linux-kernel - Re: [PATCH 00/19] VFS: Filesystem information and notifications [ver #16]

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Message-ID: <1811033.1582289832@warthog.procyon.org.uk>
Date:   Fri, 21 Feb 2020 12:57:12 +0000
From:   David Howells <dhowells@...hat.com>
To:     Stefan Metzmacher <metze@...ba.org>
Cc:     dhowells@...hat.com, viro@...iv.linux.org.uk, raven@...maw.net,
        mszeredi@...hat.com, christian@...uner.io,
        linux-api@...r.kernel.org, linux-fsdevel@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 00/19] VFS: Filesystem information and notifications [ver #16]

Stefan Metzmacher <metze@...ba.org> wrote:

> > fsinfo() may be called like the following, for example:
> > 
> > 	struct fsinfo_params params = {
> > 		.at_flags	= AT_SYMLINK_NOFOLLOW,
> 
> Shouldn't all new syscalls be able to provide the RESOLVE_ flags
> supported in openat2?

If that's the rule, then fine.  I presume these are a replacement for AT_*.
But the set of RESOLVE_* flags does not appear to be complete - and why's it
not in linux/fs.h if it's meant to be used by everything?

Anyway, it lacks a RESOLVE_NO_AUTOMOUNT flag.  This is not quite the same as
the documented behaviour of RESOLVE_NO_XDEV.

> > 	len = fsinfo(AT_FDCWD, "/afs/grand.central.org/doc", &params,
> > 		     &address, sizeof(address));
> 
> Also passing sizeof(params) would allow future updates of fsinfo_params,
> also similar to openat2(), clone3()...

I can put that at the beginning of the params block or put dirfd in there.  If
I remember rightly, 6-arg syscalls are discouraged because they may need
special handling on some arches.

David