[RFC PATCH 2/3] add statmnt(2) syscall

[Sargun Dhillon]

On Wed, Sep 13, 2023 at 9:25 AM Miklos Szeredi <mszeredi at redhat.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?