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From: Miklos Szeredi <mszeredi@redhat.com>
Date: Tue, 15 Nov 2016 14:33:22 +0100
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Subject: Re: commit d7afaec0b564f0609e116f5: fuse: add FUSE_NO_OPEN_SUPPORT
 flag to INIT
To: Nikolaus Rath <Nikolaus@rath.org>
Cc: Mike Marshall <hubcap@omnibond.com>,
        Andrew Gallagher <andrewjcg@fb.com>,
        lkml <linux-kernel@vger.kernel.org>,
        linux-fsdevel <linux-fsdevel@vger.kernel.org>
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On Fri, Nov 11, 2016 at 6:27 PM, Nikolaus Rath <Nikolaus@rath.org> wrote:

> Yeah, I'd expect most people to do that. But FUSE file systems are often
> a little more exotic and produce error conditions that don't match well
> with any of the codes documented in the manpages. If there is no good
> fit, I'd expect that most people would (as I have done so far) simply
> pick something more appropriate from errno(3). If some of these codes
> are forbidden (or only a subset allowed) I'd really like to document
> this. It's not reasonable to expect every libfuse user to start browsing
> the Linux VFS code to determine if they can use a particular error code.

The library and the kernel checks for -1000 < error <= 0.  There are
no other checks done by fuse.  However returning ENOSYS for open is
simply wrong, it's definitely not something a sane filesystem would
ever do.

Thanks,
Miklos