1 files changed, 125 insertions, 0 deletions
diff --git a/src/volatile-root/volatile-root.c b/src/volatile-root/volatile-root.c
new file mode 100644
index 0000000..5da9ce1
--- /dev/null
+++ b/src/volatile-root/volatile-root.c
@@ -0,0 +1,125 @@
+/* SPDX-License-Identifier: LGPL-2.1+ */
+
+#include <sys/mount.h>
+
+#include "alloc-util.h"
+#include "fs-util.h"
+#include "main-func.h"
+#include "mkdir.h"
+#include "mount-util.h"
+#include "mountpoint-util.h"
+#include "path-util.h"
+#include "stat-util.h"
+#include "string-util.h"
+#include "volatile-util.h"
+
+static int make_volatile(const char *path) {
+        _cleanup_free_ char *old_usr = NULL;
+        int r;
+
+        r = path_is_mount_point(path, NULL, AT_SYMLINK_FOLLOW);
+        if (r < 0)
+                return log_error_errno(r, "Couldn't determine whether %s is a mount point: %m", path);
+        if (r == 0)
+                return log_error_errno(SYNTHETIC_ERRNO(EINVAL),
+                                       "%s is not a mount point.", path);
+
+        r = path_is_temporary_fs(path);
+        if (r < 0)
+                return log_error_errno(r, "Couldn't determine whether %s is a temporary file system: %m", path);
+        if (r > 0) {
+                log_info("%s already is a temporary file system.", path);
+                return 0;
+        }
+
+        r = chase_symlinks("/usr", path, CHASE_PREFIX_ROOT, &old_usr);
+        if (r < 0)
+                return log_error_errno(r, "/usr not available in old root: %m");
+
+        r = mkdir_p("/run/systemd/volatile-sysroot", 0700);
+        if (r < 0)
+                return log_error_errno(r, "Couldn't generate volatile sysroot directory: %m");
+
+        r = mount_verbose(LOG_ERR, "tmpfs", "/run/systemd/volatile-sysroot", "tmpfs", MS_STRICTATIME, "mode=755");
+        if (r < 0)
+                goto finish_rmdir;
+
+        if (mkdir("/run/systemd/volatile-sysroot/usr", 0755) < 0) {
+                r = -errno;
+                goto finish_umount;
+        }
+
+        r = mount_verbose(LOG_ERR, old_usr, "/run/systemd/volatile-sysroot/usr", NULL, MS_BIND|MS_REC, NULL);
+        if (r < 0)
+                goto finish_umount;
+
+        r = bind_remount_recursive("/run/systemd/volatile-sysroot/usr", true, NULL);
+        if (r < 0)
+                goto finish_umount;
+
+        r = umount_recursive(path, 0);
+        if (r < 0) {
+                log_error_errno(r, "Failed to unmount %s: %m", path);
+                goto finish_umount;
+        }
+
+        if (mount(NULL, "/", NULL, MS_SLAVE|MS_REC, NULL) < 0)
+                log_warning_errno(errno, "Failed to remount %s MS_SLAVE|MS_REC: %m", path);
+
+        r = mount_verbose(LOG_ERR, "/run/systemd/volatile-sysroot", path, NULL, MS_MOVE, NULL);
+
+finish_umount:
+        (void) umount_recursive("/run/systemd/volatile-sysroot", 0);
+
+finish_rmdir:
+        (void) rmdir("/run/systemd/volatile-sysroot");
+
+        return r;
+}
+
+static int run(int argc, char *argv[]) {
+        VolatileMode m = _VOLATILE_MODE_INVALID;
+        const char *path;
+        int r;
+
+        log_setup_service();
+
+        if (argc > 3)
+                return log_error_errno(SYNTHETIC_ERRNO(EINVAL),
+                                       "Too many arguments. Expected directory and mode.");
+
+        r = query_volatile_mode(&m);
+        if (r < 0)
+                return log_error_errno(r, "Failed to determine volatile mode from kernel command line.");
+        if (r == 0 && argc >= 2) {
+                /* The kernel command line always wins. However if nothing was set there, the argument passed here wins instead. */
+                m = volatile_mode_from_string(argv[1]);
+                if (m < 0) {
+                        log_error("Couldn't parse volatile mode: %s", argv[1]);
+                        r = -EINVAL;
+                }
+        }
+
+        if (argc < 3)
+                path = "/sysroot";
+        else {
+                path = argv[2];
+
+                if (isempty(path))
+                        return log_error_errno(SYNTHETIC_ERRNO(EINVAL),
+                                               "Directory name cannot be empty.");
+                if (!path_is_absolute(path))
+                        return log_error_errno(SYNTHETIC_ERRNO(EINVAL),
+                                               "Directory must be specified as absolute path.");
+                if (path_equal(path, "/"))
+                        return log_error_errno(SYNTHETIC_ERRNO(EINVAL),
+                                               "Directory cannot be the root directory.");
+        }
+
+        if (m != VOLATILE_YES)
+                return 0;
+
+        return make_volatile(path);
+}
+
+DEFINE_MAIN_FUNCTION(run);