Re: prop_*_internalize and copyin/out for syscall ?

[Manuel Bouyer <bouyer%antioche.eu.org@localhost>]

On Mon, Jan 17, 2011 at 08:06:00AM -0800, John Nemeth wrote:
> On Jun 9, 11:09am, Manuel Bouyer wrote:
> } 
> } so I'm evaluating how to use proplib for the new quotactl(2) I'm working on.
> } I see there is already provision of function to pass property list between
> } kernel and userland using ioctl, but there is no equivalent for syscalls.
> } Should there be ?
> 
>      The way that modload(8) does it is that it calls
> prop_dictionary_externalize() to put the dictionary in a string.  It
> then fills in a structure that contains amongst other things the length
> of the string and a pointer to it (see src/sbin/modload/main.c), and
> calls modctl(2).  In the kernel, modctl(2) allocates memory based on
> the size passed in, calls copyinstr() to get the string, and then calls
> prop_dictionary_internalize() (see src/sys/kern/sys_module.c).  Whether
> or not there should be dedicated functions to do this is another
> question.

this is exactly what prop_dictionary_externalize_to_pref(3) and
prop_dictionary_copyin(9) are doing; why not use functions from the
library ?

> 
> } For kernel land, prop_{array,dictionary}_copy{in,out} would do it
> } (prop_{array,dictionary}_copyout is documented but not implemented,
> } this is easy).
> } For userland, we probably need a prop_{array,dictionary}_recv_syscall(),
> } wich takes as parameter the pref we got from kernel, and internalize it.
> } Parameters would be the pref, and a pointer to the prop_array_t or
> } prop_dictionary_t that will get the result. What this would do in
> } addition to call prop_{array,dictionary}_internalize_from_pref() is
> } to unmap the buffer the kernel mmaped for us. I don't think this details of 
> the
> } kernel/userland communication should be exposed outside of the
> } proplib code.
> 
>      modctl(2) doesn't copyout any dictionaries.  Off the top of my head,
> I'm not aware of any precedence for that.

There are precedences, but using ioctl. sysmon is an example of this.
There is a set of functions in proplib to help for this, especially dealing
with mapping to userspace and copyout() the buffer of struct pref.
The userland counterpart deals with unmapping from the process's VA 
the buffer that the kernel has mapped.

I want the same for syscalls. We can't do a nice encapsulation as what's
done for ioctl because syscalls don't all have the same prototye,
but we can have functions to deal with the struct pref* used by
the syscall.

-- 
Manuel Bouyer <bouyer%antioche.eu.org@localhost>
     NetBSD: 26 ans d'experience feront toujours la difference
--