On Mon, 5 Jun 2023 01:38:48 -0400, "Michael S. Tsirkin" [off-list ref] wrote:

On Mon, Jun 05, 2023 at 10:06:51AM +0800, Xuan Zhuo wrote:

quoted

On Sun, 4 Jun 2023 09:45:14 -0400, "Michael S. Tsirkin" [off-list ref] wrote:

quoted

On Fri, Jun 02, 2023 at 05:22:03PM +0800, Xuan Zhuo wrote:

quoted

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.

This isn't very clear from the description but virtqueue_detach is
also introduced by this patch as opposed to being used.

quoted

Signed-off-by: Xuan Zhuo <xuanzhuo@linux.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.
+ *
+ * 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

detach what from what then?
I am guessing this is not the only thing this function does?
sounds like a bad name for a function.

Let me think of a good name

quoted

quoted

+ * @_vq: the struct virtqueue we're talking about.
+ * @cursor: detach cursor
+ * @addr: the dma address

what address?  it's the 1st time you mention an address ...

Will fix.

quoted

quoted

+ * @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.

here too, pls don't return -EAGAIN not in an error case.
something like "1" will do.

While I agree with you, -EAGAIN seems to be a commonly used method.

Where is it used like this? A typical use is e.g. in read(2):

      EAGAIN The file descriptor fd refers to a file other than a socket and has been marked nonblocking (O_NONBLOCK), and  the  read
              would block.  See open(2) for further details on the O_NONBLOCK flag.

a better analog here is read filling up all its buffer, in which
case it returns the # of bytes returned.

Rethink about this, I confused some scenarios. I should return a value to
indicate there is more data. "1" might be a good choice

Will fix.

Thanks.

quoted

How about we
return EAGAIN instead of -EAGAIN ?

Thanks.

quoted

quoted

+ * -EINVAL: the process is done, should not call this function
+ * 0: no more dma info
+ */
+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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