pub fn overlay_transient(
base: impl AsFd,
source: &str,
mount_attr_flags: Option<MountAttrFlags>,
) -> Result<OwnedFd>Expand description
Creates a transient overlayfs with the passed-in fd as the lowerdir.
Returns a detached (not yet attached) OwnedFd for the overlay mount.
The caller is responsible for attaching it to the filesystem tree.
source is used verbatim as the overlay’s source fsconfig option and
appears in /proc/self/mountinfo. For the composefs root, pass
"transient:composefs=<digest_hex>" so that composefs_booted() can
recover the verity digest from the mount source after switch-root. For
non-root transient mounts (e.g. /usr, /var) pass "transient".
The SELinux label on / is fixed after boot by
bootc-early-overlay-relabel.service; no initramfs-side xattr write is
needed (kernel fs_use_trans tmpfs relabeling at policy-load time would
overwrite anything written here).