for this series.
Regards,
On Tue, 18 Jan 2022 12:43:14 -0800
Beau Belgrave <beaub@xxxxxxxxxxxxxxxxxxx> wrote:
> User mode processes that wish to use trace events to get data into
> ftrace, perf, eBPF, etc are limited to uprobes today. The user events
> features enables an ABI for user mode processes to create and write to
> trace events that are isolated from kernel level trace events. This
> enables a faster path for tracing from user mode data as well as opens
> managed code to participate in trace events, where stub locations are
> dynamic.
>
> User processes often want to trace only when it's useful. To enable this
> a set of pages are mapped into the user process space that indicate the
> current state of the user events that have been registered. User
> processes can check if their event is hooked to a trace/probe, and if it
> is, emit the event data out via the write() syscall.
>
> Two new files are introduced into tracefs to accomplish this:
> user_events_status - This file is mmap'd into participating user mode
> processes to indicate event status.
>
> user_events_data - This file is opened and register/delete ioctl's are
> issued to create/open/delete trace events that can be used for tracing.
>
> The typical scenario is on process start to mmap user_events_status. Processes
> then register the events they plan to use via the REG ioctl. The ioctl reads
> and updates the passed in user_reg struct. The status_index of the struct is
> used to know the byte in the status page to check for that event. The
> write_index of the struct is used to describe that event when writing out to
> the fd that was used for the ioctl call. The data must always include this
> index first when writing out data for an event. Data can be written either by
> write() or by writev().
>
> For example, in memory:
> int index;
> char data[];
>
> Psuedo code example of typical usage:
> struct user_reg reg;
>
> int page_fd = open("user_events_status", O_RDWR);
> char *page_data = mmap(NULL, PAGE_SIZE, PROT_READ, MAP_SHARED, page_fd, 0);
> close(page_fd);
>
> int data_fd = open("user_events_data", O_RDWR);
>
> reg.size = sizeof(reg);
> reg.name_args = (__u64)"test";
>
> ioctl(data_fd, DIAG_IOCSREG, ®);
> int status_id = reg.status_index;
> int write_id = reg.write_index;
>
> struct iovec io[2];
> io[0].iov_base = &write_id;
> io[0].iov_len = sizeof(write_id);
> io[1].iov_base = payload;
> io[1].iov_len = sizeof(payload);
>
> if (page_data[status_id])
> writev(data_fd, io, 2);
>
> User events are also exposed via the dynamic_events tracefs file for
> both create and delete. Current status is exposed via the user_events_status
> tracefs file.
>
> Simple example to register a user event via dynamic_events:
> echo u:test >> dynamic_events
> cat dynamic_events
> u:test
>
> If an event is hooked to a probe, the probe hooked shows up:
> echo 1 > events/user_events/test/enable
> cat user_events_status
> 1:test # Used by ftrace
>
> Active: 1
> Busy: 1
> Max: 4096
>
> If an event is not hooked to a probe, no probe status shows up:
> echo 0 > events/user_events/test/enable
> cat user_events_status
> 1:test
>
> Active: 1
> Busy: 0
> Max: 4096
>
> Users can describe the trace event format via the following format:
> name[:FLAG1[,FLAG2...] [field1[;field2...]]
>
> Each field has the following format:
> type name
>
> Example for char array with a size of 20 named msg:
> echo 'u:detailed char[20] msg' >> dynamic_events
> cat dynamic_events
> u:detailed char[20] msg
>
> Data offsets are based on the data written out via write() and will be
> updated to reflect the correct offset in the trace_event fields. For dynamic
> data it is recommended to use the new __rel_loc data type. This type will be
> the same as __data_loc, but the offset is relative to this entry. This allows
> user_events to not worry about what common fields are being inserted before
> the data.
>
> The above format is valid for both the ioctl and the dynamic_events file.
>
> V2:
> Fixed kmalloc vs kzalloc for register_page.
> Renamed user_event_mmap to user_event_status.
> Renamed user_event prefix from ue to u.
> Added seq_* operations to user_event_status to enable cat output.
> Aligned field parsing to synth_events format (+ size specifier for
> custom/user types).
> Added uapi header user_events.h to align kernel and user ABI definitions.
>
> V3:
> Updated ABI to handle single FD into many events via an int header.
> Added iovec/writev support to enable int header without payload changes.
> Updated bpf context to describe if data is coming from user, kernel or
> raw iovec.
> Added flag support for registering event, allows forcing BPF to always
> recieve the direct iovecs for sensitive code paths that do not want
> copies.
>
> V4:
> Moved to struct user_reg for registering events via ioctl.
> Added unit tests for ftrace, dyn_events and perf integration.
> Added print_fmt generation and proper dyn_events matching statements.
> Reduced time in preemption disabled paths.
> Added documentation file.
> Pre-fault in data when preemption is enabled and use no-fault copy in probes.
> Fixed MIPs missing PAGE_READONLY define.
>
> V5:
> Rebase to linux-trace for-next branch.
> Added sample code into samples/user_events.
> Switched to str_has_prefix in various locations.
> Allow hex in array sizes and ensure reasonable sizes are used.
> Moved lifetime of name buffer when parsing to the caller for failure paths.
> Fixed documentation nits and index.
> Ensure event isn't busy before freeing through dyn_events.
> Properly handle failure case for ftrace and perf in fault cases for buffers.
> Ensure write data is over min size and null terminated for dynamic arrays.
>
> V6:
> Fixed endian issue with dyn loc decoding (use u32).
> Fixed size_t conversion warning on hexagon arch (min vs min_t).
> Handle cases for __get_str vs __get_rel_str in print_fmt generation.
> Add additional comments around various event member lifetimes.
> Reduced max field array size to 1K.
>
> V7:
> Acquire reg_mutex during release, ensure refs cannot change under any situation.
> Remove default n from Kconfig.
> Move from static 0644 mode to TRACE_MODE_WRITE.
>
> V8:
> Squashed UABI header into ftrace minimal patch thread.
> Moved pagefault_disable/enable into copy_nofault.
> Moved to strscpy vs custom copy when getting array size from type.
> Made patch bisect friendly by ensuring tests are split from kernel code.
>
> V9:
> Rebase to linux-trace ftrace/core branch.
> Added comments for user_reg and other structs in user_events.h.
> Moved from delayed seq_file to pre-created seq_file for status file.
> Added deleting events to documentation and expanded registering section.
> Reordered patches to make reviewing easier.
> Fixed nitpicks.
>
> V10:
> Fix struct size case not writing size out to dynamic_events.
> Fix warning for NULL pointer arithmetic in user_seq_start.
>
> Beau Belgrave (12):
> user_events: Add minimal support for trace_event into ftrace
> user_events: Add print_fmt generation support for basic types
> user_events: Handle matching arguments from dyn_events
> user_events: Add basic perf and eBPF support
> user_events: Optimize writing events by only copying data once
> user_events: Validate user payloads for size and null termination
> user_events: Add self-test for ftrace integration
> user_events: Add self-test for dynamic_events integration
> user_events: Add self-test for perf_event integration
> user_events: Add self-test for validator boundaries
> user_events: Add sample code for typical usage
> user_events: Add documentation file
>
> Documentation/trace/index.rst | 1 +
> Documentation/trace/user_events.rst | 216 +++
> include/uapi/linux/user_events.h | 116 ++
> kernel/trace/Kconfig | 14 +
> kernel/trace/Makefile | 1 +
> kernel/trace/trace_events_user.c | 1617 +++++++++++++++++
> samples/user_events/Makefile | 5 +
> samples/user_events/example.c | 91 +
> tools/testing/selftests/user_events/Makefile | 9 +
> .../testing/selftests/user_events/dyn_test.c | 130 ++
> .../selftests/user_events/ftrace_test.c | 452 +++++
> .../testing/selftests/user_events/perf_test.c | 168 ++
> tools/testing/selftests/user_events/settings | 1 +
> 13 files changed, 2821 insertions(+)
> create mode 100644 Documentation/trace/user_events.rst
> create mode 100644 include/uapi/linux/user_events.h
> create mode 100644 kernel/trace/trace_events_user.c
> create mode 100644 samples/user_events/Makefile
> create mode 100644 samples/user_events/example.c
> create mode 100644 tools/testing/selftests/user_events/Makefile
> create mode 100644 tools/testing/selftests/user_events/dyn_test.c
> create mode 100644 tools/testing/selftests/user_events/ftrace_test.c
> create mode 100644 tools/testing/selftests/user_events/perf_test.c
> create mode 100644 tools/testing/selftests/user_events/settings
>
>
> base-commit: 85c62c8c3749eec02ba81217bdcac26867dc262e
> --
> 2.17.1
>
--
Masami Hiramatsu <mhiramat@xxxxxxxxxx>
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