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Message-ID: <20200811160534.GL1236603@ZenIV.linux.org.uk>
Date: Tue, 11 Aug 2020 17:05:34 +0100
From: Al Viro <viro@...iv.linux.org.uk>
To: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: Miklos Szeredi <miklos@...redi.hu>,
linux-fsdevel <linux-fsdevel@...r.kernel.org>,
David Howells <dhowells@...hat.com>,
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 Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: file metadata via fs API (was: [GIT PULL] Filesystem Information)
On Tue, Aug 11, 2020 at 08:20:24AM -0700, Linus Torvalds wrote:
> I don't think this works for the reasons Al says, but a slight
> modification might.
>
> IOW, if you do something more along the lines of
>
> fd = open(""foo/bar", O_PATH);
> metadatafd = openat(fd, "metadataname", O_ALT);
>
> it might be workable.
>
> So you couldn't do it with _one_ pathname, because that is always
> fundamentally going to hit pathname lookup rules.
>
> But if you start a new path lookup with new rules, that's fine.
Except that you suddenly see non-directory dentries get children.
And a lot of dcache-related logics needs to be changed if that
becomes possible.
I agree that xattrs are garbage, but this approach won't be
a straightforward solution. Can those suckers be passed to
...at() as starting points? Can they be bound in namespace?
Can something be bound *on* them? What do they have for inodes
and what maintains their inumbers (and st_dev, while we are at
it)? Can _they_ have secondaries like that (sensu Swift)?
Is that a flat space, or can they be directories?
Only a part of the problems is implementation-related (and those are
not trivial at all); most the fun comes from semantics of those things.
And answers to the implementation questions are seriously dependent upon
that...
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