tmpfiles: make "f" lines behaviour match what the documentation says

CHANGE OF BEHAVIOUR — with this commit "f" line's behaviour is altered
to match what the documentation says: if an "argument" string is
specified it is written to the file only when the file didn't exist
before. Previously, it would be appended to the file each time
systemd-tmpfiles was invoked — which is not a particularly useful
behaviour as the tool is not idempotent then and the indicated files
grow without bounds each time the tool is invoked.

I did some spelunking whether this change in behaviour would break
things, but afaics nothing relies on the previous O_APPEND behaviour of
this line type, hence I think it's relatively safe to make "f" lines
work the way the docs say, rather than adding a new modifier for it or
so.

Triggered by:

https://lists.freedesktop.org/archives/systemd-devel/2018-January/040171.html

1 files changed, 10 insertions, 18 deletions

diff --git a/man/tmpfiles.d.xml b/man/tmpfiles.d.xml
index 30aa886388..c3a43d36e4 100644
--- a/man/tmpfiles.d.xml
+++ b/man/tmpfiles.d.xml
@@ -147,9 +147,8 @@ L     /tmp/foobar -    -    -    -   /dev/null</programlisting>
       <variablelist>
         <varlistentry>
           <term><varname>f</varname></term>
-          <listitem><para>Create a file if it does not exist yet. If
-          the argument parameter is given, it will be written to the
-          file. Does not follow symlinks.</para></listitem>
+          <listitem><para>Create a file if it does not exist yet. If the argument parameter is given and the file did
+          not exist yet, it will be written to the file. Does not follow symlinks.</para></listitem>
         </varlistentry>
 
         <varlistentry>
@@ -585,21 +584,14 @@ r! /tmp/.X[0-9]*-lock</programlisting>
     <refsect2>
       <title>Argument</title>
 
-      <para>For <varname>L</varname> lines determines the destination
-      path of the symlink. For <varname>c</varname> and
-      <varname>b</varname>, determines the major/minor of the device
-      node, with major and minor formatted as integers, separated by
-      <literal>:</literal>, e.g.  <literal>1:3</literal>. For
-      <varname>f</varname>, <varname>F</varname>, and
-      <varname>w</varname>, the argument may be used to specify a short string that
-      is written to the file, suffixed by a newline. For
-      <varname>C</varname>, specifies the source file or
-      directory. For <varname>t</varname> and <varname>T</varname>,
-      determines extended attributes to be set. For
-      <varname>a</varname> and <varname>A</varname>, determines ACL
-      attributes to be set. For <varname>h</varname> and
-      <varname>H</varname>, determines the file attributes to
-      set. Ignored for all other lines.</para>
+      <para>For <varname>L</varname> lines determines the destination path of the symlink. For <varname>c</varname> and
+      <varname>b</varname>, determines the major/minor of the device node, with major and minor formatted as integers,
+      separated by <literal>:</literal>, e.g.  <literal>1:3</literal>. For <varname>f</varname>, <varname>F</varname>,
+      and <varname>w</varname>, the argument may be used to specify a short string that is written to the file,
+      suffixed by a newline. For <varname>C</varname>, specifies the source file or directory. For <varname>t</varname>
+      and <varname>T</varname>, determines extended attributes to be set. For <varname>a</varname> and
+      <varname>A</varname>, determines ACL attributes to be set. For <varname>h</varname> and <varname>H</varname>,
+      determines the file attributes to set. Ignored for all other lines.</para>
 
       <para>This field can contain specifiers, see below.</para>
     </refsect2>