Crate vmbus_user_channel

Support for a vmbus channel client via the /dev/uioX devices.

This mechanism works as follows. The uio_vmbus_client kernel driver can be configured to bind to devices of a given vmbus device ID by writing the device ID to to /sys/bus/vmbus/uio_vmbus_client/new_id. Then, for each vmbus channel with that device ID, the driver will create a device named /dev/uioX.

When this device is opened, the driver will allocate a ring buffer and open the corresponding vmbus channel. The channel can then be controlled in the following ways:

• Ring buffer memory can be accessed by using mmap to map the memory into user mode.

• The host can be signaled by using write to write an 4-byte non-zero value. This is the same mechanism as eventfd.

• The guest can wait for a signal by using read to read an 4-byte value. The file can be marked non-blocking, in which case the read will fail with EAGAIN if there is no signal. The guest can additionally use the kernel’s poll infrastructure to wait for a signal to be available by waiting for POLLIN readiness.

Currently there is no mechanism to discover that the channel has been revoked.

Structs

• Error
  An error connecting to the vmbus channel.
• MappedRingMem
  Ring buffer memory backed by a memory mapped channel.

Functions

• byte_pipe
  Opens a byte pipe for the channel with a file from open_uio_device.
• channel
  Opens a channel with a file from open_uio_device.
• message_pipe
  Opens a message pipe for the channel with a file from open_uio_device.
• open_uio_device
  Opens the UIO device for passing to channel.