linux-kernel - Re: [PATCH 1/4] statx: Add a system call to make enhanced file info available

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Message-ID: <9047.1479811169@warthog.procyon.org.uk>
Date:   Tue, 22 Nov 2016 10:39:29 +0000
From:   David Howells <dhowells@...hat.com>
To:     Dave Chinner <david@...morbit.com>
Cc:     dhowells@...hat.com, Andreas Dilger <adilger@...ger.ca>,
        linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/4] statx: Add a system call to make enhanced file info available

Dave Chinner <david@...morbit.com> wrote:

> No. Just provide a 64 bit high resoultion field, and define it to
> contain nanoseconds. When we need higher resolution to be exported
> to userspace, we use a /feature flag/ to indicate that is contains
> something like attoseconds or the like.

That sounds suspiciously like a bad idea - if you're talking about a flag with
a currently undefined meaning that the kernel can inflict on userspace without
warning to change the meaning of the nanoseconds field to something we haven't
defined yet.

Userspace would have to ask for it.

David