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authorRusty Russell <rusty@rustcorp.com.au>2012-01-12 15:44:42 +1030
committerRusty Russell <rusty@rustcorp.com.au>2012-01-12 15:44:42 +1030
commit5dfc17628d57f9e62043ed0cba03a6e3eb019a78 (patch)
treea488dd3ea081166342904224db3cf039758f23d4 /drivers/virtio
parent1e214a5c1a7e901fc8e98ad6ef84f11005f9ee9d (diff)
downloadlinux-5dfc17628d57f9e62043ed0cba03a6e3eb019a78.tar.bz2
virtio: document functions better.
The old documentation is left over from when we used a structure with strategy pointers. And move the documentation to the C file as per kernel practice. Though I disagree... Signed-off-by: Rusty Russell <rusty@rustcorp.com.au> Reviewed-by: Christoph Hellwig <hch@lst.de>
Diffstat (limited to 'drivers/virtio')
-rw-r--r--drivers/virtio/virtio_ring.c92
1 files changed, 91 insertions, 1 deletions
diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c
index 50da92046092..fe50486341a4 100644
--- a/drivers/virtio/virtio_ring.c
+++ b/drivers/virtio/virtio_ring.c
@@ -166,6 +166,23 @@ static int vring_add_indirect(struct vring_virtqueue *vq,
return head;
}
+/**
+ * virtqueue_add_buf_gfp - expose buffer to other end
+ * @vq: the struct virtqueue we're talking about.
+ * @sg: the description of the buffer(s).
+ * @out_num: the number of sg readable by other side
+ * @in_num: the number of sg which are writable (after readable ones)
+ * @data: the token identifying the buffer.
+ * @gfp: how to do memory allocations (if necessary).
+ *
+ * Caller must ensure we don't call this with other virtqueue operations
+ * at the same time (except where noted).
+ *
+ * Returns remaining capacity of queue or a negative error
+ * (ie. ENOSPC). Note that it only really makes sense to treat all
+ * positive return values as "available": indirect buffers mean that
+ * we can put an entire sg[] array inside a single queue entry.
+ */
int virtqueue_add_buf_gfp(struct virtqueue *_vq,
struct scatterlist sg[],
unsigned int out,
@@ -244,6 +261,16 @@ add_head:
}
EXPORT_SYMBOL_GPL(virtqueue_add_buf_gfp);
+/**
+ * virtqueue_kick - update after add_buf
+ * @vq: the struct virtqueue
+ *
+ * After one or more virtqueue_add_buf_gfp calls, invoke this to kick
+ * the other side.
+ *
+ * Caller must ensure we don't call this with other virtqueue
+ * operations at the same time (except where noted).
+ */
void virtqueue_kick(struct virtqueue *_vq)
{
struct vring_virtqueue *vq = to_vvq(_vq);
@@ -300,6 +327,22 @@ static inline bool more_used(const struct vring_virtqueue *vq)
return vq->last_used_idx != vq->vring.used->idx;
}
+/**
+ * virtqueue_get_buf - get the next used buffer
+ * @vq: the struct virtqueue we're talking about.
+ * @len: the length written into the buffer
+ *
+ * If the driver 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).
+ *
+ * Returns NULL if there are no used buffers, or the "data" token
+ * handed to virtqueue_add_buf_gfp().
+ */
void *virtqueue_get_buf(struct virtqueue *_vq, unsigned int *len)
{
struct vring_virtqueue *vq = to_vvq(_vq);
@@ -351,6 +394,15 @@ void *virtqueue_get_buf(struct virtqueue *_vq, unsigned int *len)
}
EXPORT_SYMBOL_GPL(virtqueue_get_buf);
+/**
+ * virtqueue_disable_cb - disable callbacks
+ * @vq: the struct virtqueue we're talking about.
+ *
+ * Note that this is not necessarily synchronous, hence unreliable and only
+ * useful as an optimization.
+ *
+ * Unlike other operations, this need not be serialized.
+ */
void virtqueue_disable_cb(struct virtqueue *_vq)
{
struct vring_virtqueue *vq = to_vvq(_vq);
@@ -359,6 +411,17 @@ void virtqueue_disable_cb(struct virtqueue *_vq)
}
EXPORT_SYMBOL_GPL(virtqueue_disable_cb);
+/**
+ * virtqueue_enable_cb - restart callbacks after disable_cb.
+ * @vq: the struct virtqueue we're talking about.
+ *
+ * This re-enables callbacks; it returns "false" if there are pending
+ * buffers in the queue, to detect a possible race between the driver
+ * checking for more work, and enabling callbacks.
+ *
+ * Caller must ensure we don't call this with other virtqueue
+ * operations at the same time (except where noted).
+ */
bool virtqueue_enable_cb(struct virtqueue *_vq)
{
struct vring_virtqueue *vq = to_vvq(_vq);
@@ -383,6 +446,19 @@ bool virtqueue_enable_cb(struct virtqueue *_vq)
}
EXPORT_SYMBOL_GPL(virtqueue_enable_cb);
+/**
+ * virtqueue_enable_cb_delayed - restart callbacks after disable_cb.
+ * @vq: the struct virtqueue we're talking about.
+ *
+ * This re-enables callbacks but hints to the other side to delay
+ * interrupts until most of the available buffers have been processed;
+ * it returns "false" if there are many pending buffers in the queue,
+ * to detect a possible race between the driver checking for more work,
+ * and enabling callbacks.
+ *
+ * Caller must ensure we don't call this with other virtqueue
+ * operations at the same time (except where noted).
+ */
bool virtqueue_enable_cb_delayed(struct virtqueue *_vq)
{
struct vring_virtqueue *vq = to_vvq(_vq);
@@ -410,6 +486,14 @@ bool virtqueue_enable_cb_delayed(struct virtqueue *_vq)
}
EXPORT_SYMBOL_GPL(virtqueue_enable_cb_delayed);
+/**
+ * virtqueue_detach_unused_buf - detach first unused buffer
+ * @vq: the struct virtqueue we're talking about.
+ *
+ * Returns NULL or the "data" token handed to virtqueue_add_buf_gfp().
+ * This is not valid on an active queue; it is useful only for device
+ * shutdown.
+ */
void *virtqueue_detach_unused_buf(struct virtqueue *_vq)
{
struct vring_virtqueue *vq = to_vvq(_vq);
@@ -538,7 +622,13 @@ void vring_transport_features(struct virtio_device *vdev)
}
EXPORT_SYMBOL_GPL(vring_transport_features);
-/* return the size of the vring within the virtqueue */
+/**
+ * virtqueue_get_vring_size - return the size of the virtqueue's vring
+ * @vq: the struct virtqueue containing the vring of interest.
+ *
+ * Returns the size of the vring. This is mainly used for boasting to
+ * userspace. Unlike other operations, this need not be serialized.
+ */
unsigned int virtqueue_get_vring_size(struct virtqueue *_vq)
{