• Steven Rostedt (Red Hat)'s avatar
    tracing: Add help of snapshot feature when snapshot is empty · d8741e2e
    Steven Rostedt (Red Hat) authored
    When cat'ing the snapshot file, instead of showing an empty trace
    header like the trace file does, show how to use the snapshot
    feature.
    
    Also, this is a good place to show if the snapshot has been allocated
    or not. Users may want to "pre allocate" the snapshot to have a fast
    "swap" of the current buffer. Otherwise, a swap would be slow and might
    fail as it would need to allocate the snapshot buffer, and that might
    fail under tight memory constraints.
    
    Here's what it looked like before:
    
     # tracer: nop
     #
     # entries-in-buffer/entries-written: 0/0   #P:4
     #
     #                              _-----=> irqs-off
     #                             / _----=> need-resched
     #                            | / _---=> hardirq/softirq
     #                            || / _--=> preempt-depth
     #                            ||| /     delay
     #           TASK-PID   CPU#  ||||    TIMESTAMP  FUNCTION
     #              | |       |   ||||       |         |
    
    Here's what it looks like now:
    
     # tracer: nop
     #
     #
     # * Snapshot is freed *
     #
     # Snapshot commands:
     # echo 0 > snapshot : Clears and frees snapshot buffer
     # echo 1 > snapshot : Allocates snapshot buffer, if not already allocated.
     #                      Takes a snapshot of the main buffer.
     # echo 2 > snapshot : Clears snapshot buffer (but does not allocate)
     #                      (Doesn't have to be '2' works with any number that
     #                       is not a '0' or '1')
    Acked-by: default avatarHiraku Toyooka <hiraku.toyooka.gu@hitachi.com>
    Signed-off-by: default avatarSteven Rostedt <rostedt@goodmis.org>
    d8741e2e
trace.c 123 KB