Re: silent semantic changes with reiser4

Linus Torvalds
2004-08-26T00:27:31Z

On Thu, 26 Aug 2004, Mikulas Patocka wrote:
>
> Stupid question: who will use it? And why?
>
> Anyone can write an userspace library, that implements function
> set_attribute(char *file, char *attribute, char *value), that creates
> directory ".attr/file" in file's directory and stores attribute there.
> (and you can get list of attributes from shell too:
> ls `echo "$filename" |sed 's/\/\([^\/]*\)$/\/\.attr\/\1/'`
> ). There's no need to add extra functionality to kernel and filesystem.

..and the above is, roughly, what I understand samba etc falls back on.

The problem ends up being that the above isn't in any way safe from people
moving files around (oops, where did those attributes go?) nor does it
have any consistency guarantees. So it only works well if _one_
application does this, and that application follows all the locking rules.

Is it enough? It may have to be.

> The only way xattrs are useful is that backup/restore software doesn't
> have to know about every filesystem with it's specific attributes and
> every magic ioctl for setting them. Instead it can save/restore
> filesystem-specific attributes without understanding what do they mean.
> However there's no need why application should use them. And no
> application does.

If no application does, then why back them up? Why implement them in the
first place?

In other words - some apps obviously do want to use the. Sadly.

Linus