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From:   Shunsuke Mie <mie@igel.co.jp>
Date:   Tue, 27 Dec 2022 16:05:45 +0900
Message-ID: <CANXvt5rfXDYa0nLzKW5-Q-hjhw-19npXVneqBO1TcsariU6rWg@mail.gmail.com>
Subject: Re: [RFC PATCH 2/9] vringh: remove vringh_iov and unite to vringh_kiov
To:     Jason Wang <jasowang@redhat.com>
Cc:     "Michael S. Tsirkin" <mst@redhat.com>,
        Rusty Russell <rusty@rustcorp.com.au>, kvm@vger.kernel.org,
        virtualization@lists.linux-foundation.org, netdev@vger.kernel.org,
        linux-kernel@vger.kernel.org
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2022=E5=B9=B412=E6=9C=8827=E6=97=A5(=E7=81=AB) 15:04 Jason Wang <jasowang@r=
edhat.com>:
>
> On Tue, Dec 27, 2022 at 10:25 AM Shunsuke Mie <mie@igel.co.jp> wrote:
> >
> > struct vringh_iov is defined to hold userland addresses. However, to us=
e
> > common function, __vring_iov, finally the vringh_iov converts to the
> > vringh_kiov with simple cast. It includes compile time check code to ma=
ke
> > sure it can be cast correctly.
> >
> > To simplify the code, this patch removes the struct vringh_iov and unif=
ies
> > APIs to struct vringh_kiov.
> >
> > Signed-off-by: Shunsuke Mie <mie@igel.co.jp>
>
> 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.
I didn't see the iov iterator yet, thank you for informing me.
Is that iov_iter? https://lwn.net/Articles/625077/
> 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 =3D=3D vrh->vring.num)
> >                 return 0;
> >
> > -       /* We need the layouts to be the identical for this to work */
> > -       BUILD_BUG_ON(sizeof(struct vringh_kiov) !=3D sizeof(struct vrin=
gh_iov));
> > -       BUILD_BUG_ON(offsetof(struct vringh_kiov, iov) !=3D
> > -                    offsetof(struct vringh_iov, iov));
> > -       BUILD_BUG_ON(offsetof(struct vringh_kiov, i) !=3D
> > -                    offsetof(struct vringh_iov, i));
> > -       BUILD_BUG_ON(offsetof(struct vringh_kiov, used) !=3D
> > -                    offsetof(struct vringh_iov, used));
> > -       BUILD_BUG_ON(offsetof(struct vringh_kiov, max_num) !=3D
> > -                    offsetof(struct vringh_iov, max_num));
> > -       BUILD_BUG_ON(sizeof(struct iovec) !=3D sizeof(struct kvec));
> > -       BUILD_BUG_ON(offsetof(struct iovec, iov_base) !=3D
> > -                    offsetof(struct kvec, iov_base));
> > -       BUILD_BUG_ON(offsetof(struct iovec, iov_len) !=3D
> > -                    offsetof(struct kvec, iov_len));
> > -       BUILD_BUG_ON(sizeof(((struct iovec *)NULL)->iov_base)
> > -                    !=3D sizeof(((struct kvec *)NULL)->iov_base));
> > -       BUILD_BUG_ON(sizeof(((struct iovec *)NULL)->iov_len)
> > -                    !=3D sizeof(((struct kvec *)NULL)->iov_len));
> > -
> >         *head =3D err;
> >         err =3D __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 c=
onsume)
> >   * @dst: the place to copy.
> >   * @len: the maximum length to copy.
> >   *
> >   * Returns the bytes copied <=3D 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 *r=
iov, 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 c=
onsume)
> >   * @src: the place to copy from.
> >   * @len: the maximum length to copy.
> >   *
> >   * Returns the bytes copied <=3D 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 feat=
ures,
> >                      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 =3D iov->i =3D 0;
> > -       iov->consumed =3D 0;
> > -       iov->max_num =3D num;
> > -       iov->iov =3D iovec;
> > -}
> > -
> > -static inline void vringh_iov_reset(struct vringh_iov *iov)
> > -{
> > -       iov->iov[iov->i].iov_len +=3D iov->consumed;
> > -       iov->iov[iov->i].iov_base -=3D iov->consumed;
> > -       iov->consumed =3D 0;
> > -       iov->i =3D 0;
> > -}
> > -
> > -static inline void vringh_iov_cleanup(struct vringh_iov *iov)
> > -{
> > -       if (iov->max_num & VRINGH_IOV_ALLOCATED)
> > -               kfree(iov->iov);
> > -       iov->max_num =3D iov->used =3D iov->i =3D iov->consumed =3D 0;
> > -       iov->iov =3D 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
> >
>
Best,
Shunsuke