[OE-core] [PATCH] volatile-binds: use overlayfs if available

[Matt Hoosier]

Hi; any interest in this one?

On Fri, Oct 19, 2018 at 11:04 AM Matt Hoosier <matt.hoosier at gmail.com>
wrote:

> From: Matt Hoosier <matt.hoosier at garmin.com>
>
> Copying files from the read-only root filesystem to the tmpfs
> providing the volatile directories can be slow and waste memory.
> If the kernel supports the overlay filesystem, use it to mount
> a writable tmpfs on top of the read-only directory from the
> rootfs and avoid copies.
>
> Analogous to the modification made to initscripts's
> read-only-rootfs-hook in 370fda1b2e8d5dc011522131bba4106de26bfb19.
>
> Signed-off-by: Matt Hoosier <matt.hoosier at gmail.com>
> ---
>  .../volatile-binds/files/mount-copybind       | 30 ++++++++++++++++---
>  1 file changed, 26 insertions(+), 4 deletions(-)
>
> diff --git a/meta/recipes-core/volatile-binds/files/mount-copybind
> b/meta/recipes-core/volatile-binds/files/mount-copybind
> index 2aeaf84ddb..fddf520053 100755
> --- a/meta/recipes-core/volatile-binds/files/mount-copybind
> +++ b/meta/recipes-core/volatile-binds/files/mount-copybind
> @@ -8,7 +8,10 @@ if [ $# -lt 2 ]; then
>      exit 1
>  fi
>
> +# e.g. /var/volatile/lib
>  spec=$1
> +
> +# e.g. /var/lib
>  mountpoint=$2
>
>  if [ $# -gt 2 ]; then
> @@ -20,15 +23,34 @@ fi
>  [ -n "$options" ] && options=",$options"
>
>  mkdir -p "${spec%/*}"
> +
>  if [ -d "$mountpoint" ]; then
> -    if [ ! -d "$spec" ]; then
> +
> +    if [ -d "$spec" ]; then
> +        specdir_existed=yes
> +    else
> +        specdir_existed=no
>          mkdir "$spec"
> -        cp -pPR "$mountpoint"/. "$spec/"
> +    fi
> +
> +    # Fast version of calculating `dirname ${spec}`/.`basename
> ${spec}`-work
> +    overlay_workdir="${spec%/*}/.${spec##*/}-work"
> +    mkdir "${overlay_workdir}"
> +
> +    # Try to mount using overlay, which is must faster than copying files.
> +    # If that fails, fall back to slower copy.
> +    if ! mount -t overlay overlay
> -olowerdir="$mountpoint",upperdir="$spec",workdir="$overlay_workdir"
> "$mountpoint" > /dev/null 2>&1; then
> +
> +        if [ "$specdir_existed" != "yes" ]; then
> +            cp -pPR "$mountpoint"/. "$spec/"
> +        fi
> +
> +        mount -o "bind$options" "$spec" "$mountpoint"
>      fi
>  elif [ -f "$mountpoint" ]; then
>      if [ ! -f "$spec" ]; then
>          cp -pP "$mountpoint" "$spec"
>      fi
> -fi
>
> -mount -o "bind$options" "$spec" "$mountpoint"
> +    mount -o "bind$options" "$spec" "$mountpoint"
> +fi
> --
> 2.17.2
>
>
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