kernel/git/next/linux-next.git/fs/nullfs.c, branch master

Merge branch 'vfs-7.3.kthread' into vfs.all

2026-07-02T08:00:13+00:00

Signed-off-by: Christian Brauner

nullfs: make nullfs multi-instance

2026-06-29T08:54:43+00:00

Allow multiple instances of nullfs to be created. Right now we're only going to use it for kernel-internal purposes but ultimately we can allow userspace to use it too to e.g., safely overmount stuff. Link: https://patch.msgid.link/20260601-work-kthread-nullfs-v4-22-77ee053060e0@kernel.org Signed-off-by: Christian Brauner (Amutable)

fs: nullfs should include mount.h

2026-06-29T08:27:27+00:00

The nullfs_fs_type is declared in mount.h but when declared in nullfs.c there is a warning as mount.h is not being included. Add include of "mount.h" to remove the following sparse warning: fs/nullfs.c:66:25: warning: symbol 'nullfs_fs_type' was not declared. Should it be static? Signed-off-by: Ben Dooks Link: https://patch.msgid.link/20260617104721.900914-1-ben.dooks@codethink.co.uk Signed-off-by: Christian Brauner (Amutable)

fs: add immutable rootfs

2026-01-12T15:52:09+00:00

Currently pivot_root() doesn't work on the real rootfs because it cannot be unmounted. Userspace has to do a recursive removal of the initramfs contents manually before continuing the boot. Really all we want from the real rootfs is to serve as the parent mount for anything that is actually useful such as the tmpfs or ramfs for initramfs unpacking or the rootfs itself. There's no need for the real rootfs to actually be anything meaningful or useful. Add a immutable rootfs called "nullfs" that can be selected via the "nullfs_rootfs" kernel command line option. The kernel will mount a tmpfs/ramfs on top of it, unpack the initramfs and fire up userspace which mounts the rootfs and can then just do: chdir(rootfs); pivot_root(".", "."); umount2(".", MNT_DETACH); and be done with it. (Ofc, userspace can also choose to retain the initramfs contents by using something like pivot_root(".", "/initramfs") without unmounting it.) Technically this also means that the rootfs mount in unprivileged namespaces doesn't need to become MNT_LOCKED anymore as it's guaranteed that the immutable rootfs remains permanently empty so there cannot be anything revealed by unmounting the covering mount. In the future this will also allow us to create completely empty mount namespaces without risking to leak anything. systemd already handles this all correctly as it tries to pivot_root() first and falls back to MS_MOVE only when that fails. This goes back to various discussion in previous years and a LPC 2024 presentation about this very topic. Link: https://patch.msgid.link/20260112-work-immutable-rootfs-v2-3-88dd1c34a204@kernel.org Signed-off-by: Christian Brauner