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From:   David Howells <dhowells@redhat.com>
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To:     Miklos Szeredi <miklos@szeredi.hu>
Cc:     dhowells@redhat.com, "Eric W. Biederman" <ebiederm@xmission.com>,
        Al Viro <viro@zeniv.linux.org.uk>,
        Linux API <linux-api@vger.kernel.org>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH 28/33] vfs: syscall: Add fsconfig() for configuring and managing a context [ver #11]
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Date:   Thu, 09 Aug 2018 17:33:20 +0100
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Miklos Szeredi <miklos@szeredi.hu> wrote:

> > However, as I have said, I *am* willing to add one of more flags to help
> > with this, but I can't make any "legacy" fs honour them as this requires
> > the fs_context to be passed down to sget_fc() and the filesystem - which
> > is why I was considering leaving it for later.
>
> You can determine at fsopen() time whether the filesystem is able to
> support the O_EXCL behavior?  If so, then it's trivial to enable this
> conditionally.  I think that's what Eric is asking for, it's obviously
> not fair to ask for a change in behavior of the legacy interface.

What do you mean by "enable it conditionally"?  It cannot be enabled for
filesystems that don't pass fs_context down to sget().

mount(2) mustn't enable it lest it break userspace.

fsopen(2) can let userspace set a flag to enable it.

David