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From
SubjectRe: patch for fs/dcache race
Date
Followup to:  <9708122052.AA17214@nyx.net>
By author: colin@nyx.net (Colin Plumb)
In newsgroup: linux.dev.kernel
>
> There are only two characters not legal in a file name in Unix,
> '\0' and '/'. Perhaps some simple scheme like doubling the
> slash before deleted names would be less ambiguous?
>
> E.g.
>
> /foo//bar//baz
>
> Means that "bar" and "baz" are deleted, but not "foo".
> Compare with /foo/bar//baz, where nothing has happened to the
> parent directory.
>
> Or is that overloading too heavily used anyway? Or doesn't anyone care
> if it's ambiguous?
>

It breaks POSIX, and a helluva lot of tools. Unix has the "multiple
slash rule", which says that multiple slashes are treated as one (in
fact, traditional Unices treat // as /./) and a final slash like a
final slash-dot.

POSIX does allow for one exception to the multiple slash rule: exactly
two slashes at the beginning may be used to escape to a higher
namespace. Also /.. is allowed to escape to a higher namespace.
Both, however, are bad ideas, as a lot of traditional Unix tools
assume that /.. == / and // == /.

An undelete utility also needs to take into account multiple
generations of a file, which may all have the same name. The only
commonly used syntax for that is <filename>;version -- presumably if
there is no version you are talking the "current" (i.e. not deleted)
version. This would not be a part of the standard Linux filename
resolution, but could be used by a special set of system calls related
to undeletion of files. They would have to provide for some mechanism
to escape the semicolon (maybe ; -> ;;) if a filename does actually
contain one.

-hpa
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