User programs can now ask user_events to handle the synchronization of multiple different formats for an event with the same name via the new USER_EVENT_REG_MULTI_FORMAT flag.
Add a section for USER_EVENT_REG_MULTI_FORMAT that explains the intended purpose and caveats of using it. Explain how deletion works in these cases and how to use /sys/kernel/tracing/dynamic_events for per-version deletion. Signed-off-by: Beau Belgrave <be...@linux.microsoft.com> --- Documentation/trace/user_events.rst | 27 ++++++++++++++++++++++++++- 1 file changed, 26 insertions(+), 1 deletion(-) diff --git a/Documentation/trace/user_events.rst b/Documentation/trace/user_events.rst index d8f12442aaa6..1d5a7626e6a6 100644 --- a/Documentation/trace/user_events.rst +++ b/Documentation/trace/user_events.rst @@ -92,6 +92,24 @@ The following flags are currently supported. process closes or unregisters the event. Requires CAP_PERFMON otherwise -EPERM is returned. ++ USER_EVENT_REG_MULTI_FORMAT: The event can contain multiple formats. This + allows programs to prevent themselves from being blocked when their event + format changes and they wish to use the same name. When this flag is used the + tracepoint name will be in the new format of "name.unique_id" vs the older + format of "name". A tracepoint will be created for each unique pair of name + and format. This means if several processes use the same name and format, + they will use the same tracepoint. If yet another process uses the same name, + but a different format than the other processes, it will use a different + tracepoint with a new unique id. Recording programs need to scan tracefs for + the various different formats of the event name they are interested in + recording. The system name of the tracepoint will also use "user_events_multi" + instead of "user_events". This prevents single-format event names conflicting + with any multi-format event names within tracefs. The unique_id is output as + a hex string. Recording programs should ensure the tracepoint name starts with + the event name they registered and has a suffix that starts with . and only + has hex characters. For example to find all versions of the event "test" you + can use the regex "^test\.[0-9a-fA-F]+$". + Upon successful registration the following is set. + write_index: The index to use for this file descriptor that represents this @@ -106,6 +124,9 @@ or perf record -e user_events:[name] when attaching/recording. **NOTE:** The event subsystem name by default is "user_events". Callers should not assume it will always be "user_events". Operators reserve the right in the future to change the subsystem name per-process to accommodate event isolation. +In addition if the USER_EVENT_REG_MULTI_FORMAT flag is used the tracepoint name +will have a unique id appended to it and the system name will be +"user_events_multi" as described above. Command Format ^^^^^^^^^^^^^^ @@ -156,7 +177,11 @@ to request deletes than the one used for registration due to this. to the event. If programs do not want auto-delete, they must use the USER_EVENT_REG_PERSIST flag when registering the event. Once that flag is used the event exists until DIAG_IOCSDEL is invoked. Both register and delete of an -event that persists requires CAP_PERFMON, otherwise -EPERM is returned. +event that persists requires CAP_PERFMON, otherwise -EPERM is returned. When +there are multiple formats of the same event name, all events with the same +name will be attempted to be deleted. If only a specific version is wanted to +be deleted then the /sys/kernel/tracing/dynamic_events file should be used for +that specific format of the event. Unregistering ------------- -- 2.34.1
