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ADB SHELL DD的秘密

问题

在工作中会遇到需要模拟存储空间不足的场景，以验证某功能点或复现某些特殊bug。常规做法是通过手工拷贝大文件到测试设备，模拟存储空间不足，当涉及机型适配时得在N个设备重复操作N次，手工操作非常繁琐，该如何高效解决这个问题呢？

解决方案

是否有方法可以模拟设备存储空间不足的场景，此时联想到adb shell dd命令就可以很好地实现我们的需求，它支持生成指定大小的块文件，具体命令和参数解释如下

adb shell dd命令

adb shell dd if=/dev/zero of=/sdcard/tmp/auto_dd_file bs=1024 count=1

###参数含义
if=文件：读取内容，而非标准输入的数据 
of=文件：将数据写入的文件，而不在标准输出显示
bs=bytes：同时设置读入/输出的块大小为bytes字节，未填写时默认512 bytes
ibs：一次读入bytes个字节，即指定一个块大小为bytes字节
obs=bytes：一次输出bytes个字节，即指定一个块大小为bytes字节。
count ：创建/拷贝blocks个数，块大小等于bs指定的字节数。

注：单位是byte，如需要1000M大文件，bs=1024*1024*100，单位不支持M或Kb

如果要生成一个10M和20M文件，可以这样使用

C:Userszhongyaqi>adb shell dd if=/dev/zero of=/sdcard/tmp/auto_dd_file1 bs=102
4*1024*10 count=1
1+0 records in
1+0 records out
10485760 bytes transferred in 0.042 secs (249660952 bytes/sec)

C:Userszhongyaqi>adb shell dd if=/dev/zero of=/sdcard/tmp/auto_dd_file2 bs=102
4*1024*10 count=2
2+0 records in
2+0 records out
20971520 bytes transferred in 0.081 secs (258907654 bytes/sec)

验证执行结果，在/sdcard/tmp/目录下生成了10M和20M的文件

C:Userszhongyaqi>adb shell
PD1709:/ $ cd /sdcard/tmp/
cd /sdcard/tmp/
PD1709:/sdcard/tmp $ ls -l -h
ls -l -h
total 131M
-rw-rw---- 1 root sdcard_rw  10M 2020-04-25 17:11 auto_dd_file1
-rw-rw---- 1 root sdcard_rw  20M 2020-04-25 17:11 auto_dd_file2

Python脚本实现

在上一篇文章中，实现批量复制文件前，进行了检查adb连接状态等操作，同样该该操作也适用于本篇文章使用的场景，有兴趣的请参考Python脚本葵花宝典之一键批量复制文件

def run_create_file(self, byte, count, path):
        """
        :param byte: The unit is byte
        :param count: Number of blocks created
        :param path: THE path of file that includes file name
        :return:
        for example
        byte = 1024*1024*100
        count = 1
        path = '/sdcard/tmp/test_dd'
        """
        print("step2 Create file and check status")
        ADB_SHELL_DD = "adb shell dd if=/dev/zero of=%s bs=%d count=%d " % (path,byte,count)
        os.system(ADB_SHELL_DD)
        adbfile = os.popen(ADB_SHELL_DD, "r")
        result = adbfile.read()
        if "%s bytes transferred in" % str(byte) in result:
            print("Create file success，file size is %sM ,and file path is %s " % (str(byte/1024/1024),path))
        else:
            print("Create file failed
")

脚本执行结果如下

step1 Check adb status
adb connect success

step2 Create file and check status
1+0 records in
1+0 records out
104857600 bytes transferred in 0.179 secs (585796648 bytes/sec)
Create file success，file size is 100.0M ,and file path is /sdcard/tmp/test_dd

adb shell 其他命令

adb shell dd还有复制文件的功能，如下

adb shell dd if=/sdcard/DCIM/camera/timg.jpg of=/sdcard/tmp/timg_cp.jpg
#以上命令将/sdcard/DCIM/camera/timg.jpg文件复制到/sdcard/tmp/timg_cp.jpg

如果想了解adb shell 还支持哪些命令，adb shell 进入/system/bin目录，执行ls -l即可。

由于文章长度限制，仅截取部分结果如下

lrwxr-xr-x 1 root shell       6 2009-01-01 00:00 chown -> toybox
lrwxr-xr-x 1 root shell       6 2009-01-01 00:00 chroot -> toybox
lrwxr-xr-x 1 root shell       6 2009-01-01 00:00 chrt -> toybox
lrwxr-xr-x 1 root shell       6 2009-01-01 00:00 cksum -> toybox
lrwxr-xr-x 1 root shell       6 2009-01-01 00:00 clear -> toybox
-rwxr-xr-x 1 root shell  479432 2009-01-01 00:00 climax
-rwxr-xr-x 1 root shell   65208 2009-01-01 00:00 cmd
lrwxr-xr-x 1 root shell       6 2009-01-01 00:00 cmp -> toybox
lrwxr-xr-x 1 root shell       6 2009-01-01 00:00 comm -> toybox
-rwxr-xr-x 1 root shell     207 2009-01-01 00:00 content
lrwxr-xr-x 1 root shell       6 2009-01-01 00:00 cp -> toybox
-rwxr-xr-x 1 root shell  137224 2009-01-01 00:00 cp_log
lrwxr-xr-x 1 root shell       6 2009-01-01 00:00 cpio -> toybox
-rwxr-xr-x 1 root shell  102080 2009-01-01 00:00 crash_dump32
-rwxr-xr-x 1 root shell  123360 2009-01-01 00:00 crash_dump64
-rwxr-xr-x 1 root shell  410384 2009-01-01 00:00 curl
-rwxr-xr-x 1 root shell   11040 2009-01-01 00:00 custtest
lrwxr-xr-x 1 root shell       6 2009-01-01 00:00 cut -> toybox
lrwxr-xr-x 1 root shell      10 2009-01-01 00:00 dalvikvm -> dalvikvm64
-rwxr-xr-x 1 root shell   24648 2009-01-01 00:00 dalvikvm32
-rwxr-xr-x 1 root shell   19488 2009-01-01 00:00 dalvikvm64
lrwxr-xr-x 1 root shell       6 2009-01-01 00:00 date -> toybox
lrwxr-xr-x 1 root shell       7 2009-01-01 00:00 dd -> toolbox
-rwxr-xr-x 1 root shell   11184 2009-01-01 00:00 debuggerd
-rwxr-xr-x 1 root shell  141940 2009-01-01 00:00 dex2oat
-rwxr-xr-x 1 root shell   27784 2009-01-01 00:00 dexdiag
-rwxr-xr-x 1 root shell  104384 2009-01-01 00:00 dexdump
-rwxr-xr-x 1 root shell   15416 2009-01-01 00:00 dexlist
lrwxr-xr-x 1 root shell       6 2009-01-01 00:00 df -> toybox
-rwxr-xr-x 1 root shell   11152 2009-01-01 00:00 dhrystone64_bit.elf
-rwxr-xr-x 1 root shell   19664 2009-01-01 00:00 diag_command
lrwxr-xr-x 1 root shell       6 2009-01-01 00:00 diff -> toybox
lrwxr-xr-x 1 root shell       6 2009-01-01 00:00 dirname -> toybox
lrwxr-xr-x 1 root shell       6 2009-01-01 00:00 dmesg -> toybox
lrwxr-xr-x 1 root shell       6 2009-01-01 00:00 dos2unix -> toybox
-rwxr-xr-x 1 root shell     156 2009-01-01 00:00 dpm
lrwxr-xr-x 1 root shell       6 2009-01-01 00:00 du -> toybox
-rwxr-xr-x 1 root shell   40336 2009-01-01 00:00 dumpsys
-rwxr-xr-x 1 root shell    6904 2009-01-01 00:00 ebtables
lrwxr-xr-x 1 root shell       6 2009-01-01 00:00 echo -> toybox