cmd/zgenhostid: replace with simple c implementation

It was discovered that dracut scripts and zgenhostid
always generate little-endian /etc/hostid.

This commit provides simple endianess-aware binary
and updates the scripts to use it.

New features include:
 -f flag to force overwrite.
 -o flag to write to different file (for dracut)
 accepting both 0x01234567 and 01234567 values as input

Reviewed-by: Brian Behlendorf <[email protected]>
Reviewed-by: Olaf Faaland <[email protected]>
Signed-off-by: Georgy Yakovlev <[email protected]>
Closes #10887 
Closes #10925 

4 files changed, 158 insertions, 62 deletions

diff --git a/cmd/zgenhostid/.gitignore b/cmd/zgenhostid/.gitignore
new file mode 100644
index 000000000..072246c73
--- /dev/null
+++ b/cmd/zgenhostid/.gitignore
@@ -0,0 +1 @@
+/zgenhostid
diff --git a/cmd/zgenhostid/Makefile.am b/cmd/zgenhostid/Makefile.am
index 69c99ca9d..0ba791f7c 100644
--- a/cmd/zgenhostid/Makefile.am
+++ b/cmd/zgenhostid/Makefile.am
@@ -1 +1,5 @@
-dist_bin_SCRIPTS = zgenhostid
+include $(top_srcdir)/config/Rules.am
+
+bin_PROGRAMS = zgenhostid
+
+zgenhostid_SOURCES = zgenhostid.c
diff --git a/cmd/zgenhostid/zgenhostid b/cmd/zgenhostid/zgenhostid
deleted file mode 100755
index 8b468740c..000000000
--- a/cmd/zgenhostid/zgenhostid
+++ /dev/null
@@ -1,61 +0,0 @@
-#!/usr/bin/env bash
-
-# Emulate genhostid(1) available on RHEL/CENTOS, for use on distros
-# which do not provide that utility.
-#
-# Usage:
-#    zgenhostid
-#    zgenhostid <value>
-#
-# If /etc/hostid already exists and is size > 0, the script exits immediately
-# and changes nothing.  Unlike genhostid, this generates an error message.
-#
-# The first form generates a random hostid and stores it in /etc/hostid.
-# The second form checks that the provided value is between 0x1 and 0xFFFFFFFF
-# and if so, stores it in /etc/hostid.  This form is not supported by
-# genhostid(1).
-
-hostid_file=/etc/hostid
-
-function usage {
-	echo "$0 [value]"
-	echo "If $hostid_file is not present, store a hostid in it." >&2
-	echo "The optional value must be an 8-digit hex number between" >&2
-	echo "1 and 2^32-1.  If no value is provided, a random one will" >&2
-	echo "be generated.  The value must be unique among your systems." >&2
-}
-
-# hostid(1) ignores contents of /etc/hostid if size < 4 bytes.  It would
-# be better if this checked size >= 4 bytes but it the method must be
-# widely portable.
-if [ -s $hostid_file ]; then
-	echo "$hostid_file already exists.  No change made." >&2
-	exit 1
-fi
-
-if [ -n "$1" ]; then
-	host_id=$1
-else
-	# $RANDOM goes from 0..32k-1
-	number=$((((RANDOM % 4) * 32768 + RANDOM) * 32768 + RANDOM))
-	host_id=$(printf "%08x" $number)
-fi
-
-if egrep -o '^0{8}$' <<< $host_id >/dev/null 2>&1; then
-	usage
-	exit 2
-fi
-
-if ! egrep -o '^[a-fA-F0-9]{8}$' <<< $host_id >/dev/null 2>&1; then
-	usage
-	exit 3
-fi
-
-a=${host_id:6:2}
-b=${host_id:4:2}
-c=${host_id:2:2}
-d=${host_id:0:2}
-
-echo -ne \\x$a\\x$b\\x$c\\x$d > $hostid_file
-
-exit 0
diff --git a/cmd/zgenhostid/zgenhostid.c b/cmd/zgenhostid/zgenhostid.c
new file mode 100644
index 000000000..562262928
--- /dev/null
+++ b/cmd/zgenhostid/zgenhostid.c
@@ -0,0 +1,152 @@
+/*
+ * CDDL HEADER START
+ *
+ * The contents of this file are subject to the terms of the
+ * Common Development and Distribution License (the "License").
+ * You may not use this file except in compliance with the License.
+ *
+ * You can obtain a copy of the license at usr/src/OPENSOLARIS.LICENSE
+ * or http://www.opensolaris.org/os/licensing.
+ * See the License for the specific language governing permissions
+ * and limitations under the License.
+ *
+ * When distributing Covered Code, include this CDDL HEADER in each
+ * file and include the License file at usr/src/OPENSOLARIS.LICENSE.
+ * If applicable, add the following below this CDDL HEADER, with the
+ * fields enclosed by brackets "[]" replaced with your own identifying
+ * information: Portions Copyright [yyyy] [name of copyright owner]
+ *
+ * CDDL HEADER END
+ */
+
+/*
+ * Copyright (c) 2020, Georgy Yakovlev.  All rights reserved.
+ */
+
+#include <errno.h>
+#include <fcntl.h>
+#include <getopt.h>
+#include <inttypes.h>
+#include <limits.h>
+#include <stdint.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <sys/stat.h>
+#include <time.h>
+#include <unistd.h>
+
+static void usage(void);
+
+static void
+usage(void)
+{
+	(void) fprintf(stderr,
+	    "usage: zgenhostid [-fh] [-o path] [value]\n\n"
+	    "  -f\t\t force hostid file write\n"
+	    "  -h\t\t print this usage and exit\n"
+	    "  -o <filename>\t write hostid to this file\n\n"
+	    "If hostid file is not present, store a hostid in it.\n"
+	    "The optional value must be an 8-digit hex number between"
+	    "1 and 2^32-1.\n"
+	    "If no value is provided, a random one will"
+	    "be generated.\n"
+	    "The value must be unique among your systems.\n");
+	exit(EXIT_FAILURE);
+	/* NOTREACHED */
+}
+
+int
+main(int argc, char **argv)
+{
+	/* default file path, can be optionally set by user */
+	char path[PATH_MAX] = "/etc/hostid";
+	/* holds converted user input or lrand48() generated value */
+	unsigned long input_i = 0;
+
+	int opt;
+	int pathlen;
+	int force_fwrite = 0;
+	while ((opt = getopt_long(argc, argv, "fo:h?", 0, 0)) != -1) {
+		switch (opt) {
+		case 'f':
+			force_fwrite = 1;
+			break;
+		case 'o':
+			pathlen = snprintf(path, sizeof (path), "%s", optarg);
+			if (pathlen >= sizeof (path)) {
+				fprintf(stderr, "%s\n", strerror(EOVERFLOW));
+				exit(EXIT_FAILURE);
+			} else if (pathlen < 1) {
+				fprintf(stderr, "%s\n", strerror(EINVAL));
+				exit(EXIT_FAILURE);
+			}
+			break;
+		case 'h':
+		case '?':
+			usage();
+		}
+	}
+
+	char *in_s = argv[optind];
+	if (in_s != NULL) {
+		/* increment pointer by 2 if string is 0x prefixed */
+		if (strncasecmp("0x", in_s, 2) == 0) {
+			in_s += 2;
+		}
+
+		/* need to be exactly 8 characters */
+		const char *hex = "0123456789abcdefABCDEF";
+		if (strlen(in_s) != 8 || strspn(in_s, hex) != 8) {
+			fprintf(stderr, "%s\n", strerror(ERANGE));
+			usage();
+		}
+
+		input_i = strtoul(in_s, NULL, 16);
+		if (errno != 0) {
+			perror("strtoul");
+			exit(EXIT_FAILURE);
+		}
+
+		if (input_i < 0x1 || input_i > UINT32_MAX) {
+			fprintf(stderr, "%s\n", strerror(ERANGE));
+			usage();
+		}
+	}
+
+	struct stat fstat;
+	if (force_fwrite == 0 && stat(path, &fstat) == 0 &&
+	    S_ISREG(fstat.st_mode)) {
+		fprintf(stderr, "%s: %s\n", path, strerror(EEXIST));
+			exit(EXIT_FAILURE);
+	}
+
+	/*
+	 * generate if not provided by user
+	 * also handle unlikely zero return from lrand48()
+	 */
+	while (input_i == 0) {
+		srand48(getpid() ^ time(NULL));
+		input_i = lrand48();
+	}
+
+	FILE *fp = fopen(path, "wb");
+	if (!fp) {
+		perror("fopen");
+		exit(EXIT_FAILURE);
+	}
+
+	/*
+	 * we need just 4 bytes in native endianess
+	 * not using sethostid() because it may be missing or just a stub
+	 */
+	uint32_t hostid = input_i;
+	int written = fwrite(&hostid, 1, 4, fp);
+	if (written != 4) {
+		perror("fwrite");
+		exit(EXIT_FAILURE);
+	}
+
+	fclose(fp);
+	exit(EXIT_SUCCESS);
+}