是否可以使用“/"?在文件名中? [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，但是有没有办法在 Linux 中使用通常在文件名中分隔目录的斜杠字符?

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?

推荐答案

答案是你不能，除非你的文件系统有错误.原因如下:

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

有一个用于重命名在 fs/namei.c 中定义的文件的系统调用，称为 renameat:

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)

当系统调用被调用时，它会在名称上进行路径查找 (do_path_lookup).继续跟踪这个，我们得到 link_path_walk 有这个:

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;
...

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传递带有实际 '/' 字符的参数作为文件名，它将无法执行您想要的操作.没有办法逃避这个角色.如果文件系统支持"这一点，那是因为它们要么:

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:

• 使用 unicode 字符或看起来像斜杠但不是斜杠的东西.
• 他们有一个错误.

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

此外，如果您确实进入并编辑字节以在文件名中添加斜杠字符，则会发生不好的事情.那是因为您永远无法按名称引用此文件 :( 因为无论何时您这样做，Linux 都会假定您引用的是一个不存在的目录.使用 'rm *' 技术也不起作用，因为 bash 只是将其扩展为文件名.甚至 rm -rf 也行不通，因为一个简单的 strace 揭示了引擎盖下的事情(缩短):

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
...

请注意，这些对 unlinkat 的调用将失败，因为它们需要按名称引用文件.

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

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