Sukadev Bhattiprolu <sukadev@xxxxxxxxxxxxxxxxxx> writes: > Eric W. Biederman [ebiederm@xxxxxxxxxxxx] wrote: > | Sukadev Bhattiprolu <sukadev@xxxxxxxxxxxxxxxxxx> writes: > | > | > === NEW CLONE() 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, clone_with_pids() that lets a > | > process specify the pids of the child process. > | > > | > Patches 1 through 5 are helpers and we believe they are needed for application > | > restart, regardless of the kernel implementation of application restart. > | > | I'm not very impressed. > | > | - static int alloc_pidmap(struct pid_namespace *pid_ns) > | + static int alloc_pidmap(struct pid_namespace *pid_ns, int pid_max, int last_pid) > | > | Do that. > | > | That is pass in pid_max and last_pid, and you don't have to do weird > | things in alloc_pidmap, and no set_pidmap is needed. > > But last_pid is from the pid_ns. Do you mean to have alloc_pidmap() > take a pid_min and pid_max and when choosing a specific pid, have > pid_min == pid_max == target_pid ? Yes. It already takes a pid_min and a pid_max from the environment. I guess the pid_min is RESERVED_PIDS by default. > | No changes to copy_process are needed it already takes a struct pid > | argument. > > > I see your point about passing in both 'struct pid*' and target_pids[]. > But in the common case the struct pid passed into copy_process() is > NULL - allocating pid in do_fork() would significantly alter the > existing control flow - no ? alloc_pid() assumes any new pid namespace > has been created - in copy_namespaces(). Moving the alloc_pid() to > do_fork() would require parsing clone_flags in do_fork() and pulling > pid namespace code out of copy_namespaces(). Why change do_fork? > | I haven't been following closely what is gained by having a clone_with_pids > | syscall? > > When restarting an application from a checkpoint, the application must get > the same pid it had at the time of checkpoint. clone_with_pids() would be > used during restart so the child can be created with a specific set of pids. That part I understand. What I don't understand is why have that one part be special and have user space do the work? > | As for new namespaces that don't need to happen at process creation time > | (which is just about anything that is left) we can create a new syscall that > | unshares just that one. > | > > Ok. If all new namespaces can be handled with a variant of unshare(), we can > decouple clone_with_pids() from the clone-flags issue. What I mean is we should be able to get away things like: sys_new_timens(); Very very simple syscalls. One per each kind of namespace we want new instances of. Eric _______________________________________________ Containers mailing list Containers@xxxxxxxxxxxxxxxxxxxxxxxxxx https://lists.linux-foundation.org/mailman/listinfo/containers
