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added some partitioning-related stuff

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XeonSquared 9 months ago
parent
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dc55813b69
2 changed files with 81 additions and 0 deletions
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      partition/README.md
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      partition/partition.lua

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partition/README.md View File

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# 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.

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partition/partition.lua View File

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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

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