svn commit: r339620 - head/usr.bin/ktrdump

[John Baldwin]

Author: jhb
Date: Mon Oct 22 21:25:28 2018
New Revision: 339620
URL: https://svnweb.freebsd.org/changeset/base/339620

Log:
  Add a "live" mode to ktrdump.
  
  Support a "live" mode in ktrdump enabled via the -l flag.  In this
  mode, ktrdump polls the kernel's trace buffer periodically (currently
  hardcoded as a 50 millisecond interval) and dumps any newly added
  entries.  Fancier logic for the timeout (e.g. a command line option or
  some kind of backoff based on the time since the last entry) can be
  added later as the need arises.
  
  While here, fix some bugs from when this was Capsicum-ized:
  - Use caph_limit_stream() for the output stream so that isatty() works
    and the output can be line-buffered (especially useful for live
    mode).
  - Use caph_limit_stderr() to permit error messages to be displayed if
    an error occurs after cap_enter().
  
  Reviewed by:	kib, 0mp (manpage)
  MFC after:	2 months
  Differential Revision:	https://reviews.freebsd.org/D17315

Modified:
  head/usr.bin/ktrdump/ktrdump.8
  head/usr.bin/ktrdump/ktrdump.c

Modified: head/usr.bin/ktrdump/ktrdump.8
==============================================================================
--- head/usr.bin/ktrdump/ktrdump.8	Mon Oct 22 21:17:36 2018	(r339619)
+++ head/usr.bin/ktrdump/ktrdump.8	Mon Oct 22 21:25:28 2018	(r339620)
@@ -25,7 +25,7 @@
 .\"
 .\" $FreeBSD$
 .\"
-.Dd February 6, 2015
+.Dd October 22, 2018
 .Dt KTRDUMP 8
 .Os
 .Sh NAME
@@ -33,7 +33,7 @@
 .Nd print kernel ktr trace buffer
 .Sh SYNOPSIS
 .Nm
-.Op Fl cfqrtH
+.Op Fl cflqrtH
 .Op Fl i Ar ktrfile
 .Op Fl M Ar core
 .Op Fl N Ar system
@@ -47,6 +47,9 @@ The following options are available:
 .Bl -tag -width ".Fl i Ar ktrfile"
 .It Fl c
 Print the CPU number that each entry was logged from.
+.It Fl l
+Poll the kernel ktr trace buffer periodically dumping any new events after
+each poll.
 .It Fl f
 Print the file and line number that each entry was logged from.
 .It Fl q

Modified: head/usr.bin/ktrdump/ktrdump.c
==============================================================================
--- head/usr.bin/ktrdump/ktrdump.c	Mon Oct 22 21:17:36 2018	(r339619)
+++ head/usr.bin/ktrdump/ktrdump.c	Mon Oct 22 21:25:28 2018	(r339620)
@@ -51,7 +51,7 @@ __FBSDID("$FreeBSD$");
 
 #define	SBUFLEN	128
 #define	USAGE \
-	"usage: ktrdump [-cfqrtH] [-i ktrfile] [-M core] [-N system] [-o outfile]\n"
+	"usage: ktrdump [-cflqrtH] [-i ktrfile] [-M core] [-N system] [-o outfile]\n"
 
 static void usage(void);
 
@@ -65,6 +65,7 @@ static struct nlist nl[] = {
 
 static int cflag;
 static int fflag;
+static int lflag;
 static int Mflag;
 static int Nflag;
 static int qflag;
@@ -111,7 +112,7 @@ main(int ac, char **av)
 	 * Parse commandline arguments.
 	 */
 	out = stdout;
-	while ((c = getopt(ac, av, "cfqrtHe:i:m:M:N:o:")) != -1)
+	while ((c = getopt(ac, av, "cflqrtHe:i:m:M:N:o:")) != -1)
 		switch (c) {
 		case 'c':
 			cflag = 1;
@@ -136,6 +137,9 @@ main(int ac, char **av)
 				err(1, "unable to limit rights for %s",
 				    optarg);
 			break;
+		case 'l':
+			lflag = 1;
+			break;
 		case 'M':
 		case 'm':
 			if (strlcpy(corefile, optarg, sizeof(corefile))
@@ -169,9 +173,10 @@ main(int ac, char **av)
 	if (ac != 0)
 		usage();
 
-	cap_rights_init(&rights, CAP_FSTAT, CAP_WRITE);
-	if (cap_rights_limit(fileno(out), &rights) < 0 && errno != ENOSYS)
+	if (caph_limit_stream(fileno(out), CAPH_WRITE) < 0)
 		err(1, "unable to limit rights for %s", outfile);
+	if (caph_limit_stderr() < 0)
+		err(1, "unable to limit rights for stderr");
 
 	/*
 	 * Open our execfile and corefile, resolve needed symbols and read in
@@ -258,15 +263,29 @@ main(int ac, char **av)
 		fprintf(out, "\n");
 	}
 
+	tlast = -1;
 	/*
 	 * Now tear through the trace buffer.
+	 *
+	 * In "live" mode, find the oldest entry (first non-NULL entry
+	 * after index2) and walk forward.  Otherwise, start with the
+	 * most recent entry and walk backwards.
 	 */
 	if (!iflag) {
-		i = index - 1;
-		if (i < 0)
-			i = entries - 1;
+		if (lflag) {
+			i = index2 + 1 % entries;
+			while (buf[i].ktr_desc == NULL && i != index) {
+				i++;
+				if (i == entries)
+					i = 0;
+			}
+		} else {
+			i = index - 1;
+			if (i < 0)
+				i = entries - 1;
+		}
 	}
-	tlast = -1;
+dump_entries:
 	for (;;) {
 		if (buf[i].ktr_desc == NULL)
 			break;
@@ -338,14 +357,40 @@ next:			if ((c = *p++) == '\0')
 			 * 'index2' were in flux while the KTR buffer was
 			 * being copied to userspace we don't dump them.
 			 */
-			if (i == index2)
-				break;
-			if (--i < 0)
-				i = entries - 1;
+			if (lflag) {
+				if (++i == entries)
+					i = 0;
+				if (i == index)
+					break;
+			} else {
+				if (i == index2)
+					break;
+				if (--i < 0)
+					i = entries - 1;
+			}
 		} else {
 			if (++i == entries)
 				break;
 		}
+	}
+
+	/*
+	 * In "live" mode, poll 'ktr_idx' periodically and dump any
+	 * new entries since our last pass through the ring.
+	 */
+	if (lflag && !iflag) {
+		while (index == index2) {
+			usleep(50 * 1000);
+			if (kvm_read(kd, nl[2].n_value, &index2,
+			    sizeof(index2)) == -1)
+				errx(1, "%s", kvm_geterr(kd));
+		}
+		i = index;
+		index = index2;
+		if (kvm_read(kd, bufptr, buf, sizeof(*buf) * entries) == -1 ||
+		    kvm_read(kd, nl[2].n_value, &index2, sizeof(index2)) == -1)
+			errx(1, "%s", kvm_geterr(kd));
+		goto dump_entries;
 	}
 
 	return (0);