linux-kernel - Re: [PATCH 01/14] VFS: Add additional RESOLVE

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Date:   Thu, 12 Mar 2020 14:48:54 -0700
From:   Jeremy Allison <jra@...ba.org>
To:     Stefan Metzmacher <metze@...ba.org>
Cc:     Linus Torvalds <torvalds@...ux-foundation.org>,
        David Howells <dhowells@...hat.com>,
        Aleksa Sarai <cyphar@...har.com>,
        Al Viro <viro@...iv.linux.org.uk>, Ian Kent <raven@...maw.net>,
        Miklos Szeredi <mszeredi@...hat.com>,
        Christian Brauner <christian@...uner.io>,
        Jann Horn <jannh@...gle.com>,
        "Darrick J. Wong" <darrick.wong@...cle.com>,
        Karel Zak <kzak@...hat.com>, jlayton@...hat.com,
        Linux API <linux-api@...r.kernel.org>,
        linux-fsdevel <linux-fsdevel@...r.kernel.org>,
        LSM List <linux-security-module@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Ralph Böhme <slow@...ba.org>,
        Volker Lendecke <vl@...net.de>
Subject: Re: [PATCH 01/14] VFS: Add additional RESOLVE_* flags [ver #18]

On Thu, Mar 12, 2020 at 06:11:09PM +0100, Stefan Metzmacher wrote:
> Am 12.03.20 um 17:24 schrieb Linus Torvalds:
> > On Thu, Mar 12, 2020 at 2:08 AM Stefan Metzmacher <metze@...ba.org> wrote:
> >>
> >> The whole discussion was triggered by the introduction of a completely
> >> new fsinfo() call:
> >>
> >> Would you propose to have 'at_flags' and 'resolve_flags' passed in here?
> > 
> > Yes, I think that would be the way to go.
> 
> Ok, that's also fine for me:-)
> 
> >>> If we need linkat2() and friends, so be it. Do we?
> >>
> >> Yes, I'm going to propose something like this, as it would make the life
> >> much easier for Samba to have the new features available on all path
> >> based syscalls.
> > 
> > Will samba actually use them? I think we've had extensions before that
> > weren't worth the non-portability pain?
> 
> Yes, we're currently moving to the portable *at() calls as a start.
> And we already make use of Linux only feature for performance reasons
> in other places. Having the new resolve flags will make it possible to
> move some of the performance intensive work into non-linux specific
> modules as fallback.
> 
> I hope that we'll use most of this through io_uring in the end,
> that's the reason Jens added the IORING_REGISTER_PERSONALITY feature
> used for IORING_OP_OPENAT2.
> 
> > But yes, if we have a major package like samba use it, then by all
> > means let's add linkat2(). How many things are we talking about? We
> > have a number of system calls that do *not* take flags, but do do
> > pathname walking. I'm thinking things like "mkdirat()"?)
> 
> I haven't looked them up in detail yet.
> Jeremy can you provide a list?

Fixing the flags argument on fchmodat() to actually *implement*
AT_SYMLINK_NOFOLLOW would be a good start :-).

As for the syscalls that don't have
flags I'm thinking of the things like:

getxattr/setxattr/removexattr just off the top of my head.

Jeremy.