Hi all,
I'm looking to implement new features in TMF about filter expressions
using the state system. I would appreciate receiving your feedback on
the proposal.
Currently, we can only specify constraints on the event context and payload.
For example : /event_type == sys_read && fd == 3/
* *Specify filter expression using state information*
The first feature is to add the use of state system attributes, to be
mixed with payload and context information. For example : //event/type
== "sys_read" && ///system/${/event/pid}/files/${/event/fd}/pathname ==
"/etc/passwd"/
I want to propose a syntax to make this expression. The nodes in the
attribute tree are referenced using a hierarchical path. This path is a
sequence of names and can be expressed with the usual notation, e.g.
/processes/cpu/state. Each path component can be a constant string, or a
quoted string to escape special characters. Alternatively a component
can also be a number which is the put in []. This is used for directory
nodes where all childs use integers as names, which is more efficient
than treating numbers as strings and using strings. Finally, a component
can be a variable where the value of the component is obtained by
referencing a path; the $ notation is used as in shell scripts. We use
the C/Java syntax, '==' to compare and '=' to assign.
/processes/[4]/state == RUNNING
/processes/[4]/state_start_time == 012032432
/processes/[4]/PPID == 1
/processes/[4]/user_mode/cumulative_time == 5789357
/cpu/[0]/current_process == /processes/[1]
/processes/[${/processes/[4]/PPID}]/childs_cumulative_time
The model of the attribute tree is extended to make available as well
some dynamically computed information related to the current context
(channel, event). This additional information is not assigned nor saved
in the history tree. For example, some information is associated with
the current channel such as the CPU. In addition, all the fields of the
current event as well are made available through the attribute tree
syntax. For example, the following information may be accessed through
the associated paths.
/event/timestamp
/event/type
/event/TID
/event/CPU
/event/field/next_process
/event/field/poll_array/[4]
These values can be used in logical and arithmetic expressions for
expressing conditions or assignments. Conditions are primarily used in
filters, for example in the detailed event list view. They are also used
as guards for state changes or as trigger for creating abstract events.
* *Specify expressions to determine state entry / exit*
The second feature is to provide expression for state change.
Currently this logic is coded in Java in files such as :
org.eclipse.linuxtools.lttng2.kernel.core/src/org/eclipse/linuxtools/internal/lttng2/kernel/core/stateprovider/CtfKernelStateInput.java
It would be nice to be able to provide expressions for that. This way,
adding state for specific needs would not require programming and we
could import/export new types of state systems easily (as part of the
CTF metadata for example).
Upon event of type sys_open:
/processes/${/event/pid}/files/${/event/fd}/pathname = name
/processes/${/event/pid}/files/${/event/fd}/mode = mode
Once we can easily refer to state using such expressions, several
additional features become relatively easy to add such as new "virtual"
columns in the detailed event list computed based on an expression
instead of being "event context" or "payload information". In addition,
such expressions could become part of the CTF metadata to describe
states, state entry expressions, colors to associate with specific
states in the control flow view...
I would like to have the developers' opinion on these two features. Do
you see any major problem or easy simplification for this syntax?
Thanks,
Florian
------------------------------------------------------------------------------------------------
Complete examples for transcription of the CtfKernetStateInput.java :
case 1: // "exit_syscall":
/* Clear the current system call on the process */
/Threads/[${/CPUs/[${/event/Cpu}]/Current_thread}]/System_call = NULL
/* Put the process' status back to user mode */
/Threads/[${/CPUs/[${/event/Cpu}]/Current_thread}]/Status =
PROCESS_STATUS_RUN_USERMODE
/* Put the CPU's status back to user mode */
/CPUs/[${/event/Cpu}]/Status = CPU_STATUS_RUN_USERMODE
case 8: // "sched_process_fork":
/* Assign the PPID to the new process */
/Threads/[${/event/child_tid}]/PPID = /event/parent_tid
/* Set the new process' exec_name */
/Threads/[${/event/child_tid}]/Exec_name = /event/child_comm
/* Set the new process' status */
/Threads/[${/event/child_tid}]/Status = PROCESS_STATUS_WAIT_FOR_CPU
/* Set the process' syscall name, to be the same as the parent's */
/Threads/[${/event/child_tid}]/System_call =
/Threads/[${/event/parent_tid}]/System_call
case 11: // "lttng_statedump_process_state":
/* Set the process' name */
if( /Threads/[/event/tid]/Exec_name == Null)
/Threads/[/event/tid]/Exec_name = /event/name
/* Set the process' PPID */
if( /Threads/[/event/tid]/PPID == Null)
/Threads/[/event/tid]/PPID = /event/ppid
/* Set the process' status */
if( /Threads/[/event/tid]/Status == Null)
if(/event/status == 2)
/Threads/[/event/tid]/Status = PROCESS_STATUS_WAIT_FOR_CPU
else if(/event/status == 5)
/Threads/[/event/tid]/Status = PROCESS_STATUS_WAIT_BLOCKED
else
/Threads/[/event/tid]/Status = PROCESS_STATUS_UNKNOWN
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