lualoader: allow the local module to filter out the BE list

This allows something like the following local.lua to install a filter
to implement its own notion of hidden BEs using a naming convention of
a leading dot to hide them:

-- file: /boot/lua/local.lua
local core = require("core")

local function be_hide(be)
    if core.isSingleUserBoot() then
        -- All BEs are accepted for single-user
        return true
    end

    local name = be:match("/([^/]+)$")
    if not name then
        -- Accept malformed BEs, for whatever reason
        return true
    end

    return name:match("^%.") == nil
end

if core.bootenvFilter then
    -- Just in case we need to be compatible with older versions of
    -- core.lua without the filtering functionality.
    core.bootenvFilter(be_hide)
end
-- EOF

Requested by:	Marek Zarychta
Reviewed by:	imp

(cherry picked from commit bf0881060ecd75ce79683b82ebcd4809eadf7cf5)

1 files changed, 18 insertions, 2 deletions

diff --git a/stand/lua/core.lua b/stand/lua/core.lua
index ccd8213a718d..4091f446e1f1 100644
--- a/stand/lua/core.lua
+++ b/stand/lua/core.lua
@@ -303,6 +303,15 @@ function core.bootenvDefault()
 	return loader.getenv("zfs_be_active")
 end
 
+function core.bootenvFilter(func)
+	local oldf = core.bootenv_filter
+
+	-- Filter contract: returns true if the BE should be kept, false if it
+	-- should be hidden.
+	core.bootenv_filter = func
+	return oldf
+end
+
 function core.bootenvList()
 	local bootenv_count = tonumber(loader.getenv(bootenv_list .. "_count"))
 	local bootenvs = {}
@@ -330,11 +339,18 @@ function core.bootenvList()
 	for curenv_idx = 0, bootenv_count - 1 do
 		curenv = loader.getenv(bootenv_list .. "[" .. curenv_idx .. "]")
 		if curenv ~= nil and unique[curenv] == nil then
-			envcount = envcount + 1
-			bootenvs[envcount] = curenv
 			unique[curenv] = true
+
+			-- If we have a filter installed (by a local module), we
+			-- give it a chance to veto the BE.
+			if not core.bootenv_filter or
+			    core.bootenv_filter(curenv) then
+				envcount = envcount + 1
+				bootenvs[envcount] = curenv
+			end
 		end
 	end
+
 	return bootenvs
 end