4 files changed, 29 insertions, 20 deletions
diff --git a/src/core/machine-id-setup.c b/src/core/machine-id-setup.c
index 62f80833dd..423d4ff69d 100644
--- a/src/core/machine-id-setup.c
+++ b/src/core/machine-id-setup.c
@@ -295,9 +295,13 @@ int machine_id_setup(const char *root, sd_id128_t machine_id) {
 int machine_id_commit(const char *root) {
         _cleanup_close_ int fd = -1, initial_mntns_fd = -1;
         const char *etc_machine_id;
-        char id[34]; /* 32 + \n + \0 */
+        sd_id128_t id;
         int r;
 
+        /* Replaces a tmpfs bind mount of /etc/machine-id by a proper file, atomically. For this, the umount is removed
+         * in a mount namespace, a new file is created at the right place. Afterwards the mount is also removed in the
+         * original mount namespace, thus revealing the file that was just created. */
+
         etc_machine_id = prefix_roota(root, "/etc/machine-id");
 
         r = path_is_mount_point(etc_machine_id, 0);
@@ -313,10 +317,6 @@ int machine_id_commit(const char *root) {
         if (fd < 0)
                 return log_error_errno(errno, "Cannot open %s: %m", etc_machine_id);
 
-        r = read_machine_id(fd, id);
-        if (r < 0)
-                return log_error_errno(r, "We didn't find a valid machine ID in %s.", etc_machine_id);
-
         r = fd_is_temporary_fs(fd);
         if (r < 0)
                 return log_error_errno(r, "Failed to determine whether %s is on a temporary file system: %m", etc_machine_id);
@@ -325,6 +325,10 @@ int machine_id_commit(const char *root) {
                 return -EROFS;
         }
 
+        r = id128_read_fd(fd, ID128_PLAIN, &id);
+        if (r < 0)
+                return log_error_errno(r, "We didn't find a valid machine ID in %s.", etc_machine_id);
+
         fd = safe_close(fd);
 
         /* Store current mount namespace */
@@ -343,15 +347,9 @@ int machine_id_commit(const char *root) {
                 return log_error_errno(errno, "Failed to unmount transient %s file in our private namespace: %m", etc_machine_id);
 
         /* Update a persistent version of etc_machine_id */
-        fd = open(etc_machine_id, O_RDWR|O_CREAT|O_CLOEXEC|O_NOCTTY, 0444);
-        if (fd < 0)
-                return log_error_errno(errno, "Cannot open for writing %s. This is mandatory to get a persistent machine-id: %m", etc_machine_id);
-
-        r = write_machine_id(fd, id);
+        r = id128_write(etc_machine_id, ID128_PLAIN, id, true);
         if (r < 0)
-                return log_error_errno(r, "Cannot write %s: %m", etc_machine_id);
-
-        fd = safe_close(fd);
+                return log_error_errno(r, "Cannot write %s. This is mandatory to get a persistent machine ID: %m", etc_machine_id);
 
         /* Return to initial namespace and proceed a lazy tmpfs unmount */
         r = namespace_enter(-1, initial_mntns_fd, -1, -1, -1);
diff --git a/src/libsystemd/sd-id128/id128-util.c b/src/libsystemd/sd-id128/id128-util.c
index c1742cab0e..aaac838b59 100644
--- a/src/libsystemd/sd-id128/id128-util.c
+++ b/src/libsystemd/sd-id128/id128-util.c
@@ -18,6 +18,7 @@
 ***/
 
 #include <fcntl.h>
+#include <unistd.h>
 
 #include "fd-util.h"
 #include "hexdecoct.h"
@@ -140,9 +141,10 @@ int id128_read(const char *p, Id128Format f, sd_id128_t *ret) {
         return id128_read_fd(fd, f, ret);
 }
 
-int id128_write_fd(int fd, Id128Format f, sd_id128_t id) {
+int id128_write_fd(int fd, Id128Format f, sd_id128_t id, bool do_sync) {
         char buffer[36 + 2];
         size_t sz;
+        int r;
 
         assert(fd >= 0);
         assert(f < _ID128_FORMAT_MAX);
@@ -157,15 +159,24 @@ int id128_write_fd(int fd, Id128Format f, sd_id128_t id) {
                 sz = 37;
         }
 
-        return loop_write(fd, buffer, sz, false);
+        r = loop_write(fd, buffer, sz, false);
+        if (r < 0)
+                return r;
+
+        if (do_sync) {
+                if (fsync(fd) < 0)
+                        return -errno;
+        }
+
+        return r;
 }
 
-int id128_write(const char *p, Id128Format f, sd_id128_t id) {
+int id128_write(const char *p, Id128Format f, sd_id128_t id, bool do_sync) {
         _cleanup_close_ int fd = -1;
 
         fd = open(p, O_WRONLY|O_CREAT|O_CLOEXEC|O_NOCTTY, 0444);
         if (fd < 0)
                 return -errno;
 
-        return id128_write_fd(fd, f, id);
+        return id128_write_fd(fd, f, id, do_sync);
 }
diff --git a/src/libsystemd/sd-id128/id128-util.h b/src/libsystemd/sd-id128/id128-util.h
index 73e4c710c4..3ba59acbca 100644
--- a/src/libsystemd/sd-id128/id128-util.h
+++ b/src/libsystemd/sd-id128/id128-util.h
@@ -41,5 +41,5 @@ typedef enum Id128Format {
 int id128_read_fd(int fd, Id128Format f, sd_id128_t *ret);
 int id128_read(const char *p, Id128Format f, sd_id128_t *ret);
 
-int id128_write_fd(int fd, Id128Format f, sd_id128_t id);
-int id128_write(const char *p, Id128Format f, sd_id128_t id);
+int id128_write_fd(int fd, Id128Format f, sd_id128_t id, bool do_sync);
+int id128_write(const char *p, Id128Format f, sd_id128_t id, bool do_sync);
diff --git a/src/nspawn/nspawn.c b/src/nspawn/nspawn.c
index 4c1d79418d..da8bee3244 100644
--- a/src/nspawn/nspawn.c
+++ b/src/nspawn/nspawn.c
@@ -1287,7 +1287,7 @@ static int setup_boot_id(const char *dest) {
         if (r < 0)
                 return log_error_errno(r, "Failed to generate random boot id: %m");
 
-        r = id128_write(from, ID128_UUID, rnd);
+        r = id128_write(from, ID128_UUID, rnd, false);
         if (r < 0)
                 return log_error_errno(r, "Failed to write boot id: %m");