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From: Al Viro <viro@zeniv.linux.org.uk>
To: Matthew Wilcox <willy@infradead.org>
Cc: Dave Chinner <david@fromorbit.com>,
	Christian Schoenebeck <qemu_oss@crudebyte.com>,
	"Dr. David Alan Gilbert" <dgilbert@redhat.com>,
	Greg Kurz <groug@kaod.org>,
	linux-fsdevel@vger.kernel.org, stefanha@redhat.com,
	mszeredi@redhat.com, vgoyal@redhat.com, gscrivan@redhat.com,
	dwalsh@redhat.com, chirantan@chromium.org
Subject: Re: xattr names for unprivileged stacking?
Date: Sat, 29 Aug 2020 20:40:42 +0100	[thread overview]
Message-ID: <20200829194042.GT1236603@ZenIV.linux.org.uk> (raw)
In-Reply-To: <20200829191751.GT14765@casper.infradead.org>

On Sat, Aug 29, 2020 at 08:17:51PM +0100, Matthew Wilcox wrote:

> I probably have the wrong nomenclature for what I'm proposing.
> 
> So here's a concrete API.  What questions need to be answered?
> 
> fd = open("real", O_RDWR);
> 
> // fetch stream names
> sfd = open_stream(fd, NULL);
> read(sfd, names, length);

	1) what does fstat() on sfd return?
	2) what does keeping it open do to underlying file?
	3) what happens to it if that underlying file is unlinked?
	4) what does it do to underlying filesystem?  Can it be unmounted?

> close(sfd);

> 
> // open the first one
> sfd = open_stream(fd, names);
> read(sfd, buffer, buflen);
> close(sfd);
> 
> // create a new anonymous stream
> sfd = open_stream(fd, "");
> write(sfd, buffer, buflen);
> // name it
> linkat(sfd, NULL, fd, "newstream", AT_EMPTY_PATH);

Oh, lovely - so linkat() *CAN* get that for dirfd and must somehow tell
it from the normal case.  With the semantics entirely unrelated to the normal
one.  And on top of everything else, we have
	5) what are the permissions involved?  When are they determined, BTW?

> close(sfd);
> 
>  - Stream names are NUL terminated and may contain any other character.
>    If you want to put a '/' in a stream name, that's fine, but there's
>    no hierarchy.  Ditto "//../././../../..//./."  It's just a really
>    oddly named stream.

Er...  Whatever for?

>  - linkat() will fail if 'fd' does not match where 'sfd' was created.

	6) "match" in the above being what, exactly?

Incidentally, how do you remove those?

  reply	other threads:[~2020-08-29 19:40 UTC|newest]

Thread overview: 62+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-07-28 10:55 Dr. David Alan Gilbert
2020-07-28 13:08 ` Greg Kurz
2020-07-28 13:55   ` Christian Schoenebeck
2020-08-04 11:28     ` Dr. David Alan Gilbert
2020-08-04 13:51       ` Christian Schoenebeck
2020-08-12 11:18         ` Dr. David Alan Gilbert
2020-08-12 13:34           ` Christian Schoenebeck
2020-08-12 14:33             ` Dr. David Alan Gilbert
2020-08-13  9:01               ` Christian Schoenebeck
2020-08-16 22:56                 ` Dave Chinner
2020-08-16 23:09                   ` Matthew Wilcox
2020-08-17  0:29                     ` Dave Chinner
2020-08-17 10:37                       ` file forks vs. xattr (was: xattr names for unprivileged stacking?) Christian Schoenebeck
2020-08-23 23:40                         ` Dave Chinner
2020-08-24 15:30                           ` Christian Schoenebeck
2020-08-24 20:01                             ` Miklos Szeredi
2020-08-24 21:26                             ` Frank van der Linden
2020-08-24 22:29                             ` Theodore Y. Ts'o
2020-08-25 15:12                               ` Christian Schoenebeck
2020-08-25 15:32                                 ` Miklos Szeredi
2020-08-27 12:02                                   ` Christian Schoenebeck
2020-08-27 12:25                                     ` Matthew Wilcox
2020-08-27 13:48                                       ` Christian Schoenebeck
2020-08-27 14:01                                         ` Matthew Wilcox
2020-08-27 14:23                                           ` Christian Schoenebeck
2020-08-27 14:25                                             ` Matthew Wilcox
2020-08-27 14:44                                             ` Al Viro
2020-08-27 16:29                                               ` Dr. David Alan Gilbert
2020-08-27 16:35                                                 ` Matthew Wilcox
2020-08-28  9:11                                                 ` Christian Schoenebeck
2020-08-28 14:46                                                   ` Theodore Y. Ts'o
2020-08-27 15:22                       ` xattr names for unprivileged stacking? Matthew Wilcox
2020-08-27 22:24                         ` Dave Chinner
2020-08-29 16:07                           ` Matthew Wilcox
2020-08-29 16:13                             ` Al Viro
2020-08-29 17:51                               ` Miklos Szeredi
2020-08-29 18:04                                 ` Al Viro
2020-08-29 18:22                                   ` Christian Schoenebeck
2020-08-29 19:13                                   ` Miklos Szeredi
2020-08-29 19:25                                     ` Al Viro
2020-08-30 19:05                                       ` Miklos Szeredi
2020-08-30 19:10                                         ` Matthew Wilcox
2020-08-31  7:34                                           ` Miklos Szeredi
2020-08-31 11:37                                             ` Matthew Wilcox
2020-08-31 11:51                                               ` Miklos Szeredi
2020-08-31 13:23                                                 ` Matthew Wilcox
2020-08-31 14:21                                                   ` Miklos Szeredi
2020-08-31 14:25                                                   ` Theodore Y. Ts'o
2020-08-31 14:45                                                     ` Matthew Wilcox
2020-08-31 14:49                                                       ` Miklos Szeredi
2020-09-01  3:34                                                     ` Dave Chinner
2020-09-01 14:52                                                       ` Theodore Y. Ts'o
2020-09-01 15:14                                                         ` Theodore Y. Ts'o
2020-09-02  5:19                                                           ` Dave Chinner
2020-08-31 18:02                                                   ` Andreas Dilger
2020-09-01  3:48                                                     ` Dave Chinner
2020-08-29 19:17                               ` Matthew Wilcox
2020-08-29 19:40                                 ` Al Viro [this message]
2020-08-29 20:12                                   ` Matthew Wilcox
2020-08-31 14:23                                     ` Theodore Y. Ts'o
2020-08-31 14:40                                       ` Matthew Wilcox
2020-08-31 16:11                                       ` Christian Schoenebeck

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