• Beau Belgrave's avatar
    tracing/user_events: Introduce multi-format events · 64805e40
    Beau Belgrave authored
    Currently user_events supports 1 event with the same name and must have
    the exact same format when referenced by multiple programs. This opens
    an opportunity for malicious or poorly thought through programs to
    create events that others use with different formats. Another scenario
    is user programs wishing to use the same event name but add more fields
    later when the software updates. Various versions of a program may be
    running side-by-side, which is prevented by the current single format
    requirement.
    
    Add a new register flag (USER_EVENT_REG_MULTI_FORMAT) which indicates
    the user program wishes to use the same user_event name, but may have
    several different formats of the event. When this flag is used, create
    the underlying tracepoint backing the user_event with a unique name
    per-version of the format. It's important that existing ABI users do
    not get this logic automatically, even if one of the multi format
    events matches the format. This ensures existing programs that create
    events and assume the tracepoint name will match exactly continue to
    work as expected. Add logic to only check multi-format events with
    other multi-format events and single-format events to only check
    single-format events during find.
    
    Change system name of the multi-format event tracepoint to ensure that
    multi-format events are isolated completely from single-format events.
    This prevents single-format names from conflicting with multi-format
    events if they end with the same suffix as the multi-format events.
    
    Add a register_name (reg_name) to the user_event struct which allows for
    split naming of events. We now have the name that was used to register
    within user_events as well as the unique name for the tracepoint. Upon
    registering events ensure matches based on first the reg_name, followed
    by the fields and format of the event. This allows for multiple events
    with the same registered name to have different formats. The underlying
    tracepoint will have a unique name in the format of {reg_name}.{unique_id}.
    
    For example, if both "test u32 value" and "test u64 value" are used with
    the USER_EVENT_REG_MULTI_FORMAT the system would have 2 unique
    tracepoints. The dynamic_events file would then show the following:
      u:test u64 count
      u:test u32 count
    
    The actual tracepoint names look like this:
      test.0
      test.1
    
    Both would be under the new user_events_multi system name to prevent the
    older ABI from being used to squat on multi-formatted events and block
    their use.
    
    Deleting events via "!u:test u64 count" would only delete the first
    tracepoint that matched that format. When the delete ABI is used all
    events with the same name will be attempted to be deleted. If
    per-version deletion is required, user programs should either not use
    persistent events or delete them via dynamic_events.
    
    Link: https://lore.kernel.org/linux-trace-kernel/20240222001807.1463-3-beaub@linux.microsoft.comSigned-off-by: default avatarBeau Belgrave <beaub@linux.microsoft.com>
    Signed-off-by: default avatarSteven Rostedt (Google) <rostedt@goodmis.org>
    64805e40
trace_events_user.c 65.8 KB