[systemd-devel] [PATCH] Generate a fake systemd-fsck-root.service in the initramfs

[Zbigniew Jędrzejewski-Szmek]

In the initramfs, we run systemd-fsck@<sysroot-device>.service.
In the real system we run systemd-fsck-root.service. Generate
a fake systemd-fsck-root.service if we are running a unit check
for the root file system. We don't really care if the real fsck unit
fails, because the failure will be handled in some other way.

This fake unit is created and pulled in only when we actually plan to
check the file system for /sysroot. This way we avoid having an
active/exited systemd-fsck-root.service in the main filesystem if
we didn't do anything.

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

C.f. 956eaf2b8d6c9999024705ddadc7393bc707de02.
---
Something like this?

 TODO                   |  5 -----
 src/shared/generator.c | 30 ++++++++++++++++++++++++++++++
 2 files changed, 30 insertions(+), 5 deletions(-)

diff --git a/TODO b/TODO
index 430a354e84..cc827701f0 100644
--- a/TODO
+++ b/TODO
@@ -113,9 +113,6 @@ 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
@@ -153,8 +150,6 @@ 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..813ce1af9a 100644
--- a/src/shared/generator.c
+++ b/src/shared/generator.c
@@ -28,8 +28,32 @@
 #include "generator.h"
 #include "path-util.h"
 #include "fstab-util.h"
+#include "fileio.h"
 #include "dropin.h"
 
+static int write_fsck_root_service(const char *dir) {
+        const char *unit;
+        int r;
+
+        unit = strjoina(dir, "/systemd-fsck-root.service");
+        log_debug("Creating %s.", unit);
+
+        r = write_string_file_atomic(unit,
+                "# Automatically generated by a systemd-fstab-generator or similar\n\n"
+                "[Unit]\n"
+                "Description=Root File System Check Placeholder\n"
+                "DefaultDependencies=no\n"
+                "Before=shutdown.target\n"
+                "\n"
+                "[Service]\n"
+                "ExecStart=/bin/true\n"
+                "Type=oneshot\n"
+                "RemainAfterExit=yes\n");
+        if (r < 0)
+                log_warning_errno(errno, "Failed to write unit file %s: %m", unit);
+        return r;
+}
+
 int generator_write_fsck_deps(
                 FILE *f,
                 const char *dir,
@@ -79,6 +103,12 @@ int generator_write_fsck_deps(
                         "RequiresOverridable=%1$s\n"
                         "After=%1$s\n",
                         fsck);
+
+                if (in_initrd() && path_equal(where, "/sysroot")) {
+                        (void) write_fsck_root_service(dir);
+                        fprintf(f,
+                                "Wants=systemd-fsck-root.service\n");
+                }
         }
 
         return 0;
-- 
2.3.5