实现页面卷曲功能(Implementing page curl feature)

 在Linux上，该进程使用内存映射将可执行文件的文本部分和共享库直接映射到正在运行的进程内存。 所以如果你可以覆盖可执行文件，它会影响正在运行的进程。 但是，禁止写入映射为执行的文件 - 您会收到“文本文件忙”错误。 
 
 但是，您仍然可以重新编译该程序。 如果编译器（实际上是链接器）出现此错误，它将删除旧的可执行文件并创建一个新文件。 在Unix上，如果删除正在使用的文件，则文件内容实际上并未从磁盘中删除，只删除目录条目中的引用; 在所有对它的引用（目录项，文件描述符和内存映射）消失之前，该文件并未完全删除。 因此，正在运行的进程将继续映射到旧的无名文件。 您可以通过以下演示来看到这一点： 
 
barmar@dev:~$ ls -li testsleep
229774 -rwxr-xr-x 1 barmar adm 4584 Apr 24 04:30 testsleep
barmar@dev:~$ ./testsleep &
[1] 17538
barmar@dev:~$ touch testsleep.c
barmar@dev:~$ make testsleep
cc     testsleep.c   -o testsleep
barmar@dev:~$ ls -li testsleep
229779 -rwxr-xr-x 1 barmar adm 4584 Apr 24 04:32 testsleep
 
 当我在程序运行时重新编译程序时，inode号从229774改为229779 ，表示创建了一个新文件。 

On Linux, the process uses memory mapping to map the text section of the executable file and shared libraries directly into the running process memory. So if you could overwrite the executable file, it would affect the running process. However, writing into a file that's mapped for execution is prohibited -- you get a "Text file busy" error.
 
However, you can still recompile the program. If the compiler (actually the linker) gets this error, it removes the old executable file and creates a new one. On Unix, if you remove a file that's in use, the file contents are not actually removed from the disk, only the reference from the directory entry is removed; the file isn't fully deleted until all references to it (directory entries, file descriptors and memory mappings) go away. So the running process continues to be mapped to the old, nameless file. You can see this with the following demonstration:
 
barmar@dev:~$ ls -li testsleep
229774 -rwxr-xr-x 1 barmar adm 4584 Apr 24 04:30 testsleep
barmar@dev:~$ ./testsleep &
[1] 17538
barmar@dev:~$ touch testsleep.c
barmar@dev:~$ make testsleep
cc     testsleep.c   -o testsleep
barmar@dev:~$ ls -li testsleep
229779 -rwxr-xr-x 1 barmar adm 4584 Apr 24 04:32 testsleep
 
The inode number changed from 229774 to 229779 when I recompiled the program while it was running, indicating that a new file was created.