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

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Date:   Wed, 20 Sep 2023 09:43:13 +0000
From:   David Laight <David.Laight@...LAB.COM>
To:     'Jeff Layton' <jlayton@...nel.org>,
        Christian Brauner <brauner@...nel.org>,
        Miklos Szeredi <miklos@...redi.hu>
CC:     Miklos Szeredi <mszeredi@...hat.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        "linux-fsdevel@...r.kernel.org" <linux-fsdevel@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-api@...r.kernel.org" <linux-api@...r.kernel.org>,
        "linux-man@...r.kernel.org" <linux-man@...r.kernel.org>,
        "linux-security-module@...r.kernel.org" 
        <linux-security-module@...r.kernel.org>,
        Karel Zak <kzak@...hat.com>, "Ian Kent" <raven@...maw.net>,
        David Howells <dhowells@...hat.com>,
        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

From: Jeff Layton
> Sent: 18 September 2023 15:30
....
> A bit tangential to this discussion, but one thing we could consider is
> adding something like a mnt_change_cookie field that increments on any
> significant changes on the mount: i.e. remounts with new options,
> changes to parentage or propagation, etc.
> 
> That might make it more palatable to do something with separate syscalls
> for the string-based fields. You could do:
> 
> statmnt(...);
> getmntattr(mnt, "mnt.fstype", ...);
> statmnt(...);
> 
> ...and then if the mnt_change_cookie hasn't changed, you know that the
> string option was stable during that window.

That would also help with the problem of the mount options
being changed while processing a page fault on the user buffer.

Of, with a call to just get the cookie, could find that nothing
has changed so there is no point looking again.

	David

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