linux-kernel - Re: [RFC PATCH 2/3] add statmnt(2) syscall

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Date:   Sun, 17 Sep 2023 12:18:15 -0600
From:   Sargun Dhillon <sargun@...gun.me>
To:     Miklos Szeredi <mszeredi@...hat.com>
Cc:     linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-api@...r.kernel.org, linux-man@...r.kernel.org,
        linux-security-module@...r.kernel.org, Karel Zak <kzak@...hat.com>,
        Ian Kent <raven@...maw.net>,
        David Howells <dhowells@...hat.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Al Viro <viro@...iv.linux.org.uk>,
        Christian Brauner <christian@...uner.io>,
        Amir Goldstein <amir73il@...il.com>
Subject: Re: [RFC PATCH 2/3] add statmnt(2) syscall

On Wed, Sep 13, 2023 at 9:25 AM Miklos Szeredi <mszeredi@...hat.com> wrote:
>
> Add a way to query attributes of a single mount instead of having to parse
> the complete /proc/$PID/mountinfo, which might be huge.
>
> Lookup the mount by the old (32bit) or new (64bit) mount ID.  If a mount
> needs to be queried based on path, then statx(2) can be used to first query
> the mount ID belonging to the path.
>
> Design is based on a suggestion by Linus:
>
>   "So I'd suggest something that is very much like "statfsat()", which gets
>    a buffer and a length, and returns an extended "struct statfs" *AND*
>    just a string description at the end."
>
> The interface closely mimics that of statx.
>
> Handle ASCII attributes by appending after the end of the structure (as per
> above suggestion).  Allow querying multiple string attributes with
> individual offset/length for each.  String are nul terminated (termination
> isn't counted in length).
>
> Mount options are also delimited with nul characters.  Unlike proc, special
> characters are not quoted.
>

Thank you for writing this patch. I wish that this had existed the many times
I've written parsers for mounts files in my life.

What do you think about exposing the locked flags, a la what happens
on propagation of mount across user namespaces?