[build] Pad .rom, .dsk, and .hd images to 512-byte boundaries

QEMU will silently round down a disk or ROM image file to the nearest
512 bytes.  Fix by always padding .rom, .dsk and .hd images to the
nearest 512-byte boundary.

Originally-fixed-by: Stefan Hajnoczi <stefanha@gmail.com>

src/util/dskpad.pl

@@ -1,12 +0,0 @@
-#!/usr/bin/perl -w
-
-use strict;
-use warnings;
-
-use constant FLOPPYSIZE => 1440 * 1024;
-
-while ( my $filename = shift ) {
-  die "$filename is not a file\n" unless -f $filename;
-  die "$filename is too large\n" unless ( -s $filename <= FLOPPYSIZE );
-  truncate $filename, FLOPPYSIZE or die "Could not truncate: $!\n";
-}

src/util/padimg.pl

@@ -0,0 +1,44 @@
+#!/usr/bin/perl -w
+
+use strict;
+use warnings;
+use Getopt::Long;
+use Fcntl;
+
+my $verbosity = 0;
+my $blksize = 512;
+my $byte = 0;
+
+my $opts = {
+  'verbose|v+' => sub { $verbosity++; },
+  'quiet|q+' => sub { $verbosity--; },
+  'blksize|s=o' => sub { $blksize = $_[1]; },
+  'byte|b=o' => sub { $byte = $_[1]; },
+};
+
+Getopt::Long::Configure ( 'bundling', 'auto_abbrev' );
+GetOptions ( { map { /^(\w+)/; $1 => $opts->{$_} } keys %$opts }, keys %$opts )
+    or die "Could not parse command-line options\n";
+
+while ( my $filename = shift ) {
+  die "$filename is not a file\n" unless -f $filename;
+  my $oldsize = -s $filename;
+  my $newsize = ( ( $oldsize + $blksize - 1 ) & ~( $blksize - 1 ) );
+  my $padsize = ( $newsize - $oldsize );
+  next unless $padsize;
+  if ( $verbosity >= 1 ) {
+      printf "Padding %s from %d to %d bytes with %d x 0x%02x\n",
+	     $filename, $oldsize, $newsize, $padsize, $byte;
+  }
+  if ( $byte ) {
+    sysopen ( my $fh, $filename, ( O_WRONLY | O_APPEND ) )
+	or die "Could not open $filename for appending: $!\n";
+    syswrite $fh, ( chr ( $byte ) x $padsize )
+	or die "Could not append to $filename: $!\n";
+    close ( $fh );
+  } else {
+    truncate $filename, $newsize
+	or die "Could not resize $filename: $!\n";
+  }
+  die "Failed to pad $filename\n" unless -s $filename == $newsize;
+}