Re: [RFC][v7][PATCH 0/9] Implement clone2() system call

[Oren Laadan <orenl@librato.com>]

Sukadev Bhattiprolu wrote:
> Oren Laadan [orenl@librato.com] wrote:
> | 
> | 
> | Sukadev Bhattiprolu wrote:
> | > 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;
> | 
> | So @parent_tid and @child_tid are pointers to userspace memory and
> | require 'u64' (and it won't hurt to make @reserved1 a 'u64' as well).
> 
> No, as Arnd pointed out, we already pass in a pointer to 'struct clone_struct'
> and the kernel can use that pointer to copy the parent and child tids.

In this form, you place a constraints on where userspace may
place the {parent,child}_tid variable, and require that this
particular clone_struct remain valid memory in the parent until
the child terminates.  This may break existing programs that
use this (threads libraries ?)

Oren.

> 
> | 
> | > 		u32 reserved1;
> | > 		u64 reserved2;
> | > 	};
> | > 
> | 
> | Also, for forward/backward compatibility, explicitly state in the
> | documentation, and enforce in the kernel, that flags which are not
> | defined must not be set, and that reserved{1,2} must remain 0.
> 
> Good idea. Will do.
> 
> Thanks,
> 
> Sukadev