SD expand

Author: FolderLevel

README.md

@@ -12,6 +12,7 @@
 
 NO.|文件名称|摘要
 :--:|:--|:--
+0022| [SD卡自动扩容](docs/0022_SD卡自动扩容.md) | 理解SD卡自动扩容工作原理
 0021| [wav声音PCM数据分析](docs/0021_wav声音PCM数据分析.md) | 通过wav文件了解PCM数据
 0020| [Android_Binder通信](docs/0020_Android_Binder通信.md) | 在树莓派中理解Android Binder通信
 0019| [USB_OTG虚拟串口](docs/0019_USB_OTG虚拟串口.md) | USB OTG虚拟串口，可用于学习串口通信

docs/0022_SD卡自动扩容.md

@@ -0,0 +1,102 @@
+# SD卡自动扩容
+
+理解SD卡自动扩容工作原理
+
+## steps
+
+* sudo raspi-config
+  * Advanced Options
+    * Expand Filesystem 
+* /usr/bin/raspi-config
+  ```sh
+  do_expand_rootfs() {
+    # -h : FILE exists and is a symbolic link (same as -L)
+    if ! [ -h /dev/root ]; then
+      whiptail --msgbox "/dev/root does not exist or is not a symlink. Don't know how to expand" 20 60 2
+      return 0
+    fi
+  
+    # readlink用来找出符号链接所指向的位置。 
+    ROOT_PART=$(readlink /dev/root)
+    # 从变量$string的开头, 删除最短匹配$substring的子串
+    PART_NUM=${ROOT_PART#mmcblk0p}
+    if [ "$PART_NUM" = "$ROOT_PART" ]; then
+      whiptail --msgbox "/dev/root is not an SD card. Don't know how to expand" 20 60 2
+      return 0
+    fi
+  
+    # NOTE: the NOOBS partition layout confuses parted. For now, let's only 
+    # agree to work with a sufficiently simple partition layout
+    if [ "$PART_NUM" -ne 2 ]; then
+      whiptail --msgbox "Your partition layout is not currently supported by this tool. You are probably using NOOBS, in which case your root filesystem is already expanded anyway." 20 60 2
+      return 0
+    fi
+  
+    # 再次确认分区表和设备节点提取的数值是否一致
+    # 
+    # shell script:
+    #   root@zengjf:/home/zengjf/hacking# parted /dev/sdb -ms unit s p 
+    #   BYT;
+    #   /dev/sdb:1953525168s:scsi:512:4096:gpt:ATA ST1000LM035-1RK1:;
+    #   1:2048s:943720448s:943718401s:ntfs:Basic data partition:msftdata;
+    #   2:943722496s:1953523711s:1009801216s:ntfs:Basic data partition:msftdata;
+    LAST_PART_NUM=$(parted /dev/mmcblk0 -ms unit s p | tail -n 1 | cut -f 1 -d:)
+    if [ "$LAST_PART_NUM" != "$PART_NUM" ]; then
+      whiptail --msgbox "/dev/root is not the last partition. Don't know how to expand" 20 60 2
+      return 0
+    fi
+  
+    # Get the starting offset of the root partition
+    # 获取文件系统分区起始位置
+    PART_START=$(parted /dev/mmcblk0 -ms unit s p | grep "^${PART_NUM}" | cut -f 2 -d:)
+    [ "$PART_START" ] || return 1
+    # Return value will likely be error for fdisk as it fails to reload the
+    # partition table because the root fs is mounted
+    fdisk /dev/mmcblk0 <<EOF
+  p
+  d
+  $PART_NUM
+  n
+  p
+  $PART_NUM
+  $PART_START
+  
+  p
+  w
+  EOF
+    ASK_TO_REBOOT=1
+  
+    # now set up an init.d script
+  cat <<\EOF > /etc/init.d/resize2fs_once &&
+  #!/bin/sh
+  ### BEGIN INIT INFO
+  # Provides:          resize2fs_once
+  # Required-Start:
+  # Required-Stop:
+  # Default-Start: 2 3 4 5 S
+  # Default-Stop:
+  # Short-Description: Resize the root filesystem to fill partition
+  # Description:
+  ### END INIT INFO
+  . /lib/lsb/init-functions
+  case "$1" in
+    start)
+      log_daemon_msg "Starting resize2fs_once" &&
+      resize2fs /dev/root &&                       # 真正调整大小的地方
+      rm /etc/init.d/resize2fs_once &&             # 删除文件，表明该文件只能被运行一次
+      update-rc.d resize2fs_once remove &&
+      log_end_msg $?
+      ;;
+    *)
+      echo "Usage: $0 start" >&2
+      exit 3
+      ;;
+  esac
+  EOF
+    chmod +x /etc/init.d/resize2fs_once &&         # 给出下次运行的权限
+    update-rc.d resize2fs_once defaults &&         # 默认运行
+    if [ "$INTERACTIVE" = True ]; then
+      whiptail --msgbox "Root partition has been resized.\nThe filesystem will be enlarged upon the next reboot" 20 60 2
+    fi
+  }
+  ```