On Sat, Dec 19, 2015 at 7:59 PM, Frederick Grose <fgrose@gmail.com> wrote:
> This post may be of interest,
> http://article.gmane.org/gmane.linux.kernel.initramfs/4308
>
> ---------- Forwarded message ----------
> From: Frederick Grose <fgrose@gmail.com>
> Date: Sat, Dec 19, 2015 at 7:51 PM
> Subject: OverlayFS support for LiveOS
> To: initramfs@vger.kernel.org
>
>
> See this pull request, https://github.com/haraldh/dracut/pull/107
> and issue discussion, https://github.com/haraldh/dracut/issues/104
>
> This may be suitable for rawhide testing, particularly with btrfs and
> other filesystems.
>
> Commit message:
> Integrate the option to use an OverlayFS as the root filesystem
> into the 90dmsquash-live module for testing purposes.
>
> Tested primarily with transient, in-RAM overlay boots on vfat-
> formatted Live USB devices, with persistent overlay directories
> on ext4-formatted Live USB devices, and with embedded, persistent
> overlay directories on vfat-formatted devices. (Persistent overlay
> directories on a vfat-formatted device must be in an embedded
> filesystem that supports the creation of trusted.* extended attributes,
> and must provide valid d_type in readdir responses.) The
> rd.live.overlay.readonly option to allow a persistent overlayfs to be
> mounted read only through a higher level transient overlay directory
> has been implemented through the multiple lower layers feature of
> OverlayFS.
>
> This implementation currently requires the enforcing=0 kernel command
> line option. Further SELinux tuning may change this limitation.
>
> To permit easier comparison of Device-mapper vs. OverlayFS performance,
> the default transient dm overlay size has been adjusted up to 32 GiB.
> A transient dm overlay is a sparse file in memory, so this does not
> consume more RAM for legacy applications. It does permit a user to
> use all of the available root filesystem storage, and fails gently
> when it is consumed, as the available free root filesystem storage on
> a typical LiveOS build is under a few GiB. Thus, when booted on other-
> than-small RAM systems, the transient dm overlay should not overflow.
>
> OverlayFS offers the potential to use all of the available free RAM,
> or all of the available free disc storage on non-vfat-devices,
> in its overlay, even beyond the root filesystem available space,
> because the OverlayFS root filesystem is a union of directories on
> two different partitions.