linux-kernel - Re: [PATCH][RFC] open_tree(2) (was Re: [PATCH 30/32] vfs: Allow cloning of a mount tree with open(O_PATH|O_CLONE

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Message-ID: <20180604155937.GI30522@ZenIV.linux.org.uk>
Date:   Mon, 4 Jun 2018 16:59:37 +0100
From:   Al Viro <viro@...IV.linux.org.uk>
To:     Miklos Szeredi <miklos@...redi.hu>
Cc:     David Howells <dhowells@...hat.com>,
        Christoph Hellwig <hch@...radead.org>,
        linux-fsdevel <linux-fsdevel@...r.kernel.org>,
        linux-afs@...ts.infradead.org, LKML <linux-kernel@...r.kernel.org>,
        Linux API <linux-api@...r.kernel.org>
Subject: Re: [PATCH][RFC] open_tree(2) (was Re: [PATCH 30/32] vfs: Allow
 cloning of a mount tree with open(O_PATH|O_CLONE_MOUNT) [ver #8])

On Mon, Jun 04, 2018 at 04:52:05PM +0100, Al Viro wrote:
> On Mon, Jun 04, 2018 at 12:34:44PM +0200, Miklos Szeredi wrote:
> 
> > fsopen = create fsfd
> > fsmount = fsfd -> mountfd & set attr on mountfd & attach mountfd
> > fspick = path -> fsfd
> > move_mount = attach mountfd or move existing
> > fsinfo = info from path
> > open_tree = new mountfd from path or clone
> > mount_setattr = set attr on mountfd
> > 
> > Notice that fsmount() encompasses mount_setattr() + move_mount()
> > functionality.   Split those out and leave fsmount() to actually do
> > the "fsfd ->mountfd" translation?
> 
> Might make sense.

FWIW, to make it clear: fsmount(2) in this series actually does *NOT*
attach it to the tree.  Commit message definitely needs updating - as it
is, it's

+SYSCALL_DEFINE5(fsmount, int, fs_fd, unsigned int, flags, unsigned int, ms_flags,
+               void *, reserved4, void *, reserved5)

PS: IMO these reserved... arguments are in bad taste; if anyone has good reasons
for that practice in ABI design, I'd like to hear those.