Merge patch series "efivarfs: support freeze/thaw"

Merge patch series "efivarfs: support freeze/thaw"

Christian Brauner <brauner@kernel.org> says:

Allow efivarfs to partake to resync variable state during system
hibernation and suspend. Add freeze/thaw support.

This is a pretty straightforward implementation. We simply add regular
freeze/thaw support for both userspace and the kernel. This works
without any big issues and congrats afaict efivars is the first
pseudofilesystem that adds support for filesystem freezing and thawing.

The simplicity comes from the fact that we simply always resync variable
state after efivarfs has been frozen. It doesn't matter whether that's
because of suspend, userspace initiated freeze or hibernation. Efivars
is simple enough that it doesn't matter that we walk all dentries. There
are no directories and there aren't insane amounts of entries and both
freeze/thaw are already heavy-handed operations. If userspace initiated
a freeze/thaw cycle they would need CAP_SYS_ADMIN in the initial user
namespace (as that's where efivarfs is mounted) so it can't be triggered
by random userspace. IOW, we really really don't care.

* patches from https://lore.kernel.org/r/20250331-work-freeze-v1-0-6dfbe8253b9f@kernel.org:
  efivarfs: support freeze/thaw
  libfs: export find_next_child()

Link: https://lore.kernel.org/r/20250331-work-freeze-v1-0-6dfbe8253b9f@kernel.org
Signed-off-by: Christian Brauner <brauner@kernel.org>