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switchroot: Use MS_MOVE to / rather than chroot

Browse Source 
This fixes a number of bugs; the two biggest are:

1) On shutdown systemd can correctly umount /
2) We can use linux-user-chroot inside the system, as is
   necessary to do upgrades

See http://lists.freedesktop.org/archives/systemd-devel/2012-September/006703.html
This commit is contained in:
Colin Walters 2013-02-11 20:46:53 -05:00
parent 1d98f8865c
commit c9f56564a3
1 changed files with 56 additions and 55 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

111
src/switchroot/ostree-switch-root.c
View File

@ -153,8 +153,7 @@ main(int argc, char *argv[])
const char *initramfs_move_mounts[] = { "/dev", "/proc", "/sys", "/run", NULL };
const char *toproot_bind_mounts[] = { "/home", "/root", "/tmp", NULL };
const char *ostree_bind_mounts[] = { "/var", NULL };
const char *readonly_bind_mounts[] = { "/bin", "/lib", "/sbin", "/usr",
NULL };
const char *readonly_bind_mounts[] = { "/usr", NULL };
const char *root_mountpoint = NULL;
const char *ostree_target = NULL;
const char *ostree_subinit = NULL;
@ -194,16 +193,6 @@ main(int argc, char *argv[])
}
ostree_osname = strndup (ostree_target, p - ostree_target);
/* For now, we just remount the root filesystem read/write. This is
* kind of ugly, but to do this properly we'd basically have to have
* to be fully integrated into the init process.
*/
if (mount (NULL, root_mountpoint, NULL, MS_MGC_VAL|MS_REMOUNT, NULL) < 0)
{
perrorv ("Failed to remount %s read/write", root_mountpoint);
exit (1);
}
snprintf (destpath, sizeof(destpath), "%s/ostree/deploy/%s",
root_mountpoint, ostree_target);
if (stat (destpath, &stbuf) < 0)
@ -212,6 +201,20 @@ main(int argc, char *argv[])
exit (1);
}
/* Work-around for a kernel bug: for some reason the kernel
* refuses switching root if any file systems are mounted
* MS_SHARED. Hence remount them MS_PRIVATE here as a
* work-around.
*
* https://bugzilla.redhat.com/show_bug.cgi?id=847418 */
if (mount(NULL, "/", NULL, MS_REC|MS_PRIVATE, NULL) < 0)
{
perrorv ("mount(/, MS_PRIVATE): ");
exit (1);
}
initramfs_fd = open ("/", O_RDONLY);
for (i = 0; initramfs_move_mounts[i] != NULL; i++)
{
const char *path = initramfs_move_mounts[i];
@ -223,42 +226,7 @@ main(int argc, char *argv[])
}
}
if (chdir (root_mountpoint) < 0)
{
perrorv ("failed to chdir to %s", root_mountpoint);
exit (1);
}
initramfs_fd = open ("/", O_RDONLY);
if (mount (root_mountpoint, "/", NULL, MS_MOVE, NULL) < 0)
{
perrorv ("failed move %s to /", root_mountpoint);
return -1;
}
if (chroot (".") < 0)
{
perrorv ("failed to chroot to .");
exit (1);
}
if (initramfs_fd >= 0)
{
cleanup_pid = fork ();
if (cleanup_pid == 0)
{
recursive_remove (initramfs_fd);
exit (0);
}
close (initramfs_fd);
}
/* From this point on we're chrooted into the real root filesystem,
* so we no longer refer to root_mountpoint.
*/
snprintf (destpath, sizeof(destpath), "/ostree/deploy/%s", ostree_target);
snprintf (destpath, sizeof(destpath), "%s/ostree/deploy/%s", root_mountpoint, ostree_target);
fprintf (stderr, "Examining %s\n", destpath);
if (lstat (destpath, &stbuf) < 0)
{
@ -279,12 +247,20 @@ main(int argc, char *argv[])
if (ostree_target_path[len-1] == '/')
ostree_target_path[len-1] = '\0';
fprintf (stderr, "Resolved OSTree target to: %s\n", ostree_target_path);
asprintf (&deploy_path, "/ostree/deploy/%s/%s", ostree_osname, ostree_target_path);
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 ("/", destpath, NULL, MS_BIND, NULL) < 0)
if (mount (root_mountpoint, destpath, NULL, MS_BIND, NULL) < 0)
{
perrorv ("Failed to bind mount / to '%s'", destpath);
perrorv ("Failed to bind mount %s to '%s'", root_mountpoint, destpath);
exit (1);
}
@ -298,8 +274,9 @@ main(int argc, char *argv[])
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 (toproot_bind_mounts[i], destpath, NULL, MS_BIND & ~MS_RDONLY, NULL) < 0)
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);
@ -308,7 +285,8 @@ main(int argc, char *argv[])
for (i = 0; ostree_bind_mounts[i] != NULL; i++)
{
snprintf (srcpath, sizeof(srcpath), "/ostree/deploy/%s%s", ostree_osname, ostree_bind_mounts[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)
{
@ -332,7 +310,19 @@ main(int argc, char *argv[])
}
}
if (chroot (deploy_path) < 0)
if (chdir (deploy_path) < 0)
{
perrorv ("failed to chdir to subroot (initial)");
exit (1);
}
if (mount (deploy_path, "/", NULL, MS_MOVE, NULL) < 0)
{
perrorv ("failed to MS_MOVE %s to /", deploy_path);
exit (1);
}
if (chroot (".") < 0)
{
perrorv ("failed to change root to '%s'", deploy_path);
exit (1);
@ -340,10 +330,21 @@ main(int argc, char *argv[])
if (chdir ("/") < 0)
{
perrorv ("failed to chdir to subroot");
perrorv ("failed to chdir to / (after MS_MOVE of /)");
exit (1);
}
if (initramfs_fd >= 0)
{
cleanup_pid = fork ();
if (cleanup_pid == 0)
{
recursive_remove (initramfs_fd);
exit (0);
}
close (initramfs_fd);
}
init_argv = malloc (sizeof (char*)*((argc-before_init_argc)+2));
init_argv[0] = (char*)ostree_subinit;
for (i = 0; i < argc-before_init_argc; i++)