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Message-ID: <20230622152420-mutt-send-email-mst@kernel.org>
Date: Thu, 22 Jun 2023 15:29:31 -0400
From: "Michael S. Tsirkin" <mst@...hat.com>
To: Xuan Zhuo <xuanzhuo@...ux.alibaba.com>
Cc: virtualization@...ts.linux-foundation.org,
Jason Wang <jasowang@...hat.com>,
"David S. Miller" <davem@...emloft.net>,
Eric Dumazet <edumazet@...gle.com>,
Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>,
Alexei Starovoitov <ast@...nel.org>,
Daniel Borkmann <daniel@...earbox.net>,
Jesper Dangaard Brouer <hawk@...nel.org>,
John Fastabend <john.fastabend@...il.com>, netdev@...r.kernel.org,
bpf@...r.kernel.org
Subject: Re: [PATCH vhost v10 07/10] virtio_ring: introduce helpers for
premapped
On Fri, Jun 02, 2023 at 05:22:03PM +0800, Xuan Zhuo wrote:
> This patch introduces three helpers for premapped mode.
>
> * virtqueue_get_buf_premapped
> * virtqueue_detach_unused_buf_premapped
>
> The above helpers work like the non-premapped funcs. But a cursor is
> passed.
>
> virtqueue_detach is used to get the dma info of the last buf by
> cursor.
>
> Signed-off-by: Xuan Zhuo <xuanzhuo@...ux.alibaba.com>
> ---
> drivers/virtio/virtio_ring.c | 83 ++++++++++++++++++++++++++++++++++++
> include/linux/virtio.h | 10 +++++
> 2 files changed, 93 insertions(+)
>
> diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c
> index cbc22daae7e1..6771b9661798 100644
> --- a/drivers/virtio/virtio_ring.c
> +++ b/drivers/virtio/virtio_ring.c
> @@ -2555,6 +2555,66 @@ void *virtqueue_get_buf(struct virtqueue *_vq, unsigned int *len)
> return virtqueue_get_buf_ctx(_vq, len, NULL);
> }
> EXPORT_SYMBOL_GPL(virtqueue_get_buf);
> +
> +/**
> + * virtqueue_get_buf_premapped - get the next used buffer
> + * @_vq: the struct virtqueue we're talking about.
> + * @len: the length written into the buffer
> + * @ctx: extra context for the token
> + * @cursor: detach cursor
> + *
> + * If the device wrote data into the buffer, @len will be set to the
> + * amount written. This means you don't need to clear the buffer
> + * beforehand to ensure there's no data leakage in the case of short
> + * writes.
> + *
> + * Caller must ensure we don't call this with other virtqueue
> + * operations at the same time (except where noted).
> + *
> + * This is used for the premapped vq. The cursor is passed by the dirver, that
> + * is used for virtqueue_detach. That will be initialized by virtio core
> + * internally.
initialized how?
> + *
> + * Returns NULL if there are no used buffers, or the "data" token
> + * handed to virtqueue_add_*().
> + */
> +void *virtqueue_get_buf_premapped(struct virtqueue *_vq, unsigned int *len,
> + void **ctx,
> + struct virtqueue_detach_cursor *cursor)
> +{
> + struct vring_virtqueue *vq = to_vvq(_vq);
> +
> + return vq->packed_ring ? virtqueue_get_buf_ctx_packed(_vq, len, ctx, cursor) :
> + virtqueue_get_buf_ctx_split(_vq, len, ctx, cursor);
> +}
> +EXPORT_SYMBOL_GPL(virtqueue_get_buf_premapped);
> +
> +/**
> + * virtqueue_detach - get the dma info of last buf
> + * @_vq: the struct virtqueue we're talking about.
> + * @cursor: detach cursor
> + * @addr: the dma address
> + * @len: the length of the dma address
> + * @dir: the direction of the dma address
> + *
> + * This is used for the premapped vq. The cursor is initialized by
> + * virtqueue_get_buf_premapped or virtqueue_detach_unused_buf_premapped.
> + *
> + * Returns:
> + * -EAGAIN: there are more dma info, this function should be called more.
dma info is singular, so "there is".
I see you kept this idea of returning -EAGAIN on success.
Pls don't.
> + * -EINVAL: the process is done, should not call this function
here you really mean "a previous call returned 0"
we generally don't do defensive programming why do it here?
> + * 0: no more dma info
"no more" normally means "nothing was returned", not
"value returned and this was the last entry".
> + */
> +int virtqueue_detach(struct virtqueue *_vq, struct virtqueue_detach_cursor *cursor,
> + dma_addr_t *addr, u32 *len, enum dma_data_direction *dir)
> +{
> + struct vring_virtqueue *vq = to_vvq(_vq);
> +
> + return vq->packed_ring ? virtqueue_detach_packed(_vq, cursor, addr, len, dir) :
> + virtqueue_detach_split(_vq, cursor, addr, len, dir);
> +}
> +EXPORT_SYMBOL_GPL(virtqueue_detach);
> +
> /**
> * virtqueue_disable_cb - disable callbacks
> * @_vq: the struct virtqueue we're talking about.
> @@ -2682,6 +2742,29 @@ void *virtqueue_detach_unused_buf(struct virtqueue *_vq)
> }
> EXPORT_SYMBOL_GPL(virtqueue_detach_unused_buf);
>
> +/**
> + * virtqueue_detach_unused_buf_premapped - detach first unused buffer
> + * @_vq: the struct virtqueue we're talking about.
> + * @cursor: detach cursor
> + *
> + * This is used for the premapped vq. The cursor is passed by the dirver, that
> + * is used for virtqueue_detach. That will be initialized by virtio core
> + * internally.
> + *
> + * Returns NULL or the "data" token handed to virtqueue_add_*().
> + * This is not valid on an active queue; it is useful for device
> + * shutdown or the reset queue.
> + */
> +void *virtqueue_detach_unused_buf_premapped(struct virtqueue *_vq,
> + struct virtqueue_detach_cursor *cursor)
> +{
> + struct vring_virtqueue *vq = to_vvq(_vq);
> +
> + return vq->packed_ring ? virtqueue_detach_unused_buf_packed(_vq, cursor) :
> + virtqueue_detach_unused_buf_split(_vq, cursor);
> +}
> +EXPORT_SYMBOL_GPL(virtqueue_detach_unused_buf_premapped);
> +
> static inline bool more_used(const struct vring_virtqueue *vq)
> {
> return vq->packed_ring ? more_used_packed(vq) : more_used_split(vq);
> diff --git a/include/linux/virtio.h b/include/linux/virtio.h
> index 7f137c7a9034..0a11c5b32fe5 100644
> --- a/include/linux/virtio.h
> +++ b/include/linux/virtio.h
> @@ -3,6 +3,7 @@
> #define _LINUX_VIRTIO_H
> /* Everything a virtio driver needs to work with any particular virtio
> * implementation. */
> +#include <linux/dma-mapping.h>
> #include <linux/types.h>
> #include <linux/scatterlist.h>
> #include <linux/spinlock.h>
> @@ -88,6 +89,10 @@ void *virtqueue_get_buf(struct virtqueue *vq, unsigned int *len);
> void *virtqueue_get_buf_ctx(struct virtqueue *vq, unsigned int *len,
> void **ctx);
>
> +void *virtqueue_get_buf_premapped(struct virtqueue *_vq, unsigned int *len,
> + void **ctx,
> + struct virtqueue_detach_cursor *cursor);
> +
> void virtqueue_disable_cb(struct virtqueue *vq);
>
> bool virtqueue_enable_cb(struct virtqueue *vq);
> @@ -101,6 +106,8 @@ bool virtqueue_poll(struct virtqueue *vq, unsigned);
> bool virtqueue_enable_cb_delayed(struct virtqueue *vq);
>
> void *virtqueue_detach_unused_buf(struct virtqueue *vq);
> +void *virtqueue_detach_unused_buf_premapped(struct virtqueue *_vq,
> + struct virtqueue_detach_cursor *cursor);
>
> unsigned int virtqueue_get_vring_size(const struct virtqueue *vq);
>
> @@ -114,6 +121,9 @@ dma_addr_t virtqueue_get_used_addr(const struct virtqueue *vq);
> int virtqueue_resize(struct virtqueue *vq, u32 num,
> void (*recycle)(struct virtqueue *vq, void *buf));
>
> +int virtqueue_detach(struct virtqueue *_vq, struct virtqueue_detach_cursor *cursor,
> + dma_addr_t *addr, u32 *len, enum dma_data_direction *dir);
> +
> /**
> * struct virtio_device - representation of a device using virtio
> * @index: unique position on the virtio bus
> --
> 2.32.0.3.g01195cf9f
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