switch_root: new command

Copied from Dracut project:
git://dracut.git.sourceforge.net/gitroot/dracut

switch_root history in dracut.git repository:

$ git shortlog switch_root.c
Harald Hoyer (5):
      replace switch_root shell script with binary
      add \n to switch_root
      use switch_root code from http://pjones.fedorapeople.org/mkstart/usr/lib/mkstart/switchroot.c
      mount move instead of umount and fix the search for fallback inits
      setsid() and set controlling terminal for real /sbin/init

Victor Lowther (2):
      Simplify switch_root.c a bit
      Remove all files on the initramfs before switching root

Signed-off-by: Peter Jones <pjones@redhat.com>
Signed-off-by: Karel Zak <kzak@redhat.com>

1 files changed, 198 insertions, 0 deletions

diff --git a/sys-utils/switch_root.c b/sys-utils/switch_root.c
new file mode 100644
index 000000000..9188006eb
--- /dev/null
+++ b/sys-utils/switch_root.c
@@ -0,0 +1,198 @@
+/*
+ * switchroot.c - switch to new root directory and start init.
+ *
+ * Copyright 2002-2008 Red Hat, Inc.  All rights reserved.
+ *
+ * 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/>.
+ *
+ * Authors:
+ *	Peter Jones <pjones@redhat.com>
+ *	Jeremy Katz <katzj@redhat.com>
+ */
+
+#define _GNU_SOURCE 1
+
+#include <sys/mount.h>
+#include <sys/types.h>
+#include <sys/stat.h>
+#include <sys/param.h>
+#include <fcntl.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <unistd.h>
+#include <string.h>
+#include <errno.h>
+#include <ctype.h>
+#include <dirent.h>
+
+#ifndef MS_MOVE
+#define MS_MOVE 8192
+#endif
+
+#ifndef MNT_DETACH
+#define MNT_DETACH 0x2
+#endif
+
+enum {
+	ok,
+	err_no_directory,
+	err_usage,
+};
+
+/* remove all files/directories below dirName -- don't cross mountpoints */
+static int
+recursiveRemove(char * dirName)
+ {
+    struct stat sb,rb;
+    DIR * dir;
+    struct dirent * d;
+    char * strBuf = alloca(strlen(dirName) + 1024);
+
+    if (!(dir = opendir(dirName))) {
+        printf("error opening %s: %m\n", dirName);
+        return 0;
+    }
+
+    if (fstat(dirfd(dir),&rb)) {
+        printf("unable to stat %s: %m\n", dirName);
+        closedir(dir);
+        return 0;
+    }
+
+    errno = 0;
+    while ((d = readdir(dir))) {
+        errno = 0;
+
+        if (!strcmp(d->d_name, ".") || !strcmp(d->d_name, "..")) {
+            errno = 0;
+            continue;
+        }
+
+        strcpy(strBuf, dirName);
+        strcat(strBuf, "/");
+        strcat(strBuf, d->d_name);
+
+        if (lstat(strBuf, &sb)) {
+            printf("failed to stat %s: %m\n", strBuf);
+            errno = 0;
+            continue;
+        }
+
+        /* only descend into subdirectories if device is same as dir */
+        if (S_ISDIR(sb.st_mode)) {
+            if (sb.st_dev == rb.st_dev) {
+	        recursiveRemove(strBuf);
+                if (rmdir(strBuf))
+                    printf("failed to rmdir %s: %m\n", strBuf);
+            }
+            errno = 0;
+            continue;
+        }
+        if (unlink(strBuf)) {
+            printf("failed to remove %s: %m\n", strBuf);
+            errno = 0;
+            continue;
+        }
+    }
+
+    if (errno) {
+        closedir(dir);
+        printf("error reading from %s: %m\n", dirName);
+        return 1;
+    }
+
+    closedir(dir);
+
+    return 0;
+ }
+
+static int switchroot(const char *newroot)
+{
+	/*  Don't try to unmount the old "/", there's no way to do it. */
+	const char *umounts[] = { "/dev", "/proc", "/sys", NULL };
+	int errnum;
+	int i;
+
+	for (i = 0; umounts[i] != NULL; i++) {
+		char newmount[PATH_MAX];
+		strcpy(newmount, newroot);
+		strcat(newmount, umounts[i]);
+		if (mount(umounts[i], newmount, NULL, MS_MOVE, NULL) < 0) {
+			fprintf(stderr, "Error mount moving old %s %s %m\n",
+				umounts[i], newmount);
+			fprintf(stderr, "Forcing unmount of %s\n", umounts[i]);
+			umount2(umounts[i], MNT_FORCE);
+		}
+	}
+
+	if (chdir(newroot) < 0) {
+	  errnum=errno;
+	  fprintf(stderr, "switchroot: chdir failed: %m\n");
+	  errno=errnum;
+	  return -1;
+	}
+	recursiveRemove("/");
+	if (mount(newroot, "/", NULL, MS_MOVE, NULL) < 0) {
+		errnum = errno;
+		fprintf(stderr, "switchroot: mount failed: %m\n");
+		errno = errnum;
+		return -1;
+	}
+
+	if (chroot(".")) {
+		errnum = errno;
+		fprintf(stderr, "switchroot: chroot failed: %m\n");
+		errno = errnum;
+		return -2;
+	}
+	return 1;
+}
+
+static void usage(FILE *output)
+{
+	fprintf(output, "usage: switchroot <newrootdir> <init> <args to init>\n");
+	if (output == stderr)
+		exit(err_usage);
+	exit(ok);
+}
+
+int main(int argc, char *argv[])
+{
+	char *newroot = argv[1];
+	char *init = argv[2];
+	char **initargs = &argv[2];
+
+	if (newroot == NULL || newroot[0] == '\0' ||
+	    init == NULL || init[0] == '\0' ) {
+		usage(stderr);
+	}
+
+	if (switchroot(newroot) < 0) {
+	  fprintf(stderr, "switchroot has failed.  Sorry.\n");
+	  return 1;
+	}
+	if (access(initargs[0], X_OK))
+	  fprintf(stderr, "WARNING: can't access %s\n", initargs[0]);
+
+	/* get session leader */
+	setsid();
+	/* set controlling terminal */
+	ioctl (0, TIOCSCTTY, 1);
+
+	execv(initargs[0], initargs);
+}
+
+/*
+ * vim:noet:ts=8:sw=8:sts=8
+ */