Re: [Minios-devel] [UNIKRAFT PATCH v2 1/5] lib/vfscore: introduce vfscore_uioforeach

[Florian Schmidt <Florian.Schmidt@xxxxxxxxx>]

Hi Yuri,


On 6/3/19 11:04 AM, Yuri Volchkov wrote:
> This is a template-type of function, to avoid code
> duplication. Compiler optimizes extra call to the function pointer
> passed as argument, so this should not have any performance impacts
>
> Signed-off-by: Yuri Volchkov <yuri.volchkov@xxxxxxxxx>
> ---
>   lib/vfscore/include/vfscore/uio.h | 39 +++++++++++++++++++++++++++++++
>   lib/vfscore/subr_uio.c            | 34 +++++++--------------------
>   2 files changed, 47 insertions(+), 26 deletions(-)
>
> diff --git a/lib/vfscore/include/vfscore/uio.h 
> b/lib/vfscore/include/vfscore/uio.h
> index c734fa19..f9885b94 100644
> --- a/lib/vfscore/include/vfscore/uio.h
> +++ b/lib/vfscore/include/vfscore/uio.h
> @@ -57,6 +57,45 @@ struct uio {
>         enum    uio_rw uio_rw;          /* operation */
>   };
>   
> +static inline
> +int vfscore_uioforeach(int (*f)(void *, void *, size_t *), void *cp,
> +                     size_t n, struct uio *uio)
Because this function is used several times to streamline code, and 
because I guess other people might want to use it in the future, I think 
this might benefit from a short comment explaining what the function 
does and how to use it for this purpose. Something like this:
/* This is a wrapper for functions f with a "memcpy-like" signature 
"dst, src,
 * cnt" to be executed over a scatter-gather list provided by a struct 
uio. f()
 * might be called multiple times to read from or write to cp up to n 
bytes of
 * data (or up to the capacity of the uio scatter-gather buffers).
 */

What do you think?

> +{
> +       int ret = 0;
> +
> +       UK_ASSERT(uio->uio_rw == UIO_READ || uio->uio_rw == UIO_WRITE);
> +
> +       while (n > 0 && uio->uio_resid) {
> +               struct iovec *iov = uio->uio_iov;
> +               size_t cnt = iov->iov_len;
> +
> +               if (cnt == 0) {
> +                       uio->uio_iov++;
> +                       uio->uio_iovcnt--;
> +                       continue;
> +               }
> +               if (cnt > n)
> +                       cnt = n;
> +
> +               if (uio->uio_rw == UIO_READ)
> +                       ret = f(iov->iov_base, cp, &cnt);
> +               else
> +                       ret = f(cp, iov->iov_base, &cnt);
> +
> +               iov->iov_base = (char *)iov->iov_base + cnt;
> +               iov->iov_len -= cnt;
> +               uio->uio_resid -= cnt;
> +               uio->uio_offset += cnt;
> +               cp = (char *)cp + cnt;
> +               n -= cnt;
> +
> +               if (ret)
> +                       break;
> +       }
> +
> +       return ret;
> +}
> +
>   int   vfscore_uiomove(void *cp, int n, struct uio *uio);
>   
>   #endif /* !_UIO_H_ */
> diff --git a/lib/vfscore/subr_uio.c b/lib/vfscore/subr_uio.c
> index aa176074..e6e1cdf0 100644
> --- a/lib/vfscore/subr_uio.c
> +++ b/lib/vfscore/subr_uio.c
> @@ -45,34 +45,16 @@
>   #include <string.h>
>   #include <vfscore/uio.h>
>   
> +static int __memcpy_wrapper(void *dst, void *src, size_t *cnt)
> +{
> +       memcpy(dst, src, *cnt);
> +       return 0;
> +}
> +
>   int
>   vfscore_uiomove(void *cp, int n, struct uio *uio)
>   {
> -       UK_ASSERT(uio->uio_rw == UIO_READ || uio->uio_rw == UIO_WRITE);
> +       int ret = vfscore_uioforeach(__memcpy_wrapper, cp, n, uio);
>   
> -	while (n > 0 && uio->uio_resid) {
> -               struct iovec *iov = uio->uio_iov;
> -               int cnt = iov->iov_len;
> -               if (cnt == 0) {
> -                       uio->uio_iov++;
> -                       uio->uio_iovcnt--;
> -                       continue;
> -               }
> -               if (cnt > n)
> -                       cnt = n;
> -
> -               if (uio->uio_rw == UIO_READ)
> -                       memcpy(iov->iov_base, cp, cnt);
> -               else
> -                       memcpy(cp, iov->iov_base, cnt);
> -
> -               iov->iov_base = (char *)iov->iov_base + cnt;
> -               iov->iov_len -= cnt;
> -               uio->uio_resid -= cnt;
> -               uio->uio_offset += cnt;
> -               cp = (char *)cp + cnt;
> -               n -= cnt;
> -       }
> -
> -       return 0;
> +       return ret;
>   }
--
Dr. Florian Schmidt
フローリアン・シュミット
Research Scientist,
Systems and Machine Learning Group
NEC Laboratories Europe
Kurfürsten-Anlage 36, D-69115 Heidelberg
Tel.     +49 (0)6221 4342-265
Fax:     +49 (0)6221 4342-155
e-mail:  florian.schmidt@xxxxxxxxx
============================================================
Registered at Amtsgericht Mannheim, Germany, HRB728558

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