From dc55813b69f515c389569bc32948bf0dd9a2b982 Mon Sep 17 00:00:00 2001
From: XeonSquared <redtailedairways@gmail.com>
Date: Wed, 19 Feb 2020 18:39:48 +1100
Subject: [PATCH] added some partitioning-related stuff

---
 partition/README.md     | 31 +++++++++++++++++++++++++
 partition/partition.lua | 50 +++++++++++++++++++++++++++++++++++++++++
 2 files changed, 81 insertions(+)
 create mode 100644 partition/README.md
 create mode 100644 partition/partition.lua

diff --git a/partition/README.md b/partition/README.md
new file mode 100644
index 0000000..5c45d76
--- /dev/null
+++ b/partition/README.md
@@ -0,0 +1,31 @@
+# Simple partition table format
+
+This document specifies a general partition table format suitable for both unmanaged disks, and tapes.
+
+## Partition table
+
+The partition table resides at the end of the disk - the last sector of the disk, for several reasons:
+
+ - 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.
+
+### Partition entry
+
+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 4-byte 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.
+
+## Booting
+
+It is suggested that firmware loads and runs the first partition with type "boot". More advanced booting logic may be implemented if desired.
diff --git a/partition/partition.lua b/partition/partition.lua
new file mode 100644
index 0000000..43e0c98
--- /dev/null
+++ b/partition/partition.lua
@@ -0,0 +1,50 @@
+local partition = {}
+
+local entryPattern = "(" .. ("."):rep(20) .. ")(....)(....)(....)"
+
+local function cint(n,l)
+ local t={}
+ for i = 0, 7 do
+  t[i+1] = (n >> (i * 8)) & 0xFF
+ end
+ return string.reverse(string.char(table.unpack(t)):sub(1,l))
+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
+end
+function partition.generate(pt)
+ local ps = ""
+ for k,v in pairs(pt) do
+  if not v.len then
+   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)
+  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