linux-kernel - Re: commit d7afaec0b564f0609e116f5: fuse: add FUSE_NO_OPEN

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Date:   Tue, 15 Nov 2016 07:50:11 -0800
From:   Nikolaus Rath <Nikolaus@...h.org>
To:     Mike Marshall <hubcap@...ibond.com>
Cc:     Miklos Szeredi <mszeredi@...hat.com>,
        Andrew Gallagher <andrewjcg@...com>,
        lkml <linux-kernel@...r.kernel.org>,
        linux-fsdevel <linux-fsdevel@...r.kernel.org>
Subject: Re: commit d7afaec0b564f0609e116f5: fuse: add FUSE_NO_OPEN_SUPPORT flag to INIT

On Nov 11 2016, Mike Marshall <hubcap@...ibond.com> wrote:
> There was a memorable place in the Orangefs code where
> the original programmer did that (pick something appropriate
> from errno.h) and put in a comment about how it was a more
> reasonable return code...
>
> When Al Viro saw it, he said it was:
>
> ... stupid.  Expected error value is not EOPNOTSUPP; pardon the bluntness,
> but your idea of what would be less misleading doesn't matter - what matters
> is what the _callers_ of link(2), mknod(2), etc. are expecting.  Which is to
> say, what does the userland code expect to get.  It's outright promised in
> POSIX, actually.


I still have to see an application that, upon receiving an error from
e.g. link(2), has special handlers for each of the 24 possible 24 error
codes. All code that I have seen (and written) check for a few specific
errors, and punts everything else to the user via strerror(). In this
case, returning more specific error codes gives the user better
information and doesn't violate any expectations of the application.

Best,
-Nikolaus
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