Fix #224: support for cmdline -- finit.fstab=/etc/fstab.secondary

This adds support for bringing up the system with an alternate fstab at
boot.  E.g., when using a primary/secondary setup for boot partitions.

By default /etc/fstab is read, like before, this can now be changed
using configure --with-fstab=/path/to/fstab.primary, which sets the
default that can be overridden using finit.fstab=/etc/fstab.secondary

If mounting, or fsck, fails in any way, Finit calls its own bundled
sulogin, or the system sulogin(8), to let the user handle the issue.
If there is no sulogin available, Finit will try to start up in its
rescue.conf boot mode.

Please note, in either of these rescue modes, use `reboot -f` to get the
system to reboot.  Finit is on pause in the background in rescue mode
and cannot be relied on (since there may not be any writable filesystems
available.).

Signed-off-by: Joachim Wiberg <troglobit@gmail.com>

Makefile.am

@@ -29,3 +29,5 @@ release: distcheck
 		printf "$$file.md5\t";    cat ../$$file.md5    | cut -f1 -d' ';	\
 		printf "$$file.sha256\t"; cat ../$$file.sha256 | cut -f1 -d' ';	\
 	done
+
+DISTCHECK_CONFIGURE_FLAGS = --with-fstab=/etc/fstab

configure.ac

@@ -96,6 +96,10 @@ AC_PLUGIN([tty],           [yes], [Automatically activate new TTYs, e.g. USB-to-
 AC_PLUGIN([urandom],       [yes], [Setup and save random seed at boot/shutdown])
 
 # Check for extra arguments or packages
+AC_ARG_WITH(fstab,
+        AS_HELP_STRING([--with-fstab=FILE], [System default fstab, default $sysconfdir/fstab]),
+	[fstab=$withval], [fstab=yes])
+
 AC_ARG_WITH(heading,
         AS_HELP_STRING([--with-heading=GREET], [Heading for boot progress. Default: PRETTY_NAME from /etc/os-release, fallback to "Finit vX.YY"]),
 	[heading=$withval], [heading=yes])
@@ -164,6 +168,12 @@ AS_IF([test "x$enable_logrotate" != "xno"], [
 AM_CONDITIONAL(LOGROTATE, [test "x$enable_logrotate" = "xyes"])
 
 ### With features ##############################################################################
+AS_IF([test "x$with_fstab" != "xno"], [
+	AS_IF([test "x$fstab" = "xyes"], [fstab=$sysconfdir/fstab])
+	AC_EXPAND_DIR(fstab_path, "$fstab")
+	AC_DEFINE_UNQUOTED(FINIT_FSTAB, "$fstab_path", [Built-in default: /etc/fstab])],[
+	AC_DEFINE_UNQUOTED(FINIT_FSTAB, NULL, [No built-in default fstab])])
+
 AS_IF([test "x$with_config" != "xno"], [
 	AS_IF([test "x$conf" = "xyes"], [
 		conf=$sysconfdir/finit.conf])])
@@ -261,6 +271,7 @@ cat <<EOF
   Exec prefix...........: $eprefix
   Sysconfdir............: `eval echo $sysconfdir`
   Localstatedir.........: `eval echo $localstatedir`
+  Default fstab.........: `eval echo $fstab`
   Finit config file.....: $conf_path
   Finit config.d path...: $rcsd_path
   Finit plugin path.....: $plugin_path

doc/cmdline.md

@@ -15,6 +15,25 @@ The `bool` setting is one of `on, off, true false, 1, 0`.
 * `finit.debug[=bool]`: Enable finit debug.  This is operated
 	independently of the kernel `debug` setting.  New as of Finit v4.
 
+* `finit.fstab=</path/to/etc/fstab.alternative>`: Tell Finit to use an
+  alternate `fstab` to mount the file system from.  Remember, this file
+  must be on the `root=...` file system provided to Finit from the
+  kernel.  By default the built-in fstab is used, which itself defaults
+  to `/etc/fstab`, but can be changed at build time with:
+
+        ./configure --with-fstab=/path/to/fstab
+
+  It is even possible to disable a built-in default using:
+
+        ./configure --without-fstab
+
+  Making `finit.fstab=/path/to/fstab` a *mandatory* command line option.
+  Note, if the command line fstab is missing, Finit falls back to the
+  built-in fstab, and if both are missing, the system treats this as a
+  bad `fsck` and thus calls `sulogin`.  If, in turn, `sulogin` is not
+  available on the system, Finit calls reboot, which is also what will
+  happen when a user exits from `sulogin`.
+
 * `finit.status[=bool]`: Control finit boot progress, including banner.
   (Used to be `finit.show_status`, which works but is deprecated.)
 

man/finit.8

@@ -13,6 +13,7 @@
 .Nm /sbin/finit
 .Op --
 .Op finit.debug
+.Op finit.fstab=/etc/fstab.alt
 .Op finit.status=<on,off>
 .Op finit.status_style=<classic,modern>
 .Op rescue | recover
@@ -77,6 +78,43 @@ Enable Finit debug messages on system console and log.  Sometimes useful
 when doing board bringup.  Before the system log daemon has started,
 Finit use the kernel ring buffer,
 .Pa /dev/kmsg .
+.It Cm finit.fstab=/path/to/fstab.alt
+Tell
+.Nm
+to use an alternate
+.Cm fstab
+to mount the file system from.  Remember, this file must be on the
+.Cm root=...
+file system provided to Finit from the kernel.  If this file is missing,
+.Nm
+falls back to its built-in default, which can be changed at build time
+using the
+.Cm --with-fstab=/path/to/footab
+configure option.  It is even possible to completely disable the
+built-in using
+.Cm --without-fstab ,
+meaning
+.Nm
+.Sy must
+be started with the
+.Cm finit.fstab
+option.
+.Pp
+Should
+.Nm
+discover that there is no fstab file available, including the fallback,
+it triggers the same failure mode as when
+.Cm fsck
+fails, starting
+.Xr sulogin 8 ,
+if that is availble.  When
+.Cm sulogin
+is missing, or when the user exits from
+.Cm sulogin ,
+the system is rebooted.
+.Pp
+Default fstab, unless changed at build-time:
+.Pa /etc/fstab
 .It Cm finit.status=<on,off>
 Control finit boot progress, including banner.  This used to be called
 .Cm finit.show_status ,
@@ -108,6 +146,10 @@ Before laucnhing services, the system needs to be bootstrapped.  This
 involves mounting all filesystems (not already mounted by an initramfs)
 in
 .Pa /etc/fstab ,
+or any alternate
+.Pa fstab
+file provided on the Finit command line using
+.Cm finit.fstab ,
 ensuring that necessary filesystems like:
 .Pa /dev ,
 .Pa /proc ,

src/conf.c

@@ -87,6 +87,7 @@ int get_bool(char *arg, int default_value)
 
 /*
  * finit.debug  = [on,off]
+ * finit.fstab  = /path/to/etc/fstab.aternative
  * finit.status = [on,off]     (compat finit.show_status)
  * finit.status_style = [old,classic,modern]
  */
@@ -103,6 +104,11 @@ static void parse_finit_opts(char *opt)
 		return;
 	}
 
+	if (string_compare(opt, "fstab")) {
+		fstab = arg;
+		return;
+	}
+
 	if (string_compare(opt, "status_style")) {
 		if (!arg) {
 			_e("status_style option requires an argument, skipping.");

src/finit.c

@@ -65,6 +65,7 @@ int   rescue    = 0;		/* rescue mode from kernel cmdline */
 int   single    = 0;		/* single user mode from kernel cmdline */
 int   bootstrap = 1;		/* set while bootrapping (for TTYs) */
 int   kerndebug = 0;		/* set if /proc/sys/kernel/printk > 7 */
+char *fstab     = FINIT_FSTAB;
 char *sdown     = NULL;
 char *network   = NULL;
 char *hostname  = NULL;
@@ -105,6 +106,35 @@ static void banner(void)
 #endif
 }
 
+static int sulogin(int do_reboot)
+{
+	int rc = EX_OSFILE;
+	char *cmd[] = {
+		_PATH_SULOGIN,
+		"sulogin",
+	};
+	size_t i;
+
+	for (i = 0; i < NELEMS(cmd); i++) {
+		char *path = which(cmd[i]);
+
+		if (access(path, X_OK)) {
+			free(path);
+			continue;
+		}
+
+		rc = systemf("%s", path);
+		break;
+	}
+
+	if (do_reboot) {
+		do_shutdown(SHUT_REBOOT);
+		exit(rc);
+	}
+
+	return rc;
+}
+
 /*
  * Check all filesystems in /etc/fstab with a fs_passno > 0
  */
@@ -114,10 +144,10 @@ static int fsck(int pass)
 	int rc = 0;
 	FILE *fp;
 
-	fp = setmntent("/etc/fstab", "r");
+	fp = setmntent(fstab, "r");
 	if (!fp) {
-		_pe("Failed opening fstab");
-		return 1;
+		_pe("Failed opening fstab: %s", fstab);
+		sulogin(1);
 	}
 
 	while ((mnt = getmntent(fp))) {
@@ -153,19 +183,8 @@ static int fsck(int pass)
 		 * errors were corrected but that the boot may proceed.
 		 */
 		if (fsck_rc > 1) {
-			char *sulogin[] = {
-				_PATH_SULOGIN,
-				"sulogin",
-			};
-			size_t i;
-
-			for (i = 0; i < NELEMS(sulogin); i++) {
-				if (systemf("%s", sulogin[i]))
-					continue;
-				break;
-			}
-
-			do_shutdown(SHUT_REBOOT);
+			logit(LOG_CONSOLE | LOG_ALERT, "Failed fsck of %s, attempting sulogin ...", mnt->mnt_fsname);
+			sulogin(1);
 		}
 		rc += fsck_rc;
 	}
@@ -208,7 +227,7 @@ static void fs_remount_root(int fsckerr)
 	struct mntent *mnt;
 	FILE *fp;
 
-	fp = setmntent("/etc/fstab", "r");
+	fp = setmntent(fstab, "r");
 	if (!fp)
 		return;
 
@@ -306,13 +325,29 @@ static void fs_finalize(void)
 
 static void fs_mount_all(void)
 {
+	char cmd[256] = "mount -na";
+
+	if (!fstab || !fexist(fstab)) {
+		logit(LOG_CONSOLE | LOG_NOTICE, "%s system fstab %s, trying fallback ...",
+		      !fstab ? "Missing" : "Cannot find", fstab ?: "\b");
+		fstab = FINIT_FSTAB;
+	}
+	if (!fstab || !fexist(fstab)) {
+		logit(LOG_CONSOLE | LOG_EMERG, "%s system fstab %s, attempting sulogin ...",
+		      !fstab ? "Missing" : "Cannot find", fstab ?: "\b");
+		sulogin(1);
+	}
+
 	if (!rescue)
 		fs_remount_root(fsck_all());
 
 	_d("Root FS up, calling hooks ...");
 	plugin_run_hooks(HOOK_ROOTFS_UP);
 
-	if (run_interactive("mount -na", "Mounting filesystems"))
+	if (fstab && strcmp(fstab, "/etc/fstab"))
+		snprintf(cmd, sizeof(cmd), "mount -na -T %s", fstab);
+
+	if (run_interactive(cmd, "Mounting filesystems from %s", fstab))
 		plugin_run_hooks(HOOK_MOUNT_ERROR);
 
 	_d("Calling extra mount hook, after mount -a ...");
@@ -595,21 +630,8 @@ int main(int argc, char *argv[])
 	/*
 	 * In case of emergency.
 	 */
-	if (rescue) {
-		char *sulogin[] = {
-			_PATH_SULOGIN,
-			"sulogin",
-		};
-		size_t i;
-
-		for (i = 0; i < NELEMS(sulogin); i++) {
-			if (systemf("%s", sulogin[i]))
-				continue;
-
-			rescue = 0;
-			break;
-		}
-	}
+	if (rescue)
+		rescue = sulogin(0);
 
 	/*
 	 * Load plugins early, the first hook is in banner(), so we
@@ -638,7 +660,10 @@ int main(int argc, char *argv[])
 	 */
 	cgroup_init(&loop);
 
-	/* Check and mount filesystems. */
+	/*
+	 * Check custom fstab from cmdline, including fallback, then run
+	 * fsck before mounting all filesystems, on error call sulogin.
+	 */
 	fs_mount_all();
 
 	/* Bootstrap conditions, needed for hooks */

src/finit.h

@@ -116,6 +116,7 @@ extern int    rescue;
 extern int    single;
 extern int    bootstrap;
 extern int    kerndebug;
+extern char  *fstab;
 extern char  *sdown;
 extern char  *network;
 extern char  *hostname;