Tom

Nomenclature: scall = system call, the user space part of it; in the library
kcall = call that the scall makes, that will actually encrypt stuff (kernel space)
uspace = user space application (protectfile)

Issues: do we check for root in scall? we should. kernel shouldnt have to check for that
so the buffer is allocated in the scall. it makes a kcall, and passes the pointer to the scall's buffer, encrypts it and returns
you don't need to be root, any user can set there own key, and e / d their own files
max 8 users as per design

what about user privs? users shouldnt have access to e / d if they dont have rights to a file

Task 1: Implement setkey(unsigned int k0, unsigned int k1) syscall / kcall
save for up to 8 users
hash on UID -> how?
If both k0, k1 == 0, disable encryption: reset key to 0

can use a struct with a key, and uid, valid bit. Make an array of them, search through every attempt, find free spot after the fact. Maybe ineffiecient.

Task 2: Enable sticky bit (S_ISVTX)
modify the ALL_MODES constant in minix/const.h to be 0007777

Task 3: uspace utility protectfile
set sticky bit appropriately by setting sticky bit using chmod scall
e / d should be done with the sticky bit off to ensure that no e / d is done automatically by the file system.

Need to obtain file ID with stat() syscall