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[WIP] prepare-root: add support for read-only ostree target #1852

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[WIP] prepare-root: add support for read-only ostree target #1852

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56 changes: 52 additions & 4 deletions src/switchroot/ostree-prepare-root.c
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Original file line number Diff line number Diff line change
Expand Up @@ -62,16 +62,28 @@
static bool running_as_pid1;

static char*
resolve_deploy_path (const char * root_mountpoint)
resolve_deploy_path (const char * root_mountpoint, bool * readonly_root)
{
char destpath[PATH_MAX];
struct stat stbuf;
char *ostree_target, *deploy_path;
char *ostree_target, *deploy_path, *deploy_mode;

ostree_target = read_proc_cmdline_ostree ();
if (!ostree_target)
errx (EXIT_FAILURE, "No OSTree target; expected ostree=/ostree/boot.N/...");

if (strlen(ostree_target) > 3 && strcmp(":ro", ostree_target + strlen(ostree_target) - 3) == 0)
{
*readonly_root = true;
deploy_mode = "Read-Only";
ostree_target[strlen(ostree_target) - 3] = 0;
}
else
{
*readonly_root = false;
deploy_mode = "Read-Write";
}

snprintf (destpath, sizeof(destpath), "%s/%s", root_mountpoint, ostree_target);
if (lstat (destpath, &stbuf) < 0)
err (EXIT_FAILURE, "Couldn't find specified OSTree root '%s'", destpath);
Expand All @@ -91,6 +103,7 @@ resolve_deploy_path (const char * root_mountpoint)
"DEPLOYMENT_PATH=%s", resolved_path,
"DEPLOYMENT_DEVICE=%u", stbuf.st_dev,
"DEPLOYMENT_INODE=%u", stbuf.st_ino,
"DEPLOYMENT_MODE=%s", deploy_mode,
NULL);
#endif
return deploy_path;
Expand Down Expand Up @@ -140,9 +153,10 @@ main(int argc, char *argv[])
}

const char *root_mountpoint = realpath (root_arg, NULL);
bool readonly_root = false;
if (root_mountpoint == NULL)
err (EXIT_FAILURE, "realpath(\"%s\")", root_arg);
char *deploy_path = resolve_deploy_path (root_mountpoint);
char *deploy_path = resolve_deploy_path (root_mountpoint, &readonly_root);

if (we_mounted_proc)
{
Expand Down Expand Up @@ -218,7 +232,7 @@ main(int argc, char *argv[])
if (mount ("overlay", "usr", "overlay", 0, usr_ovl_options) < 0)
err (EXIT_FAILURE, "failed to mount /usr overlayfs");
}
else
else if (!readonly_root)
{
/* Otherwise, a read-only bind mount for /usr */
if (mount ("usr", "usr", NULL, MS_BIND, NULL) < 0)
Expand Down Expand Up @@ -275,6 +289,40 @@ main(int argc, char *argv[])
err (EXIT_FAILURE, "failed to MS_MOVE %s to %s", deploy_path, root_mountpoint);
}

if (readonly_root)
{
/* Create overlayfs for /etc and /var:
*
* 1. Pre-mount tmpfs on /tmp
* 2. Create /tmp/run/{etc,var}-ovl-{upper,work}
* 3. Mount overlayfs
*/
if (mount("tmpfs", "tmp/", "tmpfs", 0, NULL))
err (EXIT_FAILURE, "failed to mount tmpfs to 'tmp'");
if (mkdir ("tmp/run", 0755) < 0)
err (EXIT_FAILURE, "failed to create 'tmp/run'");

if (mkdir ("tmp/run/etc-ovl-upper", 0755) < 0)
err (EXIT_FAILURE, "failed to create 'tmp/run/etc-ovl-upper'");
if (mkdir ("tmp/run/etc-ovl-work", 0755) < 0)
err (EXIT_FAILURE, "failed to create 'tmp/run/etc-ovl-work'");
const char etc_ovl_options[] = "lowerdir=etc,upperdir=tmp/run/etc-ovl-upper,workdir=tmp/run/etc-ovl-work";
if (mount ("overlay", "etc", "overlay", 0, etc_ovl_options) < 0)
err (EXIT_FAILURE, "failed to mount overlay for etc");

if (mkdir ("tmp/run/var-ovl-upper", 0755) < 0)
err (EXIT_FAILURE, "failed to create 'tmp/run/var-ovl-upper'");
if (mkdir ("tmp/run/var-ovl-work", 0755) < 0)
err (EXIT_FAILURE, "failed to create 'tmp/run/var-ovl-work'");
const char var_ovl_options[] = "lowerdir=var,upperdir=tmp/run/var-ovl-upper,workdir=tmp/run/var-ovl-work";
if (mount ("overlay", "var", "overlay", 0, var_ovl_options) < 0)
err (EXIT_FAILURE, "failed to mount overlay for var");

/* Setting sysroot as RDONLY, though systemd will remount rw if fstab is not consistent */
if (mount (".", ".", NULL, MS_REMOUNT | MS_RDONLY, NULL) < 0)
err (EXIT_FAILURE, "failed to remount RDONLY sysroot");
}

/* The /sysroot mount needs to be private to avoid having a mount for e.g. /var/cache
* also propagate to /sysroot/ostree/deploy/$stateroot/var/cache
*
Expand Down