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os: improve README for trace fs

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Christian Helmuth 2014-02-28 09:07:29 +01:00
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os/src/server/trace_fs/README
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@ -1,35 +1,35 @@
The trace_fs server provides access to a Trace_session by using a The new _trace_fs_ server provides access to a trace session by providing a
File_system_session as front end. file-system session as front end. Combined with Noux, it allows for the
interactive exploration and tracing of Genode's process tree using
traditional Unix tools.
Each trace subject is represented by a directory ('thread_name.subject') Each trace subject is represented by a directory ('thread_name.subject') that
that contains specific files ('active', 'cleanup', 'enable', 'events', contains specific files, which are used to control the tracing process of the
'buffer_size' and 'policy'), which are used to control the tracing thread as well as storing the content of its trace buffer:
process of the thread as well as storing the content of its trace
buffer.
The tracing of a thread is only activated if there is a valid policy :'enable': The tracing of a thread is activated if there is a valid policy
installed and the intend to trace the subject was made clear by writing installed and the intend to trace the subject was made clear by writing '1'
'1' to the 'enable' file. to the 'enable' file. The tracing of a thread may be deactivated by writing a
'0' to this file.
The tracing of a thread may be deactivated by writing a '0' to the :'policy': A policy may be changed by overwriting the currently used one in the
'enable' file. 'policy' file. In this case, the old policy is replaced by the new one and
automatically used by the framework.
A policy may be changed by overwriting the currently used one. In this :'buffer_size': Writing a value to the 'buffer_size' file changes the size of
case, the old policy is replaced by the new policy and is automatically the trace buffer. This value is evaluated only when reactivating the tracing
utilized. of the thread.
Writing a value to the 'buffer_size' file changes the size of :'events': The trace-buffer contents may be accessed by reading from the
the trace buffer. This value is evaluated when reactivating the 'events' file. New trace events are appended to this file.
tracing of the thread.
The content of the trace buffer may be accessed by reading from the :'active': Reading the file will return whether the tracing is active (1) or
'events' file. New trace events are appended to this file. not (0).
Nodes of UNTRACED subjects are kept as long as they do not change their :'cleanup': Nodes of untraced subjects are kept as long as they do not change
tracing state to DEAD. In this case, all nodes are removed from the their tracing state to dead. Dead untraced nodes are automatically removed
file system. Subjects that were traced before and are now UNTRACED can from the file system. Subjects that were traced before and are now untraced
be removed by writing '1' to the 'cleanup' file - even if they can be removed by writing '1' to the 'cleanup' file.
are DEAD by now.
To use the trace_fs, a configuration similar to the following may be used: To use the trace_fs, a configuration similar to the following may be used:
@ -44,19 +44,18 @@ To use the trace_fs, a configuration similar to the following may be used:
! </config> ! </config>
! </start> ! </start>
'interval' sets the period the Trace_session is polled. The :'interval': sets the period the Trace_session is polled. The
time is given in milliseconds. time is given in milliseconds.
'subject_limit' specifies how many trace subjects should by acquired at
max when the Trace_session is polled. :'subject_limit': specifies how many trace subjects should by acquired at
'trace_quota' is the amount of quota the trace_fs should use for the max when the Trace_session is polled.
Trace_session connection. The remaining amount of RAM quota will be used
for the actual nodes of the file system and the 'policy' as well as the :'trace_quota': is the amount of quota the trace_fs should use for the
'events' files. Trace_session connection. The remaining amount of RAM quota will be used
for the actual nodes of the file system and the 'policy' as well as the
'events' files.
In addition, there are 'buffer_size' and 'buffer_size_limit' that define In addition, there are 'buffer_size' and 'buffer_size_limit' that define
the initial and the upper limit of the size of a trace buffer. the initial and the upper limit of the size of a trace buffer.
Tracing of parent processes may be enabled by setting
'parent_levels' to a value greater than '0' (though this attribute is
available, the trace session component within core still lacks support
for it).
A ready-to-use run script can by found in 'ports/run/noux_trace_fs.run'. A ready-to-use run script can by found in 'ports/run/noux_trace_fs.run'.