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SubjectRe: [RFC][v8][PATCH 0/10] Implement clone3() system call
H. Peter Anvin [hpa@zytor.com] wrote:
| On 10/13/2009 04:53 PM, Roland McGrath wrote:
| >> My only concern is the support of 64-bit clone flags on 32-bit architectures.
| >
| > Oy. I didn't realize there was serious consideration of having more than
| > 32 flags. IMHO it would be a bad choice, since they could only be used via
| > clone3. Having high-bit flags work in clone on 64-bit machines but not on
| > 32-bit machines just seems like a wrongly confusing way for things to be.
| > If any high-bits flags are constrained even on 64-bit machines to uses in
| > clone3 calls for sanity purposes, then it seems questionable IMHO to have
| > them be more flags in the same u64 at all.
| >
| > Since all new features will be via this struct, various new kinds of things
| > could potentially be done by other new struct fields independent of flags.
| > But that would of course require putting enough reserved fields in now and
| > requiring that they be zero-filled now in anticipation of such future uses,
| > which is not very pleasant either.
| >
| > In short, I guess I really am saying that "clone_flags_high" (or
| > "more_flags" or something) does seem better to me than any of the
| > possibilities for having more than 32 CLONE_* in the current flags word.
| >
|
| Overall it seems sane to:
|
| a) make it an actual 3-argument call;
| b) make the existing flags a u32 forever, and make it a separate
| argument;
| c) any new expansion can be via the struct, which may want to have
| an "c3_flags" field first in the structure.

Ok, So will this work ?

struct clone_args {
u32 flags_high; /* new clone flags (higher bits) */
u32 reserved1;
u32 nr_pids;
u32 reserved2;
u64 child_stack_base;
u64 child_stack_size;
u64 parent_tid_ptr;
u64 child_tid_ptr;
u64 reserved3;
};

sys_clone3(u32 flags_low, struct clone_args *args, pid_t *pid_list)

Even on 64bit architectures the applications have to use sys_clone3() for
the extended features.


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