From mboxrd@z Thu Jan 1 00:00:00 1970 From: Christian Brauner Subject: Re: pidfd design Date: Tue, 26 Mar 2019 01:12:32 +0100 Message-ID: <20190326001231.3tnhhlvzg26mof33@brauner.io> References: <20190320185156.7bq775vvtsxqlzfn@brauner.io> <20190320191412.5ykyast3rgotz3nu@brauner.io> <20190325234547.wo6lyimrp52qie5p@brauner.io> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: Content-Disposition: inline In-Reply-To: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: driverdev-devel-bounces@linuxdriverproject.org Sender: "devel" To: Andy Lutomirski Cc: Peter Zijlstra , Tim Murray , Michal Hocko , Joel Fernandes , Sultan Alsawaf , Jonathan Kowalski , "open list:ANDROID DRIVERS" , Daniel Colascione , Suren Baghdasaryan , Ingo Molnar , kernel-team , Todd Kjos , Kees Cook , Jann Horn , Steven Rostedt , Oleg Nesterov , Martijn Coenen , Greg Kroah-Hartman , LKML , Arve =?utf-8?B?SGrDuG5uZXbDpWc=?= , Linux API List-Id: linux-api@vger.kernel.org On Mon, Mar 25, 2019 at 05:00:17PM -0700, Andy Lutomirski wrote: > On Mon, Mar 25, 2019 at 4:45 PM Christian Brauner wrote: > > > > On Mon, Mar 25, 2019 at 04:42:14PM -0700, Andy Lutomirski wrote: > > > On Mon, Mar 25, 2019 at 1:23 PM Daniel Colascione wrote: > > > > > > > > On Mon, Mar 25, 2019 at 1:14 PM Jann Horn wrote: > > > > > > > > > > On Mon, Mar 25, 2019 at 8:44 PM Andy Lutomirski wrote: > > > > > > > > One ioctl on procfs roots to translate pidfds into that procfs, > > > > > subject to both the normal lookup permission checks and only working > > > > > if the pidfd has a translation into the procfs: > > > > > > > > > > int proc_root_fd = open("/proc", O_RDONLY); > > > > > int proc_dir_fd = ioctl(proc_root_fd, PROC_PIDFD_TO_PROCFSFD, pidfd); > > > > > > > > > > And one ioctl on procfs directories to translate from PGIDs and PIDs to pidfds: > > > > > > > > > > int proc_pgid_fd = open("/proc/self", O_RDONLY); > > > > > int self_pg_pidfd = ioctl(proc_pgid_fd, PROC_PROCFSFD_TO_PIDFD, 0); > > > > > int proc_pid_fd = open("/proc/thread-self", O_RDONLY); > > > > > int self_p_pidfd = ioctl(proc_pid_fd, PROC_PROCFSFD_TO_PIDFD, 0); > > > > > > > > > > > This sounds okay to me. Or we could make it so that a procfs > > > directory fd also works as a pidfd, but that seems more likely to be > > > problematic than just allowing two-way translation like this > > > > > > > > > > > > > And then, as you proposed, the new sys_clone() can just return a > > > > > pidfd, and you can convert it into a procfs fd yourself if you want. > > > > > > > > I think that's the consensus we reached on the other thread. The > > > > O_DIRECTORY open on /proc/self/fd/mypidfd seems like it'd work well > > > > enough. > > > > > > I must have missed this particular email. > > > > > > IMO, if /proc/self/fd/mypidfd allows O_DIRECTORY open to work, then it > > > really ought to do function just like /proc/self/fd/mypidfd/. and > > > /proc/self/fd/mypidfd/status should work. And these latter two > > > options seem nutty. > > > > > > Also, this O_DIRECTORY thing is missing the entire point of the ioctl > > > interface -- it doesn't require procfs access. > > > > The other option was to encode the pid in the callers pid namespace into > > the pidfd's fdinfo so that you can parse it out and open /proc/. > > You'd just need an event on the pidfd to tell you when the process has > > died. Jonathan and I just discussed this. > > From an application developer's POV, the ioctl interface sounds much, > much nicer. Some people are strongly against ioctl()s some don't. I'm not against them so both options are fine with me if people can agree. Christian