linux-kernel - Re: file metadata via fs API (was: [GIT PULL] Filesystem Information)

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Date:   Tue, 11 Aug 2020 15:42:47 +0100
From:   Al Viro <viro@...iv.linux.org.uk>
To:     Miklos Szeredi <miklos@...redi.hu>
Cc:     linux-fsdevel@...r.kernel.org, David Howells <dhowells@...hat.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Karel Zak <kzak@...hat.com>, Jeff Layton <jlayton@...hat.com>,
        Miklos Szeredi <mszeredi@...hat.com>,
        Nicolas Dichtel <nicolas.dichtel@...nd.com>,
        Christian Brauner <christian@...uner.io>,
        Lennart Poettering <lennart@...ttering.net>,
        Linux API <linux-api@...r.kernel.org>,
        Ian Kent <raven@...maw.net>,
        LSM <linux-security-module@...r.kernel.org>,
        linux-kernel@...r.kernel.org
Subject: Re: file metadata via fs API (was: [GIT PULL] Filesystem Information)

On Tue, Aug 11, 2020 at 04:36:32PM +0200, Miklos Szeredi wrote:

> > >  - strip off trailing part after first instance of ///
> > >  - perform path lookup as normal
> > >  - resolve meta path after /// on result of normal lookup
> >
> > ... and interpolation of relative symlink body into the pathname does change
> > behaviour now, *including* the cases when said symlink body does not contain
> > that triple-X^Hslash garbage.  Wonderful...
> 
> Can you please explain?

Currently substituting the body of a relative symlink in place of its name
results in equivalent pathname.  With your patch that is not just no longer
true, it's no longer true even when the symlink body does not contain that
/// kludge - it can come in part from the symlink body and in part from the
rest of pathname.  I.e. you can't even tell if substitution is an equivalent
replacement by looking at the symlink body alone.