Based on 605f81a8968b2df8a28cca2cf11db99ab948a2af Mon Sep 17 00:00:00 2001
From: Michal Sekletar <msekleta@redhat.com>
Date: Tue, 21 Oct 2014 18:17:54 +0200
Subject: [PATCH] util: introduce sethostname_idempotent

Function queries system hostname and applies changes only when necessary. Also,
migrate all client of sethostname to sethostname_idempotent while at it.
---
 src/core/hostname-setup.c |    2 +-
 src/hostname/hostnamed.c  |    2 +-
 src/nspawn/nspawn.c       |    2 +-
 src/shared/util.c         |   20 ++++++++++++++++++++
 src/shared/util.h         |    2 ++
 5 files changed, 25 insertions(+), 3 deletions(-)

--- src/core/hostname-setup.c
+++ src/core/hostname-setup.c	2014-10-29 00:00:00.000000000 +0000
@@ -99,7 +99,7 @@ int hostname_setup(void) {
                 hn = "localhost";
         }
 
-        if (sethostname(hn, strlen(hn)) < 0) {
+        if (sethostname_idempotent(hn) < 0) {
                 log_warning("Failed to set hostname to <%s>: %m", hn);
                 return -errno;
         }
--- src/hostname/hostnamed.c
+++ src/hostname/hostnamed.c	2014-10-29 14:13:26.124337751 +0000
@@ -244,7 +244,7 @@ static int context_write_data_hostname(C
         else
                 hn = c->data[PROP_HOSTNAME];
 
-        if (sethostname(hn, strlen(hn)) < 0)
+        if (sethostname_idempotent(hn) < 0)
                 return -errno;
 
         return 0;
--- src/nspawn/nspawn.c
+++ src/nspawn/nspawn.c	2014-10-29 00:00:00.000000000 +0000
@@ -981,7 +981,7 @@ static int setup_hostname(void) {
         if (arg_share_system)
                 return 0;
 
-        if (sethostname(arg_machine, strlen(arg_machine)) < 0)
+        if (sethostname_idempotent(arg_machine) < 0)
                 return -errno;
 
         return 0;
--- src/shared/util.c
+++ src/shared/util.c	2014-10-29 00:00:00.000000000 +0000
@@ -6451,6 +6451,26 @@ int fd_warn_permissions(const char *path
         return 0;
 }
 
+int sethostname_idempotent(const char *s) {
+        int r;
+        char buf[HOST_NAME_MAX + 1] = {};
+
+        assert(s);
+
+        r = gethostname(buf, sizeof(buf));
+        if (r < 0)
+                return -errno;
+
+        if (streq(buf, s))
+                return 0;
+
+        r = sethostname(buf, strlen(buf));
+        if (r < 0)
+                return -errno;
+
+        return 1;
+}
+
 unsigned long personality_from_string(const char *p) {
 
         /* Parse a personality specifier. We introduce our own
--- src/shared/util.h
+++ src/shared/util.h	2014-10-29 14:14:15.764337717 +0000
@@ -899,3 +899,5 @@ union file_handle_union {
 };
 
 int umount_recursive(const char *target, int flags);
+
+int sethostname_idempotent(const char *s);
