/* switch_root.c - Switch from rootfs/initramfs to another filesystem * * Copyright 2005 Rob Landley <rob@landley.net> USE_SWITCH_ROOT(NEWTOY(switch_root, "<2c:h", TOYFLAG_SBIN)) config SWITCH_ROOT bool "switch_root" default y help usage: switch_root [-c /dev/console] NEW_ROOT NEW_INIT... Use from PID 1 under initramfs to free initramfs, chroot to NEW_ROOT, and exec NEW_INIT. -c Redirect console to device in NEW_ROOT -h Hang instead of exiting on failure (avoids kernel panic) */ #define FOR_switch_root #include "toys.h" #include <sys/vfs.h> GLOBALS( char *console; dev_t rootdev; ) static int del_node(struct dirtree *node) { if (node->st.st_dev == TT.rootdev && dirtree_notdotdot(node)) { int flag = 0; if (S_ISDIR(node->st.st_mode)) { if (node->data != -1) return DIRTREE_COMEAGAIN; flag = AT_REMOVEDIR; } unlinkat(dirtree_parentfd(node), node->name, flag); } return 0; } void switch_root_main(void) { char *newroot = *toys.optargs, **cmdline = toys.optargs+1; struct stat st1, st2; struct statfs stfs; int console = console; // gcc's "may be used" warnings are broken. if (getpid() != 1) error_exit("not pid 1"); // Root filesystem we're leaving must be ramfs or tmpfs if (statfs("/", &stfs) || (stfs.f_type != 0x858458f6 && stfs.f_type != 0x01021994)) { error_msg("not ramfs"); goto panic; } // New directory must be different filesystem instance if (chdir(newroot) || stat(".", &st1) || stat("/", &st2) || st1.st_dev == st2.st_dev) { error_msg("bad newroot '%s'", newroot); goto panic; } TT.rootdev=st2.st_dev; // init program must exist and be an executable file if (stat("init", &st1) || !S_ISREG(st1.st_mode) || !(st1.st_mode&0100)) { error_msg("bad init"); goto panic; } if (TT.console && -1 == (console = open(TT.console, O_RDWR))) { perror_msg("bad console '%s'", TT.console); goto panic; } // Ok, enough safety checks: wipe root partition. dirtree_read("/", del_node); if (TT.console) { int i; for (i=0; i<3; i++) if (console != i) dup2(console, i); if (console>2) close(console); } execv(*cmdline, cmdline); perror_msg("Failed to exec '%s'", *cmdline); panic: if (toys.optflags & FLAG_h) for (;;) wait(NULL); }