dpkg-gencontrol: Rework Installed-Size field default value computation

Switch from «du» to File::Find, and accumulate size usage per filesystem
object, on 1 KiB units. Use the actual size only for regular files and
symlinks, and just 1 KiB for any other filesystem object type.

This guarantees a constant and reproducible size regardless of the
build system filesystem being used.

Document how the value is computed, and that it is just a size
approximation.

Closes: #650077

debian/changelog

@@ -47,6 +47,10 @@ dpkg (1.18.0) UNRELEASED; urgency=low
   * Wrap file references in man page PO files.
   * Switch Dpkg::Checksums from using checksum programs to the more portable
     Digest modules. Obsolete the 'program' property, and add a 'name' one.
+  * Rework the Installed-Size field default value computation to make it
+    reproducible regardless of the build system filesystem, and document
+    how the value is computed and that it is just an approximation.
+    Closes: #650077
 
  -- Guillem Jover <guillem@debian.org>  Tue, 09 Dec 2014 23:53:18 +0100
 

man/deb-substvars.5

@@ -18,7 +18,7 @@
 .\" You should have received a copy of the GNU General Public License
 .\" along with this program.  If not, see <https://www.gnu.org/licenses/>.
 .
-.TH deb\-substvars 5 "2009-07-15" "Debian Project" "dpkg utilities"
+.TH deb\-substvars 5 "2015-01-20" "Debian Project" "dpkg utilities"
 .SH NAME
 deb\-substvars \- Debian source substitution variables
 .
@@ -111,13 +111,18 @@ The source package version (from the changelog file). This variable is now
 the \fBsource:Version\fP or \fBbinary:Version\fP as appropriate.
 .TP
 .B Installed\-Size
-The total size of the package's installed files. This value is copied
-into the corresponding control file field; setting it will modify the
-value of that field. If this variable isn't set
+The approximate total size of the package's installed files. This value is
+copied into the corresponding control file field; setting it will modify
+the value of that field. If this variable is not set
 .B dpkg\-gencontrol
-will use
-.B du \-k debian/tmp
-to find the default value.
+will compute the default value by accumulating the size of each regular
+file and symlink rounded to 1 KiB used units, and a baseline of 1 KiB for
+any other filesystem object type.
+
+\fBNote:\fP Take into account that this can only ever be an approximation,
+as the actual size used on the installed system will depend greatly on the
+filesystem used and its parameters, which might end up using either more
+or less space than the specified in this field.
 .TP
 .B Extra\-Size
 Additional disk space used when the package is installed. If this

scripts/dpkg-gencontrol.pl

@@ -4,7 +4,7 @@
 #
 # Copyright © 1996 Ian Jackson
 # Copyright © 2000,2002 Wichert Akkerman
-# Copyright © 2006-2014 Guillem Jover <guillem@debian.org>
+# Copyright © 2006-2015 Guillem Jover <guillem@debian.org>
 #
 # This program is free software; you can redistribute it and/or modify
 # it under the terms of the GNU General Public License as published by
@@ -23,6 +23,8 @@ use strict;
 use warnings;
 
 use POSIX qw(:errno_h :fcntl_h);
+use File::Find;
+
 use Dpkg ();
 use Dpkg::Gettext;
 use Dpkg::ErrorHandling;
@@ -334,26 +336,25 @@ if ($oppackage ne $sourcepackage || $verdiff) {
 }
 
 if (!defined($substvars->get('Installed-Size'))) {
-    my $c = open(my $du_fh, '-|');
-    if (not defined $c) {
-        syserr(g_('cannot fork for %s'), 'du');
-    }
-    if (!$c) {
-        chdir("$packagebuilddir")
-            or syserr(g_("chdir for du to \`%s'"), $packagebuilddir);
-        exec('du', '-k', '-s', '--apparent-size', '.')
-            or syserr(g_('unable to execute %s'), 'du');
-    }
-    my $duo = '';
-    while (<$du_fh>) {
-	$duo .= $_;
-    }
-    close($du_fh);
-    subprocerr(g_("du in \`%s'"), $packagebuilddir) if $?;
-    if ($duo !~ m/^(\d+)\s+\.$/) {
-        error(g_("du gave unexpected output \`%s'"), $duo);
-    }
-    $substvars->set_as_auto('Installed-Size', $1);
+    my $installed_size = 0;
+    my $scan_installed_size = sub {
+        lstat or syserr(g_('cannot stat %s'), $File::Find::name);
+
+        if (-f _ or -l _) {
+            # For filesystem objects with actual content accumulate the size
+            # in 1 KiB units.
+            $installed_size += POSIX::ceil((-s _) / 1024);
+        } else {
+            # For other filesystem objects assume a minimum 1 KiB baseline,
+            # as directories are shared resources between packages, and other
+            # object types are mainly metadata-only, supposedly consuming
+            # at most an inode.
+            $installed_size += 1;
+        }
+    };
+    find($scan_installed_size, $packagebuilddir);
+
+    $substvars->set_as_auto('Installed-Size', $installed_size);
 }
 if (defined($substvars->get('Extra-Size'))) {
     my $size = $substvars->get('Extra-Size') + $substvars->get('Installed-Size');