"Don't fear the fsync()"

For files which are vital to boot

1. Avoid opening any window where power loss will zero them out or worse.
   I know app developers all coded to the ext3 implementation, but
   the only formal documentation we have says we're broken if we actually
   rely on it.  E.g.

   * `man mount`, search for `auto_da_alloc`.
   * http://www.linux-mtd.infradead.org/faq/ubifs.html#L_atomic_change
   * https://thunk.org/tytso/blog/2009/03/15/dont-fear-the-fsync/

2. If we tell the kernel we're interested in writing them to disk, it will
   tell us if that fails.  So at minimum, this means we play our part in
   notifying the user about errors.

I refactored error-handling in `udevadm-hwdb` a little.  It turns out I did
exactly the same as had already been done in the `systemd-hwdb` version,
i.e. commit d702dcd.

1 files changed, 5 insertions, 3 deletions

diff --git a/src/firstboot/firstboot.c b/src/firstboot/firstboot.c
index b3578d3e16..586674d458 100644
--- a/src/firstboot/firstboot.c
+++ b/src/firstboot/firstboot.c
@@ -411,7 +411,8 @@ static int process_hostname(void) {
                 return 0;
 
         mkdir_parents(etc_hostname, 0755);
-        r = write_string_file(etc_hostname, arg_hostname, WRITE_STRING_FILE_CREATE);
+        r = write_string_file(etc_hostname, arg_hostname,
+                              WRITE_STRING_FILE_CREATE | WRITE_STRING_FILE_SYNC);
         if (r < 0)
                 return log_error_errno(r, "Failed to write %s: %m", etc_hostname);
 
@@ -432,7 +433,8 @@ static int process_machine_id(void) {
                 return 0;
 
         mkdir_parents(etc_machine_id, 0755);
-        r = write_string_file(etc_machine_id, sd_id128_to_string(arg_machine_id, id), WRITE_STRING_FILE_CREATE);
+        r = write_string_file(etc_machine_id, sd_id128_to_string(arg_machine_id, id),
+                              WRITE_STRING_FILE_CREATE | WRITE_STRING_FILE_SYNC);
         if (r < 0)
                 return log_error_errno(r, "Failed to write machine id: %m");
 
@@ -503,7 +505,7 @@ static int write_root_shadow(const char *path, const struct spwd *p) {
         if (putspent(p, f) != 0)
                 return errno > 0 ? -errno : -EIO;
 
-        return fflush_and_check(f);
+        return fflush_sync_and_check(f);
 }
 
 static int process_root_password(void) {