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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Date:   Mon, 4 Jun 2018 10:16:30 -0700
From:   Matthew Wilcox <willy@...radead.org>
To:     Al Viro <viro@...IV.linux.org.uk>
Cc:     David Howells <dhowells@...hat.com>,
        Christoph Hellwig <hch@...radead.org>,
        linux-fsdevel@...r.kernel.org, linux-afs@...ts.infradead.org,
        linux-kernel@...r.kernel.org, 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 Sun, Jun 03, 2018 at 01:55:37AM +0100, Al Viro wrote:
> +SYSCALL_DEFINE3(open_tree, int, dfd, const char *, filename, unsigned, flags)
> +{
> +	struct file *file;
> +	struct path path;
> +	int lookup_flags = LOOKUP_AUTOMOUNT | LOOKUP_FOLLOW;
> +	bool detached = flags & OPEN_TREE_CLONE;
> +	int error;
> +	int fd;
> +
> +	BUILD_BUG_ON(OPEN_TREE_CLOEXEC != O_CLOEXEC);

Why do we need OPEN_TREE_CLOEXEC?  Wouldn't we be better off just making
the fd returned by open_tree implicitly close-on-exec?  I can think of
no good reason for these file descriptors to be inherited across exec()
and if someone comes up with such a reason, fcntl(F_SETFD) is not an
expensive call to make.