Daniel Lezcano [daniel.lezcano@xxxxxxx] 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 "<syscall>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 _______________________________________________ Containers mailing list Containers@xxxxxxxxxxxxxxxxxxxxxxxxxx https://lists.linux-foundation.org/mailman/listinfo/containers
