Changeset 238d50a for lib/format_legacy.c

Timestamp:

02/08/10 16:43:43 (12 years ago)

Author:

Shane Alcock <salcock@…>

Branches:

4.0.1-hotfixes, cachetimestamps, develop, dpdk-ndag, etsilive, getfragoff, help, libtrace4, master, ndag_format, pfring, rc-4.0.1, rc-4.0.2, rc-4.0.3, rc-4.0.4, ringdecrementfix, ringperformance, ringtimestampfixes

Children:

d026488

Parents:

5511c14

Message:

• Updated licensing and documentation for several format modules and the format_helper code

File:

• lib/format_legacy.c (modified) (9 diffs)

lib/format_legacy.c

@@ -2 +2 @@
  * This file is part of libtrace
  *
- * Copyright (c) 2007,2008 The University of Waikato, Hamilton, New Zealand.
+ * Copyright (c) 2007,2008,2009,2010 The University of Waikato, Hamilton, 
+ * New Zealand.
+ *
  * Authors: Daniel Lawson 
- *          Perry Lorier 
+ *          Perry Lorier
+ *          Shane Alcock 
  *          
  * All rights reserved.
@@ -28 +31 @@
  *
  */
+
 #define _GNU_SOURCE
 
@@ -51 +55 @@
 #endif
 
+/* The format module deals with legacy DAG formats from older revisions of the
+ * DAG hardware and software. Aside from a few minor differences, the legacy
+ * formats are very similar so we can deal with them using the same callback
+ * functions for the most part.
+ *
+ * These formats are intended for reading old ERF traces such as the earlier
+ * Auckland traces.
+ *
+ * We definitely do not support writing using these formats - one should 
+ * convert packets to regular ERF instead before writing.
+ */
+
+/* Several formats are covered in this source file:
+ *
+ * Legacy Ethernet:     as seen in Auckland VI
+ * Legacy ATM:          as seen in Auckland II and IV
+ * Legacy PoS:          as seen in Leipzig I and II
+ * Legacy NZIX:         as seen in NZIX I
+ */
 
 /* Catch undefined O_LARGEFILE on *BSD etc */
@@ -63 +86 @@
 #define DATA(x) ((struct legacy_format_data_t *)x->format_data)
 
+/* Legacy NZIX timestamps are all relative to the start of the trace, so we
+ * have to remember all sorts of stuff so that we can convert them into a
+ * useful timestamp */
+
 struct legacy_format_data_t {
-        time_t starttime;       /* Used for legacy_nzix */
-        uint64_t ts_high;       /* Used for legacy_nzix */
-        uint32_t ts_old;        /* Used for legacy_nzix */
+        time_t starttime;       /* Time that the trace file was started */
+        uint64_t ts_high;       /* The timestamp of the last packet */
+        uint32_t ts_old;        /* The timestamp of the last packet as 
+                                   reported in the NZIX header */
 };
 
@@ -104 +132 @@
 }
 
+/* Takes a trace file name and determines the time that the capture began.
+ *
+ * NZIX only features relative timestamps so the trace file name is the only
+ * indication we have of where the relative timestamping begins from
+ */
 static time_t trtime(char *s) {
         /* XXX: this function may not be particularly portable to
@@ -143 +176 @@
 
         legacy_init_format_data(libtrace);      
+        
+        /* Check that the filename appears to contain a suitable timestamp.
+         * Without it, we have no way of determining the actual timestamps
+         * for each packet */
         if((retval = regcomp(&reg, "[0-9]{8}-[0-9]{6}", REG_EXTENDED)) != 0) {
                 trace_set_err(libtrace, errno, "Failed to compile regex");
@@ -155 +192 @@
 }
 
+/* All of the formats can be started in exactly the same way */
 static int erf_start_input(libtrace_t *libtrace)
 {
@@ -291 +329 @@
         }
 
-        /* lets move the padding so that it's in the framing header */
+        /* Lets move the padding so that it's in the framing header */
         data_ptr = ((char *)buffer) + 12;
         memmove(data_ptr + 2, data_ptr, 26);
@@ -392 +430 @@
         hdr_ts = legacy->ts;
 
-        /* seems we only need 30 bits to represent our timestamp */
+        /* Seems we only need 30 bits to represent our timestamp */
         hdr_ts >>=2;
-        /* try a sequence number wrap-around comparison */
+        
+        /* Try a sequence number wrap-around comparison */
         if (ts_cmp(hdr_ts, old_ts) > (UINT32_MAX / 2) )
-                new_ts += (1LL << 30); /* wraparound */
-        new_ts &= ~((1LL << 30) -1);    /* mask lower 30 bits */
-        new_ts += hdr_ts;               /* packet ts is the new 30 bits */
+                new_ts += (1LL << 30); /* Wraparound */
+        new_ts &= ~((1LL << 30) -1);    /* Mask lower 30 bits */
+        new_ts += hdr_ts;               /* Packet ts is the new 30 bits */
         DATA(packet->trace)->ts_old = hdr_ts;