Mini2440 root_qtopia File System Startup Process Analysis

Http://hi.baidu.com/396954504/blog/item/8c391513eb8d202fdc54010a.html

For the Startup Process of the latest root_qtopia File System of mini2440, I have made some simple analysis here and shared some experiences with you. Please also point out the shortcomings in time.
In fact, although the root _ qtopia File System GUI is based on qtopia, the initialization and startup process is mostly completed by busybox, and qtopia (qpe) is only enabled at the final stage of startup.
The default kernel command line contains init =/linuxrc. Therefore, after the file system is mountedProgramIs the linuxrc in the root directory. This is a link to/bin/busybox. That is to say, the first program running after the system is started is busybox itself.
In this case, busybox first tries to parse/etc/inittab to obtain further Initialization Configuration Information (refer to busyboxSource codeThe parse_inittab () function in init/init. C ). In fact, root_qtopia does not have the/etc/inittab configuration file. According to the busybox logic, it will generate the default configuration.

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2. Static void parse_inittab (void)
4. {
6. # If enable_feature_use_inittab
8. Char * token [4];
10. Parser_t * parser = config_open2 ("/etc/inittab", fopen_for_read );
14. If (parser = NULL)
16. # Endif
18. {
20. /* No inittab file -- set up some default behavior */
22. /* Reboot on CTRL-alt-del */
24. New_init_action (ctrlaltdel, "reboot ","");
26. /* Umount all filesystems on halt/reboot */
28. New_init_action (shutdown, "umount-a-r ","");
30. /* Swapoff on halt/reboot */
32. If (enable_swaponoff)
34. New_init_action (shutdown, "swapoff-","");
36. /* Prepare to restart init when a quit is already ed */
38. New_init_action (restart, "init ","");
40. /* Askfirst shell on tty1-4 */
42. New_init_action (askfirst, bb_default_login_shell ,"");
44. // Todo: vc_1 instead ""? "" Is console-> ctty problems-> angry users
46. New_init_action (askfirst, bb_default_login_shell, vc_2 );
48. New_init_action (askfirst, bb_default_login_shell, vc_3 );
50. New_init_action (askfirst, bb_default_login_shell, vc_4 );
52. /* Sysinit */
54. New_init_action (sysinit, init_script ,"");
56. Return;
58. }

Among them, the most important one is new_init_action (sysinit, init_script, ""), which determines that the subsequent initialization script is the value defined by init_script. The default value of this macro is "/etc/init. d/RCS ".
The following is the content of/etc/init. d/RCS in the file system, which is also the focus of our analysis.

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2. #! /Bin/sh
6. Path =/sbin:/bin:/usr/sbin:/usr/bin:/usr/local/bin:
8. Runlevel = s
10. Prevlevel = N
12. Umask 022
14. Export path runlevel prevlevel
18. #
20. # Trap CTRL-C & C only in this shell so we can interrupt subprocesses.
22. #
24. Trap ":" int quit tstp
26. /Bin/hostname friendlyarm
30. /Bin/Mount-n-t proc NONE/proc
32. /Bin/Mount-n-t sysfs NONE/sys
34. /Bin/Mount-n-t usbfs NONE/proc/bus/USB
36. /Bin/Mount-T ramfs NONE/dev
40. Echo/sbin/mdev>/proc/sys/kernel/hotplug
42. /Sbin/mdev-S
44. /Bin/hotplug
46. # Mounting file system specified in/etc/fstab
48. Mkdir-P/dev/PTS
50. Mkdir-P/dev/SHM
52. /Bin/Mount-n-t devpts NONE/dev/PTS-o mode = 0622
54. /Bin/Mount-n-t tmpfs/dev/SHM
56. /Bin/Mount-n-t ramfs NONE/tmp
58. /Bin/Mount-n-t ramfs NONE/var
60. Mkdir-P/var/empty
62. Mkdir-P/var/log
64. Mkdir-P/var/lock
66. Mkdir-P/var/run
68. Mkdir-P/var/tmp
72. /Sbin/hwclock-S
76. Syslogd
78. /Etc/rc. d/init. d/netd start
80. Echo "">/dev/tty1
82. Echo "Starting networking...">/dev/tty1
84. Sleep 1
86. /Etc/rc. d/init. d/httpd start
88. Echo "">/dev/tty1
90. Echo "Starting web server...">/dev/tty1
92. Sleep 1
94. /Etc/rc. d/init. d/LEDs start
96. Echo "">/dev/tty1
98. Echo "Starting LEDs service...">/dev/tty1
100. Echo ""
102. Sleep 1
106. /Sbin/ifconfig lo 127.0.0.1
108. /Etc/init. d/ifconfig-eth0
112. /Bin/qtopia &
114. Echo "">/dev/tty1
116. Echo "Starting qtopia, please waiting...">/dev/tty1

Next we will analyze them one by one:

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1. Path =/sbin:/bin:/usr/sbin:/usr/bin:/usr/local/bin:
2. Runlevel = s
3. Prevlevel = N
4. Umask 022
5. Export path runlevel prevlevel

Set necessary environment variables for the startup environment;

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1. /Bin/hostname friendlyarm

Set the machine name;

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1. /Bin/Mount-n-t proc NONE/proc
2. /Bin/Mount-n-t sysfs NONE/sys
3. /Bin/Mount-n-t usbfs NONE/proc/bus/USB
4. /Bin/Mount-T ramfs NONE/dev

Mount the "virtual" file system,/proc,/sys, and mount a ramfs in the/dev directory, it is equivalent to overwrite the read-only/dev directory on the original NAND Flash with a writable blank SDRAM.
Note that/sys and/dev with ramfs mounted are the key to creating a device node correctly. For kernel 2.6.29, devfs is no longer supported. To create a device node, there are only two ways to complete it by the file system:
1) SystemCompositionBefore creating a system image, use mknod to manually create all (including possible) device nodes in the system and add these node files to the file system image together;
2) during file system initialization, the actual device nodes in the system are dynamically created under the/dev directory based on the information output in the/sys directory.
Obviously, method 1) has great limitations. It is limited to scenarios where no devices are dynamically increased or decreased. It is not applicable to hot swapping of many devices, such as USB flash drives and SD cards. Method 2) is the current practice of Linux on most PCs (based on udev ). This method has two prerequisites: mounting the/sys directory and a writable/dev directory. This is why we need to mount/sys and ramfs in the/dev directory. In fact, this method was first designed for hot swapping. You can understand that when the system is started, all devices are "inserted" at once.
One thing to note here is that before the file system initialization runs here, the original/dev directory must have a device node:/dev/console.
Okay. Write it here today and continue tomorrow :)

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1. Echo/sbin/mdev>/proc/sys/kernel/hotplug
2. /Sbin/mdev-S
3. /Bin/hotplug

These are two things I mentioned above: 1) create necessary device nodes in the/dev directory through mdev-S; 2) Set hotplug handler of the kernel to mdev, that is, when the device is hot-swappable, mdev receives messages from the kernel and responds accordingly, such as mounting a USB flash drive.
For mdev, note that the file system contains the/etc/mdev. conf file, which contains the mdev configuration information. Through this file, we can customize the names or links of some device nodes to meet specific needs. This is the content of mdev. conf in root qtopia:

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2. # System all-writable Devices
4. Full 0: 0 0666
6. Null 0: 0 0666
8. Ptmx 0: 0 0666
10. Random 0: 0 0666
12. Tty 0666
14. Zero 0: 0 0666
18. # Console Devices
20. Tty [0-9] * 0: 5 0660
22. VC/[0-9] * 0: 5 0660
26. # Serial Port Devices
28. S3c2410_serial0 0: 5 0666 = ttysac0
30. S3c2410_serial1 0: 5 0666 = ttysac1
32. Maid = ttysac2
34. S3c2410_seri_3 0666 = ttysac3
38. # Loop Devices
40. Loop [0-9] * 0: 0 0660 = loop/
44. # I2C Devices
46. I2c-0 0: 0 0666 = I2C/0
48. I2c-1 0: 0 0666 = I2C/1
52. # Frame buffer devices
54. FB [0-9]: 0 0666
58. # Input devices
60. Mice 0: 0 0660 = input/
62. Mouse. * 0: 0 0660 = input/
64. Event. * 0: 0 0660 = input/
66. TS. * 0-0 0660 = input/
70. # RTC Devices
72. Rtc0 0: 0 0644> rtc
74. RTC [1-9]: 0 0644
78. # MISC Devices
80. Mmcblk0p1 0: 0 0600 = sdcard */bin/hotplug
82. Sda1 0-0 0600 = udisk */bin/hotplug

We can see that the device names originally registered with the serial port driver are s3c2410_serial0, s3c2410_serial1 and s3c2410_serial, while mdev generates ttysac0 in the/dev directory, ttysac1 and ttysac2 conform to the application's preference for serial device names. Similarly,/dev/sdcard and/dev/udisk always point to the first partition of the SD card and USB disk respectively. (So, if you use an SD card or USB flash disk that does not have a partition table, you can find out why ...)

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1. # Mounting file system specified in/etc/fstab
2. Mkdir-P/dev/PTS
3. Mkdir-P/dev/SHM
4. /Bin/Mount-n-t devpts NONE/dev/PTS-o mode = 0622
5. /Bin/Mount-n-t tmpfs/dev/SHM
6. /Bin/Mount-n-t ramfs NONE/tmp
7. /Bin/Mount-n-t ramfs NONE/var
8. Mkdir-P/var/empty
9. Mkdir-P/var/log
10. Mkdir-P/var/lock
11. Mkdir-P/var/run
12. Mkdir-P/var/tmp

As mentioned in the comments, this is used to mount other common file systems and create necessary directories under the/var directory (also ramfs, writable.

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1. /Sbin/hwclock-S

Used to set the system time, obtained from the hardware RTC, but it seems that there is a problem
The next step is to start the system service, including log record, network, HTTP server, and custom "marquee service "...
Continue Tomorrow :)

In mdev. conf

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1. # MISC Devices
2. Mmcblk0p1 0: 0 0600 = sdcard */bin/hotplug
3. Sda1 0-0 0600 = udisk */bin/hotplug

Some additional instructions:
When the SD card or USB flash drive is inserted/unplugged, the message is sent to the custom hot swappable handler,/bin/hotplug. this program is developed in a friendly way to automatically mount removable devices. Currently, it is an SD card and a USB flash drive. The logic is very simple. Mount the first partition of the SD card or USB flash drive as fat/FAT32 to/sdcard or/udisk.
But this also brings about a problem. When there is no partition table on the SD card or USB flash disk or the first partition is not in the fat/FAT32 format, it won't work anymore. You should be careful :)
This is the binary data segment in/bin/hotplug. You can see the logic I mentioned above:
201710d0h: 52 00 00 00 00 4D 00 00 00 00 00 41 00 00 00; r... m...
201710e0h: 43 00 00 00 54 00 00 49 00 00 00 4f 00 00 00; c... t... I... o...
201710f0h: 4E 00 00 00 00 00 00 00 00 00 45 00 00 00 00; n ...... D ...... E...
00001100 H: 56 00 00 00 4E 00 00 00 41 00 00 00 4D 00 00; V... n... a... m...
00001110 H: 45 00 00 00 00 00 00 61 00 00 00 64 00 00 00; e ...... a ...... d...
00001120 H: 64 00 00 00 00 00 00 72 00 00 00 65 00 00 00; d... r... e...
00001130 H: 6d 00 00 00 6f 00 00 00 00 00 00 65 00 00 00; m... o... V... e...
00001140 H: 00 00 00 00 2f 00 00 00 64 00 00 00 65 00 00;.../... d...
00001150 H: 76 00 00 00 2f 00 00 00 00 00 00 64 00 00 00; V.../... u... d...
00001160 H: 69 00 00 00 73 00 00 00 6B 00 00 00 00 00; I... s... k .......
00001170 H: 2f 00 00 00 64 00 00 00 65 00 00 00 76 00 00 00;/... d... e... V...
00001180 H: 2f 00 00 00 73 00 00 00 64 00 00 00 00 00;/... s... d... c...
00001190 H: 61 00 00 00 72 00 00 00 64 00 00 00 00 00; A... r... d .......
201711a0h: 4D 00 00 00 44 00 00 00 00 00 00 56 00 00 00; m... d... e... V...
201711b0h: 00 00 00 00 00 6D 00 00 00 00 00 00 00 00 00...
201711c0h: 62 00 00 00 00 6C 00 00 00 6B 00 00 30 00 00 00; B... l... k... 0...
Listen 11d0h: 70 00 00 00 31 00 00 00 00 00 73 00 00 00 00; P... 1 ...... S...
201711e0h: 64 00 00 00 61 00 00 00 00 00 00 00 00 00 00; D ...... a ...... 1 .......
201711f0h: 76 00 00 00 00 66 00 00 61 00 00 00 74 00 00 00; V... F... a... t...
00001200 H: 00 00 00 00 2f 00 00 00 64 00 00 00 65 00 00;.../... d...
00001210 H: 76 00 00 00 2f 00 00 00 00 00 00 61 00 00 00; V.../... w......
00001220 H: 74 00 00 00 63 00 00 00 68 00 00 00 64 00 00; t... c... h... d...
00001230 H: 6f 00 00 00 00 00 00 00 00 9A B2 01 81; o... g .?
00001240 H: B0 ;?

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2. Syslogd
4. /Etc/rc. d/init. d/netd start
6. Echo "">/dev/tty1
8. Echo "Starting networking...">/dev/tty1
10. Sleep 1
12. /Etc/rc. d/init. d/httpd start
14. Echo "">/dev/tty1
16. Echo "Starting web server...">/dev/tty1
18. Sleep 1
20. /Etc/rc. d/init. d/LEDs start
22. Echo "">/dev/tty1
24. Echo "Starting LEDs service...">/dev/tty1
26. Echo ""
28. Sleep 1

Start a series of services:
Syslog-used to record kernel and application debug information
Netd-inetd: A guard process that mounts and starts various network-related services.
Httpd-HTTP server guard Process
LEDs-O & M Process
The configuration file of inetd is/etc/inetd. conf, which is the file content.

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2. #/Etc/inetd. conf: see inetd (8) for further informations.
4. Echo stream tcp Nowait root internal
6. Echo dgram udp wait root internal
8. Daytime stream tcp Nowait root internal
10. Daytime dgram udp wait root internal
12. Time stream tcp Nowait root internal
14. Time dgram udp wait root internal
18. # These are standard services.
20. #
22. Ftp stream tcp Nowait root/usr/sbin/ftpd
24. Telnet stream tcp Nowait root/usr/sbin/telnetd-I

We can see that there are two network services started here: 1) FTP server and 2) Telnet server. For more information about network service ports and protocols, see/etc/services,/etc/protocols.
Next

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1. /Sbin/ifconfig lo 127.0.0.1
2. /Etc/init. d/ifconfig-eth0

Configure the network device (NIC ):
1) set the local loopback address to 127.0.0.1
2) run the NIC setup script/etc/init. d/ifconfig-eth0
This is/etc/init. d/ifconfig-eth0 content, added some of my comments

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2. #! /Bin/sh
6. Echo-N try to bring eth0 interface up...>/dev/ttysac0
10. # Determine whether the/etc/eth0-setting file exists
12. If [-F/etc/eth0-setting]; then
14. # Reading configuration file information
16. Source/etc/eth0-setting
20. # If the root file system is NFS, it indicates that the NIC has been configured with OK. No configuration is required here.
22. If grep-Q "^/dev/root/nfs"/etc/mtab; then
24. Echo-n nfs root...>/dev/ttysac0
26. # Otherwise, configure the NIC according to the Mac, IP, mask, and gateway commands in the configuration file.
28. Else
30. Ifconfig eth0 down
32. Ifconfig eth0 HW ether $ Mac
34. Ifconfig eth0 $ IP netmask $ mask up
36. Route add default GW $ Gateway
38. Fi
42. # Write the DNS settings in the configuration file to/etc/resolv. conf to take effect
44. Echo nameserver $ DNS>/etc/resolv. conf
46. # The configuration file does not exist. Use the default configuration
48. Else
52. # If the root file system is NFS, it indicates that the NIC has been configured with OK. No configuration is required here.
54. If grep-Q "^/dev/root/nfs"/etc/mtab; then
56. Echo-n nfs root...>/dev/ttysac0
58. Else
60. # Set the IP address of the NIC to 192.168.1.230
62. /Sbin/ifconfig eth0 192.168.1.230 netmask 255.255.255.0 up
64. Fi
66. Fi
70. Echo done>/dev/ttysac0

We can see that automatic identification of NFS is implemented by checking whether NFS mounting records exist in/etc/mtab.
This is the/etc/eth0-settings file in the root qtopia File System

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1. IP = 192.168.1.230
2. Mask = 255.255.255.0
3. Gateway = 192.168.1.1
4. DNS = 192.168.1.1
5. MAC = 08: 90: 90: 90: 90: 90

Finally, start the qtopia GUI environment.

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1. /Bin/qtopia &
2. Echo "">/dev/tty1
3. Echo "Starting qtopia, please waiting...">/dev/tty1

We can see that qtopia is started by running/bin/qtopia. In fact,/bin/qtopia is also a script. Its task is to set the necessary environment for qtopia to run, and finally start qtopia by calling the qpe executable file. This is all about it. I added some notes:

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2. #! /Bin/sh
6. # Tslib environment variable settings, including the touchscreen device file, tslib configuration file, tslib plug-in location, and touchscreen calibration data file
8. Export tslib_tsdevice =/dev/input/event0
10. Export tslib_conffile =/usr/local/etc/ts. conf
12. Export tslib_plugindir =/usr/local/lib/TS
14. Export tslib_calibfile =/etc/pointercal
16. # Set the qtopia environment variable and set the qtopia main file location
18. Export qtdir =/opt/qtopia
20. Export qpedir =/opt/qtopia
22. # Set path and LD_LIBRARY_PATH to include the executable files and shared library files of qtopia, so that qtopia can run correctly.
24. Export Path = $ qtdir/bin: $ path
26. Export LD_LIBRARY_PATH = $ qtdir/lib:/usr/local/lib: $ LD_LIBRARY_PATH
30. # Qtopia automatically recognizes touchscreen and USB mouse by checking whether touchscreen information is included in/sys/devices/virtual/input/input0/uevent.
32. Ts_info_file =/sys/devices/virtual/input/input0/uevent
34. If [-e $ ts_info_file-a "/bin/grep-Q touchscreen <$ ts_info_file"]; then
36. Export qws_mouse_proto = "tpanel:/dev/input/event0 USB:/dev/input/mice"
38. If [-E/etc/pointercal-! -S/etc/pointercal]; then
40. Rm/etc/pointercal
42. Fi
44. Else
46. Export qws_mouse_proto = "USB:/dev/input/mice"
48. >/Etc/pointercal
50. Fi
52. Unset ts_info_file
56. Export qws_keyboard = TTY:/dev/tty1
58. Export kdedir =/opt/KDE
62. Export Home =/root
66. # Start qtopia by calling/opt/qtopia/bin/qpe
68. Exec $ qpedir/bin/qpe 1>/dev/null 2>/dev/null

So far, the entire process from the file system initialization to the final launch of the qtopia GUI environment has ended. You can see that the "little secret" of the friendly arm is actually here, it's easy to say: as long as you can calm down and take a closer look at the script and look at the sourceCodeWith some background knowledge, it is easy to understand an embedded system.

Reference

Reference: qiu1123, 23rd floor, published on:
Is the linuxrc file useless? Can you give me a brief introduction?

Normally, the file/linuxrc is only available in
1. Initial ramdisk (initrd) is used)
2. init =/linuxrc is specified on the kernel command line.
This is useful in both cases. root_qtopia of mini2440 belongs to situation 2). In root_qtopia,/linuxrc is a symbolic link pointing to/bin/busybox, that is, the portal of the entire file system becomes the main () function of busybox. busybox supports this method to start the initialization of busybox itself and the entire file system.