[okl4-developer] What does the "STRING_major" mean?

[Josh Matthews]

Hi Cheng,

On Tue, April 21, 2009 10:44 pm, Guanghui, Cheng wrote:
> On Wednesday 22 April 2009 02:07:36 am Josh Matthews wrote:
>> On Mon, April 20, 2009 10:44 pm, Guanghui, Cheng wrote:
>> > In the pistachio/include/traceids.h/traceids.h file, there is a enum :
>> > enum trace_major_ids {
>> >     EVENT_major                         = 0,
>> >     STRING_major                        = 1,
>> >     INTERRUPT_major                     = 2,
>> >
>> >     SYSCALL_IPC_major                   = 3,
>> >     ... ...
>> > }
>> >
>> > I want to know what the STRING means? STRING_IPC or whatever.
>>
>> This functionality is all related to the tracebuffers feature. Each
>> kernel
>> event is assigned a unique trace identifier in enum trace_ids.
>> Additionally, each kernel event is assigned to a group in enum
>> trace_major_ids (as you copied above).
>>
>> Calls to tb_log_trace, passing the major (group) identifier and the
>> event
>> identifier (and potentially other data), are made by the kernel on the
>> occurrence of each event (in debug and tracebuffer builds of the kernel
>> only).
>>
>> The major identifier is useful as it allows you to mask out all events
>> of
>> particular groups that you are not interested in and focus only on those
>> groups that you are (see field log_mask in trace_buffer_t, in file
>> pistachio/include/tracebuffer.h, and see how macro TBUF_RECORD will only
>> log the event if the bit corresponding to the major number of the event
>> is
>> active in the log mask).
> Thanks for your reply.
> In the list there are several kinds of trace IDs like this:	event,
> string, interrupt, 	system call.  I don't know what the string means.

A string event is just a general event that has no other semantics beyond
some user-defined data that is passed when logging the event.

Check out dump_buffer() in pistachio/kdb/src/tracebuffer.cc - you can see
how a string event just has its data array printed as a string.

You can use it to log some information about an event in the kernel that
doesn't fit into any existing defined event or category.

Best regards,
Josh