Re: [Minios-devel] [UNIKRAFT PATCH v2 9/9] doc: add section about syscall shim layer

[Simon Kuenzer <simon.kuenzer@xxxxxxxxx>]

Reviewed-by: Simon Kuenzer <simon.kuenzer@xxxxxxxxx>

On 05.06.19 17:55, Yuri Volchkov wrote:
> Signed-off-by: Yuri Volchkov <yuri.volchkov@xxxxxxxxx>
> ---
>   doc/guides/developers-app.rst | 49 +++++++++++++++++++++++++++++++++++
>   1 file changed, 49 insertions(+)
>
> diff --git a/doc/guides/developers-app.rst b/doc/guides/developers-app.rst
> index bbd3bbda..fdde5dad 100644
> --- a/doc/guides/developers-app.rst
> +++ b/doc/guides/developers-app.rst
> @@ -323,6 +323,55 @@ An example context of extra.ld: ::
>   
>   This will add the section .uk_fs_list after the .text
>   
> +============================
> +Syscall shim layer
> +============================
> +
> +If you library provides a syscall, you need to inform Unikraft that it
> +can use your implementation. Add a line in you Makefile.uk: ::
> +
> +    UK_PROVIDED_SYSCALLS-$(CONFIG_LIBYOURLIBNAME) += 
> <syscall_name>-<number_of_arguments>
> +
> +Where `<number_of_arguments>` is how many arguments your syscall accepts.
> +
> +For example: ::
> +
> +    UK_PROVIDED_SYSCALLS-$(CONFIG_LIBVFSCORE) += writev-3
> +
> +.. note:: Please consult corresponding man page in order to keep API
> +           matching to the equivalent linux syscall
> +
> +For the implementation of you syscall use the following template:
> +
> +.. code-block:: c
> +
> +  UK_SYSCALL_DEFINE(syscall_name, arg1_type, arg1_name, arg2_type, arg2_name, 
> ..)
> +  {
> +       ret = do_cool_stuff();
> +       if (ret) {
> +               errno = ERROR_CODE;
> +               return -1;
> +       }
> +       return 0;
> +  }
> +
> +For example:
> +
> +.. code-block:: c
> +
> +  UK_SYSCALL_DEFINE(writev, unsigned long, fd, const struct iovec *, vec,
> +                 unsigned long, vlen)
> +  {
> +       return pwritev(fd, vec, vlen, -1);
> +  }
> +
> +Please note, that syscall_shim expects behavior as described in ``man 2
> +syscall``. Namely: ::
> +
> +  The return value is defined by the system call being invoked.  In
> +  general, a 0 return value indicates success.  A -1 return value
> +  indicates an error, and an error code is stored in errno.
> +
>   
>   ============================
>   Make Targets
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