Cc: LKML
Sukadev Bhattiprolu [sukadev@xxxxxxxxxxxxxxxxxx] wrote:
|
| Based on discussions on containers mailing list and IRC, we settled on
| the name eclone(). Please let me know of a better name or if there are
| other comments on the patchset.
|
| ---
|
| Subject: [v12][PATCH 0/9] Implement eclone() syscall
|
| 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 6 are helper patches needed for choosing a pid for the
| child process.
|
| PATCH 8 implements the eclone() system call on x86. The interface defined in
| PATCH 8 has been ported to s390 and ppc64 architectures, but they will be
| posted as a separate patchset if this patchset is accepted.
|
| PATCH 9 adds some documentation on the new system call, some/all of which
| will eventually go into a man page.
|
| 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;
| u64 reserved1;
| };
|
| 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 9/9).
|
| 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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