What are all the illegal characters in the XFS filesystem?

Question

Could someone provide (or point me to a list) of all the illegal characters in the XFS filesystem? I'm writing an app that needs to sanitize filenames.

EDIT:

Okay, so POSIX filesystems should allow all characters except the NUL character, forward slash, and the '.' and '..' filenames are reserved. All other exceptions are application-level. Thanks!

Answer 1

According to Wikipedia, any character except NUL is legal in an XFS filesystem file name. Of course, POSIX typically doesn't allow the forward slash '/' in a filename. Other than this, anything should be good, including international characters.

Answer 2

POSIX filesystems (including XFS) allow every character in file names, with the exception of NUL (0x00) and forward-slash (/; 0x2f).

• NUL marks the end of a C-string; so it is not allowed in file names.
• / is the directory separator, so it is not allowed.
• File names starting with a dot (.; 0x2e) are considered hidden files. This is a userland, not kernel or filesystem convention.
• There may be conventions you're following — for example, UTF-8 file names — in which case, there are many, many more restrictions including which normalization form to use.

Now, you probably want to disallow other things too; file name with all kinds of weird characters are no fun to deal with. I strongly suggest the whitelist approach.

Also, when handling file names, beware of the .. entry in every directory. You don't want to traverse it and allow an arbitrary path.

Source: Single Unix Spec v. 3, §3.169, "the characters composing the name may be selected from the set of all character values excluding the slash character and the null byte."