2 files changed, 35 insertions, 6 deletions

diff --git a/sbin/dumpon/dumpon.8 b/sbin/dumpon/dumpon.8
index b0c8e2c12de4..572bd030aef1 100644
--- a/sbin/dumpon/dumpon.8
+++ b/sbin/dumpon/dumpon.8
@@ -28,7 +28,7 @@
 .\"     From: @(#)swapon.8	8.1 (Berkeley) 6/5/93
 .\" $FreeBSD$
 .\"
-.Dd December 10, 2016
+.Dd October 24, 2017
 .Dt DUMPON 8
 .Os
 .Sh NAME
@@ -38,6 +38,7 @@
 .Nm
 .Op Fl v
 .Op Fl k Ar public_key_file
+.Op Fl z
 .Ar special_file
 .Nm
 .Op Fl v
@@ -114,6 +115,22 @@ This flag requires a kernel compiled with the
 kernel option.
 .Pp
 The
+.Fl z
+option configures the kernel to compress the dump in gzip format before writing
+it to the dump device.
+This reduces the amount of space required for the dump and accelerates
+recovery with
+.Xr savecore 8
+since less data needs to be copied from the dump device.
+When compression is enabled, the
+.Nm
+utility will not verify that the dump device is sufficiently large for a full
+dump.
+This flag requires a kernel compiled with the
+.Dv GZIO
+kernel option.
+.Pp
+The
 .Fl l
 flag causes
 .Nm
@@ -272,3 +289,7 @@ utility appeared in
 .Sh BUGS
 Because the file system layer is already dead by the time a crash dump
 is taken, it is not possible to send crash dumps directly to a file.
+.Pp
+It is currently not possible to configure both compression and encryption.
+The encrypted dump format assumes that the kernel dump size is a multiple
+of the cipher block size, which may not be true when the dump is compressed.
diff --git a/sbin/dumpon/dumpon.c b/sbin/dumpon/dumpon.c
index e3701eace3db..8530c63b889d 100644
--- a/sbin/dumpon/dumpon.c
+++ b/sbin/dumpon/dumpon.c
@@ -71,7 +71,7 @@ static void
 usage(void)
 {
 	fprintf(stderr, "%s\n%s\n%s\n",
-	    "usage: dumpon [-v] [-k public_key_file] special_file",
+	    "usage: dumpon [-v] [-k public_key_file] [-z] special_file",
 	    "       dumpon [-v] off",
 	    "       dumpon [-v] -l");
 	exit(EX_USAGE);
@@ -190,11 +190,12 @@ main(int argc, char *argv[])
 	int ch;
 	int i, fd;
 	int do_listdumpdev = 0;
-	bool enable;
+	bool enable, gzip;
 
+	gzip = false;
 	pubkeyfile = NULL;
 
-	while ((ch = getopt(argc, argv, "k:lv")) != -1)
+	while ((ch = getopt(argc, argv, "k:lvz")) != -1)
 		switch((char)ch) {
 		case 'k':
 			pubkeyfile = optarg;
@@ -205,6 +206,9 @@ main(int argc, char *argv[])
 		case 'v':
 			verbose = 1;
 			break;
+		case 'z':
+			gzip = true;
+			break;
 		default:
 			usage();
 		}
@@ -247,9 +251,11 @@ main(int argc, char *argv[])
 		fd = open(dumpdev, O_RDONLY);
 		if (fd < 0)
 			err(EX_OSFILE, "%s", dumpdev);
-		check_size(fd, dumpdev);
-		bzero(&kda, sizeof(kda));
 
+		if (!gzip)
+			check_size(fd, dumpdev);
+
+		bzero(&kda, sizeof(kda));
 		kda.kda_enable = 0;
 		i = ioctl(fd, DIOCSKERNELDUMP, &kda);
 		explicit_bzero(&kda, sizeof(kda));
@@ -260,6 +266,8 @@ main(int argc, char *argv[])
 #endif
 
 		kda.kda_enable = 1;
+		kda.kda_compression = gzip ? KERNELDUMP_COMP_GZIP :
+		    KERNELDUMP_COMP_NONE;
 		i = ioctl(fd, DIOCSKERNELDUMP, &kda);
 		explicit_bzero(kda.kda_encryptedkey, kda.kda_encryptedkeysize);
 		free(kda.kda_encryptedkey);