Add design notes

Author: harendra-kumar

src/Streamly/Coreutils/Chmod.hs

@@ -9,6 +9,47 @@
 --
 -- change file mode bits.
 
+-- TODO: change this module to Chmod.Posix and later create a portable module.
+--
+-- Design notes:
+--
+-- On Posix systems:
+--
+-- Roles: User (Owner), group (only one), others
+-- Permissions: rwxX(ugo), s(go), t(o)
+--
+-- 1. write: create or delete a file in a directory. Modify contents of a file.
+-- 2. write: modify metadata of a directory or file.
+-- 3. execute: to list a directory's contents
+--
+-- On Windows:
+--
+-- Could not find any good docs by microsoft on a google search.
+-- Managing permissions: https://learn.microsoft.com/en-us/previous-versions/windows/it-pro/windows-server-2008-R2-and-2008/cc770962(v=ws.11)
+-- https://learn.microsoft.com/en-us/windows/security/identity-protection/access-control/access-control
+--
+-- Roles: User (Owner), group (many)
+-- Permissions: read, read+execute, modify (metadata, create/delete files in
+-- dirs), write (write to a file), list dir, full control
+-- Inheritance: permissions can be inherited from parent directories
+-- Advanced Permissions: ...
+--
+-- 1. write: create or delete a file in a directory. Modify contents of a file.
+-- 2. modify: modify metadata of a directory or file.
+-- 3. list dir: to list a directory's contents
+--
+-- Common abstraction for windows/posix:
+--
+-- Roles: User/Owner
+-- Permissions:
+--
+-- 1. write on Posix: write+modify on windows
+-- 2. execute on dir: "list dir" on windows
+--
+-- Other's default permissions are controlled by umask on Posix. When setting
+-- permissions we can ensure that other's permissions are less restrictive than
+-- the owner? But we cannot do the same on windows.
+
 module Streamly.Coreutils.Chmod
     ( chmod
     )