[PATCH 0/4] fs: allow listmount() with reversed ordering

[Christian Brauner <brauner@xxxxxxxxxx>]

util-linux is about to implement listmount() and statmount() support.
Karel requested the ability to scan the mount table in backwards order
because that's what libmount currently does in order to get the latest
mount first. We currently don't support this in listmount(). Add a new
LISTMOUNT_RESERVE flag to allow listing mounts in reverse order. For
example, listing all child mounts of /sys without LISTMOUNT_REVERSE
gives:

    /sys/kernel/security @ mnt_id: 4294968369
    /sys/fs/cgroup @ mnt_id: 4294968370
    /sys/firmware/efi/efivars @ mnt_id: 4294968371
    /sys/fs/bpf @ mnt_id: 4294968372
    /sys/kernel/tracing @ mnt_id: 4294968373
    /sys/kernel/debug @ mnt_id: 4294968374
    /sys/fs/fuse/connections @ mnt_id: 4294968375
    /sys/kernel/config @ mnt_id: 4294968376

whereas with LISTMOUNT_RESERVE it gives:

    /sys/kernel/config @ mnt_id: 4294968376
    /sys/fs/fuse/connections @ mnt_id: 4294968375
    /sys/kernel/debug @ mnt_id: 4294968374
    /sys/kernel/tracing @ mnt_id: 4294968373
    /sys/fs/bpf @ mnt_id: 4294968372
    /sys/firmware/efi/efivars @ mnt_id: 4294968371
    /sys/fs/cgroup @ mnt_id: 4294968370
    /sys/kernel/security @ mnt_id: 4294968369

A few smaller cleanups included in this series.

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base-commit: 1613e604df0cd359cf2a7fbd9be7a0bcfacfabd0
change-id: 20240607-vfs-listmount-reverse-0f5d4d8248ee