可以使用“/”在文件名？ [英] Is it possible to use "/" in a filename?

问题描述

我知道这不是应该做的事情，但是有没有办法使用通常在Linux中分隔文件名中的目录的斜杠字符？

解决方案

答案是你不能，除非你的文件系统有一个错误。这就是为什么：

有一个系统调用重命名您在 fs / namei.c 中定义的文件，名为 renameat ：

  SYSCALL_DEFINE4（renameat，int，olddfd，const char __user * oldname，
 int，newdfd，const char __user *，newname）
  

当系统调用被调用，它在名称上执行路径查找（ do_path_lookup ）。继续跟踪这一点，我们得到 link_path_walk ，其中包含：

  static int link_path_walk（const char * name，struct nameidata * nd）
 {
 struct path next; 
 int err; 
 unsigned int lookup_flags = nd-> flags; 
 
 while（* name =='/'）
 name ++; 
 if（！* name）
 return 0; 
 ... 
  

此代码适用于任何文件系统。这是什么意思？这意味着如果您尝试使用传统方式将具有实际'/'字符的参数传递给文件的名称，则不会执行所需操作。没有办法逃脱角色。如果文件系统支持这一点，那是因为它们是：

• 使用unicode字符或看起来的东西


• 他们有一个错误。

此外，如果你进入并编辑字节以将斜杠字符添加到文件名中，则会发生不好的事情。这是因为你永远不可以通过这个名字来引用这个文件:(从任何时候起，Linux会假定你是指不存在的目录，使用'rm *'技术也不会奏效，因为bash只是把它扩展到文件名。即使 rm -rf 将无法正常工作，因为简单的strace显示了引擎盖下的事情（缩短）：

  $ ls testdir 
 myfile2 out 
 $ strace -vf rm -rf testdir 
 ... 
 unlinkat（3，myfile2 ，0）= 0 
 unlinkat（3，out，0）= 0 
 fcntl（3，F_GETFD）= 0x1（标志FD_CLOEXEC）
 close（3）= 0 
 unlinkat（AT_FDCWD，testdir，AT_REMOVEDIR）= 0 
 ... 
  

请注意，这些调用 unlinkat 将失败，因为他们需要按名称引用文件。

I know that this is not something that should ever be done, but is there a way to use the slash character that normally separates directories within a filename in Linux?

解决方案

The answer is that you can't, unless your filesystem has a bug. Here's why:

There is a system call for renaming your file defined in fs/namei.c called renameat:

SYSCALL_DEFINE4(renameat, int, olddfd, const char __user *, oldname,
                int, newdfd, const char __user *, newname)

When the system call gets invoked, it does a path lookup (do_path_lookup) on the name. Keep tracing this, and we get to link_path_walk which has this:

static int link_path_walk(const char *name, struct nameidata *nd)
{
       struct path next;
       int err;
       unsigned int lookup_flags = nd->flags;

       while (*name=='/')
              name++;
       if (!*name)
              return 0;
...

This code applies to any file system. What's this mean? It means that if you try to pass a parameter with an actual '/' character as the name of the file using traditional means, it will not do what you want. There is no way to escape the character. If a filesystem "supports" this, it's because they either:

• Use a unicode character or something that looks like a slash but isn't.
• They have a bug.

Furthermore, if you did go in and edit the bytes to add a slash character into a file name, bad things would happen. That's because you could never refer to this file by name :( since anytime you did, Linux would assume you were referring to a nonexistent directory. Using the 'rm *' technique would not work either, since bash simply expands that to the filename. Even rm -rf wouldn't work, since a simple strace reveals how things go on under the hood (shortened):

$ ls testdir
myfile2 out
$ strace -vf rm -rf testdir
...
unlinkat(3, "myfile2", 0)               = 0
unlinkat(3, "out", 0)                   = 0
fcntl(3, F_GETFD)                       = 0x1 (flags FD_CLOEXEC)
close(3)                                = 0
unlinkat(AT_FDCWD, "testdir", AT_REMOVEDIR) = 0
...

Notice that these calls to unlinkat would fail because they need to refer to the files by name.

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