add file system helpers that take kernel pointers for the init code v4

From: Christoph Hellwig
Date: Tue Jul 28 2020 - 12:36:34 EST

Hi Al and Linus,

currently a lot of the file system calls in the early in code (and the
devtmpfs kthread) rely on the implicit set_fs(KERNEL_DS) during boot.
This is one of the few last remaining places we need to deal with to kill
off set_fs entirely, so this series adds new helpers that take kernel
pointers. These helpers are in init/ and marked __init and thus will
be discarded after bootup. A few also need to be duplicated in devtmpfs,
though unfortunately.

The series sits on top of my previous

"decruft the early init / initrd / initramfs code v2"


Git tree:

git:// init_path


Changes since v3:
- rename fs/for_init.c to fs/init.c
- document the purpose of the routines in fs/init.c with a comment
- don't mark devtmpfs __init as that will cause it to get overwritten
by initmem poisoning
- add an init_dup helper to make Al more happy than with the version
commit to the "decruft the early init / initrd / initramfs code v2"

Changes since v2:
- move to fs/for_init.c
- reuse the init routines in devtmpfs after refactoring devtmpfsd
(and thus the broken error handling in the previous version)
- actually use kern_path in a place where user_path_at sneaked back in

Changes since v1:
- avoid most core VFS changes
- renamed the functions and move them to init/ and devtmpfs
- drop a bunch of cleanups that can be submitted independently now