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

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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(<path>, O_PATH);}, we can call {openat(opath_fd, "", O_EMPTY_PATH | O_RDWR)} instead of going through procfs {open(/proc/self/fd/<opath_fd>, O_RDWR)}.
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