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From:   Sargun Dhillon <sargun@sargun.me>
Date:   Sun, 17 Sep 2023 12:18:15 -0600
Message-ID: <CAMp4zn-r5BV_T9VBPJf8Z-iG6=ziDEpCdmPgHRRXF78UoOjTjQ@mail.gmail.com>
Subject: Re: [RFC PATCH 2/3] add statmnt(2) syscall
To:     Miklos Szeredi <mszeredi@redhat.com>
Cc:     linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org,
        linux-api@vger.kernel.org, linux-man@vger.kernel.org,
        linux-security-module@vger.kernel.org, Karel Zak <kzak@redhat.com>,
        Ian Kent <raven@themaw.net>,
        David Howells <dhowells@redhat.com>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Al Viro <viro@zeniv.linux.org.uk>,
        Christian Brauner <christian@brauner.io>,
        Amir Goldstein <amir73il@gmail.com>
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On Wed, Sep 13, 2023 at 9:25=E2=80=AFAM Miklos Szeredi <mszeredi@redhat.com=
> wrote:
>
> Add a way to query attributes of a single mount instead of having to pars=
e
> 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 que=
ry
> 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 ge=
ts
>    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 p=
er
> above suggestion).  Allow querying multiple string attributes with
> individual offset/length for each.  String are nul terminated (terminatio=
n
> isn't counted in length).
>
> Mount options are also delimited with nul characters.  Unlike proc, speci=
al
> characters are not quoted.
>

Thank you for writing this patch. I wish that this had existed the many tim=
es
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?