=== 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, clone2() that lets a process specify the pids of the child process. Patches 1 through 6 are helper patches, needed for choosing a pid for the child process. Patch 8 defines a prototype of the new system call. Patch 9 adds some documentation on the new system call, some/all of which will eventually go into a man page. Changelog[v7]: - [Peter Zijlstra, Arnd Bergmann] Rename clone_with_pids() to clone2(). Also group the arguments to clone2() into a 'struct clone_struct' to workaround the issue of exceeding 6 arguments to the system call. Also define clone-flags as u64 to allow additional clone-flags. Changelog[v6]: - [Nathan Lynch, Arnd Bergmann, H. Peter Anvin, Linus Torvalds] Change 'pid_set.pids' to 'pid_t pids[]' so sizeof(struct pid_set) is constant across architectures (Patches 7, 8). - (Nathan Lynch) Change pid_set.num_pids to unsigned and remove 'unum_pids < 0' check (Patches 7,8) - (Pavel Machek) New patch (Patch 9) to add some documentation. Changelog[v5]: - Make 'pid_max' a property of pid_ns (Integrated Serge Hallyn's patch into this set) - (Eric Biederman): Avoid the new function, set_pidmap() - added couple of checks on 'target_pid' in alloc_pidmap() itself. === IMPORTANT TODO: clone() system call has another limitation - all available bits in clone-flags are in use and any new clone-flag will need a variant of the clone() system call. It appears to make sense to try and extend this new system call to address this limitation as well. The requirements of a new clone system call could then be summarized as: - do everything clone() does today, and - give application an ability to choose pids for the child process in all ancestor pid namespaces, and - allow more clone_flags Contstraints: - system-calls are restricted to 6 parameters and clone() already takes 5 parameters, any extension to clone() interface would require one or more copy_from_user(). (Not sure if copy_from_user() of ~40 bytes would have a significant impact on performance of clone() on any architecture). Based on these requirements and constraints, we explored a couple of system call interfaces (in earlier versions of this patchset) and currently define the system call as: struct clone_struct { u64 flags; u64 child_stack; u32 nr_pids; u32 parent_tid; u32 child_tid; u32 reserved1; u64 reserved2; }; sys_clone2(struct clone_struct __user *cs, pid_t __user *pids) Signed-off-by: Sukadev Bhattiprolu <suka...@linux.vnet.ibm.com> _______________________________________________ Containers mailing list contain...@lists.linux-foundation.org https://lists.linux-foundation.org/mailman/listinfo/containers _______________________________________________ Devel mailing list Devel@openvz.org https://openvz.org/mailman/listinfo/devel