[lttng-dev] Machine Interface

[Woegerer, Paul]

Hi Simon,

On 02/06/2014 02:32 PM, Simon Marchi wrote:
> script) is easier than XML, but it's still not bulletproof. Consider
> this eventual yaml structure I just made up for the output of the
> session list.
> 
> sessions:
>   - name: my_session
>     domain: kernel
>     events:
>       - name: sched_switch
>         filter: prev_pid == 1234
>       - name: sched_migrate_task
>         otherproperty: "something"
>   - name: another_session
>     domain: ust
>     events:
>       - name: event_hello
>       - name: event_bonjour
>         loglevel: 3
> 
> If you want to get the list of sessions, you'll probably want to grep
> the "name: " entries, but then event names would match as well. Of
> course, names could be different, or you could grep for the
> appropriate amount of spaces/tabs at the beginning of the line. But
> then it also depends if the name dictionary entry is the first, then
> it will have a "-" in front... It's possible, but it will also be very
> easy to break scripts.

The following simple script below would e.g. give you the list of
sessions for you example above. To demonstrate the flexibility it
also generates the event list for session my_session. This is just
a quick prototype but it should make clear that YAML is considerably
easier to parse from a shell script than any other option (and also
reasonably robust). Also notice that no external helpers (like grep)
are needed.

list_of_sessions=''
current_session=''
my_session_events=''

while IFS= read -r; do
	line=$REPLY
	case "${line}" in 
		"      - "*)
			;&
		"        "*)
			L2_key=${line:8}
			L2_key=${L2_key%:*}
			let vpos=2+8+${#L2_key}
			L2_value=${line:${vpos}}
			;;
		"  - "*)
			# New L1 list elem -> reset L2 state
			L2_key=''
			L2_value=''
			;&
		"    "*)
			L1_key=${line:4}
			L1_key=${L1_key%:*}
			let vpos=2+4+${#L1_key}
			L1_value=${line:${vpos}}
			;;
	esac
	echo "($L1_key,$L1_value), ($L2_key,$L2_value)"

	# Collect the session names
	if [ "$L1_key" = "name" ]; then
		current_session="$L1_value"
		list_of_sessions="$list_of_sessions $current_session"
	fi
	# Which events are in session my_session ?
	if [ "$current_session" = "my_session" ] && [ "$L1_key" = "events" ] && [ "$L2_key" = "name" ]; then
		my_session_events="$my_session_events $L2_value"
	fi
done
echo
echo List of sessions: $list_of_sessions
echo my_session events: $my_session_events
echo


Thanks,
Paul

-- 
Paul Woegerer, SW Development Engineer
Sourcery Analyzer <http://go.mentor.com/sourceryanalyzer>
Mentor Graphics, Embedded Software Division