[oe-commits] [openembedded-core] 15/16: volatile-binds: use overlayfs if available

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rpurdie pushed a commit to branch master
in repository openembedded-core.

commit b4976f3cf8cd028f165100b67867adb862da4d7f
Author: Matt Hoosier <matt.hoosier at garmin.com>
AuthorDate: Fri Oct 19 11:04:55 2018 -0500

    volatile-binds: use overlayfs if available
    
    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>
    Signed-off-by: Richard Purdie <richard.purdie at linuxfoundation.org>
---
 .../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 2aeaf84..fddf520 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

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