OC-misc/partition/driveboot.lua

function computer.getBootAddress()
 return component.invoke(component.list("eeprom")(),"getData")
end
function computer.setBootAddress(a)
 return component.invoke(component.list("eeprom")(),"setData",a)
end
return (function()
local rv
local function getProxy(addr)
 if type(addr) == "string" then
  return component.proxy(addr)
 end
 return addr
end
local function aop(td,n,mn,...)
 local rts = td.seek(-math.huge)
 td.seek(n)
 local rv = {td[mn](...)}
 td.seek(-math.huge)
 td.seek(rts)
 return table.unpack(rv)
end

local eformat = "c20c4>I4>I4"
function parsePartitions(s)
 local rt = {}
 for i = 1, s:len(), 32 do
  local n, t, start, length = string.unpack(eformat, s, i)
  n = n:gsub("\0", "")
  if n ~= "" then
   rt[#rt+1] = {n,t,start,length}
  end
 end
 return rt
end

function getPartitions(drive)
 local rv
 if drive.type == "tape_drive" then
  local ts = drive.getSize()
  local lso = (math.floor(ts / 512) - 1) * 512
  rv = parsePartitions(aop(drive, lso, "read", ts - lso))
 else
  rv = parsePartitions(drive.readSector(drive.getCapacity() / drive.getSectorSize()))
 end
 return rv[1][2] == "mtpt" and rv
end

local function offsetSector(part,sector)
 if sector < 1 or sector > part[4] then error("invalid offset, not in a usable sector") end
 return (part[3] - 1) + sector
end
local function readSector(drive,part,sector)
 return drive.readSector(offsetSector(part,sector)):gsub("\0+$","")
end
local function readPart(drive,part)
 if drive.type == "tape_drive" then
  return aop(drive, (part[3]-1)*512, "read", part[4] * 512)
 end
 local rv = ""
 for i = 1, part[4] do
  rv=rv .. readSector(drive,part,i)
 end
 return rv
end

local pB = computer.getBootAddress()
local candidates={pB,[pB] = true}
if not component.type(pB) then candidates[1] = nil end
for a,t in component.list() do
 candidates[#candidates+1] = not candidates[a] and (t == "drive" or t == "filesystem" or t == "tape_drive") and a or nil
 candidates[a] = true
end

local function wL()
 return false
end
local cL = wL
local ga, sa = component.list("gpu")(), component.list("screen")()
if ga and sa then
 local g, cl = component.proxy(ga), 1
 g.bind(sa)
 g.setResolution(g.maxResolution())
 function wL(s)
  g.set(1,cl,s)
  cl = cl + 1
 end
 function cL()
  g.fill(1,1,160,50, " ")
  cl = 1
 end
 local function drawOptions()
  cL()
  wL(string.format("SKS Enhanced BIOS - %0.0fK RAM",computer.totalMemory()/1024))
  cl=cl+1
  wL(tostring(#candidates).." devices, press listed key to select")
  wL("key  address       type label")
  for k,v in ipairs(candidates) do
   wL(string.format("[%s] %s %10s %s",string.char(k+96),v:sub(1,8), component.type(v), component.invoke(v, "getLabel") or ""))
  end
 end
 local to = computer.uptime() + 2.5
 drawOptions()
 repeat
  local tE = {computer.pullSignal(to - computer.uptime())}
  if tE[1] == "key_down" and candidates[tE[3]-96] then
   to = computer.uptime() + 2.5
   table.insert(candidates, 1, table.remove(candidates,tE[3]-96))
   drawOptions()
  end
 until computer.uptime() >= to
end

for i,a in ipairs(candidates) do
 computer.beep(("."):rep(i))
 wL("Attempting to load from "..a)
 local d = getProxy(a)
 if type(d) == "table" and d.type == "filesystem" then
  if d.exists("/init.lua") then
   local rb, b = "", ""
   local f = d.open("/init.lua","rb")
   repeat
    b = d.read(f, 2048) or ""
    rb = rb .. b
   until b == ""
   d.close(f)
   local rv = load(rb,a.."/init.lua")
   if rv then
    computer.beep("-")
    computer.setBootAddress(a)
    cL()
    return rv
   end
  end
 elseif type(d) == "table" and (d.type == "drive" or d.type == "tape_drive") then
  for k,v in ipairs(getPartitions(d)) do
   if v[2] == "boot" then
    local rv = load(readPart(d,v), a.."/"..tostring(k))
    if rv then
     computer.beep("-")
     computer.setBootAddress(a)
     cL()
     return rv
    end
   end
  end
 end
end
error("no bootable devices found")
end)()()