Re: RFC: Illegal Characters in File Names

[Jan Hudec <bulb@ucw.cz>]

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On Sun, Jul 18, 2004 at 19:41:32 -0500, Joseph Wagner wrote:
> IMHO, e2fsck is not sufficiently aggressive in examining a file name for 
> illegal characters. While it is possible to place non-printing control 

There are just two illegal characters. '\0' and '/'. All other
characters are *permited*.

> characters in a file name, few (if any) programs support opening a file 
> with control characters in the file name.  In fact, 'rm' doesn't even 
> support control characters.  To remove such a file, one must substitute a
> wildcard character and run rm interactively (i.e. 'rm -i').

rm does perfectly support control characters! As do ALL the standard
utilities. What rm especialy does NOT support is the wildcard! It's the
shell that expands these. It's the shell that has problems with these,
but it's not a show-stopper:

$ touch "$(echo foo\\nbar)"
$ ls
foo?bar
$ ls -Q
"foo\nbar"
$ rm 'foo
quote> bar'
$ ls
$

$ touch foo^Bbar
$ ls
foo?bar
$ ls -Q
"foo\002bar"
$ rm foo^Bbar
$ ls
$

(note, that the ^B was written as Ctrl-V Ctrl-B)

Perfectly legal. Everything is right. You can write each and every
control char this way, just some of them must be in single quotes.

> Some of us in the e2fsprogs project are considering a change which would 
> mark all non-printing control characters (i.e. ASCII <=31 and ASCII == 127) 
> as illegal.

They are not illegal. The shell has problems with them, and the problems
are not absolute. You CAN type them in if you try. The file managers
will operate on them without problems, too.

> I decided not to flag characters > ASCII 127 as illegal in case some day in 
> the future the encoding changes to UTF-8, in which case valid printing 
> non-control characters exist > 127.  On the flip side, ASCII and UTF-8 are 
> 100% compatible when <= 127, so the changes I did make will be fine with 
> both.

The system is 8-bit clean an is relied upon by many users. I have LOTS
of files with iso-8859-2 encoded names on my filesystem.

> Can anyone suggest a good reason not to good forward with this?
> 
> If it is OK to go forward, should the kernel be changed to disallow a file 
> name from having these same non-printing control characters?

No, it's not OK. These characters are perfectly legal. Actualy, more
programs will have problems with filename containing a ':', that with
a filename containing, say, a '\b'. (usualy because they accept URI
arguments and use presence of : to distinguish plain filename and an
URI).

-------------------------------------------------------------------------------
						 Jan 'Bulb' Hudec <bulb@ucw.cz>

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