BZ 6894: Enhance d_namlen description

[Andreas Jaeger]

d_namlen is not really marked as optional, let's explain this,

Ok to commit?

Andreas

2012-04-08  Andreas Jaeger  <aj@suse.de>

	[BZ #6894]
	* manual/filesys.texi (Directory Entries): Mention that d_namlen
	is an optional BSD extension.

diff --git a/manual/filesys.texi b/manual/filesys.texi
index 04f4376..b9c6fee 100644
--- a/manual/filesys.texi
+++ b/manual/filesys.texi
@@ -247,9 +247,11 @@ systems, for most files this the same as the 
@code{st_ino} member that
  @code{stat} will return for the file.  @xref{File Attributes}.

  @item unsigned char d_namlen
-This is the length of the file name, not including the terminating null
-character.  Its type is @code{unsigned char} because that is the integer
-type of the appropriate size
+This is the length of the file name, not including the terminating
+null character.  Its type is @code{unsigned char} because that is the
+integer type of the appropriate size. This member is a BSD extension.
+The symbol @code{_DIRENT_HAVE_D_NAMLEN} is defined if this member is
+available.

  @item unsigned char d_type
  This is the type of the file, possibly unknown.  The following constants

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  Andreas Jaeger aj@{suse.com,opensuse.org} Twitter/Identica: jaegerandi
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