core: add comment why we don't bother with MS_SHARED remounting of / in containers

diff --git a/src/core/mount-setup.c b/src/core/mount-setup.c
index 6338067d7ebf9eac8ae480afa3f681391d7ee7b5..9c2bf3a0efec1d4293d34ba6dbbcdb3389962786 100644 (file)
--- a/src/core/mount-setup.c
+++ b/src/core/mount-setup.c
@@ -360,7 +360,6 @@ int mount_setup(bool loaded_policy) {
         int r = 0;
 
         r = mount_points_setup(ELEMENTSOF(mount_table), loaded_policy);
-
         if (r < 0)
                 return r;
 
@@ -391,25 +390,24 @@ int mount_setup(bool loaded_policy) {
          * udevd. */
         dev_setup(NULL, UID_INVALID, GID_INVALID);
 
-        /* Mark the root directory as shared in regards to mount
-         * propagation. The kernel defaults to "private", but we think
-         * it makes more sense to have a default of "shared" so that
-         * nspawn and the container tools work out of the box. If
-         * specific setups need other settings they can reset the
-         * propagation mode to private if needed. */
+        /* Mark the root directory as shared in regards to mount propagation. The kernel defaults to "private", but we
+         * think it makes more sense to have a default of "shared" so that nspawn and the container tools work out of
+         * the box. If specific setups need other settings they can reset the propagation mode to private if
+         * needed. Note that we set this only when we are invoked directly by the kernel. If we are invoked by a
+         * container manager we assume the container manager knows what it is doing (for example, because it set up
+         * some directories with different propagation modes). */
         if (detect_container() <= 0)
                 if (mount(NULL, "/", NULL, MS_REC|MS_SHARED, NULL) < 0)
                         log_warning_errno(errno, "Failed to set up the root directory for shared mount propagation: %m");
 
-        /* Create a few directories we always want around, Note that
-         * sd_booted() checks for /run/systemd/system, so this mkdir
-         * really needs to stay for good, otherwise software that
-         * copied sd-daemon.c into their sources will misdetect
-         * systemd. */
+        /* Create a few directories we always want around, Note that sd_booted() checks for /run/systemd/system, so
+         * this mkdir really needs to stay for good, otherwise software that copied sd-daemon.c into their sources will
+         * misdetect systemd. */
         (void) mkdir_label("/run/systemd", 0755);
         (void) mkdir_label("/run/systemd/system", 0755);
-        (void) mkdir_label("/run/systemd/inaccessible", 0000);
+
         /* Set up inaccessible items */
+        (void) mkdir_label("/run/systemd/inaccessible", 0000);
         (void) mknod("/run/systemd/inaccessible/reg", S_IFREG | 0000, 0);
         (void) mkdir_label("/run/systemd/inaccessible/dir", 0000);
         (void) mknod("/run/systemd/inaccessible/chr", S_IFCHR | 0000, makedev(0, 0));