Queued for v19-rc2 to replace old clone-with-pids.
Oren.
Sukadev Bhattiprolu wrote:
> Andrew,
>
> We ported the syscall to x86_64, powerpc and s390 and in the process hashed
> out couple of minor issues in the interface.
>
> Can you please merge or let me know if there are other comments ?
>
> ---
>
> Subject: [v13][PATCH 00/12] Implement eclone() 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, eclone() 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.
>
> Patches 8 through 11 implement the eclone() system call on x86, x86_64, s390
> and powerpc.
>
> Patch 12 documents the new system call, some/all of which will eventually
> go into a man page.
>
> 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 12/12).
>
> 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)
>
> Signed-off-by: Sukadev Bhattiprolu <sukadev@xxxxxxxxxxxxxxxxxx>
>
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