linux-kernel - Re: [PATCH v2] Add new open(2) flag

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Date:   Mon, 2 Jan 2023 19:35:38 +0500
From:   Ameer Hamza <ahamza@...ystems.com>
To:     David Laight <David.Laight@...LAB.COM>
Cc:     "viro@...iv.linux.org.uk" <viro@...iv.linux.org.uk>,
        "jlayton@...nel.org" <jlayton@...nel.org>,
        "chuck.lever@...cle.com" <chuck.lever@...cle.com>,
        "arnd@...db.de" <arnd@...db.de>,
        "guoren@...nel.org" <guoren@...nel.org>,
        "palmer@...osinc.com" <palmer@...osinc.com>,
        "f.fainelli@...il.com" <f.fainelli@...il.com>,
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        "mattst88@...il.com" <mattst88@...il.com>,
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        <James.Bottomley@...senPartnership.com>,
        "deller@....de" <deller@....de>,
        "davem@...emloft.net" <davem@...emloft.net>,
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        "linux-parisc@...r.kernel.org" <linux-parisc@...r.kernel.org>,
        "linux-alpha@...r.kernel.org" <linux-alpha@...r.kernel.org>
Subject: Re: [PATCH v2] Add new open(2) flag - O_EMPTY_PATH

On Mon, Jan 02, 2023 at 02:01:38PM +0000, David Laight wrote:
> From: Ameer Hamza
> > Sent: 31 December 2022 23:56
> > 
> > This patch adds a new flag O_EMPTY_PATH that allows openat and open
> > system calls to open a file referenced by fd if the path is empty,
> > and it is very similar to the FreeBSD O_EMPTY_PATH flag. This can be
> > beneficial in some cases since it would avoid having to grant /proc
> > access to things like samba containers for reopening files to change
> > flags in a race-free way.
> > 
> 
> But what does it do?
> (Apart from add code to a common kernel code path.)
> 
> 	David
It can convert an O_PATH descriptor to one suitable for r/w work.
If we already have a file descriptor: {opath_fd = open(&lt;path&gt;, O_PATH);}, we can call {openat(opath_fd, "", O_EMPTY_PATH | O_RDWR)} instead of going through procfs {open(/proc/self/fd/&lt;opath_fd&gt;, O_RDWR)}.
> 
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