doc/proposals/0004-lttng-address-api.txt

   1 RFC - LTTng address API proposal
   2
   3 Author: David Goulet <david.goulet@efficios.com>
   4
   5 Contributors:
   6     * Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
   7         * Yannick Brosseau <yannick.brosseau@polymtl.ca>
   8
   9 Version:
  10     - v0.1: 31/07/2012
  11         * Initial proposal
  12         - v0.2: 07/08/2012
  13                 * Remove lttng_create_session_addr
  14                 * Describe URL string format
  15                 * Add set_consumer_url examples
  16
  17 Introduction
  18 -----------------
  19
  20 This document proposes the use of string URLs to the command line interface and
  21 API which will deprecate a function and propose new ones.
  22
  23 The purpose of this proposal is to support network streaming using URL string
  24 format that you can find in proposal doc/proposals/0003-network.consumer.txt,
  25 remove the lttng_uri structure from the API and integrate the URL string to the
  26 API.
  27
  28 API
  29 -----------------
  30
  31 In order NOT to expose the new lttng_uri structure used to identify trace
  32 location for lttng consumer, the public API will only use string address where
  33 it will be converted in a lttng_uri and sent to the session daemon.
  34
  35 [*] Create session:
  36
  37 With the introduction of the enable-consumer command used for network
  38 streaming, the create session command has been modified so the user could
  39 define a consumer location either on the network or local with the command.
  40
  41 This does NOT change the current API call but rather simply rename _path_ to
  42 _url_ and how it is used in the lttng-ctl library.
  43
  44 Call changed from:
  45 --> lttng_create_session(const char *name, const char *path);
  46
  47 To:
  48 --> lttng_create_session(const char *name, const char *url);
  49
  50 The _name_ argument is the session name and _url_ is a string representing the
  51 URL specified by the user which is define like so:
  52
  53 PROTO://[HOSTNAME|IP][:PORT][/PATH]
  54
  55 The proto supported at this stage are (6 means IPv6):
  56
  57         * net, net6, tcp, tcp6, file
  58
  59 If the proto is NOT recognized, the string is considered to be a simple path on
  60 the local filesystem relative to the process CWD unless it starts with a "/".
  61
  62 The PATH is relative to a subdirectory "hostname", under the remote relayd
  63 "virtual" root directory. This directory can be changed with the -o, --output
  64 option when starting the lttng-relayd. This default is at:
  65
  66         * $USER/lttng-traces
  67
  68 For example, this URL results in writing the trace data in
  69 "$USER/lttng-traces/<target_hostname>/foo/bar".
  70
  71         * net://hostname/foo/bar
  72
  73 The PATH part can not be bigger than PATH_MAX (define in limits.h) which is
  74 4096 bytes at the time of this proposal. Moreover, "../" is ignored and
  75 removed. For instance, using "net://localhost/../../" will set the path to the
  76 default one.
  77
  78 The <net(6)> protocol has a special case where the user can input two ports
  79 respectively being the control and data port.
  80
  81         * net://[HOSTNAME|IP][:CTRL_PORT][:DATA_PORT][/PATH]
  82
  83 If _url_ is not NULL, in addition to creating the session, the
  84 lttng_create_session will use the two following API calls:
  85
  86         1) lttng_set_consumer_url(handle, url);
  87         2) lttng_enable_consumer(handle);
  88
  89 If _url_ is NULL, then NO consumer is created for this tracing session and
  90 subsequent calls are needed to set up a consumer (i.e lttng_enable_consumer and
  91 lttng_set_consumer_url).
  92
  93 [*] Consumer:
  94
  95 This call is simply renamed.
  96
  97 From:
  98 --> lttng_set_consumer_uri(...)
  99
 100 To:
 101 --> lttng_set_consumer_url(struct lttng_handle *handle,
 102                                 const char *url);
 103
 104 For both functions (consumer and create), the _url_ will be parsed into a
 105 lttng_uri in the liblttng-ctl and sent to the session daemon.
 106
 107 Example:
 108
 109         lttng_set_consumer_url(handle, "net://42.42.42.2");
 110
 111
 112 With all this, the lttng_uri data structure will NOT be exposed to the public
 113 API and the user command line interface.