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*------------------------------------------------------------------------------
* Netrace: A network packet trace reader
* 
* Joel Hestness
* hestness@cs.utexas.edu
* Computer Architecture and Technology Laboratory
* Department of Computer Science
* University of Texas - Austin
*------------------------------------------------------------------------------

Netrace is a network packet trace reader library for use with network
simulators. It reads packets from tracefiles of a standardized, flexible
file format. This README contains information about compilation and use
of the netrace library.

EXAMPLE CODE:
-------------
There is an example of how netrace can be used in the file `main.c'. It
implements a simple cycle-driven network simulator with queuing of 
packets. To build and run it, simply run make:
 > make
 > ./main testraces/shrtex.tra.bz2

TRACE VIEWER:
-------------
This package also contains a utility to dump information about the network
traces to the command line. It is called `trace_viewer' and can be found in
the `util' directory:
 > cd util
 > make
 > ./trace_viewer ../testraces/example.tra.bz2
Here, the header of the tracefile is printed, including the benchmark name,
the number of packets and cycles for the trace, notes about the trace,
and phase information.

API:
----
Netrace implements a very simple example programming interface. In general,
the use of the reader proceeds as follows: (1) open tracefile, (2) seek to
the phase of interest in the tracefile, (3) read packets from the tracefile,
(4) when a packet is to be injected, check if all upward dependences
have been cleared, (5) upon eject of packet, clear its downward
dependences, and free packet, (6) close the tracefile.  Each of these
steps is represented by a function call to the reader library as described
here:

* Interface Functions:
  --------------------
void nt_open_trfile()

  To open a tracefile, call `nt_open_trfile'. The character string passed
  should be the path to the tracefile. Note that the reader only handles
  bzip2 traces in an effort to keep files small.

void nt_seek_region( nt_regionhead_t* )

  To seek to a particular portion of the trace specified by a region
  header, call `nt_seek_region', passing the region header. Use the
  trace_viewer to see the phase information for a tracefile.

nt_packet_t* nt_read_packet( void )

  To read a packet from the tracefile, call `nt_read_packet'. The read
  function returns packets in chronological order by cycle. Packet cycle
  is determined through simulation of a full-system, and the cycle
  represents the earliest time that the packet could be injected into the
  network.

int nt_dependencies_cleared( nt_packet_t* )

  Once a packet has been returned from `nt_read_packet', it is live and
  can be injected into the network. However, if injection of this packet
  is dependent on the receipt of another packet, it should be held in
  wait while the packets on which it depends are in flight in the network.
  To that end, we provide `nt_depends_cleared', a function to test if
  the upward dependences of a packet have been cleared. The trace reader
  tracks all packet dependences, and quickly returns 1 if the packet
  passed has no more upward dependences, or 0 if it still depends on
  packets that have not been ejected from the network.

void nt_clear_dependencies_free_packet( nt_packet_t* )

  This function should be called when a packet is ejected from the network.
  `nt_clear_depends_free' clears all of the downward dependences of the
  packet that is passed (i.e. if it is the last packet on which packet "A"
  depends, then a further call to `nt_depends_cleared(A)' will return true,
  indicating that A can be injected into the network). After clearing its
  dependences, this function frees the packet that is passed.

  If 'nt_init_cleared_packets_list' was called at the beginning of tracing,
  the packets whose dependencies have been cleared will be added to the
  cleared packets list.

void nt_close_trfile( void )

  As the name suggests, this function closes the currently open tracefile,
  or returns immediately if one is not open. It also resets all dependency
  tracking structures.

void nt_disable_dependencies( void )

  Disable dependency tracking. Use this function if you are just reading
  and using packets, but do not care about the dependencies between them.

void nt_init_cleared_packets_list()

  Instead of testing each live packet each cycle to see if it can be
  injected into the network, we provide a cleared packets list that can
  be read each cycle. This list contains the set of packets whose
  upward dependencies were cleared since the last time that
  'nt_empty_cleared_packets_list' was called. For more details on using
  the cleared packets list, see main.c.

nt_packet_list_t* nt_get_cleared_packets_list()

  Call this function to get the cleared packets list each cycle. Packets
  in the list can be injected into the network because all of their
  dependencies have been cleared.

void nt_empty_cleared_packets_list()

  Call this function after reading the cleared packets list to empty the
  list for the next period of network activity.