From 986b12d391b8de6c820da1af9bfdb4153c340370 Mon Sep 17 00:00:00 2001

From: Kairui Song <kasong@redhat.com>

Date: Wed, 25 Jul 2018 16:47:37 +0800

Subject: [PATCH] lsinitrd: optimize performance when handling multiple files

Currently, when trying to unpack or print the content of multiple

files, lsinitrd will decompress the image and pipe the decompressed

content to cpio to retrive each file if the image is compressed.

Which mean if we want to extract 10 files the image will be decompressed

10 times, which is a waste of time.

This patch will let lsinitrd decompress the image file to a temp file

first if multiple file names are given, then cpio will read from the

decompressed temp file, which will speed up a lot.

Time consumption test for command:

`lsinitrd initramfs-4.16.15-300.fc28.x86_64.img \

    usr/lib/dracut/build-parameter.txt \

    usr/lib/dracut/modules.txt \

    etc/machine-id \

    etc/hostname \

    usr/lib/udev/rules.d/99-systemd.rules`

Before the patch:

2.37user 0.33system 0:02.12elapsed

After the patch:

0.50user 0.42system 0:00.72elapsed

There would be a more significant time difference if we try to

extract more files.

---

 lsinitrd.sh | 11 +++++++++++

 1 file changed, 11 insertions(+)

diff --git a/lsinitrd.sh b/lsinitrd.sh

index 1b9a93b6..0cb89e9c 100755

--- a/lsinitrd.sh

+++ b/lsinitrd.sh

@@ -251,6 +251,17 @@ if [[ $SKIP ]]; then

     CAT=skipcpio

 fi

+if (( ${#filenames[@]} > 1 )); then

+    TMPFILE="$(mktemp -t --suffix=.cpio lsinitrd.XXXXXX)"

+    $CAT "$image" 2>/dev/null > $TMPFILE

+    trap "rm -f '$TMPFILE'" EXIT

+    pre_decompress()

+    {

+        cat $TMPFILE

+    }

+    CAT=pre_decompress

+fi

+

 ret=0

 if [[ -n "$unpack" ]]; then