The above code has an issue where in the non VM path it doesn't subtract from the len variable, this the code returns non zero, which causes the block based virtio wrappers to return an error.
Really, the function should return the total number of queued bytes and the wrapper should pass back non zero, but both the VM and non VM path need to be cleaned up and fixed.
https://github.com/littlekernel/lk/blob/5cbe21919bd4310fc13eb05816a8fed64f7079b9/dev/virtio/block/virtio-block.c#L237
The above code has an issue where in the non VM path it doesn't subtract from the len variable, this the code returns non zero, which causes the block based virtio wrappers to return an error.
Really, the function should return the total number of queued bytes and the wrapper should pass back non zero, but both the VM and non VM path need to be cleaned up and fixed.