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From: Amir Goldstein <amir73il@gmail.com>
To: "Darrick J. Wong" <darrick.wong@oracle.com>
Cc: Dave Chinner <david@fromorbit.com>,
	linux-fsdevel <linux-fsdevel@vger.kernel.org>,
	linux-xfs <linux-xfs@vger.kernel.org>,
	Olga Kornievskaia <olga.kornievskaia@gmail.com>,
	Linux NFS Mailing List <linux-nfs@vger.kernel.org>,
	overlayfs <linux-unionfs@vger.kernel.org>,
	ceph-devel@vger.kernel.org, linux-cifs@vger.kernel.org
Subject: Re: [PATCH 08/11] vfs: push EXDEV check down into ->remap_file_range
Date: Tue, 4 Dec 2018 11:17:38 +0200
Message-ID: <CAOQ4uxgRe8yqeRv-UEqCa+YD2buTUq5FdguHtJoQAgtBEpTTVw@mail.gmail.com> (raw)
In-Reply-To: <20181203235837.GF24487@magnolia>

> > > I think this is sort of backwards -- the checks should stay in
> > > do_clone_file_range, and vfs_copy_file_range should be calling that
> > > instead of directly calling ->remap_range():
> > >
> > > vfs_copy_file_range()
> > > {
> > >     file_start_write(...);
> > >     ret = do_clone_file_range(...);
> > >     if (ret > 0)
> > >             return ret;
> > >     ret = do_copy_file_range(...);
> > >     file_end_write(...);
> > >     return ret;
> > > }
> >
> > I'm already confused by the way we weave in and out of "vfs_/do_*"
> > functions, and this just makes it worse.
> >
> > Just what the hell is supposed to be in a "vfs_" prefixed function,
> > and why the hell is it considered a "vfs" level function if we then
> > export it's internal functions for individual filesystems to use?
>
> I /think/ vfs_ functions are file_start_write()/file_end_write()
> wrappers around a similarly named function that lacks the freeze
> protection??

That is definitely not an official definition of vfs_ vs. do_, but I found
this rule to be a common practice, which is why I swapped
{do,vfs}_clone_file_range(). But around vfs you can find many examples
where do_ helpers wrap vfs_ helpers.

>
> (AFAICT Amir made that split so that overlayfs could use these
> functions, though I do not know if everything vfs_ was made that way
> /specifically/ for overlayfs or if that's the way things have been and
> ovlfs simply takes advantage of it...)
>
> Guhhh, none of this is documented......
>

It looks like in git epoc, things were pretty straight forward.
vfs_XXX was the interface called after sys_XXX converted
userspace arguments (e.g. char *name, int fd) to vfs objects
(e.g. struct path,dentry,inode,file). Sometimes vfs_ helpers called
do_ helpers for several reasons. See for example epoc version
of fs/namei.c fs/read_write.c.
Even then there were exception. For example do_sendfile()
doesn't even have a vfs_ interface, although it is clear what
that prospect interface would look like.
To that end, do_splice_direct() acts as the standard do_ helper
to that non-existing vfs_ interface.

From there on, I guess things kinda grew organically.
fs/namei.c syscalls grew do_XXXat() helpers between syscalls
and vfs_XXX interface.

Overlayfs uses vfs_ interface 99% of the time, so from that perspective
it is regarded as an interface with vfs objects as arguments that does
NOT skip security_ checks and does NOT bypass freeze protection.

Overlayfs calling do_clone_file_range() and do_splice_direct() are
the only exception to this rule.
If we would want to replace those calls in ovl_copy_up_data() with
a single call to do_copy_file_range(), than said helper should NOT
be taking freeze protection and should do the fallback between
filesystem copy_file_range and generic_copy_file_range.

Cheers,
Amir.

  reply index

Thread overview: 83+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-12-03  8:34 [PATCH 0/11] fs: fixes for major copy_file_range() issues Dave Chinner
2018-12-03  8:34 ` [PATCH 01/11] vfs: copy_file_range source range over EOF should fail Dave Chinner
2018-12-03 12:46   ` Amir Goldstein
2018-12-04 15:13     ` Christoph Hellwig
2018-12-04 21:29       ` Dave Chinner
2018-12-04 21:47         ` Olga Kornievskaia
2018-12-04 22:31           ` Dave Chinner
2018-12-05 16:51             ` bfields
2019-05-20  9:10             ` Amir Goldstein
2019-05-20 13:12               ` Olga Kornievskaia
2019-05-20 13:36                 ` Amir Goldstein
2019-05-20 13:58                   ` Olga Kornievskaia
2019-05-20 14:02                     ` Amir Goldstein
2018-12-05 14:12         ` Christoph Hellwig
2018-12-05 21:08           ` Dave Chinner
2018-12-05 21:30             ` Christoph Hellwig
2018-12-03  8:34 ` [PATCH 02/11] vfs: introduce generic_copy_file_range() Dave Chinner
2018-12-03 10:03   ` Amir Goldstein
2018-12-03 23:00     ` Dave Chinner
2018-12-04 15:14   ` Christoph Hellwig
2018-12-03  8:34 ` [PATCH 03/11] vfs: no fallback for ->copy_file_range Dave Chinner
2018-12-03 10:22   ` Amir Goldstein
2018-12-03 23:02     ` Dave Chinner
2018-12-06  4:16       ` Amir Goldstein
2018-12-06 21:30         ` Dave Chinner
2018-12-07  5:38           ` Amir Goldstein
2018-12-03 18:23   ` Anna Schumaker
2018-12-04 15:16   ` Christoph Hellwig
2018-12-03  8:34 ` [PATCH 04/11] vfs: add missing checks to copy_file_range Dave Chinner
2018-12-03 12:42   ` Amir Goldstein
2018-12-03 19:04   ` Darrick J. Wong
2018-12-03 21:33   ` Olga Kornievskaia
2018-12-03 23:04     ` Dave Chinner
2018-12-04 15:18   ` Christoph Hellwig
2018-12-12 11:31   ` Luis Henriques
2018-12-12 16:42     ` Darrick J. Wong
2018-12-12 18:55     ` Olga Kornievskaia
2018-12-12 19:42       ` Matthew Wilcox
2018-12-12 20:22         ` Olga Kornievskaia
2018-12-13 10:29           ` Luis Henriques
2018-12-03  8:34 ` [PATCH 05/11] vfs: use inode_permission in copy_file_range() Dave Chinner
2018-12-03 12:47   ` Amir Goldstein
2018-12-03 18:18   ` Darrick J. Wong
2018-12-03 23:55     ` Dave Chinner
2018-12-05 17:28       ` bfields
2018-12-03 18:53   ` Eric Biggers
2018-12-04 15:19   ` Christoph Hellwig
2018-12-03  8:34 ` [PATCH 06/11] vfs: copy_file_range needs to strip setuid bits Dave Chinner
2018-12-03 12:51   ` Amir Goldstein
2018-12-04 15:21   ` Christoph Hellwig
2018-12-03  8:34 ` [PATCH 07/11] vfs: copy_file_range should update file timestamps Dave Chinner
2018-12-03 10:47   ` Amir Goldstein
2018-12-03 17:33     ` Olga Kornievskaia
2018-12-03 18:22       ` Darrick J. Wong
2018-12-03 23:19     ` Dave Chinner
2018-12-04 15:24   ` Christoph Hellwig
2018-12-03  8:34 ` [PATCH 08/11] vfs: push EXDEV check down into ->remap_file_range Dave Chinner
2018-12-03 11:04   ` Amir Goldstein
2018-12-03 19:11     ` Darrick J. Wong
2018-12-03 23:37       ` Dave Chinner
2018-12-03 23:58         ` Darrick J. Wong
2018-12-04  9:17           ` Amir Goldstein [this message]
2018-12-03 23:34     ` Dave Chinner
2018-12-03 18:24   ` Darrick J. Wong
2018-12-04  8:18   ` Olga Kornievskaia
2018-12-03  8:34 ` [PATCH 09/11] vfs: push copy_file_ranges -EXDEV checks down Dave Chinner
2018-12-03 12:36   ` Amir Goldstein
2018-12-03 17:58   ` Olga Kornievskaia
2018-12-03 18:53   ` Anna Schumaker
2018-12-03 19:27     ` Olga Kornievskaia
2018-12-03 23:40     ` Dave Chinner
2018-12-04 15:43   ` Christoph Hellwig
2018-12-04 22:18     ` Dave Chinner
2018-12-04 23:33       ` Olga Kornievskaia
2018-12-05 14:09       ` Christoph Hellwig
2018-12-05 17:01         ` Olga Kornievskaia
2018-12-03  8:34 ` [PATCH 10/11] vfs: allow generic_copy_file_range to copy across devices Dave Chinner
2018-12-03 12:54   ` Amir Goldstein
2018-12-03  8:34 ` [PATCH 11/11] ovl: allow cross-device copy_file_range calls Dave Chinner
2018-12-03 12:55   ` Amir Goldstein
2018-12-03  8:39 ` [PATCH 12/11] man-pages: copy_file_range updates Dave Chinner
2018-12-03 13:05   ` Amir Goldstein
2019-05-21  5:52   ` Amir Goldstein

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