Merge pull request #19817 from keszybz/switch-root-serialization

Drop serialization of mounts and automounts over root switch

src/core/automount.c

@@ -1087,6 +1087,7 @@ const UnitVTable automount_vtable = {
         .can_transient = true,
         .can_fail = true,
         .can_trigger = true,
+        .exclude_from_switch_root_serialization = true,
 
         .init = automount_init,
         .load = automount_load,

src/core/manager.c

@@ -3321,11 +3321,7 @@ int manager_serialize(
                 if (u->id != t)
                         continue;
 
-                /* Start marker */
-                fputs(u->id, f);
-                fputc('\n', f);
-
-                r = unit_serialize(u, f, fds, !switching_root);
+                r = unit_serialize(u, f, fds, switching_root);
                 if (r < 0)
                         return r;
         }

src/core/mount.c

@@ -2176,6 +2176,7 @@ const UnitVTable mount_vtable = {
 
         .can_transient = true,
         .can_fail = true,
+        .exclude_from_switch_root_serialization = true,
 
         .init = mount_init,
         .load = mount_load,

src/core/unit-serialize.c

@@ -89,13 +89,25 @@ static const char *const io_accounting_metric_field_last[_CGROUP_IO_ACCOUNTING_M
         [CGROUP_IO_WRITE_OPERATIONS] = "io-accounting-write-operations-last",
 };
 
-int unit_serialize(Unit *u, FILE *f, FDSet *fds, bool serialize_jobs) {
+int unit_serialize(Unit *u, FILE *f, FDSet *fds, bool switching_root) {
         int r;
 
         assert(u);
         assert(f);
         assert(fds);
 
+        if (switching_root && UNIT_VTABLE(u)->exclude_from_switch_root_serialization) {
+                /* In the new root, paths for mounts and automounts will be different, so it doesn't make
+                 * much sense to serialize things. API file systems will be moved to the new root, but we
+                 * don't have mount units for those. */
+                log_unit_debug(u, "not serializing before switch-root");
+                return 0;
+        }
+
+        /* Start marker */
+        fputs(u->id, f);
+        fputc('\n', f);
+
         if (unit_can_serialize(u)) {
                 r = UNIT_VTABLE(u)->serialize(u, f, fds);
                 if (r < 0)
@@ -175,7 +187,7 @@ int unit_serialize(Unit *u, FILE *f, FDSet *fds, bool serialize_jobs) {
                         (void) serialize_item_format(f, ip_accounting_metric_field[m], "%" PRIu64, v);
         }
 
-        if (serialize_jobs) {
+        if (!switching_root) {
                 if (u->job) {
                         fputs("job\n", f);
                         job_serialize(u->job, f);

src/core/unit.h

@@ -543,8 +543,8 @@ typedef struct UnitVTable {
 
         bool (*can_reload)(Unit *u);
 
-        /* Write all data that cannot be restored from other sources
-         * away using unit_serialize_item() */
+        /* Serialize state and file descriptors that should be carried over into the new
+         * instance after reexecution. */
         int (*serialize)(Unit *u, FILE *f, FDSet *fds);
 
         /* Restore one item from the serialization */
@@ -646,7 +646,7 @@ typedef struct UnitVTable {
         /* Type specific cleanups. */
         void (*shutdown)(Manager *m);
 
-        /* If this function is set and return false all jobs for units
+        /* If this function is set and returns false all jobs for units
          * of this type will immediately fail. */
         bool (*supported)(void);
 
@@ -654,25 +654,28 @@ typedef struct UnitVTable {
         UnitStatusMessageFormats status_message_formats;
 
         /* True if transient units of this type are OK */
-        bool can_transient:1;
+        bool can_transient;
 
         /* True if cgroup delegation is permissible */
-        bool can_delegate:1;
+        bool can_delegate;
 
         /* True if the unit type triggers other units, i.e. can have a UNIT_TRIGGERS dependency */
-        bool can_trigger:1;
+        bool can_trigger;
 
         /* True if the unit type knows a failure state, and thus can be source of an OnFailure= dependency */
-        bool can_fail:1;
+        bool can_fail;
 
         /* True if units of this type shall be startable only once and then never again */
-        bool once_only:1;
+        bool once_only;
+
+        /* Do not serialize this unit when preparing for root switch */
+        bool exclude_from_switch_root_serialization;
 
         /* True if queued jobs of this type should be GC'ed if no other job needs them anymore */
-        bool gc_jobs:1;
+        bool gc_jobs;
 
         /* True if systemd-oomd can monitor and act on this unit's recursive children's cgroup(s)  */
-        bool can_set_managed_oom:1;
+        bool can_set_managed_oom;
 } UnitVTable;
 
 extern const UnitVTable * const unit_vtable[_UNIT_TYPE_MAX];