3928 `tail -f ...` doesn't notice file truncation

3929 `man tail` doesn't mentioned "-F" option
3930 'tail -F ...' not resetting the offset of file rotation properly
3968 want FILE_TRUNC event for PORT_SOURCE_FILE
Reviewed by: Gordon Ross <gordon.ross@nexenta.com>
Approved by: Dan McDonald <danmcd@nexenta.com>

18 files changed, 752 insertions, 116 deletions

diff --git a/usr/src/cmd/tail/extern.h b/usr/src/cmd/tail/extern.h
index 147a887272..7f121b2d9d 100644
--- a/usr/src/cmd/tail/extern.h
+++ b/usr/src/cmd/tail/extern.h
@@ -28,6 +28,12 @@
  *
  */
 
+#ifndef	_TAIL_EXTERN_H
+#define	_TAIL_EXTERN_H
+
+#include <sys/types.h>
+#include <sys/stat.h>
+#include <port.h>
 
 #define	WR(p, size) do { \
 	if (write(STDOUT_FILENO, p, size) != (ssize_t)size) \
@@ -48,6 +54,7 @@ struct file_info {
 	FILE *fp;
 	char *file_name;
 	struct stat st;
+	file_obj_t fobj[2];
 };
 
 typedef struct file_info file_info_t;
@@ -67,3 +74,5 @@ int mapprint(struct mapinfo *, off_t, off_t);
 int maparound(struct mapinfo *, off_t);
 
 extern int Fflag, fflag, qflag, rflag, rval, no_files;
+
+#endif	/* _TAIL_EXTERN_H */
diff --git a/usr/src/cmd/tail/forward.c b/usr/src/cmd/tail/forward.c
index e4f22582f3..8b87dfff06 100644
--- a/usr/src/cmd/tail/forward.c
+++ b/usr/src/cmd/tail/forward.c
@@ -31,9 +31,7 @@
  */
 
 /*
- * Solaris porting notes:  the original FreeBSD version made use of the
- *                         BSD kqueue event notification framework; this
- *                         was changed to use usleep()
+ * Copyright (c) 2013, Joyent, Inc. All rights reserved.
  */
 
 #include <sys/param.h>
@@ -53,6 +51,7 @@
 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>
+#include <strings.h>
 #include <unistd.h>
 
 #include "extern.h"
@@ -63,9 +62,11 @@ static void set_events(file_info_t *files);
 
 /* defines for inner loop actions */
 #define	USE_SLEEP	0
+#define	USE_PORT	1
 #define	ADD_EVENTS	2
 
-int action = USE_SLEEP;
+int port;
+int action = USE_PORT;
 
 static const file_info_t *last;
 
@@ -261,6 +262,107 @@ show(file_info_t *file)
 }
 
 static void
+associate(file_info_t *file, boolean_t assoc, port_event_t *ev)
+{
+	char buf[64], *name;
+	int i;
+
+	if (action != USE_PORT || file->fp == NULL)
+		return;
+
+	if (!S_ISREG(file->st.st_mode)) {
+		/*
+		 * For FIFOs, we use PORT_SOURCE_FD as our port event source.
+		 */
+		if (assoc) {
+			(void) port_associate(port, PORT_SOURCE_FD,
+			    fileno(file->fp), POLLIN, file);
+		} else {
+			(void) port_dissociate(port, PORT_SOURCE_FD,
+			    fileno(file->fp));
+		}
+
+		return;
+	}
+
+	bzero(&file->fobj, sizeof (file->fobj));
+
+	if (!Fflag) {
+		/*
+		 * PORT_SOURCE_FILE only allows us to specify a file name, not
+		 * a file descriptor.  If we are following a specific file (as
+		 * opposed to a file name) and we were to specify the name of
+		 * the file to port_associate() and that file were moved
+		 * aside, we would not be able to reassociate an event because
+		 * we would not know a name that would resolve to the new file
+		 * (indeed, there might not be such a name -- the file may
+		 * have been unlinked).  But there _is_ a name that we know
+		 * maps to the file and doesn't change: the name of the
+		 * representation of the open file descriptor in /proc.  We
+		 * therefore associate with this name (and the underlying
+		 * file), not the name of the file as specified at the command
+		 * line.  This also has the (desirable) side-effect of
+		 * insulating against FILE_RENAME_FROM and FILE_RENAME_TO
+		 * events that we need to ignore to assure that we don't lose
+		 * FILE_TRUNC events.
+		 */
+		(void) snprintf(buf,
+		    sizeof (buf), "/proc/self/fd/%d", fileno(file->fp));
+		name = buf;
+	} else {
+		name = file->file_name;
+	}
+
+	/*
+	 * Note that portfs uses the address of the specified file_obj_t to
+	 * tag an association; if one creates a different association with a
+	 * (different) file_obj_t that happens to be at the same address,
+	 * the first association will be implicitly removed.  To assure that
+	 * each association has a disjoint file_obj_t, we allocate the memory
+	 * for each in the file_info, not on the stack.
+	 */
+	file->fobj[0].fo_name = name;
+	file->fobj[1].fo_name = name;
+
+	if (assoc) {
+		/*
+		 * To assure that we cannot possibly drop a FILE_TRUNC event,
+		 * we have two different PORT_SOURCE_FILE associations with the
+		 * port:  one to get only FILE_MODIFIED events and another to
+		 * get only FILE_TRUNC events.  This assures that we always
+		 * have an active association for FILE_TRUNC events when the
+		 * seek offset is non-zero.  Note that the association order
+		 * _must_ be FILE_TRUNC followed by FILE_MODIFIED:  if a single
+		 * event induces both a FILE_TRUNC and a FILE_MODIFIED (as
+		 * a VE_CREATE vnode event does), we must process the
+		 * FILE_TRUNC before FILE_MODIFIED -- and the order in which
+		 * these are processed will be the association order.  So
+		 * if we see a FILE_TRUNC, we dissociate/reassociate the
+		 * FILE_MODIFIED association.
+		 */
+		if (ev == NULL || (ev->portev_events & FILE_TRUNC) ||
+		    !(ev->portev_events & (FILE_MODIFIED | FILE_TRUNC))) {
+			(void) port_associate(port, PORT_SOURCE_FILE,
+			    (uintptr_t)&file->fobj[0], FILE_TRUNC, file);
+			(void) port_dissociate(port, PORT_SOURCE_FILE,
+			    (uintptr_t)&file->fobj[1]);
+			ev = NULL;
+		}
+
+		if (ev == NULL || (ev->portev_events & FILE_MODIFIED) ||
+		    !(ev->portev_events & (FILE_MODIFIED | FILE_TRUNC))) {
+			(void) port_associate(port, PORT_SOURCE_FILE,
+			    (uintptr_t)&file->fobj[1], FILE_MODIFIED, file);
+		}
+	} else {
+		for (i = 0; i <= 1; i++) {
+			(void) port_dissociate(port, PORT_SOURCE_FILE,
+			    (uintptr_t)&file->fobj[i]);
+		}
+	}
+}
+
+static void
 set_events(file_info_t *files)
 {
 	int i;
@@ -271,6 +373,8 @@ set_events(file_info_t *files)
 			continue;
 
 		(void) fstat(fileno(file->fp), &file->st);
+
+		associate(file, B_TRUE, NULL);
 	}
 }
 
@@ -284,6 +388,8 @@ follow(file_info_t *files, enum STYLE style, off_t off)
 	int active, ev_change, i, n = -1;
 	struct stat sb2;
 	file_info_t *file;
+	struct timespec ts;
+	port_event_t ev;
 
 	/* Position each of the files */
 
@@ -307,6 +413,12 @@ follow(file_info_t *files, enum STYLE style, off_t off)
 		return;
 
 	last = --file;
+
+	if (action == USE_PORT &&
+	    (stat("/proc/self/fd", &sb2) == -1 || !S_ISDIR(sb2.st_mode) ||
+	    (port = port_create()) == -1))
+		action = USE_SLEEP;
+
 	set_events(files);
 
 	for (;;) {
@@ -341,12 +453,13 @@ follow(file_info_t *files, enum STYLE style, off_t off)
 				    sb2.st_dev != file->st.st_dev ||
 				    sb2.st_nlink == 0) {
 					(void) show(file);
+					associate(file, B_FALSE, NULL);
 					file->fp = freopen(file->file_name, "r",
 					    file->fp);
-					if (file->fp != NULL)
+					if (file->fp != NULL) {
 						(void) memcpy(&file->st, &sb2,
 						    sizeof (struct stat));
-					else if (errno != ENOENT)
+					} else if (errno != ENOENT)
 						ierr(file->file_name);
 					ev_change++;
 				}
@@ -361,6 +474,26 @@ follow(file_info_t *files, enum STYLE style, off_t off)
 			set_events(files);
 
 		switch (action) {
+		case USE_PORT:
+			ts.tv_sec = 1;
+			ts.tv_nsec = 0;
+
+			/*
+			 * In the -F case we set a timeout to ensure that
+			 * we re-stat the file at least once every second.
+			 */
+			n = port_get(port, &ev, Fflag ? &ts : NULL);
+
+			if (n == 0) {
+				file = (file_info_t *)ev.portev_user;
+				associate(file, B_TRUE, &ev);
+
+				if (ev.portev_events & FILE_TRUNC)
+					(void) fseek(file->fp, 0, SEEK_SET);
+			}
+
+			break;
+
 		case USE_SLEEP:
 			(void) usleep(250000);
 			break;
diff --git a/usr/src/cmd/tail/tests/tailtests.sh b/usr/src/cmd/tail/tests/tailtests.sh
index 57ec1c46cc..d3a8bb1cf2 100644
--- a/usr/src/cmd/tail/tests/tailtests.sh
+++ b/usr/src/cmd/tail/tests/tailtests.sh
@@ -13,129 +13,468 @@
 
 #
 # Copyright 2010 Chris Love.  All rights reserved.
+# Copyright (c) 2013, Joyent, Inc. All rights reserved.
 #
 
+checktest()
+{
+	local actual=$1
+	local output=$2
+	local test=$3
+
+	if [[ "$actual" != "$output" ]]; then
+		echo "$CMD: test $test: FAIL"
+		echo -e "$CMD: test $test: expected output:\n$output"
+		echo -e "$CMD: test $test: actual output:\n$actual"
+	else
+		echo "$CMD: test $test: pass"
+	fi
+}
 
 # 
 # Test cases for 'tail', some based on CoreUtils test cases (validated
-# with legacy Solaris 'tail' and/or xpg4 'tail')
+# with legacy Solaris 'tail' and/or xpg4 'tail').  Note that this is designed
+# to be able to run on BSD systems as well to check our behavior against
+# theirs (some behavior that is known to be idiosyncratic to illumos is
+# skipped on non-illumos systems).
 #
 PROG=/usr/bin/tail
+CMD=`basename $0`
+DIR=""
+
+while [[ $# -gt 0 ]]; do
+	case $1 in
+	    -x)
+		PROG=/usr/xpg4/bin/tail
+		shift
+		;;
+	    -o)
+		PROG=$2
+		shift 2
+		;;
+	    -d)
+		DIR=$2
+		shift 2
+		;;
+	    *)
+		echo "Usage: tailtests.sh" \
+		    "[-x][-o <override tail executable>]" \
+		    "[-d <override output directory>]"
+		exit 1
+		;;
+	esac
+done
 
-case $1 in 
-    -x)
-    	PROG=/usr/xpg4/bin/tail
-	;;
-    -o)
-    	PROG=$2
-	;;
-    -?)
-    	echo "Usage: tailtests.sh [-x][-o <override tail executable>]"
-	exit 1
-	;;
-esac
-
-echo "Using $PROG"
+#
+# Shut bash up upon receiving a term so we can drop it on our children
+# without disrupting the output.
+#
+trap "exit 0" TERM
+
+echo "$CMD: program is $PROG"
+
+if [[ $DIR != "" ]]; then
+	echo "$CMD: directory is $DIR"
+fi
 
 o=`echo -e "bcd"`
 a=`echo -e "abcd" | $PROG +2c`
-[[ "$a" != "$o" ]] && echo "Fail test 1 - $a"
+checktest "$a" "$o" 1
 
 o=`echo -e ""`
 a=`echo "abcd" | $PROG +8c`
-[[ "$a" != "$o" ]] && echo "Fail test 2 - $a"
+checktest "$a" "$o" 2
 
 o=`echo -e "abcd"`
 a=`echo "abcd" | $PROG -9c`
-[[ "$a" != "$o" ]] && echo "Fail test 3 - $a"
+checktest "$a" "$o" 3
 
 o=`echo -e "x"`
 a=`echo -e "x" | $PROG -1l`
-[[ "$a" != "x" ]] && echo "Fail test 4 - $a"
+checktest "$a" "$o" 4
 
 o=`echo -e "\n"`
 a=`echo -e "x\ny\n" | $PROG -1l`
-[[ "$a" != "$o" ]] && echo "Fail test 5 - $a"
+checktest "$a" "$o" 5
 
 o=`echo -e "y\n"`
 a=`echo -e "x\ny\n" | $PROG -2l`
-[[ "$a" != "$o" ]] && echo "Fail test 6 - $a"
+checktest "$a" "$o" 6
 
 o=`echo -e "y"`
 a=`echo -e "x\ny" | $PROG -1l`
-[[ "$a" != "$o" ]] && echo "Fail test 7 - $a"
+checktest "$a" "$o" 7
 
 o=`echo -e "x\ny\n"`
 a=`echo -e "x\ny\n" | $PROG +1l`
-[[ "$a" != "$o" ]] && echo "Fail test 8 - $a"
+checktest "$a" "$o" 8
 
 o=`echo -e "y\n"`
 a=`echo -e "x\ny\n" | $PROG +2l`
-[[ "$a" != "$o" ]] && echo "Fail test 9 - $a"
+checktest "$a" "$o" 9
 
 o=`echo -e "x"`
 a=`echo -e "x" | $PROG -1`
-[[ "$a" != "$o" ]] && echo "Fail test 10 - $a"
+checktest "$a" "$o" 10
 
 o=`echo -e "\n"`
 a=`echo -e "x\ny\n" | $PROG -1`
-[[ "$a" != "$o" ]] && echo "Fail test 11 - $a"
+checktest "$a" "$o" 11
 
 o=`echo -e "y\n"`
 a=`echo -e "x\ny\n" | $PROG -2`
-[[ "$a" != "$o" ]] && echo "Fail test 12 - $a"
+checktest "$a" "$o" 12
 
 o=`echo -e "y"`
 a=`echo -e "x\ny" | $PROG -1`
-[[ "$a" != "$o" ]] && echo "Fail test 13 - $a"
+checktest "$a" "$o" 13
 
 o=`echo -e "x\ny\n"`
 a=`echo -e "x\ny\n" | $PROG +1`
-[[ "$a" != "$o" ]] && echo "Fail test 14 - $a"
+checktest "$a" "$o" 14
 
 o=`echo -e "y\n"`
 a=`echo -e "x\ny\n" | $PROG +2`
-[[ "$a" != "$o" ]] && echo "Fail test 15 - $a"
+checktest "$a" "$o" 15
 
-# For compatibility with Legacy Solaris tail this should also work as '+c'
 o=`echo -e "yyz"`
 a=`echo -e "xyyyyyyyyyyz" | $PROG +10c`
-[[ "$a" != "$o" ]] && echo "Fail test 16 - $a"
-
-o=`echo -e "yyz"`
-a=`echo -e "xyyyyyyyyyyz" | $PROG +c`
-[[ "$a" != "$o" ]] && echo "Fail test 16a - $a"
-
+checktest "$a" "$o" 16
 
-# For compatibility with Legacy Solaris tail this should also work as '+l'
 o=`echo -e "y\ny\nz"`
 a=`echo -e "x\ny\ny\ny\ny\ny\ny\ny\ny\ny\ny\nz" | $PROG +10l`
-[[ "$a" != "$o" ]] && echo "Fail test 17 - $a"
+checktest "$a" "$o" 17
 
-o=`echo -e "y\ny\nz"`
-a=`echo -e "x\ny\ny\ny\ny\ny\ny\ny\ny\ny\ny\nz" | $PROG +l`
-[[ "$a" != "$o" ]] && echo "Fail test 17a - $a"
-
-
-# For compatibility with Legacy Solaris tail this should also work as '-l'
 o=`echo -e "y\ny\ny\ny\ny\ny\ny\ny\ny\nz"`
 a=`echo -e "x\ny\ny\ny\ny\ny\ny\ny\ny\ny\ny\nz" | $PROG -10l`
-[[ "$a" != "$o" ]] && echo "Fail test 18 - $a"
+checktest "$a" "$o" 18
 
-o=`echo -e "y\ny\ny\ny\ny\ny\ny\ny\ny\nz"`
-a=`echo -e "x\ny\ny\ny\ny\ny\ny\ny\ny\ny\ny\nz" | $PROG -l`
-[[ "$a" != "$o" ]] && echo "Fail test 18a - $a"
+#
+# For reasons that are presumably as accidental as they are ancient, legacy
+# (and closed) Solaris tail(1) allows +c, +l and -l to be aliases for +10c,
+# +10l and -10l, respectively.  If we are on SunOS, verify that this silly
+# behavior is functional.
+#
+if [[ `uname -s` == "SunOS" ]]; then
+	o=`echo -e "yyz"`
+	a=`echo -e "xyyyyyyyyyyz" | $PROG +c`
+	checktest "$a" "$o" 16a
+
+	o=`echo -e "y\ny\nz"`
+	a=`echo -e "x\ny\ny\ny\ny\ny\ny\ny\ny\ny\ny\nz" | $PROG +l`
+	checktest "$a" "$o" 17a
+
+	o=`echo -e "y\ny\ny\ny\ny\ny\ny\ny\ny\nz"`
+	a=`echo -e "x\ny\ny\ny\ny\ny\ny\ny\ny\ny\ny\nz" | $PROG -l`
+	checktest "$a" "$o" 18a
+fi
 
 o=`echo -e "c\nb\na"`
 a=`echo -e "a\nb\nc" | $PROG -r`
-[[ "$a" != "$o" ]] && echo "Fail test 19 - $a"
+checktest "$a" "$o" 19
+
+#
+# Now we want to do a series of follow tests.
+#
+if [[ $DIR == "" ]]; then
+	export TMPDIR=/var/tmp
+	tdir=$(mktemp -d -t tailtest.XXXXXXXX || exit 1)
+else
+	tdir=$(mktemp -d $DIR/tailtest.XXXXXXXX || exit 1)
+fi
+
+follow=$tdir/follow
+moved=$tdir/follow.moved
+out=$tdir/out
+
+#
+# First, verify that following works in its most basic sense.
+#
+echo -e "a\nb\nc" > $follow
+$PROG -f $follow > $out 2> /dev/null &
+child=$!
+sleep 2
+echo -e "d\ne\nf" >> $follow
+sleep 1
+kill $child
+sleep 1
+
+o=`echo -e "a\nb\nc\nd\ne\nf\n"`
+a=`cat $out`
+checktest "$a" "$o" 20
+rm $follow
+
+#
+# Now verify that following correctly follows the file being moved.
+#
+echo -e "a\nb\nc" > $follow
+$PROG -f $follow > $out 2> /dev/null &
+child=$!
+sleep 2
+mv $follow $moved
+
+echo -e "d\ne\nf" >> $moved
+sleep 1
+kill $child
+sleep 1
+
+o=`echo -e "a\nb\nc\nd\ne\nf\n"`
+a=`cat $out`
+checktest "$a" "$o" 21
+rm $moved
+
+#
+# And now truncation with the new offset being less than the old offset.
+#
+echo -e "a\nb\nc" > $follow
+$PROG -f $follow > $out 2> /dev/null &
+child=$!
+sleep 2
+echo -e "d\ne\nf" >> $follow
+sleep 1
+echo -e "g\nh\ni" > $follow
+sleep 1
+kill $child
+sleep 1
+
+o=`echo -e "a\nb\nc\nd\ne\nf\ng\nh\ni\n"`
+a=`cat $out`
+checktest "$a" "$o" 22
+rm $follow
+
+#
+# And truncation with the new offset being greater than the old offset.
+#
+echo -e "a\nb\nc" > $follow
+sleep 1
+$PROG -f $follow > $out 2> /dev/null &
+child=$!
+sleep 2
+echo -e "d\ne\nf" >> $follow
+sleep 1
+echo -e "g\nh\ni\nj\nk\nl\nm\no\np\nq" > $follow
+sleep 1
+kill $child
+sleep 1
+
+o=`echo -e "a\nb\nc\nd\ne\nf\ng\nh\ni\nj\nk\nl\nm\no\np\nq"`
+a=`cat $out`
+checktest "$a" "$o" 23
+rm $follow
+
+#
+# Verify that we can follow the moved file and correctly see a truncation.
+#
+echo -e "a\nb\nc" > $follow
+$PROG -f $follow > $out 2> /dev/null &
+child=$!
+sleep 2
+mv $follow $moved
+
+echo -e "d\ne\nf" >> $moved
+sleep 1
+echo -e "g\nh\ni\nj\nk\nl\nm\no\np\nq" > $moved
+sleep 1
+kill $child
+sleep 1
+
+o=`echo -e "a\nb\nc\nd\ne\nf\ng\nh\ni\nj\nk\nl\nm\no\np\nq"`
+a=`cat $out`
+checktest "$a" "$o" 24
+rm $moved
+
+#
+# Verify that capital-F follow properly deals with truncation
+#
+echo -e "a\nb\nc" > $follow
+$PROG -F $follow > $out 2> /dev/null &
+child=$!
+sleep 2
+echo -e "d\ne\nf" >> $follow
+sleep 1
+echo -e "g\nh\ni" > $follow
+sleep 1
+kill $child
+sleep 1
+
+o=`echo -e "a\nb\nc\nd\ne\nf\ng\nh\ni\n"`
+a=`cat $out`
+checktest "$a" "$o" 25
+rm $follow
+
+#
+# Verify that capital-F follow _won't_ follow the moved file and will
+# correctly deal with recreation of the original file.
+#
+echo -e "a\nb\nc" > $follow
+$PROG -F $follow > $out 2> /dev/null &
+child=$!
+sleep 2
+mv $follow $moved
+
+echo -e "x\ny\nz" >> $moved
+
+#
+# At this point, tail is polling on stat'ing the missing file; we need to
+# be sure to sleep long enough after recreating it to know that it will pick
+# it up.
+#
+echo -e "d\ne\nf" > $follow
+sleep 5
+kill $child
+sleep 1
+
+o=`echo -e "a\nb\nc\nd\ne\nf\n"`
+a=`cat $out`
+checktest "$a" "$o" 26
+rm $moved
+
+#
+# Verify that following two files works.
+#
+echo -e "one" > $follow
+echo -e "two" > $moved
+$PROG -f $follow $moved > $out 2> /dev/null &
+child=$!
+sleep 2
+echo -e "three" >> $follow
+sleep 1
+echo -e "four" >> $moved
+sleep 1
+echo -e "five" >> $follow
+sleep 1
+kill $child
+sleep 1
+
+# There is a bug where the content comes before the header lines,
+# where rlines/mapprint happens before the header.  A pain to fix.
+# In this test, just make sure we see both files change.
+o="one
+
+==> $follow <==
+two
+
+==> $moved <==
+
+==> $follow <==
+three
+
+==> $moved <==
+four
+
+==> $follow <==
+five"
+a=`cat $out`
+checktest "$a" "$o" 27
+rm $follow $moved
+
+if [[ `uname -s` == "SunOS" ]]; then
+	#
+	# Use DTrace to truncate the file between the return from port_get()
+	# and the reassociation of the file object with the port, exposing
+	# any race conditions whereby FILE_TRUNC events are lost.
+	#
+	cat /dev/null > $follow
+	dtrace -c "$PROG -f $follow" -s /dev/stdin > $out <<EOF
+		#pragma D option destructive
+		#pragma D option quiet 
+
+		pid\$target::port_get:return
+		/++i == 5/
+		{
+			stop();
+			system("cat /dev/null > $follow");
+			system("prun %d", pid);
+		}
+
+		tick-1sec
+		{
+			system("echo %d >> $follow", j++);
+		}
+
+		tick-1sec
+		/j == 10/
+		{
+			exit(0);
+		}
+EOF
+
+	o=`echo -e "0\n1\n2\n3\n5\n6\n7\n8\n9\n"`
+	a=`cat $out`
+	checktest "$a" "$o" 27a
+	rm $follow
+
+	cat /dev/null > $follow
+	dtrace -c "$PROG -f $follow" -s /dev/stdin > $out <<EOF
+		#pragma D option destructive
+		#pragma D option quiet 
+
+		pid\$target::port_get:return
+		/++i == 5/
+		{
+			stop();
+			system("mv $follow $moved");
+			system("cat /dev/null > $moved");
+			system("prun %d", pid);
+		}
+
+		tick-1sec
+		{
+			system("echo %d >> %s", j++,
+			    i < 5 ? "$follow" : "$moved");
+		}
+
+		tick-1sec
+		/j == 10/
+		{
+			exit(0);
+		}
+EOF
+
+	o=`echo -e "0\n1\n2\n3\n5\n6\n7\n8\n9\n"`
+	a=`cat $out`
+	checktest "$a" "$o" 27b
+	rm $moved
+
+	#
+	# Verify that -F will deal properly with the file being truncated
+	# not by truncation, but rather via an ftruncate() from logadm.
+	#
+	cat /dev/null > $follow
+	( $PROG -F $follow > $out ) &
+	child=$!
+	echo -e "a\nb\nc\nd\ne\nf" >> $follow
+	logadm -c $follow
+	sleep 2
+	echo -e "g\nh\ni" >> $follow
+	sleep 2
+	kill $child
+	sleep 1
+
+	o=`echo -e "a\nb\nc\nd\ne\nf\ng\nh\ni\n"`
+	a=`cat $out`
+	checktest "$a" "$o" 27c
+fi
+
+#
+# We're now going to test that while we may miss output due to truncations
+# occurring faster than tail can read, we don't ever repeat output.
+#
+cat /dev/null > $follow
+( $PROG -f $follow > $out ) &
+tchild=$!
+( let i=0 ; while true; do echo $i > $follow ; sleep 0.1; let i=i+1 ; done ) &
+child=$!
+sleep 10
+kill $tchild
+kill $child
+
+a=`sort $out | uniq -c | sort -n | tail -1 | awk '{ print $1 }'`
+o=1
 
+checktest "$a" "$o" 28
 
-echo "Completed"
+echo "$CMD: completed"
 
-exit 0
+exit $errs
 
-# Template for additional test cases
-#o=`echo -e ""`
-#a=`echo -e "" | $PROG `
-#[[ "$a" != "$o" ]] && echo "Fail test  - $a"
diff --git a/usr/src/man/man1/tail.1 b/usr/src/man/man1/tail.1
index aca819269e..b96e6400dd 100644
--- a/usr/src/man/man1/tail.1
+++ b/usr/src/man/man1/tail.1
@@ -23,12 +23,12 @@ tail \- deliver the last part of a file
 
 .LP
 .nf
-\fB/usr/bin/tail\fR [\(+- \fInumber\fR [lbcf]] [\fIfile\fR]
+\fB/usr/bin/tail\fR [\(+- \fInumber\fR [lbcfF]] [\fIfile\fR]
 .fi
 
 .LP
 .nf
-\fB/usr/bin/tail\fR [\fB-lbcf\fR] [\fIfile\fR]
+\fB/usr/bin/tail\fR [\fB-lbcfF\fR] [\fIfile\fR]
 .fi
 
 .LP
@@ -92,11 +92,24 @@ Units of bytes.
 \fB\fB-f\fR \fR
 .ad
 .RS 7n
-Follow. If the input-file is not a pipe, the program does not terminate after
-the line of the input-file has been copied, but enters an endless loop, wherein
-it sleeps for a second and then attempts to read and copy further records from
-the input-file. Thus it can be used to monitor the growth of a file that is
-being written by some other process.
+Follow. If the input-file is not a pipe, \fBtail\fR does not terminate after
+the last line of the input-file has been copied, but enters an endless loop,
+wherein it watches the file for modifications and attempts to read and copy
+further records from the input-file. Thus it can be used to monitor the growth
+of a file that is being written by some other process. If the watched file is
+truncated \fBtail\fR will begin reading records from the start of the file.
+.RE
+
+.sp
+.ne 2
+.na
+\fB\fB-F\fR \fR
+.ad
+.RS 7n
+Follow named file. Operates as with \fB-f\fR, except that if the file is moved
+(e.g. if a watched log file is rotated) \fBtail\fR will close the original file
+and begin reading records from the start of the file with the specified name
+if and when that file is recreated.
 .RE
 
 .sp
diff --git a/usr/src/man/man3c/port_associate.3c b/usr/src/man/man3c/port_associate.3c
index d876b5c9d7..f6e66b0d65 100644
--- a/usr/src/man/man3c/port_associate.3c
+++ b/usr/src/man/man3c/port_associate.3c
@@ -73,21 +73,21 @@ the port.
 .LP
 Objects of type \fBPORT_SOURCE_FILE\fR are pointer to the structure
 \fBfile_obj\fR defined in \fB<sys/port.h>\fR. This event source provides event
-notification when the specified file/directory is accessed or modified or when
-its status changes. The path name of the file/directory to be watched is passed
-in the \fBstruct file_obj\fR along with the \fBaccess\fR, \fBmodification\fR,
-and \fBchange\fR time stamps acquired from a \fBstat\fR(2) call. If the file
-name is a symbolic links, it is followed by default. The \fBFILE_NOFOLLOW\fR
-needs to be passed in along with the specified events if the symbolic link
-itself needs to be watched and \fBlstat()\fR needs to be used to get the file
-status of the symbolic link file.
+notification when the specified file/directory is accessed, modified,
+truncated or when its status changes. The path name of the file/directory to
+be watched is passed in the \fBstruct file_obj\fR along with the \fBaccess\fR,
+\fBmodification\fR, and \fBchange\fR time stamps acquired from a \fBstat\fR(2)
+call. If the file name is a symbolic link, it is followed by default. The
+\fBFILE_NOFOLLOW\fR needs to be passed in along with the specified events if
+the symbolic link itself needs to be watched and \fBlstat()\fR needs to be
+used to get the file status of the symbolic link file.
 .sp
 .LP
 The \fBstruct file_obj\fR contains the following elements:
 .sp
 .in +2
 .nf
-timestruc_t     fo_atime;  /* Access time got from stat() */
+timestruc_t     fo_atime;  /* Access time from stat() */
 timestruc_t     fo_mtime;  /* Modification time from stat() */
 timestruc_t     fo_ctime;  /* Change time from stat() */
 char            *fo_name;  /* Pointer to a null terminated path name */
@@ -104,11 +104,13 @@ occurs.
 .sp
 .LP
 The event types that can be specified at \fBport_associate()\fR time for
-\fBPORT_SOURCE_FILE\fR are \fBFILE_ACCESS\fR, \fBFILE_MODIFIED\fR, and
-\fBFILE_ATTRIB\fR, corresponding to the three time stamps. An \fBfo_atime\fR
-change results in the \fBFILE_ACCESS\fR event, an \fBfo_mtime\fR change results
-in the \fBFILE_MODIFIED\fR event, and an \fBfo_time\fR change results in the
-\fBFILE_ATTRIB\fR event.
+\fBPORT_SOURCE_FILE\fR are \fBFILE_ACCESS\fR, \fBFILE_MODIFIED\fR,
+\fBFILE_ATTRIB\fR, and \fbFILE_TRUNC\fR. The first three of these correspond
+to the three time stamps: an \fBfo_atime\fR change results in the
+\fBFILE_ACCESS\fR event, an \fBfo_mtime\fR change results in the
+\fBFILE_MODIFIED\fR event, and an \fBfo_ctime\fR change results in the
+\fBFILE_ATTRIB\fR event. If the operation that induced the time stamp update
+also truncated the file, \fBFILE_TRUNC\fR will be set in the resulting event.
 .sp
 .LP
 The following exception events are delivered when they occur. These event types
diff --git a/usr/src/uts/common/fs/nfs/nfs3_vnops.c b/usr/src/uts/common/fs/nfs/nfs3_vnops.c
index d31b53d2e9..fd1595b9f5 100644
--- a/usr/src/uts/common/fs/nfs/nfs3_vnops.c
+++ b/usr/src/uts/common/fs/nfs/nfs3_vnops.c
@@ -28,6 +28,10 @@
  *	All rights reserved.
  */
 
+/*
+ * Copyright (c) 2013, Joyent, Inc. All rights reserved.
+ */
+
 #include <sys/param.h>
 #include <sys/types.h>
 #include <sys/systm.h>
@@ -1327,7 +1331,12 @@ nfs3_setattr(vnode_t *vp, struct vattr *vap, int flags, cred_t *cr,
 	if (error)
 		return (error);
 
-	return (nfs3setattr(vp, vap, flags, cr));
+	error = nfs3setattr(vp, vap, flags, cr);
+
+	if (error == 0 && (vap->va_mask & AT_SIZE) && vap->va_size == 0)
+		vnevent_truncate(vp, ct);
+
+	return (error);
 }
 
 static int
@@ -2298,6 +2307,12 @@ top:
 						vattr.va_mask = AT_SIZE;
 						error = nfs3setattr(vp,
 						    &vattr, 0, cr);
+
+						/*
+						 * Existing file was truncated;
+						 * emit a create event.
+						 */
+						vnevent_create(vp, ct);
 					}
 				}
 			}
@@ -2306,12 +2321,9 @@ top:
 		if (error) {
 			VN_RELE(vp);
 		} else {
-			/*
-			 * existing file got truncated, notify.
-			 */
-			vnevent_create(vp, ct);
 			*vpp = vp;
 		}
+
 		return (error);
 	}
 
@@ -5514,6 +5526,9 @@ nfs3_space(vnode_t *vp, int cmd, struct flock64 *bfp, int flag,
 			va.va_mask = AT_SIZE;
 			va.va_size = bfp->l_start;
 			error = nfs3setattr(vp, &va, 0, cr);
+
+			if (error == 0 && bfp->l_start == 0)
+				vnevent_truncate(vp, ct);
 		} else
 			error = EINVAL;
 	}
diff --git a/usr/src/uts/common/fs/nfs/nfs4_vnops.c b/usr/src/uts/common/fs/nfs/nfs4_vnops.c
index 5ae2c28d53..0c97fcc176 100644
--- a/usr/src/uts/common/fs/nfs/nfs4_vnops.c
+++ b/usr/src/uts/common/fs/nfs/nfs4_vnops.c
@@ -31,6 +31,10 @@
  *	All Rights Reserved
  */
 
+/*
+ * Copyright (c) 2013, Joyent, Inc. All rights reserved.
+ */
+
 #include <sys/param.h>
 #include <sys/types.h>
 #include <sys/systm.h>
@@ -3712,6 +3716,8 @@ static int
 nfs4_setattr(vnode_t *vp, struct vattr *vap, int flags, cred_t *cr,
     caller_context_t *ct)
 {
+	int error;
+
 	if (vap->va_mask & AT_NOSET)
 		return (EINVAL);
 
@@ -3727,8 +3733,12 @@ nfs4_setattr(vnode_t *vp, struct vattr *vap, int flags, cred_t *cr,
 	 * to setattr (e.g. basic without chmod) then we will
 	 * need to add a check here before calling the server.
 	 */
+	error = nfs4setattr(vp, vap, flags, cr, NULL);
 
-	return (nfs4setattr(vp, vap, flags, cr, NULL));
+	if (error == 0 && (vap->va_mask & AT_SIZE) && vap->va_size == 0)
+		vnevent_truncate(vp, ct);
+
+	return (error);
 }
 
 /*
@@ -6653,16 +6663,20 @@ top:
 	} else {
 		vnode_t *tvp;
 		rnode4_t *trp;
-		/*
-		 * existing file got truncated, notify.
-		 */
 		tvp = vp;
 		if (vp->v_type == VREG) {
 			trp = VTOR4(vp);
 			if (IS_SHADOW(vp, trp))
 				tvp = RTOV4(trp);
 		}
-		vnevent_create(tvp, ct);
+
+		if (must_trunc) {
+			/*
+			 * existing file got truncated, notify.
+			 */
+			vnevent_create(tvp, ct);
+		}
+
 		*vpp = vp;
 	}
 	return (error);
@@ -10991,6 +11005,9 @@ nfs4_space(vnode_t *vp, int cmd, struct flock64 *bfp, int flag,
 			va.va_mask = AT_SIZE;
 			va.va_size = bfp->l_start;
 			error = nfs4setattr(vp, &va, 0, cr, NULL);
+
+			if (error == 0 && bfp->l_start == 0)
+				vnevent_truncate(vp, ct);
 		} else
 			error = EINVAL;
 	}
diff --git a/usr/src/uts/common/fs/nfs/nfs_vnops.c b/usr/src/uts/common/fs/nfs/nfs_vnops.c
index a3f43a4e95..df128f4bc6 100644
--- a/usr/src/uts/common/fs/nfs/nfs_vnops.c
+++ b/usr/src/uts/common/fs/nfs/nfs_vnops.c
@@ -25,6 +25,10 @@
  *	All rights reserved.
  */
 
+/*
+ * Copyright (c) 2013, Joyent, Inc. All rights reserved.
+ */
+
 #include <sys/param.h>
 #include <sys/types.h>
 #include <sys/systm.h>
@@ -1167,7 +1171,12 @@ nfs_setattr(vnode_t *vp, struct vattr *vap, int flags, cred_t *cr,
 	if (error)
 		return (error);
 
-	return (nfssetattr(vp, vap, flags, cr));
+	error = nfssetattr(vp, vap, flags, cr);
+
+	if (error == 0 && (mask & AT_SIZE) && vap->va_size == 0)
+		vnevent_truncate(vp, ct);
+
+	return (error);
 }
 
 static int
@@ -2030,6 +2039,14 @@ nfs_create(vnode_t *dvp, char *nm, struct vattr *va, enum vcexcl exclusive,
 				    vp->v_type == VREG) {
 					vattr.va_mask = AT_SIZE;
 					error = nfssetattr(vp, &vattr, 0, cr);
+
+					if (!error) {
+						/*
+						 * Existing file was truncated;
+						 * emit a create event.
+						 */
+						vnevent_create(vp, ct);
+					}
 				}
 			}
 		}
@@ -2037,10 +2054,6 @@ nfs_create(vnode_t *dvp, char *nm, struct vattr *va, enum vcexcl exclusive,
 		if (error) {
 			VN_RELE(vp);
 		} else {
-			/*
-			 * existing file got truncated, notify.
-			 */
-			vnevent_create(vp, ct);
 			*vpp = vp;
 		}
 		return (error);
@@ -4610,6 +4623,9 @@ nfs_space(vnode_t *vp, int cmd, struct flock64 *bfp, int flag,
 			va.va_mask = AT_SIZE;
 			va.va_size = bfp->l_start;
 			error = nfssetattr(vp, &va, 0, cr);
+
+			if (error == 0 && bfp->l_start == 0)
+				vnevent_truncate(vp, ct);
 		} else
 			error = EINVAL;
 	}
diff --git a/usr/src/uts/common/fs/pcfs/pc_vnops.c b/usr/src/uts/common/fs/pcfs/pc_vnops.c
index ce9711140b..e2c6f3a371 100644
--- a/usr/src/uts/common/fs/pcfs/pc_vnops.c
+++ b/usr/src/uts/common/fs/pcfs/pc_vnops.c
@@ -24,6 +24,10 @@
  * Use is subject to license terms.
  */
 
+/*
+ * Copyright (c) 2013, Joyent, Inc. All rights reserved.
+ */
+
 #include <sys/param.h>
 #include <sys/t_lock.h>
 #include <sys/systm.h>
@@ -772,8 +776,12 @@ pcfs_setattr(
 			goto out;
 		}
 		error = pc_truncate(pcp, (uint_t)vap->va_size);
+
 		if (error)
 			goto out;
+
+		if (vap->va_size == 0)
+			vnevent_truncate(vp, ct);
 	}
 	/*
 	 * Change file modified times.
diff --git a/usr/src/uts/common/fs/portfs/port_fop.c b/usr/src/uts/common/fs/portfs/port_fop.c
index 2852a98f52..03a03dd2a6 100644
--- a/usr/src/uts/common/fs/portfs/port_fop.c
+++ b/usr/src/uts/common/fs/portfs/port_fop.c
@@ -23,6 +23,9 @@
  * Use is subject to license terms.
  */
 
+/*
+ * Copyright (c) 2013, Joyent, Inc. All rights reserved.
+ */
 
 /*
  * File Events Notification
@@ -1256,7 +1259,7 @@ port_associate_fop(port_t *pp, int source, uintptr_t object, int events,
     void *user)
 {
 	portfop_cache_t	*pfcp;
-	vnode_t		*vp, *dvp, *oldvp = NULL, *olddvp = NULL;
+	vnode_t		*vp, *dvp, *oldvp = NULL, *olddvp = NULL, *orig;
 	portfop_t	*pfp;
 	int		error = 0;
 	file_obj_t	fobj;
@@ -1313,8 +1316,7 @@ port_associate_fop(port_t *pp, int source, uintptr_t object, int events,
 		goto errout;
 	}
 
-	vp = port_resolve_vp(vp);
-
+	vp = port_resolve_vp(orig = vp);
 
 	if (vp != NULL && vnevent_support(vp, NULL)) {
 		error = ENOTSUP;
@@ -1322,10 +1324,14 @@ port_associate_fop(port_t *pp, int source, uintptr_t object, int events,
 	}
 
 	/*
-	 * If dvp belongs to a different filesystem just ignore it.
-	 * Hardlinks cannot exist across filesystems.
+	 * If dvp belongs to a different filesystem just ignore it, as hard
+	 * links cannot exist across filesystems.  We make an exception for
+	 * procfs, however, the magic of which we treat semantically as a hard
+	 * link, allowing one to use /proc/[pid]/fd/[fd] for PORT_SOURCE_FILE
+	 * and avoid spurious FILE_RENAME_FROM/FILE_RENAME_TO events.
 	 */
-	if (dvp != NULL && dvp->v_vfsp != vp->v_vfsp) {
+	if (dvp != NULL && dvp->v_vfsp != vp->v_vfsp &&
+	    !(orig->v_type == VPROC && vp != NULL && vp->v_type != VPROC)) {
 		VN_RELE(dvp);
 		dvp = NULL;
 	}
@@ -1822,12 +1828,19 @@ port_fop_sendevent(vnode_t *vp, int events, vnode_t *dvp, char *cname)
 	if (!removeall) {
 		/*
 		 * All the active ones are in the beginning of the list.
+		 * Note that we process this list in reverse order to assure
+		 * that events are delivered in the order that they were
+		 * associated.
 		 */
-		for (pfp = (portfop_t *)list_head(&pvp->pvp_pfoplist);
-		    pfp && pfp->pfop_flags & PORT_FOP_ACTIVE; pfp = npfp) {
+		for (pfp = (portfop_t *)list_tail(&pvp->pvp_pfoplist);
+		    pfp && !(pfp->pfop_flags & PORT_FOP_ACTIVE); pfp = npfp) {
+			npfp = list_prev(&pvp->pvp_pfoplist, pfp);
+		}
+
+		for (; pfp != NULL; pfp = npfp) {
 			int levents = events;
 
-			npfp = list_next(&pvp->pvp_pfoplist, pfp);
+			npfp = list_prev(&pvp->pvp_pfoplist, pfp);
 			/*
 			 * Hard links case - If the file is being
 			 * removed/renamed, and the name matches
@@ -1965,7 +1978,9 @@ port_fop(vnode_t *vp, int op, int retval)
 	if (op & FOP_ATTRIB_MASK) {
 		event  |= FILE_ATTRIB;
 	}
-
+	if (op & FOP_TRUNC_MASK) {
+		event  |= FILE_TRUNC;
+	}
 	if (event) {
 		port_fop_sendevent(vp, 	event, NULL, NULL);
 	}
@@ -2147,6 +2162,9 @@ port_fop_setattr(femarg_t *vf, vattr_t *vap, int flags, cred_t *cr,
 	int		events = 0;
 
 	retval = vnext_setattr(vf, vap, flags, cr, ct);
+	if (vap->va_mask & AT_SIZE) {
+		events |= FOP_FILE_TRUNC;
+	}
 	if (vap->va_mask & (AT_SIZE|AT_MTIME)) {
 		events |= FOP_FILE_SETATTR_MTIME;
 	}
@@ -2322,8 +2340,8 @@ port_fop_vnevent(femarg_t *vf, vnevent_t vnevent, vnode_t *dvp, char *name,
 			port_fop_sendevent(vp, FILE_DELETE, dvp, name);
 		break;
 	case	VE_CREATE:
-			port_fop_sendevent(vp, FILE_MODIFIED|FILE_ATTRIB,
-			    NULL, NULL);
+			port_fop_sendevent(vp,
+			    FILE_MODIFIED|FILE_ATTRIB|FILE_TRUNC, NULL, NULL);
 		break;
 	case	VE_LINK:
 			port_fop_sendevent(vp, FILE_ATTRIB, NULL, NULL);
@@ -2337,6 +2355,9 @@ port_fop_vnevent(femarg_t *vf, vnevent_t vnevent, vnode_t *dvp, char *name,
 	case	VE_MOUNTEDOVER:
 			port_fop_sendevent(vp, MOUNTEDOVER, NULL, NULL);
 		break;
+	case	VE_TRUNCATE:
+			port_fop_sendevent(vp, FILE_TRUNC, NULL, NULL);
+		break;
 	default:
 		break;
 	}
diff --git a/usr/src/uts/common/fs/tmpfs/tmp_vnops.c b/usr/src/uts/common/fs/tmpfs/tmp_vnops.c
index 61d72a4015..e44bba1252 100644
--- a/usr/src/uts/common/fs/tmpfs/tmp_vnops.c
+++ b/usr/src/uts/common/fs/tmpfs/tmp_vnops.c
@@ -24,6 +24,10 @@
  * Use is subject to license terms.
  */
 
+/*
+ * Copyright (c) 2012, Joyent, Inc. All rights reserved.
+ */
+
 #include <sys/types.h>
 #include <sys/param.h>
 #include <sys/t_lock.h>
@@ -780,6 +784,10 @@ tmp_setattr(
 		error = tmpnode_trunc(tm, tp, (ulong_t)vap->va_size);
 		rw_exit(&tp->tn_contents);
 		rw_exit(&tp->tn_rwlock);
+
+		if (error == 0 && vap->va_size == 0)
+			vnevent_truncate(vp, ct);
+
 		goto out1;
 	}
 out:
@@ -978,6 +986,8 @@ again:
 	}
 
 	if (error == 0) {	/* name found */
+		boolean_t trunc = B_FALSE;
+
 		ASSERT(oldtp);
 
 		rw_enter(&oldtp->tn_rwlock, RW_WRITER);
@@ -1005,6 +1015,7 @@ again:
 			rw_enter(&oldtp->tn_contents, RW_WRITER);
 			(void) tmpnode_trunc(tm, oldtp, 0);
 			rw_exit(&oldtp->tn_contents);
+			trunc = B_TRUE;
 		}
 		rw_exit(&oldtp->tn_rwlock);
 		if (IS_DEVVP(*vpp)) {
@@ -1019,9 +1030,9 @@ again:
 			*vpp = newvp;
 		}
 
-		if (error == 0) {
+		if (trunc)
 			vnevent_create(*vpp, ct);
-		}
+
 		return (0);
 	}
 
@@ -2318,6 +2329,9 @@ tmp_space(
 		if ((bfp->l_start > MAXOFF_T) || (bfp->l_len > MAXOFF_T))
 			return (EFBIG);
 		error = tmp_freesp(vp, bfp, flag);
+
+		if (error == 0 && bfp->l_start == 0)
+			vnevent_truncate(vp, ct);
 	}
 	return (error);
 }
diff --git a/usr/src/uts/common/fs/udfs/udf_vnops.c b/usr/src/uts/common/fs/udfs/udf_vnops.c
index 90ad1b8d48..307d3987ed 100644
--- a/usr/src/uts/common/fs/udfs/udf_vnops.c
+++ b/usr/src/uts/common/fs/udfs/udf_vnops.c
@@ -23,6 +23,10 @@
  * Copyright (c) 1998, 2010, Oracle and/or its affiliates. All rights reserved.
  */
 
+/*
+ * Copyright (c) 2013, Joyent, Inc. All rights reserved.
+ */
+
 #include <sys/types.h>
 #include <sys/t_lock.h>
 #include <sys/param.h>
@@ -564,6 +568,9 @@ udf_setattr(
 		if (error = ud_itrunc(ip, vap->va_size, 0, cr)) {
 			goto update_inode;
 		}
+
+		if (vap->va_size == 0)
+			vnevent_truncate(vp, ct);
 	}
 	/*
 	 * Change file access or modified times.
@@ -1621,6 +1628,9 @@ udf_space(
 		error =  EINVAL;
 	} else if ((error = convoff(vp, bfp, 0, offset)) == 0) {
 		error = ud_freesp(vp, bfp, flag, cr);
+
+		if (error == 0 && bfp->l_start == 0)
+			vnevent_truncate(vp, ct);
 	}
 
 	return (error);
diff --git a/usr/src/uts/common/fs/ufs/ufs_vnops.c b/usr/src/uts/common/fs/ufs/ufs_vnops.c
index e210339dfb..92bdb0d0a7 100644
--- a/usr/src/uts/common/fs/ufs/ufs_vnops.c
+++ b/usr/src/uts/common/fs/ufs/ufs_vnops.c
@@ -21,6 +21,7 @@
 
 /*
  * Copyright (c) 1984, 2010, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2013, Joyent, Inc. All rights reserved.
  */
 
 /*	Copyright (c) 1983, 1984, 1985, 1986, 1987, 1988, 1989 AT&T	*/
@@ -2191,6 +2192,9 @@ again:
 			rw_enter(&ip->i_contents, RW_WRITER);
 			goto update_inode;
 		}
+
+		if (error == 0 && vap->va_size)
+			vnevent_truncate(vp, ct);
 	}
 
 	if (ulp) {
@@ -4460,6 +4464,9 @@ ufs_space(struct vnode *vp, int cmd, struct flock64 *bfp, int flag,
 			if (error)
 				return (error);
 			error = ufs_freesp(vp, bfp, flag, cr);
+
+			if (error == 0 && bfp->l_start == 0)
+				vnevent_truncate(vp, ct);
 		} else if (cmd == F_ALLOCSP) {
 			error = ufs_lockfs_begin(ufsvfsp, &ulp,
 			    ULOCKFS_FALLOCATE_MASK);
diff --git a/usr/src/uts/common/fs/vnode.c b/usr/src/uts/common/fs/vnode.c
index 382369c7fc..d67d164286 100644
--- a/usr/src/uts/common/fs/vnode.c
+++ b/usr/src/uts/common/fs/vnode.c
@@ -21,6 +21,7 @@
 
 /*
  * Copyright (c) 1988, 2010, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2013, Joyent, Inc. All rights reserved.
  */
 
 /*	Copyright (c) 1983, 1984, 1985, 1986, 1987, 1988, 1989 AT&T	*/
@@ -2582,6 +2583,15 @@ vnevent_mountedover(vnode_t *vp, caller_context_t *ct)
 	(void) VOP_VNEVENT(vp, VE_MOUNTEDOVER, NULL, NULL, ct);
 }
 
+void
+vnevent_truncate(vnode_t *vp, caller_context_t *ct)
+{
+	if (vp == NULL || vp->v_femhead == NULL) {
+		return;
+	}
+	(void) VOP_VNEVENT(vp, VE_TRUNCATE, NULL, NULL, ct);
+}
+
 /*
  * Vnode accessors.
  */
diff --git a/usr/src/uts/common/fs/zfs/zfs_vnops.c b/usr/src/uts/common/fs/zfs/zfs_vnops.c
index 6fa1d83700..78e2a8cce5 100644
--- a/usr/src/uts/common/fs/zfs/zfs_vnops.c
+++ b/usr/src/uts/common/fs/zfs/zfs_vnops.c
@@ -2756,6 +2756,9 @@ top:
 			ZFS_EXIT(zfsvfs);
 			return (err);
 		}
+
+		if (vap->va_size == 0)
+			vnevent_truncate(ZTOV(zp), ct);
 	}
 
 	if (mask & (AT_ATIME|AT_MTIME) ||
@@ -4770,6 +4773,9 @@ zfs_space(vnode_t *vp, int cmd, flock64_t *bfp, int flag,
 
 	error = zfs_freesp(zp, off, len, flag, TRUE);
 
+	if (error == 0 && off == 0 && len == 0)
+		vnevent_truncate(ZTOV(zp), ct);
+
 	ZFS_EXIT(zfsvfs);
 	return (error);
 }
diff --git a/usr/src/uts/common/sys/port.h b/usr/src/uts/common/sys/port.h
index ccb0308255..d4d74d55ea 100644
--- a/usr/src/uts/common/sys/port.h
+++ b/usr/src/uts/common/sys/port.h
@@ -24,11 +24,13 @@
  * Use is subject to license terms.
  */
 
+/*
+ * Copyright (c) 2012, Joyent, Inc. All rights reserved.
+ */
+
 #ifndef	_SYS_PORT_H
 #define	_SYS_PORT_H
 
-#pragma ident	"%Z%%M%	%I%	%E% SMI"
-
 #ifdef	__cplusplus
 extern "C" {
 #endif
@@ -106,6 +108,7 @@ typedef	struct	port_notify32 {
 #define	FILE_ACCESS		0x00000001
 #define	FILE_MODIFIED		0x00000002
 #define	FILE_ATTRIB		0x00000004
+#define	FILE_TRUNC		0x00100000
 #define	FILE_NOFOLLOW		0x10000000
 
 /*
diff --git a/usr/src/uts/common/sys/port_impl.h b/usr/src/uts/common/sys/port_impl.h
index 9f3f291874..504fb9ece1 100644
--- a/usr/src/uts/common/sys/port_impl.h
+++ b/usr/src/uts/common/sys/port_impl.h
@@ -24,6 +24,10 @@
  * Use is subject to license terms.
  */
 
+/*
+ * Copyright (c) 2012, Joyent, Inc. All rights reserved.
+ */
+
 #ifndef	_SYS_PORT_IMPL_H
 #define	_SYS_PORT_IMPL_H
 
@@ -311,6 +315,7 @@ typedef struct portfop_vp {
 #define	FOP_FILE_SETATTR_MTIME	0x00080000
 #define	FOP_FILE_SETATTR_CTIME	0x00100000
 #define	FOP_FILE_LINK_SRC	0x00200000
+#define	FOP_FILE_TRUNC		0x00400000
 
 /*
  * File modification event.
@@ -339,10 +344,15 @@ typedef struct portfop_vp {
 
 
 /*
+ * File trunc event
+ */
+#define	FOP_TRUNC_MASK		(FOP_FILE_TRUNC|FOP_FILE_CREATE)
+
+/*
  * valid watchable events
  */
 #define	FILE_EVENTS_MASK	(FILE_ACCESS|FILE_MODIFIED|FILE_ATTRIB \
-				|FILE_NOFOLLOW)
+				|FILE_NOFOLLOW|FILE_TRUNC)
 /* --- End file events --- */
 
 /*
diff --git a/usr/src/uts/common/sys/vnode.h b/usr/src/uts/common/sys/vnode.h
index d29152346e..af9516fe52 100644
--- a/usr/src/uts/common/sys/vnode.h
+++ b/usr/src/uts/common/sys/vnode.h
@@ -21,6 +21,7 @@
 
 /*
  * Copyright (c) 1988, 2010, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2013, Joyent, Inc. All rights reserved.
  */
 
 /*	Copyright (c) 1983, 1984, 1985, 1986, 1987, 1988, 1989 AT&T	*/
@@ -733,7 +734,8 @@ typedef enum vnevent	{
 	VE_CREATE	= 5,	/* Create with vnode's name which exists */
 	VE_LINK		= 6, 	/* Link with vnode's name as source */
 	VE_RENAME_DEST_DIR	= 7, 	/* Rename with vnode as target dir */
-	VE_MOUNTEDOVER	= 8 	/* File or Filesystem got mounted over vnode */
+	VE_MOUNTEDOVER	= 8, 	/* File or Filesystem got mounted over vnode */
+	VE_TRUNCATE = 9		/* Truncate */
 } vnevent_t;
 
 /*
@@ -1290,6 +1292,7 @@ void	vnevent_create(vnode_t *, caller_context_t *);
 void	vnevent_link(vnode_t *, caller_context_t *);
 void	vnevent_rename_dest_dir(vnode_t *, caller_context_t *ct);
 void	vnevent_mountedover(vnode_t *, caller_context_t *);
+void	vnevent_truncate(vnode_t *, caller_context_t *);
 int	vnevent_support(vnode_t *, caller_context_t *);
 
 /* Vnode specific data */