10.1, Android Input System _ Linux programming Knowledge _inotify and Epoll

<span id="Label3"></p><p><p>1. INotify and Epoll</p></p><p><p>How to monitor keyboard access and unplug?</p></p><p><p>(1) hotplug mechanism: Kernel discovery keyboard Access/unplug ==> start hotplug process ==> Send message to input system</p></p><p><p>(2) inotify mechanism: The input system uses inotify to monitor the Directory/dev/input</p></p><p><p>Android using inofity mechanism</p></p><p><p></p></p><p><p>When inserting multiple keyboards, How does the system know which keyboard is being pressed?</p></p><p><p>Using Epoll under android, You can monitor multiple files at the same time, and when a file changes, it will know who changed</p></p><p><p></p></p><p><p>Reference code:<br>Frameworks\native\services\inputflinger\eventhub.cpp</p></p><p><p>Reference article:<br>Deep understanding of Android Volume III fifth in-depth understanding of the Android input system<br>http://blog.csdn.net/innost/article/details/47660387</p></p><p><p></p></p><p><p>Use of inotify (monitoring of changes in directories or files)</p></p><p><p>(1) FD = Inotify_init ()</p></p><p><p>(2) inotify_add_watch (directory name/file name, Create/delete)</p></p><p><p>(3) read (fd), usually the directory and files are not created or deleted, will hibernate, changed after read return multiple inotify_event structure</p></p><p><p>Inotify_event.name Saves the name, Inotify_event.len indicates the length of the name, inotify_event.mask indicates that a change in the description has occurred (create or Delete)</p></p><p><p></p></p><p><p>INOTIFY.C writing (usage:inotify <dir> changes in this Directory)</p></p><p><p>#include <unistd.h></p></p><p><p>#include <stdio.h></p></p><p><p>#include <sys/inotify.h></p></p><p><p>#include <string.h></p></p><p><p>#include <errno.h></p></p><p><p>int read_process_inotify_fd (int Fd) {</p></p><p><p>int res;</p></p><p><p>Char event_buf[512];</p></p><p><p>int event_size;</p></p><p><p>int event_pos = 0;</p></p><p><p>struct Inotify_event *event;</p></p><p><p>res = Read (fd,event_buf,sizeof (event_buf));</p></p><p><p>If (res < (int) sizeof (*event)) {</p></p><p><p>if (errno = = Eintr)</p></p><p><p>Return 0;</p></p><p><p>printf ("could not get event,%s\n", strerror (errno));</p></p><p><p>return-1;</p></p><p><p>}</p></p><p><p>Process the data, read the data is one or more inotify_event, they len different, processing individually</p></p><p><p>While (res >= (int) sizeof (*event)) {</p></p><p><p>event = (struct inotify_event *) (event_buf+event_pos);</p></p><p><p>If (event->len) {</p></p><p><p>If (event->mask & In_create) {</p></p><p><p>printf ("create file:%s\n", event->name);</p></p><p><p>}else{</p></p><p><p>printf ("delete file:%s\n", event->name);</p></p><p><p>}</p></p><p><p>}</p></p><p><p>event_size = sizeof (*event) +event->len;</p></p><p><p>res-= event_size;</p></p><p><p>Event_pos + = event_size;</p></p><p><p>}</p></p><p><p>Return 0;</p></p><p><p>}</p></p><p><p></p></p><p><p>int main (int Argc,char **argv)</p></p><p><p>{</p></p><p><p>int minotifyfd;</p></p><p><p>int result;</p></p><p><p>If (argc! = 2)</p></p><p><p>{</p></p><p><p>printf ("usage:%s <dir>\n", argv[0]);</p></p><p><p>return-1;</p></p><p><p>}</p></p><p><p>MINOTIFYFD = Inotify_init ();</p></p><p><p>result = Inotify_add_watch (minotifyfd,argv[1],in_delete | in_create);</p></p><p><p>While (1)</p></p><p><p>{</p></p><p><p>READ_PROCESS_INOTIFY_FD (minotifyfd);</p></p><p><p>}</p></p><p><p>Return 0;</p></p><p><p></p></p><p><p>}<br>Gcc-o inotify inotify.c<br>mkdir tmp<br>./inotify TMP &</p></p><p><p>echo > TMP/1<br>echo > TMP/2<br>RM TMP/1 TMP/2</p></p><p><p></p></p><p><p>Epoll is used to detect multiple files with or without data for reading, there is no space for writing</p></p><p><p>(1) epoll_create//create FD</p></p><p><p>(2) for each file execution Epoll_ctl (..., epoll_ctl_add,) means to monitor it</p></p><p><p>(3) epoll_wait//wait for a file to be available</p></p><p><p>(4) do not want to monitor a file available execution Epoll_ctl (..., epoll_ctl_del,)</p></p><p><p><br>epoll, fifo:<br>Http://stackoverflow.com/questions/15055065/o-rdwr-on-named-pipes-with-poll</p></p><p><p>Using FIFO yes, our Epoll program is reader<br>echo AA > TMP/1 is writer<br>A.<br>If reader takes o_rdonly| O_nonblock Open a FIFO file,<br>When writer writes data, Epoll_wait will return immediately;<br>When writer closes the fifo, reader calls epoll_wait again and it returns immediately (reason is eppllhup, the descriptor is hung Up)<br>B.<br>If reader opens a FIFO file with O_rdwr<br>When writer writes data, Epoll_wait will return immediately;<br>When writer closes the fifo, reader calls epoll_wait again, it does not return immediately, but continues to wait for the data</p></p><p><p>Epoll.c</p></p><p><p>/*usage:epoll <file1> [file2] [file3]*/</p></p><p><p>#include <sys/epoll.h></p></p><p><p>#include <unistd.h></p></p><p><p>#include <stdio.h></p></p><p><p>#include <sys/types.h></p></p><p><p>#include <sys/stat.h></p></p><p><p>#include <fcntl.h></p></p><p><p>#include <string.h></p></p><p><p>#define Data_max_len 500</p></p><p><p>int Add_to_epoll (int Fd,int epollfd)</p></p><p><p>{</p></p><p><p>int result;</p></p><p><p>struct Epoll_event eventitem;</p></p><p><p>Memset (&eventitem,0,sizeof (eventitem));</p></p><p><p>Eventitem.events = Epollin;//means monitoring its data</p></p><p><p>eventitem.data.fd=fd;</p></p><p><p>result = Epoll_ctl (epollfd,epoll_ctl_add,fd,&eventitem);</p></p><p><p>Return result;</p></p><p><p>}</p></p><p><p>void Rm_from_epoll (int Fd,int epollfd)</p></p><p><p>{</p></p><p><p>result = Epoll_ctl (epollfd,epoll_ctl_del,fd,null);</p></p><p><p>}</p></p><p><p>int main (int Argc,char **argv)</p></p><p><p>{</p></p><p><p>int mepollfd;</p></p><p><p>int i;</p></p><p><p>Char buf[data_max_len];</p></p><p><p>static const int epoll_max_events = 16;//epoll_wait maximum number of monitored events</p></p><p><p>struct Epoll_event mpendingeventitems[epoll_max_events];</p></p><p><p>If (ARGC < 2)</p></p><p><p>{</p></p><p><p>printf ("usage:%s<file1> [file2] [file3] \ n", argv[0]);</p></p><p><p>return-1;</p></p><p><p>}</p></p><p><p>MEPOLLFD = Epoll_create (8);</p></p><p><p>/*for each file:open it/add it to epoll*/</p></p><p><p>For (i = 1;i < Argc;i++)</p></p><p><p>{</p></p><p><p>int TMPFD = Open (argv[i],o_rdwr);</p></p><p><p>Add_to_epoll (tmpfd,mepollfd);</p></p><p><p>}</p></p><p><p>/*epoll_wait*/</p></p><p><p>While (1) {</p></p><p><p>int pollresult = epoll_wait (mepollfd, mpendingeventitems,epoll_max_events,-1);//-1 means forever monitoring does not exit</p></p><p><p>For (i=0;i<pollresult;i++)</p></p><p><p>{</p></p><p><p>int Len =read (mpendingeventitems[i].data.fd,buf,data_max_len);</p></p><p><p>buf[len] = ' + ';</p></p><p><p>printf ("get data:%s\n", buf);</p></p><p><p>}</p></p><p><p>}</p></p><p><p>Return 0;</p></p><p><p>}</p></p><p><p><br>Gcc-o Epoll EPOLL.C<br>mkdir tmp<br>Mkfifo TMP/1 TMP/2 TMP/3<br>./epoll tmp/1 TMP/2 TMP/3 &<br>echo AAA > TMP/1<br>echo BBB > TMP/2</p></p><p><p></p></p><p><p>After-school assignments:<br>Write inotify_epoll.c, use it to monitor the tmp/directory: there are files created/deleted, there are files to read the data<br>A. When a file is created under tmp/, it is immediately monitored and used epoll to monitor the file<br>B. When the file has data, read the data<br>C. When the tmp/file is deleted, it is immediately monitored and removed from the epoll no longer monitored</p></p><p><p>Inotify_epoll.c<br>Gcc-o Inotify_epoll INOTIFY_EPOLL.C<br>mkdir tmp<br>./inotify_epoll tmp/&<br>Mkfifo TMP/1 TMP/2 TMP/3<br>echo AAA > TMP/1<br>echo BBB > TMP/2<br>RM TMP/3</p></p><p><p>10.1, Android Input System _ Linux programming Knowledge _inotify and Epoll</p></p></span>