From ce4d2336bdb0942fcdb1013e2d24a64d7649f31a Mon Sep 17 00:00:00 2001
From: Roy Marples <roy@marples.name>
Date: Mon, 1 Feb 2021 14:08:41 +0000
Subject: [PATCH] With kqueue, we don't need to constantly check the snippet

Constantly going to the start of the logfile, checking the snippet,
going back to where we were and then reading is a massive drain
on the filesystem for zero benefit with kqueue.
---
 src/goaccess.c | 34 +++++++++++++++++++++++++---------
 src/parser.c   |  8 ++++++--
 2 files changed, 31 insertions(+), 11 deletions(-)

diff --git a/src/goaccess.c b/src/goaccess.c
index 985d507e7a..f67c780b25 100644
--- a/src/goaccess.c
+++ b/src/goaccess.c
@@ -776,28 +776,39 @@ parse_tail_follow (GLog * glog) {
 static void
 verify_inode (GLog * glog) {
   struct stat fdstat;
+  uint64_t oldsize;
 
   if (stat (glog->filename, &fdstat) == -1)
     FATAL ("Unable to stat the specified log file '%s'. %s", glog->filename, strerror (errno));
 
+  oldsize = glog->size;
   glog->size = fdstat.st_size;
   /* Either the log got smaller, probably was truncated so start reading from 0
    * and reset snippet.
    * If the log changed its inode, more likely the log was rotated, so we set
    * the initial snippet for the new log for future iterations */
-  if (fdstat.st_ino != glog->inode || glog->snippet[0] == '\0' || 0 == glog->size) {
+#ifdef HAVE_KQUEUE
+  if (fdstat.st_ino != glog->inode || 0 == glog->size || glog->size < oldsize) {
+    rewind(glog->fp);
+    glog->length = glog->bytes = 0;
+  }
+#else
+  if (fdstat.st_ino != glog->inode || 0 == glog->size || glog->size < oldsize || glog->snippet[0] == '\0') {
     glog->length = glog->bytes = 0;
     set_initial_persisted_data (glog);
   }
+#endif
   glog->inode = fdstat.st_ino;
 }
 
 /* Process appended log data */
 static void
 perform_tail_follow (GLog * glog) {
+#ifndef HAVE_KQUEUE
   char buf[READ_BYTES + 1] = { 0 };
   uint16_t len = 0;
   uint64_t length = 0;
+#endif
 
   if (glog->piping) {
     if (glog->fp == NULL) {
@@ -816,6 +827,13 @@ perform_tail_follow (GLog * glog) {
   if (logs->load_from_disk_only)
     return;
 
+#ifdef HAVE_KQUEUE
+  verify_inode (glog);
+  parse_tail_follow (glog);
+  /* did we read something from the pipe? */
+  if (0 == glog->bytes)
+    return;
+#else
   length = file_size (glog->filename);
 
   /* file hasn't changed */
@@ -824,14 +842,10 @@ perform_tail_follow (GLog * glog) {
   if (length == glog->length)
     return;
 
-#ifdef HAVE_KQUEUE
-  rewind (glog->fp);
-#else
   if (glog->fp != NULL)
     fclose (glog->fp);
   if (!(glog->fp = fopen (glog->filename, "r")))
     FATAL ("Unable to read the specified log file '%s'. %s", glog->filename, strerror (errno));
-#endif
 
   verify_inode (glog);
 
@@ -851,7 +865,6 @@ perform_tail_follow (GLog * glog) {
   if (fseeko (glog->fp, glog->length, SEEK_SET) == 0)
     parse_tail_follow (glog);
 
-#ifndef HAVE_KQUEUE
   fclose (glog->fp);
   glog->fp = NULL;
 #endif
@@ -936,7 +949,6 @@ process_html (const char *filename) {
     } else {
       if (glog->fp == NULL && (glog->fp = fopen (glog->filename, "r")) == NULL)
         FATAL ("Unable to read the specified log file '%s'. %s", glog->filename, strerror (errno));
-      verify_inode (glog);
       EV_SET (&ke,
               fileno (glog->fp),
 	      EVFILT_VNODE,
@@ -998,8 +1010,11 @@ process_html (const char *filename) {
                 glog);
         if (kevent (kq, &ke, 1, NULL, 0, NULL) == -1)
           FATAL ("kevent directory setup: %s", strerror (errno));
-      } else if (ke.fflags & NOTE_WRITE)
+      } else if (ke.fflags & NOTE_WRITE) {
+        /* Clear EOF from last parse */
+        clearerr(glog->fp);
         perform_tail_follow (glog);
+      }
     }
 
     /* Directory event. */
@@ -1019,11 +1034,12 @@ process_html (const char *filename) {
         LOG_DEBUG (("%s: failed to re-open log file", glog->filename));
         continue;
       }
-      verify_inode (glog);
 
       /* Closing the descriptor removes the event from the kqueue. */
       close ((int)ke.ident);
 
+      perform_tail_follow (glog);
+
       /* Re-add the log file event. */
       EV_SET (&ke,
               fileno (glog->fp),
diff --git a/src/parser.c b/src/parser.c
index c56337f1ab..cd15788f87 100644
--- a/src/parser.c
+++ b/src/parser.c
@@ -3236,6 +3236,7 @@ read_lines (GLog * glog, int dry_run) {
 }
 #endif
 
+#ifndef HAVE_KQUEUE
 /* Read the given log file and attempt to mmap a fixed number of bytes so we
  * can compare its content on future runs.
  *
@@ -3261,16 +3262,17 @@ set_initial_persisted_data (GLog * glog) {
 
   return 0;
 }
+#endif
 
 static void
 persist_last_parse (GLog * glog) {
   /* insert last parsed data for the recently file parsed */
   if (glog->inode && glog->size) {
     glog->lp.line = glog->read;
+#ifndef HAVE_KQUEUE
     glog->lp.snippetlen = glog->snippetlen;
-
     memcpy (glog->lp.snippet, glog->snippet, glog->snippetlen);
-
+#endif
     ht_insert_last_parse (glog->inode, glog->lp);
   }
   /* probably from a pipe */
@@ -3299,7 +3301,9 @@ read_log (GLog * glog, int dry_run) {
     if (stat (glog->filename, &fdstat) == 0) {
       glog->inode = fdstat.st_ino;
       glog->size = glog->lp.size = fdstat.st_size;
+#ifndef HAVE_KQUEUE
       set_initial_persisted_data (glog);
+#endif
     }
   }