Struct VirtQueue

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pub struct VirtQueue<H: Hal, const SIZE: usize> { /* private fields */ }

Expand description

The mechanism for bulk data transport on virtio devices.

Each device can have zero or more virtqueues.

SIZE: The size of the queue. This is both the number of descriptors, and the number of slots in the available and used rings. It must be a power of 2 and fit in a u16.

Implementations§

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impl<H: Hal, const SIZE: usize> VirtQueue<H, SIZE>

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pub fn new<T: Transport>( transport: &mut T, idx: u16, indirect: bool, event_idx: bool, ) -> Result<Self>

Creates a new VirtQueue.

indirect: Whether to use indirect descriptors. This should be set if the VIRTIO_F_INDIRECT_DESC feature has been negotiated with the device.
event_idx: Whether to use the used_event and avail_event fields for notification suppression. This should be set if the VIRTIO_F_EVENT_IDX feature has been negotiated with the device.

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pub unsafe fn add<'a, 'b>( &mut self, inputs: &'a [&'b [u8]], outputs: &'a mut [&'b mut [u8]], ) -> Result<u16>

Add buffers to the virtqueue, return a token.

The buffers must not be empty.

Ref: linux virtio_ring.c virtqueue_add

§Safety

The input and output buffers must remain valid and not be accessed until a call to pop_used with the returned token succeeds.

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pub fn add_notify_wait_pop<'a>( &mut self, inputs: &'a [&'a [u8]], outputs: &'a mut [&'a mut [u8]], transport: &mut impl Transport, ) -> Result<u32>

Add the given buffers to the virtqueue, notifies the device, blocks until the device uses them, then pops them.

This assumes that the device isn’t processing any other buffers at the same time.

The buffers must not be empty.

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pub fn set_dev_notify(&mut self, enable: bool)

Advise the device whether used buffer notifications are needed.

See Virtio v1.1 2.6.7 Used Buffer Notification Suppression

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pub fn should_notify(&self) -> bool

Returns whether the driver should notify the device after adding a new buffer to the virtqueue.

This will be false if the device has suppressed notifications.

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pub fn can_pop(&self) -> bool

Returns whether there is a used element that can be popped.

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pub fn peek_used(&self) -> Option<u16>

Returns the descriptor index (a.k.a. token) of the next used element without popping it, or None if the used ring is empty.

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pub fn available_desc(&self) -> usize

Returns the number of free descriptors.

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pub unsafe fn pop_used<'a>( &mut self, token: u16, inputs: &'a [&'a [u8]], outputs: &'a mut [&'a mut [u8]], ) -> Result<u32>

If the given token is next on the device used queue, pops it and returns the total buffer length which was used (written) by the device.

Ref: linux virtio_ring.c virtqueue_get_buf_ctx

§Safety

The buffers in inputs and outputs must match the set of buffers originally added to the queue by add when it returned the token being passed in here.