update mtpt for how it's actually being used now

partition/README.md

@@ -9,7 +9,7 @@ The partition table resides at the end of the disk - the last sector of the disk
  - Ease of implementation for firmware to load from first partition
  - Compatibility with existing partition table formats
 
-The partition table takes one sector (512 bytes) and is divided into 16 entries, 32 bytes each.
+The partition table takes one sector (512 bytes) and is divided into 16 entries, 32 bytes each. The first entry must have a type of `mtpt` or the partition table is to be considered invalid. This first entry's name should be considered the label for the whole disk.
 
 ### Partition entry
 
@@ -17,14 +17,14 @@ Each entry consists of:
 
  - A 20 byte name field, padded with null characters.
  - A 4 byte type field. This can be used either as a number or a string.
- - A 4-byte start sector field.
+ - A 32-bit big-endian start sector field.
- - A 4-byte length field.
+ - A 32-bit big-endian length field.
 
 Any entry with no name should be ignored.
 
 ## Tape considerations
 
-It may prove easier to use a tape if one were to implement a virtual drive component that maps to the data on a tape.
+In the case of tapes, the partition table uses the last whole sector and any remaining space, as some tapes aren't evenly divisible by 512 bytes.
 
 ## Booting
 

partition/partition.lua

@@ -1,50 +1,23 @@
 local partition = {}
 
-local entryPattern = "(" .. ("."):rep(20) .. ")(....)(....)(....)"
+local eformat = "c20c4>I4>I4"
-
+function partition.parse(s)
-local function cint(n,l)
+ local rt = {}
- local t={}
+ for i = 1, s:len(), 32 do
- for i = 0, 7 do
+  local n, t, start, length = string.unpack(eformat, s, i)
-  t[i+1] = (n >> (i * 8)) & 0xFF
+  n = n:gsub("\0", "")
- end
+  if n ~= "" then
- return string.reverse(string.char(table.unpack(t)):sub(1,l))
+   rt[#rt+1] = {n,t,start,length}
-end
-local function toint(s)
- local n = 0
- local i = 1
- for p in s:gmatch(".") do
-  n = n << 8
-  n = n | string.byte(p)
-  i=i+1
- end
- return n
-end
-
-function partition.parse(sector)
- local pt = {}
- for name,ptype,sstart,slen in sector:gmatch(entryPattern) do
-  local pte = {}
-  pte.name = name:gsub("\0","")
-  if pte.name:len() > 0 then
-   pte.type = ptype
-   pte.start = toint(sstart)
-   pte.len = toint(slen)
-   pte.last = pte.start + toint(slen)
-   pt[#pt+1] = pte
   end
  end
- return pt
+ return rt
 end
 function partition.generate(pt)
  local ps = ""
- for k,v in pairs(pt) do
+ for k,v in ipairs(pt) do
-  if not v.len then
+  ps = ps .. string.pack(eformat, table.unpack(v))
-   v.len = v.last - v.start
  end
---  ps = ps .. ("\0"):rep(math.max(20-v.name:len(),0)) .. v.name:sub(1,20) .. v.type:sub(1,4) .. cint(v.start,4) .. cint(v.len,4)
+ return ps
-  ps = ps .. (("\0"):rep(20) .. v.name):sub(-20) .. v.type:sub(1,4) .. cint(v.start,4) .. cint(v.len,4)
- end
- return ps..("\0"):rep(512-ps:len())
 end
 
 return partition