368 lines
10 KiB
C
368 lines
10 KiB
C
/* -*- c-file-style: "gnu" -*-
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* Switch to new root directory and start init.
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*
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* Copyright 2011,2012,2013 Colin Walters <walters@verbum.org>
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*
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* Based on code from util-linux/sys-utils/switch_root.c,
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* Copyright 2002-2009 Red Hat, Inc. All rights reserved.
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* Authors:
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* Peter Jones <pjones@redhat.com>
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* Jeremy Katz <katzj@redhat.com>
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*
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* Relicensed with permission to LGPLv2+.
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*
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* This library is free software; you can redistribute it and/or
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* modify it under the terms of the GNU Lesser General Public
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* License as published by the Free Software Foundation; either
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* version 2 of the License, or (at your option) any later version.
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*
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* This library is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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* Lesser General Public License for more details.
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*
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* You should have received a copy of the GNU Lesser General Public
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* License along with this library; if not, write to the
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* Free Software Foundation, Inc., 59 Temple Place - Suite 330,
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* Boston, MA 02111-1307, USA.
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*/
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#include "config.h"
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#include <sys/mount.h>
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#include <sys/types.h>
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#include <sys/stat.h>
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#include <sys/param.h>
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#include <sys/syscall.h>
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#include <fcntl.h>
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#include <stdio.h>
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#include <stdarg.h>
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#include <stdlib.h>
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#include <unistd.h>
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#include <string.h>
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#include <errno.h>
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#include <ctype.h>
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#include "ostree-mount-util.h"
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static char *
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read_proc_cmdline (void)
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{
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FILE *f = fopen("/proc/cmdline", "r");
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char *cmdline = NULL;
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size_t len;
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if (!f)
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goto out;
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/* Note that /proc/cmdline will not end in a newline, so getline
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* will fail unelss we provide a length.
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*/
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if (getline (&cmdline, &len, f) < 0)
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goto out;
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/* ... but the length will be the size of the malloc buffer, not
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* strlen(). Fix that.
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*/
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len = strlen (cmdline);
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if (cmdline[len-1] == '\n')
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cmdline[len-1] = '\0';
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out:
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if (f)
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fclose (f);
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return cmdline;
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}
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static char *
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parse_ostree_cmdline (void)
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{
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char *cmdline = NULL;
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const char *iter;
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char *ret = NULL;
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int tmp_errno;
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cmdline = read_proc_cmdline ();
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if (!cmdline)
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{
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// Mount proc
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if (mount ("proc", "/proc", "proc", 0, NULL) < 0)
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{
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perrorv ("failed to mount proc on /proc: ");
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exit (EXIT_FAILURE);
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}
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cmdline = read_proc_cmdline ();
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tmp_errno = errno;
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/* Leave the filesystem in the state that we found it: */
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if (umount ("/proc"))
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{
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perrorv ("failed to umount proc from /proc: ");
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exit (EXIT_FAILURE);
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}
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errno = tmp_errno;
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if (!cmdline)
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{
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perrorv ("failed to read /proc/cmdline: ");
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exit (EXIT_FAILURE);
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}
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}
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iter = cmdline;
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while (iter != NULL)
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{
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const char *next = strchr (iter, ' ');
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const char *next_nonspc = next;
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while (next_nonspc && *next_nonspc == ' ')
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next_nonspc += 1;
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if (strncmp (iter, "ostree=", strlen ("ostree=")) == 0)
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{
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const char *start = iter + strlen ("ostree=");
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if (next)
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ret = strndup (start, next - start);
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else
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ret = strdup (start);
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break;
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}
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iter = next_nonspc;
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}
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free (cmdline);
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return ret;
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}
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/* This is an API for other projects to determine whether or not the
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* currently running system is ostree-controlled.
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*/
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static void
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touch_run_ostree (void)
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{
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int fd;
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fd = open ("/run/ostree-booted", O_CREAT | O_WRONLY | O_NOCTTY, 0640);
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/* We ignore failures here in case /run isn't mounted...not much we
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* can do about that, but we don't want to fail.
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*/
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if (fd == -1)
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return;
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(void) close (fd);
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}
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static char*
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resolve_deploy_path (const char * root_mountpoint)
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{
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char destpath[PATH_MAX];
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struct stat stbuf;
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char *ostree_target, *deploy_path;
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ostree_target = parse_ostree_cmdline ();
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if (!ostree_target)
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{
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fprintf (stderr, "No OSTree target; expected ostree=/ostree/boot.N/...\n");
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exit (EXIT_FAILURE);
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}
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snprintf (destpath, sizeof(destpath), "%s/%s", root_mountpoint, ostree_target);
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printf ("Examining %s\n", destpath);
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if (lstat (destpath, &stbuf) < 0)
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{
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perrorv ("Couldn't find specified OSTree root '%s': ", destpath);
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exit (EXIT_FAILURE);
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}
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if (!S_ISLNK (stbuf.st_mode))
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{
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fprintf (stderr, "OSTree target is not a symbolic link: %s\n", destpath);
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exit (EXIT_FAILURE);
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}
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deploy_path = realpath (destpath, NULL);
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if (deploy_path == NULL)
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{
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perrorv ("realpath(%s) failed: ", destpath);
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exit (EXIT_FAILURE);
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}
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printf ("Resolved OSTree target to: %s\n", deploy_path);
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return deploy_path;
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}
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static int
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pivot_root(const char * new_root, const char * put_old)
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{
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return syscall(__NR_pivot_root, new_root, put_old);
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}
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int
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main(int argc, char *argv[])
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{
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const char *root_mountpoint = NULL;
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char *deploy_path = NULL;
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char srcpath[PATH_MAX];
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struct stat stbuf;
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if (argc < 2)
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root_mountpoint = "/";
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else
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root_mountpoint = argv[1];
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root_mountpoint = realpath (root_mountpoint, NULL);
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deploy_path = resolve_deploy_path (root_mountpoint);
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/* Work-around for a kernel bug: for some reason the kernel
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* refuses switching root if any file systems are mounted
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* MS_SHARED. Hence remount them MS_PRIVATE here as a
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* work-around.
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*
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* https://bugzilla.redhat.com/show_bug.cgi?id=847418 */
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if (mount (NULL, "/", NULL, MS_REC|MS_PRIVATE, NULL) < 0)
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{
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perrorv ("failed to make \"/\" private mount: %m");
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exit (EXIT_FAILURE);
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}
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/* Make deploy_path a bind mount, so we can move it later */
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if (mount (deploy_path, deploy_path, NULL, MS_BIND, NULL) < 0)
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{
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perrorv ("failed to make initial bind mount %s", deploy_path);
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exit (EXIT_FAILURE);
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}
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/* chdir to our new root. We need to do this after bind-mounting it over
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* itself otherwise our cwd is still on the non-bind-mounted filesystem
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* below. */
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if (chdir (deploy_path) < 0)
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{
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perrorv ("failed to chdir to deploy_path");
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exit (EXIT_FAILURE);
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}
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/* Link to the deployment's /var */
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if (mount ("../../var", "var", NULL, MS_MGC_VAL|MS_BIND, NULL) < 0)
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{
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perrorv ("failed to bind mount ../../var to var");
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exit (EXIT_FAILURE);
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}
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/* If /boot is on the same partition, use a bind mount to make it visible
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* at /boot inside the deployment. */
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snprintf (srcpath, sizeof(srcpath), "%s/boot/loader", root_mountpoint);
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if (lstat (srcpath, &stbuf) == 0 && S_ISLNK (stbuf.st_mode))
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{
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if (lstat ("boot", &stbuf) == 0 && S_ISDIR (stbuf.st_mode))
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{
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snprintf (srcpath, sizeof(srcpath), "%s/boot", root_mountpoint);
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if (mount (srcpath, "boot", NULL, MS_BIND, NULL) < 0)
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{
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perrorv ("failed to bind mount %s to boot", srcpath);
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exit (EXIT_FAILURE);
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}
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}
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}
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/* Do we have a persistent overlayfs for /usr? If so, mount it now. */
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if (lstat (".usr-ovl-work", &stbuf) == 0)
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{
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const char usr_ovl_options[] = "lowerdir=usr,upperdir=.usr-ovl-upper,workdir=.usr-ovl-work";
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/* Except overlayfs barfs if we try to mount it on a read-only
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* filesystem. For this use case I think admins are going to be
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* okay if we remount the rootfs here, rather than waiting until
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* later boot and `systemd-remount-fs.service`.
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*/
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if (path_is_on_readonly_fs ("."))
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{
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if (mount (".", ".", NULL, MS_REMOUNT | MS_SILENT, NULL) < 0)
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{
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perrorv ("failed to remount rootfs writable (for overlayfs)");
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exit (EXIT_FAILURE);
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}
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}
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if (mount ("overlay", "usr", "overlay", 0, usr_ovl_options) < 0)
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{
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perrorv ("failed to mount /usr overlayfs");
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exit (EXIT_FAILURE);
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}
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}
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else
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{
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/* Otherwise, a read-only bind mount for /usr */
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if (mount ("usr", "usr", NULL, MS_BIND, NULL) < 0)
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{
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perrorv ("failed to bind mount (class:readonly) /usr");
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exit (EXIT_FAILURE);
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}
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if (mount ("usr", "usr", NULL, MS_BIND | MS_REMOUNT | MS_RDONLY, NULL) < 0)
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{
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perrorv ("failed to bind mount (class:readonly) /usr");
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exit (EXIT_FAILURE);
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}
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}
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touch_run_ostree ();
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if (strcmp(root_mountpoint, "/") == 0)
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{
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/* pivot_root rotates two mount points around. In this instance . (the
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* deploy location) becomes / and the existing / becomes /sysroot. We
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* have to use pivot_root rather than mount --move in this instance
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* because our deploy location is mounted as a subdirectory of the real
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* sysroot, so moving sysroot would also move the deploy location. In
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* reality attempting mount --move would fail with EBUSY. */
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if (pivot_root (".", "sysroot") < 0)
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{
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perrorv ("failed to pivot_root to deployment");
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exit (EXIT_FAILURE);
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}
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}
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else
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{
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/* In this instance typically we have our ready made-up up root at
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* /sysroot/ostree/deploy/.../ (deploy_path) and the real rootfs at
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* /sysroot (root_mountpoint). We want to end up with our made-up root at
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* /sysroot/ and the real rootfs under /sysroot/sysroot as systemd will be
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* responsible for moving /sysroot to /.
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*
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* We need to do this in 3 moves to avoid trying to move /sysroot under
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* itself:
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*
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* 1. /sysroot/ostree/deploy/... -> /sysroot.tmp
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* 2. /sysroot -> /sysroot.tmp/sysroot
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* 3. /sysroot.tmp -> /sysroot
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*/
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if (mkdir ("/sysroot.tmp", 0755) < 0)
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{
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perrorv ("couldn't create temporary sysroot /sysroot.tmp: ");
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exit (EXIT_FAILURE);
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}
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if (mount (deploy_path, "/sysroot.tmp", NULL, MS_MOVE, NULL) < 0)
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{
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perrorv ("failed to MS_MOVE '%s' to '/sysroot.tmp'", deploy_path);
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exit (EXIT_FAILURE);
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}
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if (mount (root_mountpoint, "sysroot", NULL, MS_MOVE, NULL) < 0)
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{
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perrorv ("failed to MS_MOVE '%s' to 'sysroot'", root_mountpoint);
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exit (EXIT_FAILURE);
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}
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if (mount (".", root_mountpoint, NULL, MS_MOVE, NULL) < 0)
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{
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perrorv ("failed to MS_MOVE %s to %s", deploy_path, root_mountpoint);
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exit (EXIT_FAILURE);
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}
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}
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if (getpid() == 1)
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{
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execl ("/sbin/init", "/sbin/init", NULL);
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perrorv ("failed to exec init inside ostree");
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exit (EXIT_FAILURE);
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}
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else
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{
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exit (EXIT_SUCCESS);
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}
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}
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