Re: [PATCH RFC 0/1] Document how to add a new syscall

[Shuah Khan <shuahkh@osg.samsung.com>]

On 07/28/2015 10:02 AM, David Drysdale wrote:
> On Tue, Jul 28, 2015 at 3:19 PM, Peter Zijlstra <peterz@infradead.org> wrote:
>> On Tue, Jul 28, 2015 at 07:59:16AM -0600, Shuah Khan wrote:
>>> On 07/28/2015 05:41 AM, David Drysdale wrote:
>>>> Given that I've gotten some of the details wrong in the past (and I've
>>>> seen others do likewise), I thought it might be helpful to collate the
>>>> best practices for adding a new system call to the kernel.
>>>>
>>>> Apologies for the wide circulation -- I've tried to include folk who've
>>>> recently added or proposed a system call, as they're most likely to
>>>> have opinions on:
>>>>  - whether this a useful addition to Documentation/
>>>>  - whether the details of the advice are correct and complete.
>>>>
>>>> Shuah, is there anything more that should be added for the Testing
>>>> section in particular?
>>>>
>>>
>>> David,
>>>
>>> Looks good. You could add a one liner on in some cases, it might be
>>> necessary to install headers before test compiles. Other than that,
>>> the information looks good.
>>
>> For perf we still use the syscall() wrapper and we have hardcoded
>> (fallback) syscall numbers in there in case they've not yet reached
>> unistd.h.
>>
>> People update their kernels far more often than their userspace headers.
> 
> How about:
> 
> diff --git a/Documentation/adding-syscalls.txt
> b/Documentation/adding-syscalls.txt
> index 5f52edda8951..b274c3d01edb 100644
> --- a/Documentation/adding-syscalls.txt
> +++ b/Documentation/adding-syscalls.txt
> @@ -389,6 +389,11 @@ reviewers with a demonstration of how user space
> programs will use the system
>  call.  A good way to combine these aims is to include a simple self-test
>  program in a new directory under tools/testing/selftests/.
> 
> +For a new system call, there will obviously be no libc wrapper function and so
> +the test will need to invoke it using syscall(); also, if the system call
> +involves a new userspace-visible structure, the corresponding header will need
> +to be installed to compile the test.
> +

This looks good.

thanks,
-- Shuah


-- 
Shuah Khan
Sr. Linux Kernel Developer
Open Source Innovation Group
Samsung Research America (Silicon Valley)
shuahkh@osg.samsung.com | (970) 217-8978