Trying to stringify filesystem flags

flag_to_string.rb

require 'ffi'

class Filesystem
  extend FFI::Library
  ffi_lib FFI::Library::LIBC

  attach_function(:strerror, [:int], :string)
  attach_function(:getmntinfo64, [:pointer, :int], :int)

  class Statfs < FFI::Struct
    layout(
      :f_bsize, :uint32,
      :f_iosize, :int32,
      :f_blocks, :uint64,
      :f_bfree, :uint64,
      :f_bavail, :uint64,
      :f_files, :uint64,
      :f_ffree, :uint64,
      :f_fsid, [:int32, 2],
      :f_owner, :int32,
      :f_type, :uint32,
      :f_flags, :uint32,
      :f_fssubtype, :uint32,
      :f_fstypename, [:char, 16],
      :f_mntonname, [:char, 1024],
      :f_mntfromname, [:char, 1024],
      :f_reserved, [:uint32, 8]
    )
  end

  MNT_RDONLY      = 0x00000001
  MNT_SYNCHRONOUS = 0x00000002
  MNT_NOEXEC      = 0x00000004
  MNT_NOSUID      = 0x00000008
  MNT_NODEV       = 0x00000010
  MNT_UNION       = 0x00000020
  MNT_ASYNC       = 0x00000040
  MNT_CPROTECT    = 0x00000080
  MNT_EXPORTED    = 0x00000100
  MNT_QUARANTINE  = 0x00000400
  MNT_LOCAL       = 0x00001000
  MNT_QUOTA       = 0x00002000
  MNT_ROOTFS      = 0x00004000
  MNT_DOVOLFS     = 0x00008000
  MNT_DONTBROWSE  = 0x00100000
  MNT_IGNORE_OWNERSHIP = 0x00200000
  MNT_AUTOMOUNTED = 0x00400000
  MNT_JOURNALED   = 0x00800000
  MNT_NOUSERXATTR = 0x01000000
  MNT_DEFWRITE    = 0x02000000
  MNT_MULTILABEL  = 0x04000000
  MNT_NOATIME     = 0x10000000

  MNT_VISFLAGMASK = (
    MNT_RDONLY | MNT_SYNCHRONOUS | MNT_NOEXEC |
    MNT_NOSUID | MNT_NODEV | MNT_UNION |
    MNT_ASYNC  | MNT_EXPORTED | MNT_QUARANTINE |
    MNT_LOCAL  | MNT_QUOTA |
    MNT_ROOTFS | MNT_DOVOLFS | MNT_DONTBROWSE |
    MNT_IGNORE_OWNERSHIP | MNT_AUTOMOUNTED | MNT_JOURNALED |
    MNT_NOUSERXATTR | MNT_DEFWRITE  | MNT_MULTILABEL |
    MNT_NOATIME | MNT_CPROTECT
  )

  @@opt_names = {
    MNT_RDONLY           => 'read-only',
    MNT_SYNCHRONOUS      => 'synchronous',
    MNT_NOEXEC           => 'noexec',
    MNT_NOSUID           => 'nosuid',
    MNT_NODEV            => 'nodev',
    MNT_UNION            => 'union',
    MNT_ASYNC            => 'asynchronous',
    MNT_CPROTECT         => 'content-protection',
    MNT_EXPORTED         => 'exported',
    MNT_QUARANTINE       => 'quarantined',
    MNT_LOCAL            => 'local',
    MNT_QUOTA            => 'quotas',
    MNT_ROOTFS           => 'rootfs',
    MNT_DONTBROWSE       => 'nobrowse',
    MNT_IGNORE_OWNERSHIP => 'noowners',
    MNT_AUTOMOUNTED      => 'automounted',
    MNT_JOURNALED        => 'journaled',
    MNT_NOUSERXATTR      => 'nouserxattr',
    MNT_DEFWRITE         => 'defwrite',
    MNT_NOATIME          => 'noatime'
  }

  def self.info
    buf = FFI::MemoryPointer.new(:pointer)
    num = getmntinfo64(buf,0)

    raise "getmntinfo64() failed: " + strerror(FFI.errno) if num == 0

    ptr = buf.get_pointer(0)

    num.times{ |i|
      mnt = Statfs.new(ptr)

      p mnt[:f_mntonname].to_s
      p mnt[:f_flags]

      flags = mnt[:f_flags] & MNT_VISFLAGMASK
      opts  = ""

      @@opt_names.each{ |key,val|
        if flags & key > 0
          if opts.empty?
            opts = val
          else
            opts << ", #{val}"
          end
          flags &= ~key
        end
      }

      p opts

      puts "=" * 40

      ptr += Statfs.size
    }
  end
end

Filesystem.info