Re: [RFC PATCH 2/9] vringh: remove vringh_iov and unite to vringh_kiov

[Jason Wang]

On Tue, Dec 27, 2022 at 10:25 AM Shunsuke Mie <mie@xxxxxxxxxx> wrote:
>
> struct vringh_iov is defined to hold userland addresses. However, to use
> common function, __vring_iov, finally the vringh_iov converts to the
> vringh_kiov with simple cast. It includes compile time check code to make
> sure it can be cast correctly.
>
> To simplify the code, this patch removes the struct vringh_iov and unifies
> APIs to struct vringh_kiov.
>
> Signed-off-by: Shunsuke Mie <mie@xxxxxxxxxx>

While at this, I wonder if we need to go further, that is, switch to
using an iov iterator instead of a vringh customized one.

Thanks

> ---
>  drivers/vhost/vringh.c | 32 ++++++------------------------
>  include/linux/vringh.h | 45 ++++--------------------------------------
>  2 files changed, 10 insertions(+), 67 deletions(-)
>
> diff --git a/drivers/vhost/vringh.c b/drivers/vhost/vringh.c
> index 828c29306565..aa3cd27d2384 100644
> --- a/drivers/vhost/vringh.c
> +++ b/drivers/vhost/vringh.c
> @@ -691,8 +691,8 @@ EXPORT_SYMBOL(vringh_init_user);
>   * calling vringh_iov_cleanup() to release the memory, even on error!
>   */
>  int vringh_getdesc_user(struct vringh *vrh,
> -                       struct vringh_iov *riov,
> -                       struct vringh_iov *wiov,
> +                       struct vringh_kiov *riov,
> +                       struct vringh_kiov *wiov,
>                         bool (*getrange)(struct vringh *vrh,
>                                          u64 addr, struct vringh_range *r),
>                         u16 *head)
> @@ -708,26 +708,6 @@ int vringh_getdesc_user(struct vringh *vrh,
>         if (err == vrh->vring.num)
>                 return 0;
>
> -       /* We need the layouts to be the identical for this to work */
> -       BUILD_BUG_ON(sizeof(struct vringh_kiov) != sizeof(struct vringh_iov));
> -       BUILD_BUG_ON(offsetof(struct vringh_kiov, iov) !=
> -                    offsetof(struct vringh_iov, iov));
> -       BUILD_BUG_ON(offsetof(struct vringh_kiov, i) !=
> -                    offsetof(struct vringh_iov, i));
> -       BUILD_BUG_ON(offsetof(struct vringh_kiov, used) !=
> -                    offsetof(struct vringh_iov, used));
> -       BUILD_BUG_ON(offsetof(struct vringh_kiov, max_num) !=
> -                    offsetof(struct vringh_iov, max_num));
> -       BUILD_BUG_ON(sizeof(struct iovec) != sizeof(struct kvec));
> -       BUILD_BUG_ON(offsetof(struct iovec, iov_base) !=
> -                    offsetof(struct kvec, iov_base));
> -       BUILD_BUG_ON(offsetof(struct iovec, iov_len) !=
> -                    offsetof(struct kvec, iov_len));
> -       BUILD_BUG_ON(sizeof(((struct iovec *)NULL)->iov_base)
> -                    != sizeof(((struct kvec *)NULL)->iov_base));
> -       BUILD_BUG_ON(sizeof(((struct iovec *)NULL)->iov_len)
> -                    != sizeof(((struct kvec *)NULL)->iov_len));
> -
>         *head = err;
>         err = __vringh_iov(vrh, *head, (struct vringh_kiov *)riov,
>                            (struct vringh_kiov *)wiov,
> @@ -740,14 +720,14 @@ int vringh_getdesc_user(struct vringh *vrh,
>  EXPORT_SYMBOL(vringh_getdesc_user);
>
>  /**
> - * vringh_iov_pull_user - copy bytes from vring_iov.
> + * vringh_iov_pull_user - copy bytes from vring_kiov.
>   * @riov: the riov as passed to vringh_getdesc_user() (updated as we consume)
>   * @dst: the place to copy.
>   * @len: the maximum length to copy.
>   *
>   * Returns the bytes copied <= len or a negative errno.
>   */
> -ssize_t vringh_iov_pull_user(struct vringh_iov *riov, void *dst, size_t len)
> +ssize_t vringh_iov_pull_user(struct vringh_kiov *riov, void *dst, size_t len)
>  {
>         return vringh_iov_xfer(NULL, (struct vringh_kiov *)riov,
>                                dst, len, xfer_from_user);
> @@ -755,14 +735,14 @@ ssize_t vringh_iov_pull_user(struct vringh_iov *riov, void *dst, size_t len)
>  EXPORT_SYMBOL(vringh_iov_pull_user);
>
>  /**
> - * vringh_iov_push_user - copy bytes into vring_iov.
> + * vringh_iov_push_user - copy bytes into vring_kiov.
>   * @wiov: the wiov as passed to vringh_getdesc_user() (updated as we consume)
>   * @src: the place to copy from.
>   * @len: the maximum length to copy.
>   *
>   * Returns the bytes copied <= len or a negative errno.
>   */
> -ssize_t vringh_iov_push_user(struct vringh_iov *wiov,
> +ssize_t vringh_iov_push_user(struct vringh_kiov *wiov,
>                              const void *src, size_t len)
>  {
>         return vringh_iov_xfer(NULL, (struct vringh_kiov *)wiov,
> diff --git a/include/linux/vringh.h b/include/linux/vringh.h
> index 1991a02c6431..733d948e8123 100644
> --- a/include/linux/vringh.h
> +++ b/include/linux/vringh.h
> @@ -79,18 +79,6 @@ struct vringh_range {
>         u64 offset;
>  };
>
> -/**
> - * struct vringh_iov - iovec mangler.
> - *
> - * Mangles iovec in place, and restores it.
> - * Remaining data is iov + i, of used - i elements.
> - */
> -struct vringh_iov {
> -       struct iovec *iov;
> -       size_t consumed; /* Within iov[i] */
> -       unsigned i, used, max_num;
> -};
> -
>  /**
>   * struct vringh_kiov - kvec mangler.
>   *
> @@ -113,44 +101,19 @@ int vringh_init_user(struct vringh *vrh, u64 features,
>                      vring_avail_t __user *avail,
>                      vring_used_t __user *used);
>
> -static inline void vringh_iov_init(struct vringh_iov *iov,
> -                                  struct iovec *iovec, unsigned num)
> -{
> -       iov->used = iov->i = 0;
> -       iov->consumed = 0;
> -       iov->max_num = num;
> -       iov->iov = iovec;
> -}
> -
> -static inline void vringh_iov_reset(struct vringh_iov *iov)
> -{
> -       iov->iov[iov->i].iov_len += iov->consumed;
> -       iov->iov[iov->i].iov_base -= iov->consumed;
> -       iov->consumed = 0;
> -       iov->i = 0;
> -}
> -
> -static inline void vringh_iov_cleanup(struct vringh_iov *iov)
> -{
> -       if (iov->max_num & VRINGH_IOV_ALLOCATED)
> -               kfree(iov->iov);
> -       iov->max_num = iov->used = iov->i = iov->consumed = 0;
> -       iov->iov = NULL;
> -}
> -
>  /* Convert a descriptor into iovecs. */
>  int vringh_getdesc_user(struct vringh *vrh,
> -                       struct vringh_iov *riov,
> -                       struct vringh_iov *wiov,
> +                       struct vringh_kiov *riov,
> +                       struct vringh_kiov *wiov,
>                         bool (*getrange)(struct vringh *vrh,
>                                          u64 addr, struct vringh_range *r),
>                         u16 *head);
>
>  /* Copy bytes from readable vsg, consuming it (and incrementing wiov->i). */
> -ssize_t vringh_iov_pull_user(struct vringh_iov *riov, void *dst, size_t len);
> +ssize_t vringh_iov_pull_user(struct vringh_kiov *riov, void *dst, size_t len);
>
>  /* Copy bytes into writable vsg, consuming it (and incrementing wiov->i). */
> -ssize_t vringh_iov_push_user(struct vringh_iov *wiov,
> +ssize_t vringh_iov_push_user(struct vringh_kiov *wiov,
>                              const void *src, size_t len);
>
>  /* Mark a descriptor as used. */
> --
> 2.25.1
>