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Subject[RFC Patch 0/1] Merging Documentation/trace.txt with Documentation/filesystems/relay.txt
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Date
This patch merges the "trace" documentation with that of "relay" as a
part of renaming/merging "trace" with "relay. It also renames the
functions wherever required.

Signed-off-by: K.Prasad <prasad@linux.vnet.ibm.com>
---
Documentation/filesystems/relay.txt | 215 ++++++++++++++++++++++++++++++++++++
Documentation/trace.txt | 210 -----------------------------------
2 files changed, 215 insertions(+), 210 deletions(-)
Index: linux-relay_NEW-2.6.25-mm1/Documentation/filesystems/relay.txt
===================================================================
--- linux-relay_NEW-2.6.25-mm1.orig/Documentation/filesystems/relay.txt
+++ linux-relay_NEW-2.6.25-mm1/Documentation/filesystems/relay.txt
@@ -470,6 +470,213 @@ unmapped. The client can use this notif
within the kernel application, such as enabling/disabling logging to
the channel.

+Enhanced Relay interface using debugfs -- Relay debugfs
+========================================================
+Relay debugfs Setup and Control
+================================
+In the kernel, the 'relay debugfs' interface provides a simple mechanism for
+starting and managing data channels (relays) to user space. The
+'relay debugfs' interface builds on the relay interface. For a complete
+description of the relay interface, please see:
+Documentation/filesystems/relay.txt.
+
+The 'relay debugfs' interface provides a single layer in a complete tracing
+application. 'relay debugfs' provides a kernel API that can be used for the
+setup and control of tracing channels. User of 'relay debugfs' must provide a
+data layer responsible for formatting and writing data into the 'relay debugfs'
+channels.
+
+A layered approach to tracing
+=============================
+A complete kernel tracing application consists of a data provider and
+a data consumer. Both provider and consumer contain three layers; each
+layer works in tandem with the corresponding layer in the opposite side.
+The layers are represented in the following diagram.
+
+Provider Data layer
+ Formats raw data and provides data-related service.
+ For example, adding timestamps used by consumer to sort data.
+
+Provider Control layer
+ Provided by the 'relay debugfs' interface, this layer creates 'relay
+ debugfs' channels and informs the data layer and consumer of the current
+ state of the 'relay debugfs' channels.
+
+Provider Buffering layer
+ Provided by relay. This layer buffers data in the
+ kernel for consumption by the consumer's buffer
+ layer.
+
+Provider (in-kernel facility)
+-----------------------------------------------------------------------------
+Consumer (user application)
+
+
+Consumer Buffer layer
+ Reads/consumes data from the provider's data buffers.
+
+Consumer Control layer
+ Communicates to the provider's control layer to control the state
+ of the 'relay debugfs' channels.
+
+Consumer Data layer
+ Sorts and formats data as provided by the provider's data layer.
+
+The provider is coded as a kernel facility. The consumer is coded as
+a user application.
+
+
+'relay debugfs' - Features
+===========================
+'relay debugfs' exploits services and features provided by relay. These
+features are:
+- The creation and destruction of relay channels.
+- Buffer management. Overwrite or non-overwrite modes can be selected
+ as well as global or per-CPU buffering.
+
+Overwrite mode can be called "flight recorder mode". Flight recorder
+mode is selected by setting the TRACE_FLIGHT_CHANNEL flag when
+creating 'relay debugfs' channels. In flight mode when a tracing buffer is
+full, the oldest records in the buffer will be discarded to make room
+as new records arrive. In the default non-overwrite mode, new records
+may be written only if the buffer has room. In either case, to
+prevent data loss, a user space reader must keep the buffers
+drained. 'relay debugfs' provides a means to detect the number of records that
+have been dropped due to a buffer-full condition (non-overwrite mode
+only).
+
+When per-CPU buffers are used, relay creates one debugfs file for each
+running CPU. The user-space consumer of the data is responsible for
+reading the per-CPU buffers and collating the records presumably using
+a time stamp or sequence number included in the 'relay debugfs' records. The
+use of global buffers eliminates this extra work of sequencing
+records; however the provider's data layer must hold a lock when
+writing records. The lock prevents writers running on different CPUs
+from overwriting each other's data. However, buffering may be slower
+because writes to the buffer are serialized. Global buffering is
+selected by setting the TRACE_GLOBAL_CHANNEL flag when creating 'relay debugfs'
+channels.
+
+'relay debugfs' User Interface
+==============================
+When a 'relay debugfs' channel is created and started, the following
+directories and files are created in the root of the mounted debugfs.
+
+/debug (root of the debugfs)
+ /<relay_debugfs-root-dir>
+ /<relay_debugfs-name>
+ relay[0...N-1] Per-CPU 'relay debugfs' data, one
+ file per CPU.
+
+ state Start or stop tracing by
+ by writing the strings
+ "start" or "stop" to this
+ file. Read the file to get the
+ current state.
+
+ dropped The number of records dropped
+ due to a full-buffer condition,
+ for non-TRACE_FLIGHT_CHANNELs
+ only.
+
+ rewind Trigger a rewind by writing
+ to this file. i.e. start
+ next read at the beginning
+ again. Only available for
+ TRACE_FLIGHT_CHANNELS.
+
+
+ nr_sub Number of sub-buffers
+ in the channel.
+
+ sub_size Size of sub-buffers in
+ the channel.
+
+'relay debugfs' data is gathered from the 'relay debugfs'[0...N-1] files using
+one of the available interfaces provided by relay.
+
+When using the read(2) interface, as data is read it is marked as
+consumed by the relay subsystem. Therefore, subsequent reads will
+only return unconsumed data.
+
+'relay debugfs' Kernel API
+==========================
+An overview of the 'relay debugfs' Kernel API is now given. More details of the
+API can be found in linux/trace.h.
+
+The steps a kernel data provider takes to utilize the 'relay debugfs' interface
+are:
+1) Set up a 'relay debugfs' channel - relay_setup()
+2) Start the 'relay debugfs' channel - relay_start()
+3) Write one or more 'relay debugfs' records into the channel (using the relay
+ API).
+
+ Important: When writing a 'relay debugfs' record the provider must insure
+ that preemption is disabled and that 'relay debugfs' state is set to
+ "running". A typical function used to write records into a 'relay debugfs'
+ channel should follow the following semantics:
+
+ rcu_read_lock(); // disables preemption
+ if (relay_running(relay)){
+ relay_write(....); // use any available relay data
+ // function
+ }
+ rcu_read_unlock(); // enables preemption
+
+4) Stop and start tracing as desired - relay_start()/relay_stop()
+5) Destroy the 'relay debugfs' channel and underlying relay channel -
+ relay_cleanup().
+
+Kernel Configuration
+--------------------
+To use 'relay debugfs', configure your kernel with CONFIG_TRACE=y.
+'relay debugfs' depends on both CONFIG_RELAY and CONFIG_DEBUG_FS, these will be
+automatically configured when CONFIG_TRACE is selected (if not already
+configured).
+
+Using the User Interface
+------------------------
+Reading 'relay debugfs' data and controlling the 'relay debugfs' can be done
+using commands such as cat, echo and sort. However, If you are logging binary
+'relay debugfs' data a custom application may be required to read and process
+the 'relay debugfs' data. This section shows several examples of reading
+'relay debugfs' data and controling the 'relay debugfs'. All examples assume
+that the relay_debugfs directory is your current working directory.
+
+Viewing the current 'relay debugfs' state:
+$cat state
+
+Turning the 'relay debugfs' on and off:
+$echo start > state
+$echo stop > state
+
+Reading data when using global buffers (USE_GLOBAL_BUFFERS):
+$echo stop > state
+$cat relay0
+$echo start > state
+
+Reading data when using per-cpu buffers:
+When using per-cpu buffers the user should add a time stamp or sequence
+number to each 'relay debugfs' records. This is used by the consumer to sort
+the 'relay debugfs' records into chronological order. In the following example
+the user has placed a time stamp at the front of each the record. The format of
+a record is now shown.
+
+:<time stamp>:<field 1>:<field 2>:..........
+
+Collect the data from the per-cpu 'relay debugfs' buffers, sorting
+chronologically:
+$sort --field-separator=: --key=2.1 relay*
+
+Verify that no data was lost by examining the dropped file:
+$ cat dropped
+
+To collect a larger amount of data the 'relay debugfs' buffers can be read
+continuously using something like:
+
+while [ 1 ] ; do
+ sort --field-separator=: --key=2.1 relay*
+done

Resources
=========
@@ -493,3 +700,11 @@ Tom Zanussi <zanussi@us.ibm.com>

Also thanks to Hubertus Franke for a lot of useful suggestions and bug
reports.
+
+'relay debugfs' is adapted from blktrace authored by Jens Axboe
+(axboe@kernel.dk).
+
+Major contributions were made by:
+Tom Zanussi <zanussi@us.ibm.com>
+Martin Hunt <hunt@redhat.com>
+David Wilder <dwilder@us.ibm.com>
Index: linux-relay_NEW-2.6.25-mm1/Documentation/trace.txt
===================================================================
--- linux-relay_NEW-2.6.25-mm1.orig/Documentation/trace.txt
+++ /dev/null
@@ -1,210 +0,0 @@
-Trace Setup and Control
-=======================
-In the kernel, the trace interface provides a simple mechanism for
-starting and managing data channels (traces) to user space. The
-trace interface builds on the relay interface. For a complete
-description of the relay interface, please see:
-Documentation/filesystems/relay.txt.
-
-The trace interface provides a single layer in a complete tracing
-application. Trace provides a kernel API that can be used for the setup
-and control of tracing channels. User of trace must provide a data layer
-responsible for formatting and writing data into the trace channels.
-
-A layered approach to tracing
-=============================
-A complete kernel tracing application consists of a data provider and
-a data consumer. Both provider and consumer contain three layers; each
-layer works in tandem with the corresponding layer in the opposite side.
-The layers are represented in the following diagram.
-
-Provider Data layer
- Formats raw trace data and provides data-related service.
- For example, adding timestamps used by consumer to sort data.
-
-Provider Control layer
- Provided by the trace interface, this layer creates trace channels
- and informs the data layer and consumer of the current state
- of the trace channels.
-
-Provider Buffering layer
- Provided by relay. This layer buffers data in the
- kernel for consumption by the consumer's buffer
- layer.
-
-Provider (in-kernel facility)
------------------------------------------------------------------------------
-Consumer (user application)
-
-
-Consumer Buffer layer
- Reads/consumes data from the provider's data buffers.
-
-Consumer Control layer
- Communicates to the provider's control layer to control the state
- of the trace channels.
-
-Consumer Data layer
- Sorts and formats data as provided by the provider's data layer.
-
-The provider is coded as a kernel facility. The consumer is coded as
-a user application.
-
-
-Trace - Features
-================
-Trace exploits services and features provided by relay. These features
-are:
-- The creation and destruction of relay channels.
-- Buffer management. Overwrite or non-overwrite modes can be selected
- as well as global or per-CPU buffering.
-
-Overwrite mode can be called "flight recorder mode". Flight recorder
-mode is selected by setting the TRACE_FLIGHT_CHANNEL flag when
-creating trace channels. In flight mode when a tracing buffer is
-full, the oldest records in the buffer will be discarded to make room
-as new records arrive. In the default non-overwrite mode, new records
-may be written only if the buffer has room. In either case, to
-prevent data loss, a user space reader must keep the buffers
-drained. Trace provides a means to detect the number of records that
-have been dropped due to a buffer-full condition (non-overwrite mode
-only).
-
-When per-CPU buffers are used, relay creates one debugfs file for each
-running CPU. The user-space consumer of the data is responsible for
-reading the per-CPU buffers and collating the records presumably using
-a time stamp or sequence number included in the trace records. The
-use of global buffers eliminates this extra work of sequencing
-records; however the provider's data layer must hold a lock when
-writing records. The lock prevents writers running on different CPUs
-from overwriting each other's data. However, buffering may be slower
-because writes to the buffer are serialized. Global buffering is
-selected by setting the TRACE_GLOBAL_CHANNEL flag when creating trace
-channels.
-
-Trace User Interface
-===================
-When a trace channel is created and started, the following
-directories and files are created in the root of the mounted debugfs.
-
-/debug (root of the debugfs)
- /<trace-root-dir>
- /<trace-name>
- trace[0...N-1] Per-CPU trace data, one
- file per CPU.
-
- state Start or stop tracing by
- by writing the strings
- "start" or "stop" to this
- file. Read the file to get the
- current state.
-
- dropped The number of records dropped
- due to a full-buffer condition,
- for non-TRACE_FLIGHT_CHANNELs
- only.
-
- rewind Trigger a rewind by writing
- to this file. i.e. start
- next read at the beginning
- again. Only available for
- TRACE_FLIGHT_CHANNELS.
-
-
- nr_sub Number of sub-buffers
- in the channel.
-
- sub_size Size of sub-buffers in
- the channel.
-
-Trace data is gathered from the trace[0...N-1] files using one of the
-available interfaces provided by relay.
-
-When using the read(2) interface, as data is read it is marked as
-consumed by the relay subsystem. Therefore, subsequent reads will
-only return unconsumed data.
-
-Trace Kernel API
-===============
-An overview of the trace Kernel API is now given. More details of the
-API can be found in linux/trace.h.
-
-The steps a kernel data provider takes to utilize the trace interface are:
-1) Set up a trace channel - trace_setup()
-2) Start the trace channel - trace_start()
-3) Write one or more trace records into the channel (using the relay API).
-
- Important: When writing a trace record the provider must insure that
- preemption is disabled and that trace state is set to "running". A
- typical function used to write records into a trace channel should
- follow the following semantics:
-
- rcu_read_lock(); // disables preemption
- if (trace_running(trace)){
- relay_write(....); // use any available relay data
- // function
- }
- rcu_read_unlock(); // enables preemption
-
-4) Stop and start tracing as desired - trace_start()/trace_stop()
-5) Destroy the trace channel and underlying relay channel -
- trace_cleanup().
-
-Kernel Configuration
---------------------
-To use trace, configure your kernel with CONFIG_TRACE=y. Trace depends on
-both CONFIG_RELAY and CONFIG_DEBUG_FS, these will be automatically configured
-when CONFIG_TRACE is selected (if not already configured).
-
-Using the User Interface
-------------------------
-Reading trace data and controlling the trace can be done using commands such
-as cat, echo and sort. However, If you are logging binary trace data a
-custom application may be required to read and process the trace data.
-This section shows several examples of reading trace data and controling
-the trace. All examples assume that the "trace" directory is your current
-working directory.
-
-Viewing the current trace state:
-$cat state
-
-Turning the trace on and off:
-$echo start > state
-$echo stop > state
-
-Reading data when using global buffers (USE_GLOBAL_BUFFERS):
-$echo stop > state
-$cat trace0
-$echo start > state
-
-Reading data when using per-cpu buffers:
-When using per-cpu buffers the tracer should add a time stamp or sequence
-number to each trace records. This is used by the consumer to sort the trace
-records into chronological order. In the following example the tracer has
-placed a time stamp at the front of each the record. The format of a record
-is now shown.
-
-:<time stamp>:<field 1>:<field 2>:..........
-
-Collect the data from the per-cpu trace buffers, sorting chronologically:
-$sort --field-separator=: --key=2.1 trace*
-
-Verify that no data was lost by examining the dropped file:
-$ cat dropped
-
-To collect a larger amount of data the trace buffers can be read
-continuously using something like:
-
-while [ 1 ] ; do
- sort --field-separator=: --key=2.1 trace*
-done
-
-
-Credits
-=======
-Trace is adapted from blktrace authored by Jens Axboe (axboe@kernel.dk).
-
-Major contributions were made by:
-Tom Zanussi <zanussi@us.ibm.com>
-Martin Hunt <hunt@redhat.com>
-David Wilder <dwilder@us.ibm.com>

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