hostname: introduce two bus errors for updating file

src/hostname/hostnamed.c

@@ -767,6 +767,10 @@ static int method_set_static_hostname(sd_bus_message *m, void *userdata, sd_bus_
         r = context_write_data_static_hostname(c);
         if (r < 0) {
                 log_error_errno(r, "Failed to write static hostname: %m");
+                if (ERRNO_IS_PRIVILEGE(r))
+                        return sd_bus_error_set(error, BUS_ERROR_FILE_IS_PROTECTED, "Not allowed to update /etc/hostname.");
+                if (r == -EROFS)
+                        return sd_bus_error_set(error, BUS_ERROR_READ_ONLY_FILESYSTEM, "/etc/hostname is in a read-only filesystem.");
                 return sd_bus_error_set_errnof(error, r, "Failed to set static hostname: %m");
         }
 
@@ -843,6 +847,10 @@ static int set_machine_info(Context *c, sd_bus_message *m, int prop, sd_bus_mess
         r = context_write_data_machine_info(c);
         if (r < 0) {
                 log_error_errno(r, "Failed to write machine info: %m");
+                if (ERRNO_IS_PRIVILEGE(r))
+                        return sd_bus_error_set(error, BUS_ERROR_FILE_IS_PROTECTED, "Not allowed to update /etc/machine-info.");
+                if (r == -EROFS)
+                        return sd_bus_error_set(error, BUS_ERROR_READ_ONLY_FILESYSTEM, "/etc/machine-info is in a read-only filesystem.");
                 return sd_bus_error_set_errnof(error, r, "Failed to write machine info: %m");
         }
 

src/libsystemd/sd-bus/bus-common-errors.c

@@ -101,6 +101,8 @@ BUS_ERROR_MAP_ELF_REGISTER const sd_bus_error_map bus_common_errors[] = {
         SD_BUS_ERROR_MAP(BUS_ERROR_TRANSFER_IN_PROGRESS,         EBUSY),
 
         SD_BUS_ERROR_MAP(BUS_ERROR_NO_PRODUCT_UUID,              EOPNOTSUPP),
+        SD_BUS_ERROR_MAP(BUS_ERROR_FILE_IS_PROTECTED,            EACCES),
+        SD_BUS_ERROR_MAP(BUS_ERROR_READ_ONLY_FILESYSTEM,         EROFS),
 
         SD_BUS_ERROR_MAP(BUS_ERROR_SPEED_METER_INACTIVE,         EOPNOTSUPP),
         SD_BUS_ERROR_MAP(BUS_ERROR_UNMANAGED_INTERFACE,          EOPNOTSUPP),

src/libsystemd/sd-bus/bus-common-errors.h

@@ -81,6 +81,8 @@
 #define BUS_ERROR_TRANSFER_IN_PROGRESS         "org.freedesktop.import1.TransferInProgress"
 
 #define BUS_ERROR_NO_PRODUCT_UUID              "org.freedesktop.hostname1.NoProductUUID"
+#define BUS_ERROR_FILE_IS_PROTECTED            "org.freedesktop.hostname1.FileIsProtected"
+#define BUS_ERROR_READ_ONLY_FILESYSTEM         "org.freedesktop.hostname1.ReadOnlyFilesystem"
 
 #define BUS_ERROR_SPEED_METER_INACTIVE         "org.freedesktop.network1.SpeedMeterInactive"
 #define BUS_ERROR_UNMANAGED_INTERFACE          "org.freedesktop.network1.UnmanagedInterface"