linux-kernel - Re: [PATCH] open(2): document O

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Message-ID: <87fwbhhdp2.fsf@skywalker.in.ibm.com>
Date:	Thu, 03 May 2012 13:57:21 +0530
From:	"Aneesh Kumar K.V" <aneesh.kumar@...ux.vnet.ibm.com>
To:	"Ted Ts'o" <tytso@....edu>
Cc:	"Michael Kerrisk \(man-pages\)" <mtk.manpages@...il.com>,
	Mike Frysinger <vapier@...too.org>, linux-man@...r.kernel.org,
	viro@...iv.linux.org.uk, Richard Weinberger <richard@....at>,
	lkml <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] open(2): document O_PATH

Ted Ts'o <tytso@....edu> writes:

> It might also be a good idea to document explicitly whether or not
> things like fstat() and the syscalls to manipulate extended attributes
> are expected to work.
>

fstat won't work, but fstatat with an empty path name would work. O_PATH
descriptors are suppose to be used as "location only descriptors". 
We then extended the *at syscalls to work with EMPTY pathnames so that
O_PATH descriptors can be used with readlink, fchownat and fstatat().
This was done to enable us to do these operation on symlinks.
(65cfc6722361570bfe255698d9cd4dccaf47570d)

Examples for O_PATH and handle syscall can be found in qemu and
handle-test repo 

http://git.qemu.org/?p=qemu.git;a=blob;f=hw/9pfs/virtio-9p-handle.c;h=f96d17a9749a6f672741ff4dcb98da81d1dcc3ce;hb=HEAD
https://github.com/kvaneesh/handle-test/blob/master/handle.h

-aneesh

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