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authorGravatar Rob Landley <rob@landley.net>2005-10-27 22:55:50 +0000
committerGravatar Rob Landley <rob@landley.net>2005-10-27 22:55:50 +0000
commit0f34a821ab99e4936c7aa4974f58784442172211 (patch)
tree1341f988aa02110b3a997edc52e54bcc27ea1000 /util-linux/switch_root.c
parent2454ebd85ddbbdc0971e9b848032f66e23245ebe (diff)
downloadbusybox-0f34a821ab99e4936c7aa4974f58784442172211.tar.gz
busybox-0f34a821ab99e4936c7aa4974f58784442172211.tar.bz2
Add a switch_root utility (like kconfig's utils/run_init.c, although not
actuall using any of that code). This is needed because pivot_root doesn't work right under initramfs. (See the menuconfig help.)
Diffstat (limited to 'util-linux/switch_root.c')
-rw-r--r--util-linux/switch_root.c118
1 files changed, 118 insertions, 0 deletions
diff --git a/util-linux/switch_root.c b/util-linux/switch_root.c
new file mode 100644
index 000000000..242699560
--- /dev/null
+++ b/util-linux/switch_root.c
@@ -0,0 +1,118 @@
+/* vi:set ts=4:*/
+
+#include <dirent.h>
+#include <fcntl.h>
+#include <stdio.h>
+#include <sys/mount.h>
+#include <sys/stat.h>
+#include <sys/types.h>
+#include <sys/vfs.h>
+#include <unistd.h>
+
+#include "busybox.h"
+
+// Make up for header deficiencies.
+
+#ifndef RAMFS_MAGIC
+#define RAMFS_MAGIC 0x858458f6
+#endif
+
+#ifndef TMPFS_MAGIC
+#define TMPFS_MAGIC 0x01021994
+#endif
+
+#ifndef MS_MOVE
+#define MS_MOVE 8192
+#endif
+
+dev_t rootdev;
+
+// Recursively delete contents of rootfs.
+
+static void delete_contents(char *directory)
+{
+ DIR *dir;
+ struct dirent *d;
+ struct stat st;
+
+ // Don't descend into other filesystems
+ if (stat(directory,&st) || st.st_dev != rootdev) return;
+
+ // Recursively delete the contents of directories.
+ if (S_ISDIR(st.st_mode)) {
+ if((dir = opendir(directory))) {
+ while ((d = readdir(dir))) {
+ char *newdir=d->d_name;
+
+ // Skip . and ..
+ if(*newdir=='.' && (!newdir[1] || (newdir[1]=='.' && !newdir[2])))
+ continue;
+
+ // Recurse to delete contents
+ newdir = alloca(strlen(directory) + strlen(d->d_name) + 2);
+ sprintf(newdir, "%s/%s", directory, d->d_name);
+ delete_contents(newdir);
+ }
+ closedir(dir);
+
+ // Directory should now be empty. Zap it.
+ printf("rmdir %s\n",directory); // rmdir(directory);
+ }
+
+ // It wasn't a directory. Zap it.
+
+ } else printf("unlink %s\n",directory); //unlink(directory);
+}
+
+int switch_root_main(int argc, char *argv[])
+{
+ char *newroot, *console="/dev/console";
+ struct stat st1, st2;
+ struct statfs stfs;
+
+ // Parse args (-c console)
+
+ bb_opt_complementally="-2";
+ bb_getopt_ulflags(argc,argv,"c:",&console);
+
+ // Change to new root directory and verify it's a different fs.
+
+ newroot=argv[optind++];
+
+ if (chdir(newroot) || stat(".", &st1) || stat("/", &st2) ||
+ st1.st_dev == st2.st_dev)
+ {
+ bb_error_msg_and_die("bad newroot %s",newroot);
+ }
+ rootdev=st2.st_dev;
+
+ // Additional sanity checks: we're about to rm -rf /, so be REALLY SURE
+ // we mean it. (I could make this a CONFIG option, but I would get email
+ // from all the people who WILL eat their filesystemss.)
+
+ if (stat("/init", &st1) || !S_ISREG(st1.st_mode) || statfs("/", &stfs) ||
+ (stfs.f_type != RAMFS_MAGIC && stfs.f_type != TMPFS_MAGIC) ||
+ getpid() != 1)
+ {
+ bb_error_msg_and_die("not rootfs");
+ }
+
+ // Zap everything out of rootdev
+ delete_contents("/");
+
+ // Overmount / with newdir
+
+ if (mount(".", "/", NULL, MS_MOVE, NULL) || chdir("/"))
+ bb_error_msg_and_die("moving root");
+
+ // Reopen stdin/stdout/stderr to /dev/console
+ close(0);
+ if(open(console, O_RDWR) < 0)
+ bb_error_msg_and_die("Bad console '%s'",console);
+ dup2(0, 1);
+ dup2(0, 2);
+
+ // Exec real init. (This is why we must be pid 1.)
+ execv(argv[optind],argv+optind+1);
+ bb_error_msg_and_die("Bad init '%s'",argv[optind]);
+}