linux-kernel - Re: [RFD] A mount api that notices previous mounts

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Message-ID: <9871.1548853314@warthog.procyon.org.uk>
Date:   Wed, 30 Jan 2019 13:01:54 +0000
From:   David Howells <dhowells@...hat.com>
To:     Karel Zak <kzak@...hat.com>
Cc:     dhowells@...hat.com, "Eric W. Biederman" <ebiederm@...ssion.com>,
        linux-api@...r.kernel.org, linux-fsdevel@...r.kernel.org,
        linux-kernel@...r.kernel.org, Al Viro <viro@...IV.linux.org.uk>,
        Miklos Szeredi <miklos@...redi.hu>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        util-linux@...r.kernel.org, Andy Lutomirski <luto@...capital.net>
Subject: Re: [RFD] A mount api that notices previous mounts

Karel Zak <kzak@...hat.com> wrote:

> It seems more elegant is to ask for Nth option as expected by fsinfo().

More elegant yes, but there's an issue with atomiticity[*].  I'm in the
process of switching to something that returns you a single buffer with all
the options in, but each key and each value is preceded by a length count.

The reasons for not using separator characters are:

 (1) There's no separator char that cannot validly occur within an option[**].

 (2) Makes it possible to return binary values if we need to.

David

[*] Atomic with respect to remount calls, that is.

[**] Oh, and look at cifs where you can *change* the separator char during
     option parsing ("sep=<char>").