linux-kernel - Re: [PATCH 13/17] watch_queue: Implement mount topology and attribute change notifications [ver #5]

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Message-ID: <2003787.1595585999@warthog.procyon.org.uk>
Date:   Fri, 24 Jul 2020 11:19:59 +0100
From:   David Howells <dhowells@...hat.com>
To:     Miklos Szeredi <miklos@...redi.hu>
Cc:     dhowells@...hat.com,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Al Viro <viro@...iv.linux.org.uk>,
        Casey Schaufler <casey@...aufler-ca.com>,
        Stephen Smalley <sds@...ho.nsa.gov>, nicolas.dichtel@...nd.com,
        Ian Kent <raven@...maw.net>,
        Christian Brauner <christian@...uner.io>, andres@...razel.de,
        Jeff Layton <jlayton@...hat.com>, dray@...hat.com,
        Karel Zak <kzak@...hat.com>, keyrings@...r.kernel.org,
        Linux API <linux-api@...r.kernel.org>,
        linux-fsdevel@...r.kernel.org,
        LSM <linux-security-module@...r.kernel.org>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 13/17] watch_queue: Implement mount topology and attribute change notifications [ver #5]

David Howells <dhowells@...hat.com> wrote:

> > What guarantees that mount_id is going to remain a 32bit entity?
> 
> You think it likely we'd have >4 billion concurrent mounts on a system?  That
> would require >1.2TiB of RAM just for the struct mount allocations.
> 
> But I can expand it to __u64.

That said, sys_name_to_handle_at() assumes it's a 32-bit signed integer, so
we're currently limited to ~2 billion concurrent mounts:-/

David