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SubjectRe: [PATCH -mm 1/5][AIO] - Rework compat_sys_io_submit
On Wed, 29 Nov 2006 16:47:47 -0800, Zach Brown <zach.brown@oracle.com> wrote:

> On Nov 29, 2006, at 2:32 AM, Sébastien Dugué wrote:
>
> > compat_sys_io_submit() cleanup
> >
> >
> > Cleanup compat_sys_io_submit by duplicating some of the native
> > syscall
> > logic in the compat layer and directly calling io_submit_one() instead
> > of fooling the syscall into thinking it is called from a native 64-bit
> > caller.
> >
> > This is needed for the completion notification patch to avoid having
> > to rewrite each iocb on the caller stack for sys_io_submit() to
> > find the
> > sigevents.
>
> You could explicitly mention that this eliminates:
>
> - the overhead of copying nr pointers on the userspace caller's stack
>
> - the arbitrary PAGE_SIZE/(sizeof(void *)) limit on the number of
> iocbs that can be submitted
>
> Those alone make this worth merging.

Right, will add.

>
> > + if (unlikely(!access_ok(VERIFY_READ, iocb, (nr * sizeof(u32)))))
> > + return -EFAULT;
>
> I'm glad you got that right :) I no doubt would have initially
> hoisted these little checks into a shared helper function and missed
> that detail of getting the size of the access_ok() right in the
> compat case.

Thanks.

>
> > + put_ioctx(ctx);
> > +
> > + return i? i: ret;
>
> sys_io_getevents() reads:

uh! ^^^^^^^^^ you must be meaning sys_io_submit()?

>
> put_ioctx(ctx);
> return i ? i : ret;
>
> So while this compat_sys_io_submit() logic seems fine and I would be
> comfortable with it landing as-is, I'd also appreciate it if we
> didn't introduce differences between the two functions when it seems
> just as easy to make them the same. (That chunk is just one
> example. There's whitespace, missing unlikely()s, etc).
>

OK, will fix.

Thanks,

Sébastien.



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