From mboxrd@z Thu Jan 1 00:00:00 1970 From: Sukadev Bhattiprolu Subject: Re: [RFC][v8][PATCH 0/10] Implement clone3() system call Date: Fri, 16 Oct 2009 12:44:51 -0700 Message-ID: <20091016194451.GA28706@us.ibm.com> References: <20091013044925.GA28181@us.ibm.com> <4AD8C7E4.9000903@free.fr> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Content-Disposition: inline In-Reply-To: <4AD8C7E4.9000903-GANU6spQydw@public.gmane.org> Sender: linux-api-owner-u79uwXL29TY76Z2rM5mHXA@public.gmane.org To: Daniel Lezcano Cc: linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, randy.dunlap-QHcLZuEGTsvQT0dZR+AlfA@public.gmane.org, arnd-r2nGTMty4D4@public.gmane.org, Containers , Nathan Lynch , Louis.Rilling-aw0BnHfMbSpBDgjK7y7TUQ@public.gmane.org, "Eric W. Biederman" , kosaki.motohiro-+CUm20s59erQFUHtdCDX3A@public.gmane.org, hpa-YMNOUZJC4hwAvxtiuMwx3w@public.gmane.org, mingo-X9Un+BFzKDI@public.gmane.org, linux-api-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, torvalds-de/tnXTf+JLsfHDXvbKv3WD2FQJk+8+b@public.gmane.org, Alexey Dobriyan , roland-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org, Pavel Emelyanov List-Id: linux-api@vger.kernel.org Daniel Lezcano [daniel.lezcano-GANU6spQydw@public.gmane.org] wrote: > Sukadev Bhattiprolu wrote: >> Subject: [RFC][v8][PATCH 0/10] Implement clone3() system call >> >> To support application checkpoint/restart, a task must have the same pid it >> had when it was checkpointed. When containers are nested, the tasks within >> the containers exist in multiple pid namespaces and hence have multiple pids >> to specify during restart. >> >> This patchset implements a new system call, clone3() that lets a process >> specify the pids of the child process. >> >> Patches 1 through 7 are helper patches, needed for choosing a pid for the >> child process. >> >> PATCH 9 defines a prototype of the new system call. PATCH 10 adds some >> documentation on the new system call, some/all of which will eventually >> go into a man page. >> > > Sorry for jumping so late in the discussion and for having maybe my > remarks pointless... > > If this syscall is only for checkpoint / restart, why this shouldn't be > used with a future generic sys_restart syscall ? As I tried to explain in PATCH 0/9, the ability to choose a pid is only for C/R but we are also trying to clone-flags so we won't need yet another variant of clone() fairly soon. > Otherwise, shouldn't be more convenient to have something usable for > everyone, let's say: > > cloneat(pid_t pid, pid_t desiredpid, ...); > > Where 'desiredpid' is a hint of for the kernel for the pid to be > allocated (zero means the kernel will choose one for us) and the newly > allocated task is the son of 'pid'. Hmm, so P1 would call cloneat() to create a child P3 _on behalf_ of process P2 ? I did not know we had a requirement for that. Can you explain the use-case more ? IOW, why can't P2 create the child P3 by itself ? Note also that 'desiredpid' must be a list of pids (one for each pid namespaces that the child will belong to) and hence we need 'nr_pids' to specify the list. Given that we are limited to 6 parameters to the syscall, such parameters must be stuffed into 'struct clone_args'. So we should do something like: sys_clone3(u32 flags_low, pid_t pid, struct clone_args *carg, pid_t *desired_pids) or (to match the name and parameters, move 'pid' parameter into clone_args) > That looks more consistent with the "at" family, 'openat', > 'faccessat', 'readlinkat', etc ... and usable for something else than > the checkpoint / restart. The subtle difference though is that openat() does not open a file on behalf of another process and so the 'at' suffix would not apply ? > > Thanks > -- Daniel