cephadm: convert SNMPGateway create_daemon_conf to use write_new

While it is not entirely clear why this pattern of using os.open and
posix open flags instead of `open` directly was used I determined (using
strace) that the only major difference between these open flags and
those used by `open` was the lack of O_TRUNC. Unlike some other cases
this function does not use an intermediate temporary file.  This means
that if the file being written already exists and the data being written
is smaller then the remaining data will not be over-written.

Example:
```
$ cat existing
AAAAAAAA
$ cat existing
bbbAAAAA
```

I looked over the context that this function is used in and decided that
this behavior must not be intentional. Thus it should be safe
to convert this function to `write_new`.

Signed-off-by: John Mulligan <jmulligan@redhat.com>
(cherry picked from commit 6ec5a5ead36a79ce331b6943296c401feea7a896)

diff --git a/src/cephadm/cephadm.py b/src/cephadm/cephadm.py
index e797cfe7d4c338f779da92954a00cb34cecbb0a7..3284046ca610db8c5a61966b57fdaf6ea85325b4 100755 (executable)
--- a/src/cephadm/cephadm.py
+++ b/src/cephadm/cephadm.py
@@ -511,7 +511,7 @@ class SNMPGateway:
 
     def create_daemon_conf(self) -> None:
         """Creates the environment file holding 'secrets' passed to the snmp-notifier daemon"""
-        with open(os.open(self.conf_file_path, os.O_CREAT | os.O_WRONLY, 0o600), 'w') as f:
+        with write_new(self.conf_file_path, perms=0o600) as f:
             if self.snmp_version == 'V2c':
                 f.write(f'SNMP_NOTIFIER_COMMUNITY={self.snmp_community}\n')
             else: