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, eclone() that lets a process specify the pids of the child process. Summary: Patches 1 through 7 are helper patches needed for choosing a pid for the child process. Patches 8 through 10 implement the eclone() system call on x86, x86_64, s390 and powerpc. Patch 11 documents the new system call, some/all of which will eventually go into a man page. Changelog[v15]: - [Albert Cahalan, Randy Dunlap]: Specify stack as [base, offset] on all architectures rather than [base, offset] on a few and stack pointer on others. - [Randy Dunlap] Fix typos in documentation and pointer to usage examples of eclone() Changelog[v14]: - Updates to documentaiton Changelog[v13]: - Implement sys_eclone() on x86_64, s390 and powerpc architectures - Reorg x86 implementation to enable sharing code with x86_64 - [Arnd Bergmann] Remove the ->reserved1 field we now have args_size - [Nathan Lynch, Serge Hallyn]: Rename ->child_stack_base to ->child_stack and ensure ->child_stack_size is 0 on architectures that don't need the stack size. - Modify exmaple in Documentation to avoid unnecessary register copy. Changelog[v12]: - Ignore ->child_stack_size when ->child_stack_base is NULL (PATCH 8) - Cleanup/simplify example in Documentation/eclone (PATCH 9). - Rename sys call to a shorter name, eclone() Changelog[v11]: - [Dave Hansen] Move clone_args validation checks to arch-indpeendent code. - [Oren Laadan] Make args_size a parameter to system call and remove it from 'struct clone_args' Changelog[v10]: - [Linus Torvalds] Use PTREGSCALL() implementation for clone rather than the generic system call - Rename clone3() to clone_with_pids() - Update Documentation/clone_with_pids() to show example usage with the PTREGSCALL implementation. Changelog[v9]: - [Pavel Emelyanov] Drop the patch that made 'pid_max' a property of struct pid_namespace - [Roland McGrath, H. Peter Anvin and earlier on, Serge Hallyn] To avoid inadvertent truncation clone_flags, preserve the first parameter of clone3() as 'u32 clone_flags' and specify newer flags in clone_args.flags_high (PATCH 8/9 and PATCH 9/9) - [Eric Biederman] Generalize alloc_pidmap() code to simplify and remove duplication (see PATCH 3/9]. Changelog[v8]: - [Oren Laadan, Louis Rilling, KOSAKI Motohiro] The name 'clone2()' is in use - renamed new syscall to clone3(). - [Oren Laadan] ->parent_tidptr and ->child_tidptr need to be 64bit. - [Oren Laadan] Ensure that unused fields/flags in clone_struct are 0. (Added [PATCH 7/10] to the patchset). Changelog[v7]: - [Peter Zijlstra, Arnd Bergmann] Group the arguments to clone2() into a 'struct clone_arg' 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 NOTE: clone() system call has another limitation - all but one bits in clone-flags are in use and if more new clone-flags are needed, we 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()). Based on these requirements and constraints, we explored a couple of system call interfaces (in earlier versions of this patchset). Based on input from Arnd Bergmann and others, the new interface of the system call is: struct clone_args { u64 clone_flags_high; u64 child_stack_base; u64 child_stack_size; u64 parent_tid_ptr; u64 child_tid_ptr; u32 nr_pids; u32 reserved0; }; sys_eclone(u32 flags_low, struct clone_args *cargs, int args_size, pid_t *pids) Details of the struct clone_args and the usage are explained in the documentation (PATCH 11/11). NOTE: While this patchset enables support for more clone-flags, actual implementation for additional clone-flags is best implemented as a separate patchset (PATCH 8/9 identifies some TODOs) Nathan Lynch (1): eclone (10/11): Implement sys_eclone for powerpc Serge E. Hallyn (1): eclone (9/11): Implement sys_eclone for s390 Sukadev Bhattiprolu (9): eclone (1/11): Factor out code to allocate pidmap page eclone (2/11): Have alloc_pidmap() return actual error code eclone (3/11): Define set_pidmap() function eclone (4/11): Add target_pids parameter to alloc_pid() eclone (5/11): Add target_pids parameter to copy_process() eclone (6/11): Check invalid clone flags eclone (7/11): Define do_fork_with_pids() eclone (8/11): Implement sys_eclone for x86 (32,64) eclone (11/11): Document sys_eclone Documentation/eclone | 354 +++++++++++++++++++++++++++++++++++ arch/powerpc/include/asm/syscalls.h | 6 + arch/powerpc/include/asm/systbl.h | 1 + arch/powerpc/include/asm/unistd.h | 3 +- arch/powerpc/kernel/entry_32.S | 8 + arch/powerpc/kernel/entry_64.S | 5 + arch/powerpc/kernel/process.c | 62 ++++++- arch/s390/include/asm/unistd.h | 3 +- arch/s390/kernel/compat_linux.c | 17 ++ arch/s390/kernel/compat_wrapper.S | 8 + arch/s390/kernel/process.c | 39 ++++ arch/s390/kernel/syscalls.S | 1 + arch/x86/ia32/ia32entry.S | 2 + arch/x86/include/asm/syscalls.h | 2 + arch/x86/include/asm/unistd_32.h | 3 +- arch/x86/include/asm/unistd_64.h | 2 + arch/x86/kernel/entry_32.S | 14 ++ arch/x86/kernel/entry_64.S | 1 + arch/x86/kernel/process.c | 43 ++++- arch/x86/kernel/syscall_table_32.S | 1 + include/linux/pid.h | 2 +- include/linux/sched.h | 17 ++ include/linux/types.h | 10 + kernel/fork.c | 155 +++++++++++++++- kernel/pid.c | 101 +++++++--- 25 files changed, 818 insertions(+), 42 deletions(-) create mode 100644 Documentation/eclone 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