ostree-prepare-root: New binary, used for systemd-in-initramfs setups

Rather than attempting to hack up the "switch-root" functionality of
systemd, this binary allows us to simply prepare the root before we
switch into it.

Makefile-switchroot.am

@@ -17,8 +17,11 @@
 
 if !TRIGGERS_ONLY
 sbin_PROGRAMS += ostree-switch-root
+sbin_PROGRAMS += ostree-prepare-root
 endif
 
-ostree_switch_root_SOURCES = src/switchroot/ostree-switch-root.c
+ostree_prepare_root_SOURCES = src/switchroot/ostree-prepare-root.c
+ostree_prepare_root_CFLAGS = $(AM_CFLAGS)
 
+ostree_switch_root_SOURCES = src/switchroot/ostree-switch-root.c
 ostree_switch_root_CFLAGS = $(AM_CFLAGS)

src/switchroot/ostree-prepare-root.c

@@ -0,0 +1,200 @@
+/* -*- c-file-style: "gnu" -*-
+ * Switch to new root directory and start init.
+ * 
+ * Copyright 2011,2012,2013 Colin Walters <walters@verbum.org>
+ *
+ * Based on code from util-linux/sys-utils/switch_root.c, 
+ * Copyright 2002-2009 Red Hat, Inc.  All rights reserved.
+ * Authors:
+ *	Peter Jones <pjones@redhat.com>
+ *	Jeremy Katz <katzj@redhat.com>
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ *
+ */
+#define _GNU_SOURCE
+#include <sys/mount.h>
+#include <sys/types.h>
+#include <sys/stat.h>
+#include <sys/param.h>
+#include <fcntl.h>
+#include <assert.h>
+#include <stdio.h>
+#include <stdarg.h>
+#include <stdlib.h>
+#include <unistd.h>
+#include <string.h>
+#include <errno.h>
+#include <ctype.h>
+#include <dirent.h>
+
+static int
+perrorv (const char *format, ...) __attribute__ ((format (printf, 1, 2)));
+
+static int
+perrorv (const char *format, ...)
+{
+  va_list args;
+  char buf[PATH_MAX];
+  char *p;
+
+  p = strerror_r (errno, buf, sizeof (buf));
+
+  va_start (args, format);
+
+  vfprintf (stderr, format, args);
+  fprintf (stderr, ": %s\n", p);
+  fflush (stderr);
+
+  va_end (args);
+
+  sleep (3);
+	
+  return 0;
+}
+
+int
+main(int argc, char *argv[])
+{
+  const char *toproot_bind_mounts[] = { "/home", "/root", "/tmp", NULL };
+  const char *ostree_bind_mounts[] = { "/var", NULL };
+  const char *readonly_bind_mounts[] = { "/usr", NULL };
+  const char *root_mountpoint = NULL;
+  const char *ostree_target = NULL;
+  const char *p = NULL;
+  char *ostree_osname = NULL;
+  char ostree_target_path[PATH_MAX];
+  char *deploy_path = NULL;
+  char srcpath[PATH_MAX];
+  char destpath[PATH_MAX];
+  struct stat stbuf;
+  size_t len;
+  int i;
+  int before_init_argc = 0;
+
+  if (argc < 3)
+    {
+      fprintf (stderr, "usage: ostree-prepare-root SYSROOT OSTREE\n");
+      exit (1);
+    }
+
+  before_init_argc++;
+  root_mountpoint = argv[1];
+  before_init_argc++;
+  ostree_target = argv[2];
+  before_init_argc++;
+
+  p = strchr (ostree_target, '/');
+  if (p == NULL || p == ostree_target)
+    {
+      fprintf (stderr, "Malformed OSTree target %s; expected OSNAME/TREENAME\n", ostree_target);
+      exit (1);
+    }
+  ostree_osname = strndup (ostree_target, p - ostree_target);
+
+  snprintf (destpath, sizeof(destpath), "%s/ostree/deploy/%s",
+	    root_mountpoint, ostree_target);
+  if (stat (destpath, &stbuf) < 0)
+    {
+      perrorv ("Invalid OSTree root '%s'", destpath);
+      exit (1);
+    }
+
+  snprintf (destpath, sizeof(destpath), "%s/ostree/deploy/%s", root_mountpoint, ostree_target);
+  fprintf (stderr, "Examining %s\n", destpath);
+  if (lstat (destpath, &stbuf) < 0)
+    {
+      perrorv ("Second stat of OSTree root '%s' failed: ", destpath);
+      exit (1);
+    }
+  if (!S_ISLNK (stbuf.st_mode))
+    {
+      fprintf (stderr, "OSTree target is not a symbolic link: %s\n", destpath);
+      exit (1);
+    }
+  if (readlink (destpath, ostree_target_path, PATH_MAX) < 0)
+    {
+      perrorv ("readlink(%s) failed: ", destpath);
+      exit (1);
+    }
+  len = strlen (ostree_target_path);
+  if (ostree_target_path[len-1] == '/')
+    ostree_target_path[len-1] = '\0';
+  fprintf (stderr, "Resolved OSTree target to: %s\n", ostree_target_path);
+  (void) asprintf (&deploy_path, "%s/ostree/deploy/%s/%s", root_mountpoint,
+		   ostree_osname, ostree_target_path);
+  
+  /* Make deploy_path a bind mount, so we can move it later */
+  if (mount (deploy_path, deploy_path, NULL, MS_BIND, NULL) < 0)
+    {
+      perrorv ("failed to initial bind mount %s", deploy_path);
+      exit (1);
+    }
+
+  snprintf (destpath, sizeof(destpath), "%s/sysroot", deploy_path);
+  if (mount (root_mountpoint, destpath, NULL, MS_BIND, NULL) < 0)
+    {
+      perrorv ("Failed to bind mount %s to '%s'", root_mountpoint, destpath);
+      exit (1);
+    }
+
+  snprintf (srcpath, sizeof(srcpath), "%s-etc", deploy_path);
+  snprintf (destpath, sizeof(destpath), "%s/etc", deploy_path);
+  if (mount (srcpath, destpath, NULL, MS_BIND, NULL) < 0)
+    {
+      perrorv ("Failed to bind mount '%s' to '%s'", srcpath, destpath);
+      exit (1);
+    }
+
+  for (i = 0; toproot_bind_mounts[i] != NULL; i++)
+    {
+      snprintf (srcpath, sizeof(srcpath), "%s%s", root_mountpoint, toproot_bind_mounts[i]);
+      snprintf (destpath, sizeof(destpath), "%s%s", deploy_path, toproot_bind_mounts[i]);
+      if (mount (srcpath, destpath, NULL, MS_BIND & ~MS_RDONLY, NULL) < 0)
+	{
+	  perrorv ("failed to bind mount (class:toproot) %s to %s", toproot_bind_mounts[i], destpath);
+	  exit (1);
+	}
+    }
+
+  for (i = 0; ostree_bind_mounts[i] != NULL; i++)
+    {
+      snprintf (srcpath, sizeof(srcpath), "%s/ostree/deploy/%s%s", root_mountpoint,
+		ostree_osname, ostree_bind_mounts[i]);
+      snprintf (destpath, sizeof(destpath), "%s%s", deploy_path, ostree_bind_mounts[i]);
+      if (mount (srcpath, destpath, NULL, MS_MGC_VAL|MS_BIND, NULL) < 0)
+	{
+	  perrorv ("failed to bind mount (class:bind) %s to %s", srcpath, destpath);
+	  exit (1);
+	}
+    }
+
+  for (i = 0; readonly_bind_mounts[i] != NULL; i++)
+    {
+      snprintf (destpath, sizeof(destpath), "%s%s", deploy_path, readonly_bind_mounts[i]);
+      if (mount (destpath, destpath, NULL, MS_BIND, NULL) < 0)
+	{
+	  perrorv ("failed to bind mount (class:readonly) %s", destpath);
+	  exit (1);
+	}
+      if (mount (destpath, destpath, NULL, MS_BIND | MS_REMOUNT | MS_RDONLY, NULL) < 0)
+	{
+	  perrorv ("failed to bind mount (class:readonly) %s", destpath);
+	  exit (1);
+	}
+    }
+  
+  exit (0);
+}
+