Generate systemd-fsck-root.service in the initramfs

In the initrafms, generate a systemd-fsck-root.service to replace
systemd-fsck@<sysroot-device>.service. This way, after we transition
to the real root, systemd-fsck-root.service is marked as already done.

This introduces an unnecessary synchronization point, because
systemd-fsck@* is ordered after systemd-fsck-root also in the
initramfs. In practice this shouldn't be a problem.

https://bugzilla.redhat.com/show_bug.cgi?id=1201979

C.f. 956eaf2b8d6c9999024705ddadc7393bc707de02.

2 files changed, 60 insertions, 10 deletions

diff --git a/TODO b/TODO
index 23c27f51d2..a94043a81c 100644
--- a/TODO
+++ b/TODO
@@ -111,9 +111,6 @@ Features:
 * Maybe add support for the equivalent of "ethtool advertise" to .link files?
   http://lists.freedesktop.org/archives/systemd-devel/2015-April/030112.html
 
-* fstab-generator should generate systemd-fsck-root.service when
-  running in the initrd, and operate on the right device.
-
 * .timer units should optionally support CLOCK_BOOTTIME in addition to CLOCK_MONOTONIC
 
 * create a btrfs qgroup for /var/lib/machines, and add all container
@@ -151,8 +148,6 @@ Features:
 * Introduce $LISTEN_NAMES to complement $LISTEN_FDS, containing a
   colon separated list of identifiers for the fds passed.
 
-* when the fstab-generator runs in the initrd, it should create a /dev/null mask for systemd-fsck-root.service, to avoid that the the root fs is fsck'ed twice.
-
 * maybe introduce WantsMountsFor=? Usecase:
   http://lists.freedesktop.org/archives/systemd-devel/2015-January/027729.html
 
diff --git a/src/shared/generator.c b/src/shared/generator.c
index 2dc34bf738..d48b400b31 100644
--- a/src/shared/generator.c
+++ b/src/shared/generator.c
@@ -28,8 +28,52 @@
 #include "generator.h"
 #include "path-util.h"
 #include "fstab-util.h"
+#include "fileio.h"
 #include "dropin.h"
 
+static int write_fsck_sysroot_service(const char *dir, const char *what) {
+        const char *unit;
+        _cleanup_free_ char *device = NULL;
+        _cleanup_fclose_ FILE *f = NULL;
+        int r;
+
+        unit = strjoina(dir, "/systemd-fsck-root.service");
+        log_debug("Creating %s", unit);
+
+        r = unit_name_from_path(what, ".device", &device);
+        if (r < 0)
+                return log_error_errno(r, "Failed to convert device \"%s\" to unit name: %m", what);
+
+        f = fopen(unit, "wxe");
+        if (!f)
+                return log_error_errno(errno, "Failed to create unit file %s: %m", unit);
+
+        fprintf(f,
+                "# Automatically generated by %1$s\n\n"
+                "[Unit]\n"
+                "Documentation=man:systemd-fsck-root.service(8)\n"
+                "Description=File System Check on %2$s\n"
+                "DefaultDependencies=no\n"
+                "BindsTo=%3$s\n"
+                "After=%3$s\n"
+                "Before=shutdown.target\n"
+                "\n"
+                "[Service]\n"
+                "Type=oneshot\n"
+                "RemainAfterExit=yes\n"
+                "ExecStart=/usr/lib/systemd/systemd-fsck %2$s\n"
+                "TimeoutSec=0\n",
+                program_invocation_short_name,
+                what,
+                device);
+
+        fflush(f);
+        if (ferror(f))
+                return log_error_errno(errno, "Failed to write unit file %s: %m", unit);
+
+        return 0;
+}
+
 int generator_write_fsck_deps(
                 FILE *f,
                 const char *dir,
@@ -69,11 +113,22 @@ int generator_write_fsck_deps(
                         return log_error_errno(errno, "Failed to create symlink %s: %m", lnk);
 
         } else {
-                _cleanup_free_ char *fsck = NULL;
-
-                r = unit_name_from_path_instance("systemd-fsck", what, ".service", &fsck);
-                if (r < 0)
-                        return log_error_errno(r, "Failed to create fsck service name: %m");
+                _cleanup_free_ char *_fsck = NULL;
+                const char *fsck;
+
+                if (in_initrd() && path_equal(where, "/sysroot")) {
+                        r = write_fsck_sysroot_service(dir, what);
+                        if (r < 0)
+                                return r;
+
+                        fsck = "systemd-fsck-root.service";
+                } else {
+                        r = unit_name_from_path_instance("systemd-fsck", what, ".service", &_fsck);
+                        if (r < 0)
+                                return log_error_errno(r, "Failed to create fsck service name: %m");
+
+                        fsck = _fsck;
+                }
 
                 fprintf(f,
                         "RequiresOverridable=%1$s\n"