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The recvmsg syscall can split a request in multiple packets unless we use the flag MSG_WAITALL to make sure the request will wait for the whole data to be transferred before returning. This flag is needed to prevent the vhost crate from returning the error PartialMessage, which occured sporadically when using virtio-fs, and which was detected as part of our continuous integration testing. Fixes #182 Signed-off-by: Sebastien Boeuf <sebastien.boeuf@intel.com> |
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vHost
A crate to support vhost backend drivers for virtio devices.
Kernel-based vHost Backend Drivers
The vhost drivers in Linux provide in-kernel virtio device emulation. Normally the hypervisor userspace process emulates I/O accesses from the guest. Vhost puts virtio emulation code into the kernel, taking hypervisor userspace out of the picture. This allows device emulation code to directly call into kernel subsystems instead of performing system calls from userspace. The hypervisor relies on ioctl based interfaces to control those in-kernel vhost drivers, such as vhost-net, vhost-scsi and vhost-vsock etc.
vHost-user Backend Drivers
The vhost-user protocol is aiming to implement vhost backend drivers in userspace, which complements the ioctl interface used to control the vhost implementation in the Linux kernel. It implements the control plane needed to establish virtqueue sharing with a user space process on the same host. It uses communication over a Unix domain socket to share file descriptors in the ancillary data of the message.
The protocol defines two sides of the communication, master and slave. Master is the application that shares its virtqueues, slave is the consumer of the virtqueues. Master and slave can be either a client (i.e. connecting) or server (listening) in the socket communication.