New option --sort=ORDER

This option makes tar sort the entries of directories that will be
added to an archive according to ORDER (none, name, or order).

Based on proposition by Dick Streefland (https://savannah.gnu.org/patch/?7892).

* src/common.h (savedir_sort_order): New global.
* src/create.c: Pass savedir_sort_order to streamsavedir.
* src/misc.c: Likewise.
* src/tar.c: New option --sort.

* NEWS: Update.
* doc/tar.texi: Document the --sort option.
* doc/tar.1: Likewise.

doc/tar.1

@@ -13,7 +13,7 @@
 .\"
 .\" You should have received a copy of the GNU General Public License
 .\" along with this program.  If not, see <http://www.gnu.org/licenses/>.
-.TH TAR 1 "January 28, 2014" "TAR" "GNU TAR Manual"
+.TH TAR 1 "February 14, 2014" "TAR" "GNU TAR Manual"
 .SH NAME
 tar \- an archiving utility
 .SH SYNOPSIS
@@ -506,6 +506,24 @@ Try extracting files with the same ownership as exists in the archive
 .TP
 \fB\-s\fR, \fB\-\-preserve\-order\fR, \fB\-\-same\-order\fR
 Sort names to extract to match archive
+.TP
+\fB\-\-sort=\fIORDER\fR
+When creating an archive, sort directory entries according to
+\fIORDER\fR, which is one of
+.BR none ,
+.BR name ", or"
+.BR inode .
+
+The default is \fB\-\-sort=none\fR, which stores archive members in
+the same order as returned by the operating system.
+
+Using \fB\-\-sort=name\fR ensures the member ordering in the created archive
+is uniform and reproducible.
+
+Using \fB\-\-sort=inode\fR reduces the number of disk seeks made when
+creating the archive and thus can considerably speed up archivation.
+This sorting order is supported only if the underlying system provides
+the necessary information.
 .SS Device selection and switching
 .TP
 \fB\-f\fR, \fB\-\-file\fR=\fIARCHIVE\fR

doc/tar.texi

@@ -3319,6 +3319,27 @@ The @option{--warning=existing-file} option can be used together with
 this option to produce warning messages about existing old files
 (@pxref{warnings}).
 
+@opsummary{sort}
+@item --sort=@var{order}
+Specify the directory sorting order when reading directories.
+@var{Order} may be one of the following:
+
+@table @samp
+@item none
+No directory sorting is performed. This is the default.
+
+@item name
+Sort the directory entries on name. The operating system may deliver
+directory entries in a more or less random order, and sorting them
+makes archive creation reproducible.
+
+@item inode
+Sort the directory entries on inode number. Sorting directories on
+inode number may reduce the amount of disk seek operations when
+creating an archive for some file systems.
+
+@end table
+
 @opsummary{sparse}
 @item --sparse
 @itemx -S