MFC lualoader read-conf support: r360420-r360423, r360425, r360427, r360486,
\r360505-r360506

r360420:
lualoader config: don't call loader.getenv() as much

We don't actually need to fetch loader_conf_files as much as we do; we've
already fetched it once at the beginning, we only really need to fetch it
again after each file we've processed. If it changes, then we can stash that
off into our local prefiles.

While here, drop a note about the recursion so that I stop trying to
change it. It may very well make redundant some of the work we're doing, but
that's OK.

r360421:
lualoader: config: start exporting readConfFiles

In the process, change it slightly: readConfFiles will take a string like
loader_conf_files in addition to the loaded_files table that it normally
takes. This is to facilitate the addition of a read-conf CLI command, which
will just pass in the single file to read and an empty table.

r360422:
lualoader: cli: add read-conf

This is a straightforward match to the command used by many in forthloader;
it uses the newly-exported config.readConfFiles() to make sure that any
loader_conf_files gets done as appropriate.

r360423:
lualoader: cli: clobber loader_conf_files before proceeding

This makes sure that config.readConfFiles doesn't see a stale
loader_conf_files from before, in case the newly loaded file doesn't set it.

r360425:
config.lua(8): "may should" is not proper grammar

r360427:
config.lua(8): catch up to recently added hooks

While we're here, let's stylize these as functions instead of just raw text.
A future change may allow arbitrary data arguments to be passed some of
these, and the distinction is useful.

r360486:
loader.conf(5): document that loader_conf_files may be clobbered

A future change in lualoader may take some liberties with the
loader_conf_files in the name of efficiency; namely, it may start omitting
it from the loader environment entirely so that it doesn't need to worry
about maintaining any specific value.

This variable has historically been incredibly volatile anyways, as it may
get set to completely different values in any given configuration file to
trigger a load of more files.

Document now that we may not maintain it in the future, but perhaps we'll
reserve the right to change our minds and eventually formally export all of
the loader configuration files that were read using this variable.

r360505:
lualoader: config: add a table for restricted environment vars

This new table should be used for transient values that don't need to end up
in the loader environment. Generally, these will be things that are internal
details that really aren't needed or interesting outside of the config
module (e.g. if we changed how ${module}_* directives work, they might use
this instead).

To start, populate it with loader_conf_files. Any specific value of
loader_conf_files isn't all that interesting; if we're going to export it,
we should really instead export a loader_conf_files that indicates all of
the configuration files we processed. This will be used to reduce
bookkeeping overhead in a future commit that cleans up readConfFiles.

r360506:
lualoader: config: improve readConfFiles, rename to readConf

The previous interface was pretty bad, and required the caller to get some
implementation details correct that it really shouldn't need to (e.g.
loader_conf_files handling) and pass in an empty table for it to use.

The new and much improved interface, readConf, is much less of a hack;
hiding these implementation details and just doing the right thing.
config.lua will now use it to process /boot/defaults/loader.conf and the
subsequent loader_conf_files from there, and read-conf will also use it.

This improvement submitted by Olivier (cited below), loader_conf_files
handling from the original patch was changed to just clobber it before
processing and not bother restoring it after the fact following r360505
where it's now guaranteed to evade the loader environment.

PR: 244640

MFC r359072-r359073: loader: Add a "kernel.loaded" hook

This hook can be useful, for example to run a local function to choose
different modules to load when a user has picked a different kernel
from the menu.

MFC r357103-r357104: unbreak local.lua, add a modules.loaded hook

r357103:
loader.lua: re-arrange to load local.lua *after* config loading

The major problem with the current ordering is that loader.conf may contain
all of the magic we need to actually setup the console, so loading local.lua
prior to that can make it excessively difficult and annoying to debug
(whoops, sorry Ravi & Warner).

The new ordering has some implications, but I suspect they are a non-issue.
The first is that it's no longer possible for the local module to inject any
logic prior to loading config -- I suspect no one has relied on this. The
second implication is that the config.loaded hook is now useless, as the
local module will always be included after that hook would have fired.

For config.loaded, I will opt to leave it in, just in case we add an early
point for local lua to get injected or in case one wants to schedule some
deferred logic in a custom loader.lua. The overhead of having it if no hooks
will be invoked is relatively minimal.

r357104:
lua: add modules.loaded hook

This may be used for the local module to hook in and load any additional
modules that it wants, since it can't modify the modules table internal to
config. We may consider adding API to do so at a later time, but I suspect
it will be more complicated to use with little return.

status is captured but ignored for the purpose of loading the hook. status
will be false if *any* module failed to load, but we typically don't let
that halt the boot so there's no reason to let it halt hooks. Some vendors
or setups may have expected fails that would be actively thwarted by
checking it.

We may, at a later date, consider adding an API for letting non-config
modules check which modules have successfully (or not) loaded in case an
unexpected failure *should* halt whatever they are doing.

MFC r344243, r345517-r345518: lualoader: More intelligent screen clearing

r344243:
lualoader: only clear the screen before first password prompt

This was previously an unconditional screen clear, regardless of whether or
not we would be prompting for any passwords. This is pointless, given that
the screen clear is only there to put our screen into a consistent state
before we draw the prompts and do cursor manipulation.

This is also the only screen clear besides that to draw the menu. One can
now see early pre-loader and loader output with the menu disabled, which may
be useful for diagnostics.

r345517:
lualoader: Clear the screen before prompting for password

Assuming that the autoboot sequence was interrupted, we've done enough
cursor manipulation that the prompt for the password will be sufficiently
obscured a couple of lines up. Clear the screen and reset the cursor
position here, too.

r345518:
lualoader: Fix up some luacheck concerns

- Garbage collect an unused (removed because it was useless) constant
- Don't bother with vararg notation if args will not be used

MFC lualoader: r326353, r328440, r328443, r329166-r329167, r329274, r329329,
r329349-r329352, r329355-r329359, r329366-r329369, r329386-r329387, r329393,
r329413-r329415, r329417, r329424-r329436, r329457, r329473-r329474,
r329496-r329501, r329503-r329504, r329543, r329547-r329551, r329576-r329578,
r329580, r329583, r329585-r329590, r329592-r329596, r329609-r329611,
r329614, r329619, r329621-r329622, r329624, r329626-r329627,
r329629-r329632, r329640-r329641, r329643-r329646, r329649-r329650, r329654,
r329656, r329662, r329669-r329671, r329673-r329674, r329680,
r329684-r329689, r329692-r329693, r329696-r329700, r329709, r329716,
r329731, r329733-r329734, r329747-r329748, r329756, r329779, r329782,
r329784, r329786, r329804, r329806, r329809, r329811, r329836,
r329850-r329852, r329854, r329856-r329858, r329861, r329895,
r329897-r329899, r329901-r329903, r329922-r329924, r329927-r329928,
r329944-r329949, r329986-r329987, r330008-r330010, r330012, r330020,
r330082-r330084, r330087-r330088, r330098-r330101, r330138-r330139,
r330261-r330263, r330267-r330269, r330281-r330284, r330287, r330339-r330342,
r330345-r330346, r330369-r330370, r330434-r330435, r330564, r330616-r330618,
r330620, r330625, r330690, r330701, r330703, r330825, r331211, r331257,
r331259, r331281-r331282, r331304, r331314, r331476-r331477,
r331563-r331564, r331854-r331857, r331859-r331860, r332106, r334723,
r334879, r334891, r334907, r334912, r334939, r334986, r335009, r335371,
r336759, r337711, r337807-r337810, r338054, r338063, r338065-r338067,
r338083, r338085-r338086, r338108, r338167-r338168, r338173, r338203,
r338255, r338259, r338309, r338394, r338438, r338886, r338893, r339173,
r339200, r339218, r339222, r339301, r339307, r339677-r339678, r339702,
r339805, r339831, r339849, r340040, r340152

Some notes for this MFC:
- This is still pre-forth/lua coexistance; that will come shortly-ish so
that forth/lua may be installed together (with forth remaining the default)

- module_blacklist support for lualoader has been MFC'd, but the drm modules
are not blacklisted in this stable branch.

r326353: Import lua 5.3.4 to contrib
r328440: Preserve the original luaconf.h in a convenient place. Clients will
r328443: Gross hack to omit printing hex floating point when the lua number
r329166: Add Lua as a scripting langauge to /boot/loader
r329167: Add the lua scripts from the lua-bootloader SoC
r329274: stand/lua: Exit sub-menus on backspace
r329329: stand/lua: Always boot on 'enter' keypress in menus
r329349: stand/lua: Reduce magic numbers
r329350: stand/lua: Don't descend into an empty kernels submenu
r329351: stand/lua: Set reasonable ACPI default based on presence
r329352: stand/lua: Consistently use semicolons for line endings
r329355: stand/lua: Move kernel selection into main menu
r329356: stand/lua: Allow menu items to not have explicit aliases
r329357: stand/lua: Remove explicit alias from "Back to main menu"
r329358: stand/lua: Say "loader prompt" instead of "lua interpreter"
r329359: stand/lua: Remove a magic number/string (not a trivial literal)
r329366: stand/lua: Set ACPI's default the proper way (setACPI)
r329367: stand/lua: Create a "carousel" menu entry type
r329368: stand/lua: Create/use some MENU_ constants where applicable
r329369: stand/lua: Remove sneaky kernel assignment
r329386: stand/lua: Correct usage and acceptance of BACKSPACE/DELETE keys
r329387: stand/lua: Chop off the decimal for numbers passed to setcursor
r329393: stand/lua: Use escaped dot instead of single character class
r329413: stand/lua: Allow MENU_RETURN items to have func, fix esc. to prompt
r329414: stand/lua: Don't try to divide by 0; do nothing
r329415: stand/lua: Don't reload kernel config if we only have one kernel
r329417: stand/lua: Make CAROUSEL_ENTRY func parameters consistent with name
r329424: stand/lua: Don't set autoboot_delay=NO in menu autoboot sequence
r329425: stand/lua: Enable menu autoboot; it seems to work
r329426: stand/lua: Correct interpretation of autoboot_delay
r329427: stand/lua: Color non-default kernels blue
r329428: stand/lua: Correct some trivial errors in config
r329429: stand/lua: Add debug method to dump modules
r329430: stand/lua: Address some nits
r329431: stand/lua: Correct test sense, this should have been 'not nil'
r329432: stand/lua: Try to load alternate kernels as directories first
r329433: stand/lua: Add optional GELI passphrase prompt
r329434: stand/lua: Check for nil (GELI prompt)
r329435: stand/lua: Style pass
r329436: stand/lua: Debugging string snuck in...
r329457: stand/lua: dumpModules => lsModules
r329473: liblua: Clean up io/loader C module registration
r329474: liblua: Emulate DIR, opendir, fdopendir, closedir
r329496: stand/lua: Fix verbiage and some typos
r329497: stand/lua: Fix module_path handling with multiple kernels
r329498: stand/lua: Remove some debugging bits that snuck in... gr...
r329499: interp_lua: Register io/loader with regular Lua module system
r329500: Lua loader: Add barebones "lfs" module
r329501: lua loader: Auto detect eligible list of kernels to boot
r329503: liblua: Fix missing '}' in lutil.c after r329499
r329504: stand/lua: More style nits, config.lua
r329543: Create style.lua(9)
r329547: stand/lua: Allow menu items to be conditionally (in)visible
r329548: stand/lua: Addres style.lua(9) concern
r329549: stand/lua: Clear the screen before prompting for passwords
r329550: stand/lua: Store the loaded kernel as config.kernel_loaded
r329551: stand/lua: reload previously loaded kernel at config-load/reload
r329576: stand/lua: Defer kernel/module loading until boot or menu escape
r329577: stand/lua: Rename bootserial for clarity
r329578: stand/lua: Menu style.lua(9) nits
r329580: stand/lua: Remove some unused local declarations
r329583: stand/lua: Store menu entries in an "entries" table
r329585: stand/lua: Add core.isSingleUserBoot
r329586: stand/lua: Call menu_entries if it's a function
r329587: stand/lua: Swap single-/multi- user boot entries as needed
r329588: stand/lua: Re-wrap menu.lua now that I've added indentation...
r329589: stand/lua: Track env changes that come in via loader.conf(5)
r329590: stand/lua: Restore environment upon config reload
r329592: stand/lua: Remove inaccurate comment after r329590
r329593: stand/lua: Change boot menu items' names when swapped
r329594: stand/lua: Round up some more style.lua(9) concerns
r329595: stand/lua: Re-order locals after copyright notice; require first
r329596: stand/lua: Add copyright notice in places
r329609: stand/lua: Cache swapped menu, and don't create locals for swapping
r329610: style.lua(9): Note that wrapping at 80-columns is not rigid
r329611: stand/lua: Wrap tuple assignment earlier for readability
r329614: stand/lua: Don't set ACPI off just because we can't detect it.
r329619: stand/lua: Extract menu handlers out into menu.handlers table
r329621: stand/lua: Add and use drawer.menu_name_handlers
r329622: stand/lua: Move drawer.menu_name_handlers further up
r329624: stand/lua: Reduce exposure of the drawer module
r329626: stand/lua: Refactor logos into drawer.logodefs table
r329627: stand/lua: Refactor brands into drawer.branddefs
r329629: stand/lua: Use 'graphic' instead of 'logo' for depicting graphics
r329630: stand/lua: Stick a copyright notice on drawer.lua
r329631: stand/lua: Insert helpful comment for drawer.branddefs
r329632: style.lua(9): Clarify local variable guideline
r329640: stand/lua: Consistently declare local functions at module scope
r329641: stand/lua: Consistently organize modules
r329643: Implement loader.command
r329644: lualoader: Add ability to intercept cli commands
r329645: lualoader: Move carousel storage out into config
r329646: lualoader: Eliminate global namespace pollution in loader.lua
r329649: Lua lfs.attributes: Provide a more consistent error return
r329650: liblua: Add loader.machine and loader.machine_arch properties
r329654: lualoader: Ignore ACPI bits on !i386
r329656: loader.lua: Expose errno table to lua
r329662: lualoader: Replace invalid construct with valid construct
r329669: lualoader: Prefer selected kernel to currently loaded
r329670: lualoader: Don't try so hard to load a kernel
r329671: lualoader: Prepare for interception of "boot" CLI cmd
r329673: lualoader: Intercept boot cli command
r329674: lualoader: Intercept the 'autoboot' cli command
r329680: lualoader: When restoring environment, only restore unchanged vars
r329684: lualoader: Drop terminating semicolons
r329685: lualoader: Drop excessive parenthesizing
r329686: style.lua(9): Drop notes about semicolons
r329687: lualoader: Drop explicit boolean tests; b or not b
r329688: lualoader: Don't return false for failure to open config on silent
r329689: lualoader: Output "Failed to parse" messages
r329692: lualoader: Bring in local.lua module if it exists
r329693: lualoader: Return only argstr if with_kernel not requested
r329696: lualoader: Add "menu.default", initialized to menu.welcome
r329697: lualoader: Drop name requirement for menu separators
r329698: lualoader: Directly reference submenu definition with submenu key
r329699: lualoader: Simplify menu definitions a little further
r329700: lualoader: Allow carousel 'items' to be a table as well
r329709: lualoader: Don't autodetect kernels if 'kernels' is explicitly set
r329716: lualoader: Use the key that interrupts autoboot as a menu choice
r329731: lualoader: Add boot environment support
r329733: lualoader: Make kernel autodetect. contingent on loader.conf(5) var
r329734: lualoader: Don't execute menu.autoboot() for every opened menu
r329747: lualoader: Replace 8-space indentation with a single tab
r329748: lualoader: Drop password length restrictions
r329756: lualoader: Remove nasty hack for not printing out ".0"
r329779: lualoader: Split cli bits out into a cli module
r329782: lualoader: Unbreak 'boot [kernel]' by including config
r329784: lualoader: Pull argument extraction for cli funcs to cli.arguments
r329786: lualoader: Attach cli command functions to cli module
r329804: lualoader: Eliminate some unused locals
r329806: lualoader: Consistently use double quotes
r329809: lualoader: Address some 'luacheck' concerns
r329811: lualoader: Clear up an empty conditional branch
r329836: lualoader: Attend to some 80-col issues, pointed out by luacheck
r329850: lualoader: Drop unused return values; we'll only use the first
r329851: Add SPDX tags to lua files
r329852: Add copyright notice to core.lua
r329854: lualoader: shallowCopyTable => deepCopyTable
r329856: lualoader: Use "local function x()" instead "local x = function()"
r329857: Centralize lua defines
r329858: When the LUA_FLOAT_TYPE != LUA_FLOAT_INT64, we can't ref. float
r329861: lualoader: Track effective line number, use it for drawing
r329895: liblua: Implement write support
r329897: lualoader: Add nextboot support
r329898: lualoader: Plug file handle not properly closed
r329899: lualoader: Correct test and name
r329901: lualoader: Add comment on trailing space, don't operate on nil
r329902: lualoader: Remove unused variable; we now use effective line number
r329903: lualoader: Explain nextboot stuff a little bit more
r329922: lualoader: Split config file I/O out into a separate function
r329923: lualoader: Strip config.parse of its I/O privileges
r329924: lualoader: throw out nextboot's usage of standard config processing
r329927: lualoader: Clean up naming conventions a little bit
r329928: lualoader: Remove inaccurate part of comment
r329944: lualoader: Don't explicitly index tables without reason
r329945: lualoader: menu: Terminate final values in tables with a comma
r329946: lualoader: Clean up menu handling a little bit
r329947: lualoader: Pull menu redrawing specifics out of menu.process
r329948: lualoader: Pull autoboot handling out into menu.run()
r329949: lualoader: Explain deviation from naming guidelines
r329986: lualoader: Invalidate the screen from menu perspective mnu exit
r329987: lualoader: Track the menu currently drawn, instead of validity
r330008: lualoader: A little more general menu cleanup
r330009: lualoader: More argument name expansion, part 2
r330010: lualoader: screen argument fixes
r330012: style.lua(9): Add some additional notes about naming and commas
r330020: lualoader: Re-work menu skipping bits
r330082: lualoader: Add a twiddle at password prompt
r330083: lualoader: Remove remnants of testing...
r330084: lualoader: Replace instances of \027 with KEYSTR_ESCAPE
r330087: lualoader: Convert instances of KEYSTR_ESCAPE .. "[" -> KEYSTR_CSI
r330088: lualoader: Correct test sense, comments, and add some more comments
r330098: lualoader: Re-do twiddle
r330099: lualoader: Further screen cleanup
r330100: lualoader: Remove debug function
r330101: lualoader: Add note that \027 is a decimal representation
r330138: lualoader: Dedup these "Return to main menu" entries
r330139: lualoader: config: Pull some messages out into constants
r330261: lualoader: Fix some lint-mentioned errors
r330262: lualoader: Use #str instead of tracking length with 'n'
r330263: lualoader: Use string literal \xNN instead of string.char()
r330267: Add core.lua(8), but do not add to distribution
r330268: Add menu.lua(8), but do not add to distribution
r330269: core.lua(8): Add missing note about core.KEYSTR_CSI
r330281: lualoader: Steamroll the box-drawing
r330282: lualoader: Register loader.printc as global printc
r330283: lualoader: Use global printc instead of loader.printc
r330284: liblua: Use putc instead of printf for printc
r330287: lualoader: Reset the cursor position after the menu is drawn
r330339: liblua: Add loader.interpret
r330340: lualoader: Execute menu_timeout_command at the end of menu autoboot
r330341: lualoader: Respect loader_menu_title, prepare for align
r330342: lualoader: Respect loader_menu_title_align
r330345: lualoader: Tweak positioning and fix an off-by-one
r330346: lualoader: Shift menu+brand even for logo=none with customized pos
r330369: lualoader: Return meaningful value in cli_execute
r330370: lualoader: logdef -> logodef typo
r330434: lualoader: Add note about importance of including cli module early
r330435: lualoader: Use FILESDIR instead of BINDIR
r330564: lualoader: Only loadelf before boot/autoboot if no kernel loaded
r330616: lualoader: Expose loader.parse and add cli_execute_unparsed
r330617: lualoader: Fix name, cli.execute_unparsed -> cli_execute_unparsed
r330618: lualoader: Use cli_execute_unparsed instead of loader.interpret
r330620: lualoader: Use cli_execute_unparsed for commands via loader.conf
r330625: lualoader: Return status in cli_execute_unparsed properly
r330690: stand: Fix copy-paste-o, unbreaks libi386 lualoader build
r330701: lualoader: Don't redraw the autoboot message every .05s
r330703: lualoader: Cache kernel list
r330825: lualoader: Sprinkle some verbose_loading salt
r331211: lualoader: Setup default color scheme if we're using colors
r331257: lualoader: Reset attributes and color scheme with color.highlight()
r331259: lualoader: Use less atomic options for resetting colors/attributes
r331281: lualoader: Add primitive hook module to untangle bogus reference
r331282: core.lua(8): Update to reflect recently added function
r331304: lualoader: Clear up some possible naming confusion
r331314: lualoader: Use printc when we expect ANSI escape sequences
r331476: lualoader: Make config env-related bits private API
r331477: lualoader: Privatize some more config.lua bits
r331563: lualoader: Implement try_include and use it for including local
r331564: lualoader: Actually re-raise error in try_include
r331854: lualoader: Do case-insensitive comparison of "yes"
r331855: lualoader: Don't assume that {module}_load is set
r331856: lualoader: revert whitespace change that snuck in
r331857: lualoader: Simplify some expressions
r331859: lualoader: Split logodefs out into logo-* files
r331860: lualoader: Don't try to lookup a nil logo
r332106: lualoader: Fix menu skipping with loader.conf(5) vars
r334723: lualoader: Add a loaded hook for others to execute upon config load
r334879: lualoader: Add hook.lua(8) to tree
r334891: lualoader: Add cli.lua(8) to the tree
r334907: lualoader: Process loader_conf_files properly
r334912: lualoader: Support variable substitution in env var settings
r334939: lualoader: Allow brand-*.lua for adding new brands
r334986: lualoader: More black-on-white fixes
r335009: lualoader: Match Forth module-loading behavior w.r.t flags
r335371: lualoader: Correct kernel_options handling
r336759: lualoader: "nextboot_file" should be spelled "nextboot_conf"
r337711: lualoader: Fix parsing of negative number loader.conf(5) variables
r337807: Prevent a wanring about checkdp being unused.
r337808: When the LUA floating point model is INT64, we don't need to do the
r337809: For our INT64 implementation, we can compare integers and numbers
r337810: MFV r337586: lua: Update to 5.3.5
r338054: Add config.lua(8) to the tree
r338063: lualoader: Stop exporting drawer.draw
r338065: lualoader: Hide most of the internal drawing functions
r338066: lualoader: Hide the rest of the private interfaces
r338067: lualoader: Add drawer-exported variables for default logodefs
r338083: Add drawer.lua(8)
r338085: Add color.lua(8), password.lua(8), and screen.lua(8)
r338086: lualoader: Install all manpages
r338108: Serial console menus for lua.
r338167: lualoader: Just compare expression directly
r338168: lualoader: Refactor config line expressions
r338173: lualoader: Fix loader.conf(5) EOL validation for 'exec' lines
r338203: Turn off LOADER_GELI and LOADER_LUA for sparc64, until functional
r338255: lualoader: Fix (add) Xen support
r338259: lualoader: Accept that people use unquoted values in loader.conf
r338309: lualoader: Fix override of module_path on loader prompt
r338394: lualoader: fix color usage
r338438: lualoader: Handle comma-separated kernels as well
r338886: Improve loader passwords:
r338893: Set the default loader for powerpc(32- and 64-bit) back to to forth
r339173: Set the default loader for powerpc64 back to to forth too.
r339200: lualoader: Don't draw loader menu with autoboot_delay=-1
r339218: lualoader: Create a module blacklist, add DRM modules to it
r339222: lualoader: Honor boot_* variables at lua init
r339301: Loader GELI support, like lua loader, seems to be broken on PowerPC
r339307: lualoader: Provide a 'menu' command to redraw the menu at prompt
r339677: lualoader: unload upon kernel change if a kernel was loaded
r339678: menu.lua: Abort autoboot sequence on failed command
r339702: lualoader: Improve module loading diagnostics
r339805: lualoader: Always return a proper dictionary for blacklist
r339831: Move LUA_ROOT to /boot/lua
r339849: lualoader: Fix try_include error handling
r340040: lualoader: Implement boot-conf
r340152: lualoader: Add chainload menu entry

Relnotes: yes ("lualoader has been merged to stable/11, off by
default, to facilitate testing")