Pintos.pm

# Pintos helper subroutines.

# Number of bytes available for the loader at the beginning of the MBR.
# Kernel command-line arguments follow the loader.
our $LOADER_SIZE = 314;

# Partition types.
my (%role2type) = (KERNEL => 0x20,
		   FILESYS => 0x21,
		   SCRATCH => 0x22,
		   SWAP => 0x23);
my (%type2role) = reverse %role2type;

# Order of roles within a given disk.
our (@role_order) = qw (KERNEL FILESYS SCRATCH SWAP);

# Partitions.
#
# Valid keys are KERNEL, FILESYS, SCRATCH, SWAP.  Only those
# partitions which are in use are included.
#
# Each value is a reference to a hash.  If the partition's contents
# are to be obtained from a file (that will be copied into a new
# virtual disk), then the hash contains:
#
# FILE => name of file from which the partition's contents are copied
#         (perhaps "/dev/zero"),
# OFFSET => offset in bytes in FILE,
# BYTES => size in bytes of contents from FILE,
#
# If the partition is taken from a virtual disk directly, then it
# contains the following.  The same keys are also filled in once a
# file-based partition has been copied into a new virtual disk:
#
# DISK => name of virtual disk file,
# START => sector offset of start of partition within DISK,
# SECTORS => number of sectors of partition within DISK, which is usually
#            greater than round_up (BYTES, 512) due to padding.
our (%parts);

# set_part($opt, $arg)
#
# For use as a helper function for Getopt::Long::GetOptions to set
# disk sources.
sub set_part {
    my ($opt, $arg) = @_;
    my ($role, $source) = $opt =~ /^([a-z]+)(?:-([a-z]+))?/ or die;

    $role = uc $role;
    $source = 'FILE' if $source eq '';

    die "can't have two sources for \L$role\E partition"
      if exists $parts{$role};

    do_set_part ($role, $source, $arg);
}

# do_set_part($role, $source, $arg)
#
# Sets partition $role as coming from $source (one of 'file', 'from',
# or 'size').  $arg is a file name for 'file' or 'from', a size in
# megabytes for 'size'.
sub do_set_part {
    my ($role, $source, $arg) = @_;

    my ($p) = $parts{$role} = {};
    if ($source eq 'file') {
	if (read_mbr ($arg)) {
	    print STDERR "warning: $arg looks like a partitioned disk ";
	    print STDERR "(did you want --$role-from=$arg or --disk=$arg?)\n"
	}

	$p->{FILE} = $arg;
	$p->{OFFSET} = 0;
	$p->{BYTES} = -s $arg;
    } elsif ($source eq 'from') {
	my (%pt) = read_partition_table ($arg);
	my ($sp) = $pt{$role};
	die "$arg: does not contain \L$role\E partition\n" if !defined $sp;

	$p->{FILE} = $arg;
	$p->{OFFSET} = $sp->{START} * 512;
	$p->{BYTES} = $sp->{SECTORS} * 512;
    } elsif ($source eq 'size') {
	$arg =~ /^\d+(\.\d+)?|\.\d+$/ or die "$arg: not a valid size in MB\n";

	$p->{FILE} = "/dev/zero";
	$p->{OFFSET} = 0;
	$p->{BYTES} = ceil ($arg * 1024 * 1024);
    } else {
	die;
    }
}

# set_geometry('HEADS,SPT')
# set_geometry('zip')
#
# For use as a helper function for Getopt::Long::GetOptions to set
# disk geometry.
sub set_geometry {
    local ($_) = $_[1];
    if ($_ eq 'zip') {
	@geometry{'H', 'S'} = (64, 32);
    } else {
	@geometry{'H', 'S'} = /^(\d+)[,\s]+(\d+)$/
	  or die "bad syntax for geometry\n";
	$geometry{H} <= 255 or die "heads limited to 255\n";
	$geometry{S} <= 63 or die "sectors per track limited to 63\n";
    }
}

# set_align('bochs|full|none')
#
# For use as a helper function for Getopt::Long::GetOptions to set
# partition alignment.
sub set_align {
    $align = $_[1];
    die "unknown alignment type \"$align\"\n"
      if $align ne 'bochs' && $align ne 'full' && $align ne 'none';
}

# assemble_disk(%args)
#
# Creates a virtual disk $args{DISK} containing the partitions
# described by @args{KERNEL, FILESYS, SCRATCH, SWAP}.
#
# Required arguments:
#   DISK => output disk file name
#   HANDLE => output file handle (will be closed)
#
# Normally at least one of the following is included:
#   KERNEL, FILESYS, SCRATCH, SWAP => {input:
#				       FILE => file to read,
#                                      OFFSET => byte offset in file,
#                                      BYTES => byte count from file,
#
#                                      output:
#				       DISK => output disk file name,
#                                      START => sector offset in DISK,
#                                      SECTORS => sector count in DISK},
#
# Optional arguments:
#   ALIGN => 'bochs' (default), 'full', or 'none'
#   GEOMETRY => {H => heads, S => sectors per track} (default 16, 63)
#   FORMAT => 'partitioned' (default) or 'raw'
#   LOADER => $LOADER_SIZE-byte string containing the loader binary
#   ARGS => ['arg 1', 'arg 2', ...]
sub assemble_disk {
    my (%args) = @_;

    my (%geometry) = $args{GEOMETRY} || (H => 16, S => 63);

    my ($align);	# Align partition start, end to cylinder boundary?
    my ($pad);		# Pad end of disk out to cylinder boundary?
    if (!defined ($args{ALIGN}) || $args{ALIGN} eq 'bochs') {
	$align = 0;
	$pad = 1;
    } elsif ($args{ALIGN} eq 'full') {
	$align = 1;
	$pad = 0;
    } elsif ($args{ALIGN} eq 'none') {
	$align = $pad = 0;
    } else {
	die;
    }

    my ($format) = $args{FORMAT} || 'partitioned';
    die if $format ne 'partitioned' && $format ne 'raw';

    # Check that we have apartitions to copy in.
    my $part_cnt = grep (defined ($args{$_}), keys %role2type);
    die "must have exactly one partition for raw output\n"
      if $format eq 'raw' && $part_cnt != 1;

    # Calculate the disk size.
    my ($total_sectors) = 0;
    if ($format eq 'partitioned') {
	$total_sectors += $align ? $geometry{S} : 1;
    }
    for my $role (@role_order) {
	my ($p) = $args{$role};
	next if !defined $p;

	die if $p->{DISK};

	my ($bytes) = $p->{BYTES};
	my ($start) = $total_sectors;
	my ($end) = $start + div_round_up ($bytes, 512);
	$end = round_up ($end, cyl_sectors (%geometry)) if $align;

	$p->{DISK} = $args{DISK};
	$p->{START} = $start;
	$p->{SECTORS} = $end - $start;
	$total_sectors = $end;
    }

    # Write the disk.
    my ($disk_fn) = $args{DISK};
    my ($disk) = $args{HANDLE};
    if ($format eq 'partitioned') {
	# Pack loader into MBR.
	my ($loader) = $args{LOADER} || "\xcd\x18";
	my ($mbr) = pack ("a$LOADER_SIZE", $loader);

	$mbr .= make_kernel_command_line (@{$args{ARGS}});

	# Pack partition table into MBR.
	$mbr .= make_partition_table (\%geometry, \%args);

	# Add signature to MBR.
	$mbr .= pack ("v", 0xaa55);

	die if length ($mbr) != 512;
	write_fully ($disk, $disk_fn, $mbr);
	write_zeros ($disk, $disk_fn, 512 * ($geometry{S} - 1)) if $align;
    }
    for my $role (@role_order) {
	my ($p) = $args{$role};
	next if !defined $p;

	my ($source);
	my ($fn) = $p->{FILE};
	open ($source, '<', $fn) or die "$fn: open: $!\n";
	if ($p->{OFFSET}) {
	    sysseek ($source, $p->{OFFSET}, 0) == $p->{OFFSET}
	      or die "$fn: seek: $!\n";
	}
	copy_file ($source, $fn, $disk, $disk_fn, $p->{BYTES});
	close ($source) or die "$fn: close: $!\n";

	write_zeros ($disk, $disk_fn, $p->{SECTORS} * 512 - $p->{BYTES});
    }
    if ($pad) {
	my ($pad_sectors) = round_up ($total_sectors, cyl_sectors (%geometry));
	write_zeros ($disk, $disk_fn, ($pad_sectors - $total_sectors) * 512);
    }
    close ($disk) or die "$disk: close: $!\n";
}

# make_partition_table({H => heads, S => sectors}, {KERNEL => ..., ...})
#
# Creates and returns a partition table for the given partitions and
# disk geometry.
sub make_partition_table {
    my ($geometry, $partitions) = @_;
    my ($table) = '';
    for my $role (@role_order) {
	defined (my $p = $partitions->{$role}) or next;

	my $end = $p->{START} + $p->{SECTORS} - 1;
	my $bootable = $role eq 'KERNEL';

	$table .= pack ("C", $bootable ? 0x80 : 0);   # Bootable?
	$table .= pack_chs ($p->{START}, $geometry);  # CHS of partition start
	$table .= pack ("C", $role2type{$role});      # Partition type
	$table .= pack_chs($end, $geometry);          # CHS of partition end
	$table .= pack ("V", $p->{START});            # LBA of partition start
	$table .= pack ("V", $p->{SECTORS});          # Length in sectors
	die if length ($table) % 16;
    }
    return pack ("a64", $table);
}

# make_kernel_command_line(@args)
#
# Returns the raw bytes to write to an MBR at offset $LOADER_SIZE to
# set a Pintos kernel command line.
sub make_kernel_command_line {
    my (@args) = @_;
    my ($args) = join ('', map ("$_\0", @args));
    die "command line exceeds 128 bytes" if length ($args) > 128;
    return pack ("V a128", scalar (@args), $args);
}

# copy_file($from_handle, $from_file_name, $to_handle, $to_file_name, $size)
#
# Copies $size bytes from $from_handle to $to_handle.
# $from_file_name and $to_file_name are used in error messages.
sub copy_file {
    my ($from_handle, $from_file_name, $to_handle, $to_file_name, $size) = @_;

    while ($size > 0) {
	my ($chunk_size) = 4096;
	$chunk_size = $size if $chunk_size > $size;
	$size -= $chunk_size;

	my ($data) = read_fully ($from_handle, $from_file_name, $chunk_size);
	write_fully ($to_handle, $to_file_name, $data);
    }
}

# read_fully($handle, $file_name, $bytes)
#
# Reads exactly $bytes bytes from $handle and returns the data read.
# $file_name is used in error messages.
sub read_fully {
    my ($handle, $file_name, $bytes) = @_;
    my ($data);
    my ($read_bytes) = sysread ($handle, $data, $bytes);
    die "$file_name: read: $!\n" if !defined $read_bytes;
    die "$file_name: unexpected end of file\n" if $read_bytes != $bytes;
    return $data;
}

# write_fully($handle, $file_name, $data)
#
# Write $data to $handle.
# $file_name is used in error messages.
sub write_fully {
    my ($handle, $file_name, $data) = @_;
    my ($written_bytes) = syswrite ($handle, $data);
    die "$file_name: write: $!\n" if !defined $written_bytes;
    die "$file_name: short write\n" if $written_bytes != length $data;
}

sub write_zeros {
    my ($handle, $file_name, $size) = @_;

    while ($size > 0) {
	my ($chunk_size) = 4096;
	$chunk_size = $size if $chunk_size > $size;
	$size -= $chunk_size;

	write_fully ($handle, $file_name, "\0" x $chunk_size);
    }
}

# div_round_up($x,$y)
#
# Returns $x / $y, rounded up to the nearest integer.
# $y must be an integer.
sub div_round_up {
    my ($x, $y) = @_;
    return int ((ceil ($x) + $y - 1) / $y);
}

# round_up($x, $y)
#
# Returns $x rounded up to the nearest multiple of $y.
# $y must be an integer.
sub round_up {
    my ($x, $y) = @_;
    return div_round_up ($x, $y) * $y;
}

# cyl_sectors(H => heads, S => sectors)
#
# Returns the number of sectors in a cylinder of a disk with the given
# geometry.
sub cyl_sectors {
    my (%geometry) = @_;
    return $geometry{H} * $geometry{S};
}

# read_loader($file_name)
#
# Reads and returns the first $LOADER_SIZE bytes in $file_name.
# If $file_name is undefined, tries to find the default loader.
# Makes sure that the loader is a reasonable size.
sub read_loader {
    my ($name) = @_;
    $name = find_file ("loader.bin") if !defined $name;
    die "Cannot find loader\n" if !defined $name;

    my ($handle);
    open ($handle, '<', $name) or die "$name: open: $!\n";
    -s $handle == $LOADER_SIZE || -s $handle == 512
      or die "$name: must be exactly $LOADER_SIZE or 512 bytes long\n";
    $loader = read_fully ($handle, $name, $LOADER_SIZE);
    close ($handle) or die "$name: close: $!\n";
    return $loader;
}

# pack_chs($lba, {H => heads, S => sectors})
#
# Converts logical sector $lba to a 3-byte packed geometrical sector
# in the format used in PC partition tables (see [Partitions]) and
# returns the geometrical sector as a 3-byte string.
sub pack_chs {
    my ($lba, $geometry) = @_;
    my ($cyl, $head, $sect) = lba_to_chs ($lba, $geometry);
    return pack ("CCC", $head, $sect | (($cyl >> 2) & 0xc0), $cyl & 0xff);
}

# lba_to_chs($lba, {H => heads, S => sectors})
#
# Returns the geometrical sector corresponding to logical sector $lba
# given the specified geometry.
sub lba_to_chs {
    my ($lba, $geometry) = @_;
    my ($hpc) = $geometry->{H};
    my ($spt) = $geometry->{S};

    # Source:
    # http://en.wikipedia.org/wiki/CHS_conversion
    use integer;
    my $cyl = $lba / ($hpc * $spt);
    my $temp = $lba % ($hpc * $spt);
    my $head = $temp / $spt;
    my $sect = $temp % $spt + 1;

    # Source:
    # http://www.cgsecurity.org/wiki/Intel_Partition_Table
    if ($cyl <= 1023) {
        return ($cyl, $head, $sect);
    } else {
        return (1023, 254, 63);	## or should this be (1023, $hpc, $spt)?
    }
}

# read_mbr($file)
#
# Tries to read an MBR from $file.  Returns the 512-byte MBR if
# successful, otherwise numeric 0.
sub read_mbr {
    my ($file) = @_;
    my ($retval) = 0;
    open (FILE, '<', $file) or die "$file: open: $!\n";
    if (-s FILE == 0) {
	die "$file: file has zero size\n";
    } elsif (-s FILE >= 512) {
	my ($mbr);
	sysread (FILE, $mbr, 512) == 512 or die "$file: read: $!\n";
	$retval = $mbr if unpack ("v", substr ($mbr, 510)) == 0xaa55;
    }
    close (FILE);
    return $retval;
}

# interpret_partition_table($mbr, $disk)
#
# Parses the partition-table in the specified 512-byte $mbr and
# returns the partitions.  $disk is used for error messages.
sub interpret_partition_table {
    my ($mbr, $disk) = @_;
    my (%parts);
    for my $i (0...3) {
	my ($bootable, $valid, $type, $lba_start, $lba_length)
	  = unpack ("C X V C x3 V V", substr ($mbr, 446 + 16 * $i, 16));
	next if !$valid;

	(print STDERR "warning: invalid partition entry $i in $disk\n"),
	  next if $bootable != 0 && $bootable != 0x80;

	my ($role) = $type2role{$type};
	(printf STDERR "warning: non-Pintos partition type 0x%02x in %s\n",
	 $type, $disk),
	  next if !defined $role;

	(print STDERR "warning: duplicate \L$role\E partition in $disk\n"),
	  next if exists $parts{$role};

	$parts{$role} = {START => $lba_start,
			 SECTORS => $lba_length};
    }
    return %parts;
}

# find_file($base_name)
#
# Looks for a file named $base_name in a couple of likely spots.  If
# found, returns the name; otherwise, returns undef.
sub find_file {
    my ($base_name) = @_;
    -e && return $_ foreach $base_name, "build/$base_name";
    return undef;
}

# read_partition_table($file)
#
# Reads a partition table from $file and returns the parsed
# partitions.  Dies if partitions can't be read.
sub read_partition_table {
    my ($file) = @_;
    my ($mbr) = read_mbr ($file);
    die "$file: not a partitioned disk\n" if !$mbr;
    return interpret_partition_table ($mbr, $file);
}

# max(@args)
#
# Returns the numerically largest value in @args.
sub max {
    my ($max) = $_[0];
    foreach (@_[1..$#_]) {
	$max = $_ if $_ > $max;
    }
    return $max;
}

1;