1. 介绍
Xilinx VCU TRD 集成了图像和视频编解码功能，生成的根文件系统比较大，2020.1的rootfs.cpio.gz大约有114MB。工程师可以根据自己需要裁剪，减少根文件系统大小。
在Ubuntu下，解压rootfs.cpio.gz，得到rootfs.cpio，再解压，得到就是文件了。
2. 检查目录大小
使用du命令，可以检查各个文件夹的大小。
rootfs@rootfs$ du --max-depth=1 -h
4.0K ./run
8.5M ./lib
20K ./home
4.0K ./boot
4.0K ./tmp
4.0K ./sys
2.9M ./bin
4.0K ./mnt
312M ./usr
112K ./var
2.8M ./opt
2.0M ./etc
8.0K ./media
4.0K ./dev
4.0K ./proc
2.0M ./sbin
330M
也可以看更深的目录，排除占用空间小的目录。
rootfs@rootfs$ du --max-depth=2 -h | grep [0-9]M
3.1M ./lib/modules
8.5M ./lib
2.9M ./bin
206M ./usr/lib
22M ./usr/bin
1.3M ./usr/libexec
80M ./usr/share
3.8M ./usr/sbin
312M ./usr
2.8M ./opt/vcu_qt
2.8M ./opt
2.0M ./etc
2.0M ./sbin
330M .
rootfs$ du --max-depth=2 -h | grep [0-9]M
5.9M ./lib
2.9M ./bin
18M ./usr/lib
5.1M ./usr/bin
6.2M ./usr/share
3.3M ./usr/sbin
33M ./usr
2.0M ./sbin
45M .
3. 检查文件大小
目录大小有助于粗略的分析根文件系统大小。要找到真正的原因，并找到减小根文件系统大小，需要分析文件大小。
使用find命令，找到文件，再使用ls命令，查看文件大小；最后使用grep命令过滤出大文件。
rootfs$ find | xargs -n 1 ls -l -h | grep [0-9]M
total 4.3M
-rwxr-xr-x 1 hankf hankf 1.4M May 27 13:58 libc-2.30.so
-rwxr-xr-x 1 hankf hankf 1.4M May 27 13:58 ./lib/libc-2.30.so
total 2.9M
-rwxr-xr-x 1 hankf hankf 1.2M May 27 14:07 bash.bash
-rwsr-xr-x 1 hankf hankf 1.6M May 27 14:09 busybox
-rwsr-xr-x 1 hankf hankf 1.6M May 27 14:09 ./bin/busybox
-rwxr-xr-x 1 hankf hankf 1.2M May 27 14:07 ./bin/bash.bash
total 105M
-rwxr-xr-x 1 hankf hankf 1.1M May 27 14:07 libasound.so.2.0.0
-rwxr-xr-x 1 hankf hankf 1.2M May 27 05:01 libcairo.so.2.11600.0
-rwxr-xr-x 1 hankf hankf 2.5M May 27 14:04 libcrypto.so.1.1
-rwxr-xr-x 1 hankf hankf 1.3M May 27 05:00 libepoxy.so.0.0.0
-rwxr-xr-x 1 hankf hankf 1.9M May 27 14:11 libgio-2.0.so.0.6000.7
-rwxr-xr-x 1 hankf hankf 1.2M May 27 14:11 libglib-2.0.so.0.6000.7
-rwxr-xr-x 1 hankf hankf 1.8M May 27 14:13 libgnutls.so.30.24.0
-rwxr-xr-x 1 hankf hankf 1.3M May 27 14:20 libgstreamer-1.0.so.0.1601.0
-rwxr-xr-x 1 hankf hankf 7.2M May 27 05:06 libgtk-3.so.0.2404.4
-r-xr-xr-x 1 hankf hankf 3.0M May 27 14:11 libpython3.7m.so.1.0
-rwxr-xr-x 1 hankf hankf 1.9M May 27 05:27 libQt5Charts.so.5.13.2
-rwxr-xr-x 1 hankf hankf 6.3M May 27 05:18 libQt5Core.so.5.13.2
-rwxr-xr-x 1 hankf hankf 5.8M May 27 05:18 libQt5Gui.so.5.13.2
-rwxr-xr-x 1 hankf hankf 1.9M May 27 05:18 libQt5Network.so.5.13.2
-rwxr-xr-x 1 hankf hankf 4.9M May 27 05:23 libQt5Qml.so.5.13.2
-rwxr-xr-x 1 hankf hankf 4.9M May 27 05:23 libQt5Quick.so.5.13.2
-rwxr-xr-x 1 hankf hankf 1.1M May 27 05:26 libQt5WaylandClient.so.5.13.2
-rwxr-xr-x 1 hankf hankf 1.6M May 27 05:26 libQt5WaylandCompositor.so.5.13.2
-rwxr-xr-x 1 hankf hankf 6.8M May 27 05:18 libQt5Widgets.so.5.13.2
-rwxr-xr-x 1 hankf hankf 1.3M May 27 05:18 libQt5XcbQpa.so.5.13.2
-rwxr-xr-x 1 hankf hankf 1.5M May 27 14:10 libsamplerate.so.0.1.8
-rwxr-xr-x 1 hankf hankf 1.1M May 27 14:05 libsqlite3.so.0.8.6
-rwxr-xr-x 1 hankf hankf 1.8M May 27 14:02 libstdc++.so.6.0.27
-rwxr-xr-x 1 hankf hankf 1.5M May 27 14:08 libunistring.so.2.1.0
-rwxr-xr-x 1 hankf hankf 1.5M May 27 14:03 libvpx.so.6.1.0
-rwxr-xr-x 1 hankf hankf 1.3M May 27 14:07 libX11.so.6.3.0
-rwxr-xr-x 1 hankf hankf 1.4M May 27 14:14 libxml2.so.2.9.9
-r-xr-xr-x 1 hankf hankf 3.0M May 27 14:11 ./usr/lib/libpython3.7m.so.1.0
-rwxr-xr-x 1 hankf hankf 1.9M May 27 05:18 ./usr/lib/libQt5Network.so.5.13.2
-rwxr-xr-x 1 hankf hankf 1.5M May 27 14:10 ./usr/lib/libsamplerate.so.0.1.8
-rwxr-xr-x 1 hankf hankf 6.3M May 27 05:18 ./usr/lib/libQt5Core.so.5.13.2
-rwxr-xr-x 1 hankf hankf 1.5M May 27 14:08 ./usr/lib/libunistring.so.2.1.0
-rwxr-xr-x 1 hankf hankf 4.9M May 27 05:23 ./usr/lib/libQt5Quick.so.5.13.2
total 1.7M
-rw-r--r-- 1 hankf hankf 1.7M Jul 15 17:32 libMali.so.9.0
-rw-r--r-- 1 hankf hankf 1.7M Jul 15 17:32 ./usr/lib/x11/libMali.so.9.0
-rwxr-xr-x 1 hankf hankf 1.1M May 27 05:26 ./usr/lib/libQt5WaylandClient.so.5.13.2
-rwxr-xr-x 1 hankf hankf 6.8M May 27 05:18 ./usr/lib/libQt5Widgets.so.5.13.2
-rwxr-xr-x 1 hankf hankf 1.2M May 27 05:01 ./usr/lib/libcairo.so.2.11600.0
total 1.7M
-rw-r--r-- 1 hankf hankf 1.7M Jul 15 17:32 libMali.so.9.0
-rw-r--r-- 1 hankf hankf 1.7M Jul 15 17:32 ./usr/lib/headless/libMali.so.9.0
-rwxr-xr-x 1 hankf hankf 1.8M May 27 14:13 ./usr/lib/libgnutls.so.30.24.0
-rwxr-xr-x 1 hankf hankf 1.9M May 27 05:27 ./usr/lib/libQt5Charts.so.5.13.2
total 4.7M
total 4.6M
-rwxr-xr-x 1 hankf hankf 1.1M May 27 14:11 unicodedata.cpython-37m-aarch64-linux-gnu.so
-rwxr-xr-x 1 hankf hankf 1.1M May 27 14:11 ./usr/lib/python3.7/lib-dynload/unicodedata.cpython-37m-aarch64-linux-gnu.so
total 1.2M
total 2.0M
total 2.0M
-rw-r--r-- 1 hankf hankf 1.4M May 27 14:11 pip-19.2.3-py2.py3-none-any.whl
-rw-r--r-- 1 hankf hankf 1.4M May 27 14:11 ./usr/lib/python3.7/ensurepip/_bundled/pip-19.2.3-py2.py3-none-any.whl
total 1.8M
total 1.8M
total 1.3M
total 9.6M
ls: cannot access './usr/lib/python3.7/site-packages/setuptools/script': No such file or directory
ls: cannot access '(dev).tmpl': No such file or directory
ls: cannot access './usr/lib/python3.7/site-packages/setuptools/command/launcher': No such file or directory
ls: cannot access 'manifest.xml': No such file or directory
total 2.3M
total 1.1M
total 1.1M
-rwxr-xr-x 1 hankf hankf 1.3M May 27 05:18 ./usr/lib/libQt5XcbQpa.so.5.13.2
-rwxr-xr-x 1 hankf hankf 1.2M May 27 14:11 ./usr/lib/libglib-2.0.so.0.6000.7
-rwxr-xr-x 1 hankf hankf 1.9M May 27 14:11 ./usr/lib/libgio-2.0.so.0.6000.7
total 2.9M
-rw-r--r-- 1 hankf hankf 2.9M Jul 15 17:38 locale-archive
-rw-r--r-- 1 hankf hankf 2.9M Jul 15 17:38 ./usr/lib/locale/locale-archive
-rwxr-xr-x 1 hankf hankf 4.9M May 27 05:23 ./usr/lib/libQt5Qml.so.5.13.2
total 1.4M
total 1.1M
-rwxr-xr-x 1 hankf hankf 1.1M May 27 14:05 ./usr/lib/libsqlite3.so.0.8.6
-rwxr-xr-x 1 hankf hankf 1.5M May 27 14:03 ./usr/lib/libvpx.so.6.1.0
-rwxr-xr-x 1 hankf hankf 1.8M May 27 14:02 ./usr/lib/libstdc++.so.6.0.27
-rwxr-xr-x 1 hankf hankf 2.5M May 27 14:04 ./usr/lib/libcrypto.so.1.1
-rwxr-xr-x 1 hankf hankf 1.6M May 27 05:26 ./usr/lib/libQt5WaylandCompositor.so.5.13.2
-rwxr-xr-x 1 hankf hankf 1.3M May 27 14:07 ./usr/lib/libX11.so.6.3.0
-rwxr-xr-x 1 hankf hankf 1.1M May 27 14:07 ./usr/lib/libasound.so.2.0.0
-rwxr-xr-x 1 hankf hankf 1.4M May 27 14:14 ./usr/lib/libxml2.so.2.9.9
-rwxr-xr-x 1 hankf hankf 1.3M May 27 05:00 ./usr/lib/libepoxy.so.0.0.0
-rwxr-xr-x 1 hankf hankf 1.3M May 27 14:20 ./usr/lib/libgstreamer-1.0.so.0.1601.0
total 1.7M
-rw-r--r-- 1 hankf hankf 1.7M Jul 15 17:32 libMali.so.9.0
-rw-r--r-- 1 hankf hankf 1.7M Jul 15 17:32 ./usr/lib/fbdev/libMali.so.9.0
total 1.5M
total 1.7M
-rw-r--r-- 1 hankf hankf 1.7M Jul 15 17:32 libMali.so.9.0
-rw-r--r-- 1 hankf hankf 1.7M Jul 15 17:32 ./usr/lib/wayland/libMali.so.9.0
-rwxr-xr-x 1 hankf hankf 7.2M May 27 05:06 ./usr/lib/libgtk-3.so.0.2404.4
-rwxr-xr-x 1 hankf hankf 5.8M May 27 05:18 ./usr/lib/libQt5Gui.so.5.13.2
total 13M
total 1.2M
total 2.2M
total 22M
-rwxr-xr-x 1 hankf hankf 1.1M Jul 15 17:32 ctrlsw_encoder
-rwxr-xr-x 1 hankf hankf 7.7M May 27 14:28 gdb
-rwxr-xr-x 1 hankf hankf 2.2M May 27 05:03 Xorg
-rwxr-xr-x 1 hankf hankf 2.2M May 27 05:03 ./usr/bin/Xorg
-rwxr-xr-x 1 hankf hankf 1.1M Jul 15 17:32 ./usr/bin/ctrlsw_encoder
-rwxr-xr-x 1 hankf hankf 7.7M May 27 14:28 ./usr/bin/gdb
total 1.8M
total 1.2M
total 4.0M
total 1.3M
total 1.2M
total 1.3M
total 1.3M
total 1.4M
total 5.4M
-rw-r--r-- 1 hankf hankf 5.4M May 27 14:08 magic.mgc
-rw-r--r-- 1 hankf hankf 5.4M May 27 14:08 ./usr/share/misc/magic.mgc
total 1.9M
total 2.2M
-rw-r--r-- 1 hankf hankf 2.2M May 27 05:17 libpnp_basictools.a
-rw-r--r-- 1 hankf hankf 2.2M May 27 05:17 ./usr/share/examples/widgets/tools/plugandpaint/plugins/libpnp_basictools.a
total 3.8M
total 2.8M
-rwxr-xr-x 1 hankf hankf 2.7M Jul 15 17:34 vcu_qt
-rwxr-xr-x 1 hankf hankf 2.7M Jul 15 17:34 ./opt/vcu_qt/bin/vcu_qt
total 2.0M
4. 去掉不必要文件。
根据上述找到的大文件，禁止不使用的软件包，就能减小根文件系统大小。
比如，在petalinux工程中，禁止下列软件包后，rootfs.cpio.gz从114MB，减小到16.4MB。下列内容是从project-spec/configs/rootfs_config提取的。
# CONFIG_gdb is not set
# CONFIG_gdbserver is not set
# CONFIG_kernel-module-hdmi is not set
# CONFIG_packagegroup-core-x11 is not set
# CONFIG_packagegroup-petalinux-audio is not set
# CONFIG_packagegroup-petalinux-gstreamer is not set
# CONFIG_packagegroup-petalinux-matchbox is not set
# CONFIG_packagegroup-petalinux-qt is not set
# packagegroup-petalinux-v4lutils
# CONFIG_packagegroup-petalinux-v4lutils is not set
# CONFIG_packagegroup-petalinux-x11 is not set
# CONFIG_trd-init is not set
# CONFIG_vcu-gst-app is not set
# CONFIG_custom-edid is not set
# CONFIG_gst-shark is not set
# CONFIG_gstreamer-vcu-examples is not set
# CONFIG_vcu-qt is not set