Class: SlowFat::FileAllocationTable

Inherits:
Object
  • Object
show all
Defined in:
lib/slowfat/file_alloc_table.rb

Overview

FileAllocationTable represents one FAT (of two on a disk, most commonly)

Instance Attribute Summary collapse

Instance Method Summary collapse

Constructor Details

#initialize(backing:, base:, size:) ⇒ FileAllocationTable

Initialize a new FileAllocatinTable object (normally only called from Filesystem)

Parameters:

  • backing (IO) —

    the storage containing the filesystem (e.g. open file)

  • base (Integer) —

    the location of the beginning of this FAT structure within the backing device

  • size (Integer) —

    the total size of this FAT



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# File 'lib/slowfat/file_alloc_table.rb', line 12

def initialize(backing:, base:, size:)
  @backing = backing
  @base = base
  @size = size
end

Instance Attribute Details

#base ⇒ Object (readonly)

Returns the value of attribute base.



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# File 'lib/slowfat/file_alloc_table.rb', line 5

def base
  @base
end

#chains ⇒ Object (readonly)

Returns the value of attribute chains.



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# File 'lib/slowfat/file_alloc_table.rb', line 5

def chains
  @chains
end

#size ⇒ Object (readonly)

Returns the value of attribute size.



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# File 'lib/slowfat/file_alloc_table.rb', line 5

def size
  @size
end

Instance Method Details

#chain_starting_at(start_cluster) ⇒ Array<Integer>

Retrieve a full chain of cluster numbers, starting at a given cluster

Parameters:

  • start_cluster (Integer) —

    the cluster number to retrieve a chain starting from

Returns:

  • (Array<Integer>) —

    a list of clusters in the chain, starting from the cluster provided



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# File 'lib/slowfat/file_alloc_table.rb', line 22

def chain_starting_at(start_cluster)
  current_cluster = start_cluster
  current_chain = []
  while current_cluster < @size/2
    @backing.seek base + current_cluster * 2
    (next_cluster, junk) = @backing.read(2).unpack('v')
    if(current_cluster+1 == size/2) then
      #printf("current: 0x%02X next: FAT END\n", current_cluster)
      current_chain << current_cluster
      return current_chain == [] ? [start_cluster] : current_chain
    elsif(next_cluster >= 0xFFF8 and next_cluster <= 0xFFFF) then
      # end of cluster marker
      #printf("current: 0x%02X next: EOC (0x%02X)\n", current_cluster, current_cluster+1)
      current_chain << current_cluster
      return current_chain == [] ? [start_cluster] : current_chain
    elsif(next_cluster == 0x0000) then
      #printf("current: 0x%02X next: FREE (0x%02X)\n", current_cluster, current_cluster+1)
      current_cluster = current_cluster + 1
    else
      # link to next cluster
      #printf("current: 0x%02X next: 0x%02X\n", current_cluster, next_cluster)
      current_chain << current_cluster
      current_cluster = next_cluster
    end
  end
end