mount: add ReadWriteOnly property to fail on read-only mounts

Systems where a mount point is expected to be read-write needs a way to
fail mount units that fallback as read-only.

Add a property to allow setting the -w option when calling mount(8).

src/core/dbus-mount.c

@@ -51,6 +51,7 @@ const sd_bus_vtable bus_mount_vtable[] = {
         SD_BUS_PROPERTY("SloppyOptions", "b", bus_property_get_bool, offsetof(Mount, sloppy_options), SD_BUS_VTABLE_PROPERTY_CONST),
         SD_BUS_PROPERTY("LazyUnmount", "b", bus_property_get_bool, offsetof(Mount, lazy_unmount), SD_BUS_VTABLE_PROPERTY_CONST),
         SD_BUS_PROPERTY("ForceUnmount", "b", bus_property_get_bool, offsetof(Mount, force_unmount), SD_BUS_VTABLE_PROPERTY_CONST),
+        SD_BUS_PROPERTY("ReadWriteOnly", "b", bus_property_get_bool, offsetof(Mount, read_write_only), SD_BUS_VTABLE_PROPERTY_CONST),
         SD_BUS_PROPERTY("Result", "s", property_get_result, offsetof(Mount, result), SD_BUS_VTABLE_PROPERTY_EMITS_CHANGE),
         SD_BUS_PROPERTY("UID", "u", bus_property_get_uid, offsetof(Unit, ref_uid), SD_BUS_VTABLE_PROPERTY_EMITS_CHANGE),
         SD_BUS_PROPERTY("GID", "u", bus_property_get_gid, offsetof(Unit, ref_gid), SD_BUS_VTABLE_PROPERTY_EMITS_CHANGE),
@@ -102,6 +103,9 @@ static int bus_mount_set_transient_property(
         if (streq(name, "ForceUnmount"))
                 return bus_set_transient_bool(u, name, &m->force_unmount, message, flags, error);
 
+        if (streq(name, "ReadWriteOnly"))
+                return bus_set_transient_bool(u, name, &m->read_write_only, message, flags, error);
+
         return 0;
 }
 

src/core/load-fragment-gperf.gperf.m4

@@ -429,6 +429,7 @@ Mount.DirectoryMode,             config_parse_mode,                  0,
 Mount.SloppyOptions,             config_parse_bool,                  0,                             offsetof(Mount, sloppy_options)
 Mount.LazyUnmount,               config_parse_bool,                  0,                             offsetof(Mount, lazy_unmount)
 Mount.ForceUnmount,              config_parse_bool,                  0,                             offsetof(Mount, force_unmount)
+Mount.ReadWriteOnly,             config_parse_bool,                  0,                             offsetof(Mount, read_write_only)
 EXEC_CONTEXT_CONFIG_ITEMS(Mount)m4_dnl
 CGROUP_CONTEXT_CONFIG_ITEMS(Mount)m4_dnl
 KILL_CONTEXT_CONFIG_ITEMS(Mount)m4_dnl

src/core/mount.c

@@ -752,6 +752,7 @@ static void mount_dump(Unit *u, FILE *f, const char *prefix) {
                 "%sSloppyOptions: %s\n"
                 "%sLazyUnmount: %s\n"
                 "%sForceUnmount: %s\n"
+                "%sReadWriteOnly: %s\n"
                 "%sTimeoutSec: %s\n",
                 prefix, mount_state_to_string(m->state),
                 prefix, mount_result_to_string(m->result),
@@ -767,6 +768,7 @@ static void mount_dump(Unit *u, FILE *f, const char *prefix) {
                 prefix, yes_no(m->sloppy_options),
                 prefix, yes_no(m->lazy_unmount),
                 prefix, yes_no(m->force_unmount),
+                prefix, yes_no(m->read_write_only),
                 prefix, format_timespan(buf, sizeof(buf), m->timeout_usec, USEC_PER_SEC));
 
         if (m->control_pid > 0)
@@ -998,6 +1000,8 @@ static void mount_enter_mounting(Mount *m) {
                 r = exec_command_set(m->control_command, MOUNT_PATH, p->what, m->where, NULL);
                 if (r >= 0 && m->sloppy_options)
                         r = exec_command_append(m->control_command, "-s", NULL);
+                if (r >= 0 && m->read_write_only)
+                        r = exec_command_append(m->control_command, "-w", NULL);
                 if (r >= 0 && p->fstype)
                         r = exec_command_append(m->control_command, "-t", p->fstype, NULL);
                 if (r >= 0 && !isempty(opts))
@@ -1058,6 +1062,8 @@ static void mount_enter_remounting(Mount *m) {
                                      "-o", o, NULL);
                 if (r >= 0 && m->sloppy_options)
                         r = exec_command_append(m->control_command, "-s", NULL);
+                if (r >= 0 && m->read_write_only)
+                        r = exec_command_append(m->control_command, "-w", NULL);
                 if (r >= 0 && p->fstype)
                         r = exec_command_append(m->control_command, "-t", p->fstype, NULL);
         } else

src/core/mount.h

@@ -59,6 +59,8 @@ struct Mount {
         bool lazy_unmount;
         bool force_unmount;
 
+        bool read_write_only;
+
         MountResult result;
         MountResult reload_result;
         MountResult clean_result;

src/shared/bus-unit-util.c

@@ -1436,7 +1436,8 @@ static int bus_append_mount_property(sd_bus_message *m, const char *field, const
 
         if (STR_IN_SET(field, "SloppyOptions",
                               "LazyUnmount",
-                              "ForceUnmount"))
+                              "ForceUnmount",
+                              "ReadwriteOnly"))
                 return bus_append_parse_boolean(m, field, eq);
 
         return 0;

test/fuzz/fuzz-unit-file/directives.service

@@ -856,6 +856,7 @@ RateLimitIntervalSec=
 ReadKMsg=
 ReadOnly=
 ReadOnlyPaths=
+ReadWriteOnly=
 ReadWritePaths=
 RemoveIPC=
 ReserveVT=