add a kernel that can run code in userspace

build.lua

@@ -70,23 +70,69 @@ local function exportFile(srcpath, dstpath)
 		dstpath = outdir .. srcpath
 	end
 	local srcf = assert(io.open(srcpath))
+
+	--load the file to validate syntax, as a very minimal linter
+	do
+		local ok, err = loadfile(srcpath)
+		if not ok then
+			stderr:write(err, '\n')
+			os.exit(1)
+		end
+	end
+
+
 	local dstf = assert(io.open(dstpath, 'w'))
 
 	--for now, run a very minimal minifier
+	local longEnd --nil normally, some "]==]--" string if we're in a long comment
+
 	for line in srcf:lines() do
-		local comment = line:find('--', nil, true)
-		if comment then
-			assert(line:sub(comment, comment + 3) ~= '--[', 'TODO block comments')
+		::stripComments:: --strip comments, including weird ones like "--[[ ]]-- --[=[ ]=]-- --text" all in one line
+		--first, if we're in a long comment, see if that's over
+		if longEnd then
+			local i1, i2 = line:find(longEnd, 1, true)
+			if i1 then
+				--strip the long comment and mark that it ended
+				line = line:sub(i2+1)
+				longEnd = nil
+			else
+				--still in a long comment, so don't output anything
+				goto nextLine
+			end
+		end
+
+		--look for the start of the next comment
+		local comment = line:find('--', 1, true)
+		if not comment then --nothing left to do, break out of the loop
+			goto emitLine
+		end
+		if line:byte(comment+2) == string.byte('[') then --start of a long comment
+			local depth = #line:sub(comment+2):match('^%[(%=*)%[') --validating syntax earlier ensures this will match
+			longEnd = string.format(']%s]--', string.rep('=', depth))
+			line = line:sub(comment + 4 + depth) -- #'--[' + depth + #'['
+			goto stripComments --start from the beginning in case the comment ends on the same line it starts on
+		else
+			--found a short comment, remove to end of line
 			line = line:sub(1, comment - 1)
 		end
-		line = assert(line:match('^%s*(.-)%s*$'))
+
+		::emitLine::
+
+		assert(not longEnd, 'shouldn\'t emit anything in a long comment')
+		line = assert(line:match('^%s*(.-)%s*$')) --strip leading and trailing whitespace
 		if #line > 0 then
 			dstf:write(line, '\n')
 		end
+
+		::nextLine::
 	end
+	assert(not longEnd, 'unclosed long comment')
 end
 
 fs.makeDirectory(outdir)
 exportFile('boot.lua')
 
+fs.makeDirectory(outdir .. 'kitn-core/')
+exportFile('src/init.lua', outdir .. 'kitn-core/init.lua')
+
 -- vi: set ts=2:

src/init.lua

@@ -0,0 +1,258 @@
+--our own boot.lua gives us the boot [address, path] as arguments...
+local bootfs = ...
+-- ...but [lua bios, openloader] don't, so fall back to the usual way
+bootfs = bootfs or computer.getBootAddress()
+
+
+--store all functions we need in locals so userspace mischief can't replace them
+--suffix 'K' (for kernel) on any functions userspace will also have a version of to ensure kernelspace
+--function usage is intentional (ie prevent accidentally using the kernel's `load` in a userspace `loadfile`)
+local envBase = _G --used for creating process environments
+local assert, checkArg, error, loadK, ipairs, next, pairs, rawequal, rawset, setmetatable, tostring, type = assert, checkArg, error, load, ipairs, next, pairs, rawequal, rawset, setmetatable, tostring, type
+local invoke = component.invoke
+local pullSignalK, shutdown, uptime = computer.pullSignal, computer.shutdown, computer.uptime
+local co_create, co_status, co_resumeK, co_yieldK = coroutine.create, coroutine.status, coroutine.resume, coroutine.yield
+local huge = math.huge
+local format = string.format
+local pack, unpack = table.pack, table.unpack
+
+local big = math.maxinteger or huge --some large amount to read at once in readfileK
+
+
+--completely disable the environment, ensuring the kernel only uses local variables, to prevent userspace
+--mischief (somehow editing _G through a mirror) from affecting kernelspace
+_ENV = setmetatable({}, {
+	__index = function(self, key) return error(format('accessed global %q', key), 2) end,
+	__newindex = function(self, key) return error(format('assigned global %q', key), 2) end,
+})
+
+local function readfileK(path, fs)
+	fs = fs or bootfs
+	local text, chunk, fd, err = '', nil, invoke(fs, 'open', path)
+	if not fd then
+		local msg = format('can\'t open %s on %s', path, fs:sub(1, 3))
+		if not rawequal(path, err) then msg = msg .. ': ' .. err end
+		return nil, msg
+	end
+
+	repeat
+		chunk, err = invoke(fs, 'read', fd, big)
+		text = text .. (chunk or '')
+	until not chunk
+	invoke(fs, 'close', fd)
+	if err then return nil, format('reading %s: %s', path, err) end
+	return text
+end
+
+
+--[=====[ process internals ]=====]--
+local processes = {} --key is thread, value is a table of process state (ie env)
+local fillEnv --function(process:thread, env:table):() -- given a process and an empty environment, fill it in before the process runs
+
+
+--[=====[ process environments ]=====]--
+--<https://ocdoc.cil.li/tutorial:custom_oses#what_s_available>
+
+-- _G (through envBase) is used as the base for process environments, so clear it of anything process-specific
+envBase._OSVERSION = 'kitn 0.0.0' --prefer [openloader, openos] "$name $ver" over plan9k "$name/$ver"
+envBase._G, envBase.load, envBase.coroutine.resume, envBase.coroutine.yield, envBase.computer.pullSignal = nil
+
+--environment sandboxing uses mirrors: tables that provide a read-only "reflection" of what's on the other side
+local mirror --function(target:table[, mirror:table]):table -- create a mirror (or make a table into one) that reflects `target`
+local mirrors = setmetatable({}, { __mode = 'k' }) --key is mirror given to userspace, value is what it mirrors
+
+local function mirrorNext(self, prev)
+	local reflected = assert(mirrors[self], 'mirror reflects nothing')
+	local key = next(reflected, prev)
+	return key, self[key] --ensure all accesses go through the mirror so table values are mirrored too
+end
+
+local mirrormt = {
+	__metatable = '<mirror>', --hide the metatable to prevent replacing or modifying it
+	__index = function(self, key)
+		local reflected = assert(mirrors[self], 'mirror reflects nothing')
+		local val = reflected[key] --if mirrors[self] is somehow nil, erroring is fine
+		if type(val) == 'table' then val = mirror(val) end --recursively mirror tables on first access
+		if val ~= nil then rawset(self, key, val) end
+		return val
+	end,
+	__pairs = function(self)
+		--reuse a single function with the mirror as the control variable, instead of creating a new function with
+		--upvalues every time, because that seems vaguely less memory-intensive (TODO benchmark that)
+		return mirrorNext, self
+	end,
+	--mirrors allow assignment but don't do anything with it
+}
+
+function mirror(target, mirror)
+	mirror = mirror or {}
+	mirrors[mirror] = target
+	setmetatable(mirror, mirrormt)
+	return mirror
+end
+
+function fillEnv(process, env)
+	--<https://ocdoc.cil.li/tutorial:custom_oses#what_s_available>
+	mirror(envBase, env)
+
+	local function env_load(chunk, name, mode, fenv)
+		checkArg(1, chunk, 'function', 'string')
+		checkArg(2, name, 'string', 'nil')
+		checkArg(3, mode, 'string', 'nil')
+		checkArg(4, fenv, 'table', 'nil')
+		return loadK(chunk, name, mode, fenv or env)
+	end
+	local function env_loadfile(path, mode, fenv)
+		checkArg(1, path, 'string')
+		checkArg(2, mode, 'string', 'nil')
+		checkArg(3, newenv, 'table', 'nil')
+
+		local code, err = readfileK(path)
+		if not code then return nil, err end
+
+		code, err = env_load(code, '@' .. path, mode, fenv)
+		return code, err
+	end
+	local function env_dofile(path, ...)
+		checkArg(1, path, 'string')
+		local fn = assert(env_loadfile(path))
+		return fn(...)
+	end
+
+	env.load, env.loadfile, env.dofile = env_load, env_loadfile, env_dofile
+	env.coroutine = mirror(envBase.coroutine, {
+		resume = function(co, ...)
+			local results = pack(co_resume(co, ...)) --ok, os_reason, ...
+			if results[1] and results[2] then
+				return co_yieldK(unpack(results, 2, results.n))
+			else
+				return unpack(results, 1, results.n)
+			end
+		end,
+		yield = function(...) return co_yieldK(false, ...) end,
+	})
+	env.os = mirror(envBase.os, {
+		sleep = function(n)
+			checkArg(1, n, 'number')
+			return co_yieldK('deadline', n)
+		end,
+	})
+	env.computer = mirror(envBase.computer, {
+		pullSignal = function(timeout)
+			checkArg(1, timeout, 'number', 'nil')
+			return co_yieldK('signal', timeout)
+		end,
+	})
+end
+
+
+--[=====[ scheduler ]=====]--
+local runnable = {} --key is thread, value is pack(...)ed args to resume it with
+local schedDeadline = {} --key is thread, value is absolute deadline of uptime()
+local schedSignal = {} --key is thread, value is `true` (may allow specific signal names in the future)
+
+
+--[=====[ init, pid 1 ]=====]--
+do
+	local initEnv = {}
+	--since init is intended to be configured per-computer, it lives in /etc
+	local initPath = '/etc/init.lua'
+	local initCode = assert(readfileK(initPath))
+	local initFn = assert(loadK(initCode, '@' .. initPath, 'bt', initEnv))
+	fillEnv(initFn, initEnv)
+	local initThread = co_create(initFn)
+	processes[initThread] = { env = initEnv }
+	runnable[initThread] = { initPath, n = 1 }
+end
+
+
+--[=====[ scheduler main loop ]=====]--
+--logic after co_resume(process, ...) returns, in its own function to use varargs instead of table.pack
+local function postResume(co, ok, reason, ...)
+	if co_status(co) == 'dead' then
+		processes[co], runnable[co], schedDeadline[co], schedSignal[co] = nil
+		--TODO bubble to parent process
+
+		--tostring could run userspace code and even yield, but at this point we're crashing so it doesn't matter
+		if not ok then error('process crashed: ' .. tostring(reason), 0) end
+	elseif not reason then
+		--userspace called coroutine.yield(); TODO figure out what that's supposed to do
+		--for now... yield until another process resumes it?
+		schedDeadline[co], schedSignal[co] = nil
+	elseif rawequal(reason, 'signal') then
+		local timeout = ...
+		schedDeadline[co] = timeout and (uptime() + timeout)
+		schedSignal[co] = true
+	elseif rawequal(reason, 'deadline') then
+		local timeout = ...
+		schedDeadline[co] = uptime() + timeout
+		schedSignal[co] = nil
+	end
+end
+
+--logic after pullSignalK returns, in its own function to use varargs instead of table.pack
+local function postPull(signal, ...)
+	local args = pack(nil)
+	for proc, deadline in pairs(schedDeadline) do
+		if uptime() >= deadline then
+			schedDeadline[proc] = nil
+			runnable[proc] = args
+		end
+	end
+
+	--intentionally override {resumed by deadline} with {resumed by signal}
+	if signal then
+		args = pack(signal, ...)
+		for proc in pairs(schedSignal) do
+			schedDeadline[proc], schedSignal[proc] = nil
+			runnable[proc] = args
+		end
+	end
+end
+
+
+--goto instead of while-true for vague performance 
+::tickScheduler::
+
+--clear the run queue
+for proc, args in pairs(runnable) do
+	runnable[proc] = nil --the process is no longer runnable, unless it reschedules itself
+	postResume(proc, co_resumeK(proc, unpack(args, 1, args.n)))
+end
+
+local deadline = nil
+for proc, pdeadline in pairs(schedDeadline) do
+	if not deadline or pdeadline < deadline then
+		deadline = pdeadline
+	end
+end
+
+if next(schedSignal) then
+	deadline = deadline or huge
+end
+
+if not deadline then
+	--no processes are scheduled? are any still runnable somehow?
+	if next(runnable) then
+		--tail-return early to jump back to the run queue
+		goto tickScheduler
+	end
+
+	--nothing scheduled, nothing runnable; have all processes exited?
+	if not next(processes) then
+		return shutdown()
+	end
+
+	--this seems like a deadlock; the scheduler will never resume any process again
+	error('all processes are idle', 0)
+end
+
+
+--`deadline` is set, so at least one process is waiting for a deadline or signal
+postPull(pullSignalK(deadline - uptime()))
+
+--then do it again
+goto tickScheduler
+
+
+-- vi: set ts=2: