Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756487Ab0GGP1L (ORCPT ); Wed, 7 Jul 2010 11:27:11 -0400 Received: from cantor.suse.de ([195.135.220.2]:44006 "EHLO mx1.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756126Ab0GGP1J (ORCPT ); Wed, 7 Jul 2010 11:27:09 -0400 Date: Thu, 8 Jul 2010 01:27:06 +1000 From: Nick Piggin To: "Aneesh Kumar K.V" Cc: hch@infradead.org, viro@zeniv.linux.org.uk, adilger@sun.com, corbet@lwn.net, serue@us.ibm.com, neilb@suse.de, hooanon05@yahoo.co.jp, bfields@fieldses.org, linux-fsdevel@vger.kernel.org, sfrench@us.ibm.com, philippe.deniel@CEA.FR, linux-kernel@vger.kernel.org Subject: Re: [PATCH -V14 05/11] vfs: Support null pathname in readlink Message-ID: <20100707152706.GT11732@laptop> References: <1276621981-2774-1-git-send-email-aneesh.kumar@linux.vnet.ibm.com> <1276621981-2774-6-git-send-email-aneesh.kumar@linux.vnet.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1276621981-2774-6-git-send-email-aneesh.kumar@linux.vnet.ibm.com> User-Agent: Mutt/1.5.20 (2009-06-14) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2077 Lines: 57 On Tue, Jun 15, 2010 at 10:42:55PM +0530, Aneesh Kumar K.V wrote: > From: NeilBrown > > This enables to use readlink to get the link target name > from a file descriptor point to the link. This can be used > with open_by_handle syscall that returns a file descriptor for a link. > We can then use this file descriptor to get the target name. > > Signed-off-by: NeilBrown > Signed-off-by: Aneesh Kumar K.V > --- > fs/stat.c | 30 ++++++++++++++++++++++-------- > 1 files changed, 22 insertions(+), 8 deletions(-) > > diff --git a/fs/stat.c b/fs/stat.c > index c4ecd52..49b95a7 100644 > --- a/fs/stat.c > +++ b/fs/stat.c > @@ -284,26 +284,40 @@ SYSCALL_DEFINE2(newfstat, unsigned int, fd, struct stat __user *, statbuf) > SYSCALL_DEFINE4(readlinkat, int, dfd, const char __user *, pathname, > char __user *, buf, int, bufsiz) > { > - struct path path; > - int error; > + int error = 0; > + struct path path, *pp; > + struct file *file = NULL; > > if (bufsiz <= 0) > return -EINVAL; > > - error = user_path_at(dfd, pathname, 0, &path); > + if (pathname == NULL && dfd != AT_FDCWD) { > + file = fget(dfd); > + > + if (file) > + pp = &file->f_path; > + else > + error = -EBADF; > + } else { > + error = user_path_at(dfd, pathname, 0, &path); > + pp = &path; > + } This (and all the others) is really ugly overloading of syscall arguments IMO, and the changelog is seriously lacking for such changes. This also changes the the syscall API of existing calls; from reading the path at NULL, to switching to a completely different syscall. Perhaps you're assuming nobody relies on SIGSEGV / mmapped NULL address there, but even then you surely need to document the changed semantics somewhere (and document the new syscall semantics properly). -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/