[dpdk-dev] [PATCH 00/28] vhost: add virtio-vhost-user transport
Ilya Maximets
i.maximets at samsung.com
Thu Jun 20 13:32:39 CEST 2019
On 19.06.2019 18:14, Nikos Dragazis wrote:
> Hi everyone,
Hi. I didn't look at the code, just a few comments inline.
>
> this patch series introduces the concept of the virtio-vhost-user
> transport. This is actually a revised version of an earlier RFC
> implementation that has been proposed by Stefan Hajnoczi [1]. Though
> this is a great feature, it seems to have been stalled, so I’d like to
> restart the conversation on this and hopefully get it merged with your
> help. Let me give you an overview.
>
> The virtio-vhost-user transport is a vhost-user transport implementation
> that is based on the virtio-vhost-user device. Its key difference with
> the existing transport is that it allows deploying vhost-user targets
> inside dedicated Storage Appliance VMs instead of host user space. In
> other words, it allows having guests that act as vhost-user backends for
> other guests.
>
> The virtio-vhost-user device implements the vhost-user control plane
> (master-slave communication) as follows:
>
> 1. it parses the vhost-user messages from the vhost-user unix domain
> socket and forwards them to the slave guest through virtqueues
>
> 2. it maps the vhost memory regions in QEMU’s process address space and
> exposes them to the slave guest as a RAM-backed PCI MMIO region
>
> 3. it hooks up doorbells to the callfds. The slave guest can use these
> doorbells to interrupt the master guest driver
>
> The device code has not yet been merged into upstream QEMU, but this is
> definitely the end goal. The current state is that we are awaiting for
> the approval of the virtio spec.
>
> I have Cced Darek from the SPDK community who has helped me a lot by
> reviewing this series. Note that any device type could be implemented
> over this new transport. So, adding the virtio-vhost-user transport in
> DPDK would allow using it from SPDK as well.
>
> Getting into the code internals, this patch series makes the following
> changes:
>
> 1. introduce a generic interface for the transport-specific operations.
> Each of the two available transports, the pre-existing AF_UNIX
> transport and the virtio-vhost-user transport, is going to implement
> this interface. The AF_UNIX-specific code has been extracted from the
> core vhost-user code and is now part of the AF_UNIX transport
> implementation in trans_af_unix.c.
>
> 2. introduce the virtio-vhost-user transport. The virtio-vhost-user
> transport requires a driver for the virtio-vhost-user devices. The
> driver along with the transport implementation have been packed into
> a separate library in `drivers/virtio_vhost_user/`. The necessary
> virtio-pci code has been copied from `drivers/net/virtio/`. Some
> additional changes have been made so that the driver can utilize the
> additional resources of the virtio-vhost-user device.
>
> 3. update librte_vhost public API to enable choosing transport for each
> new vhost device. Extend the vhost net driver and vhost-scsi example
> application to export this new API to the end user.
>
> The primary changes I did to Stefan’s RFC implementation are the
> following:
>
> 1. moved postcopy live migration code into trans_af_unix.c. Postcopy
> live migration relies on the userfault fd mechanism, which cannot be
> supported by virtio-vhost-user.
>
> 2. moved setup of the log memory region into trans_af_unix.c. Setting up
> the log memory region involves mapping/unmapping guest memory. This
> is an AF_UNIX transport-specific operation.
Logging dirty pages is the main concept of live migration support. Does it
mean that the live migration is not supported for virtio-vhost-user at all?
>
> 3. introduced a vhost transport operation for
> process_slave_message_reply()
>
> 4. moved the virtio-vhost-user transport/driver into a separate library
> in `drivers/virtio_vhost_user/`. This required making vhost.h and
> vhost_user.h part of librte_vhost public API and exporting some
> private symbols via the version script. This looks better to me that
> just moving the entire librte_vhost into `drivers/`. I am not sure if
> this is the most appropriate solution. I am looking forward to your
> suggestions on this.
Moving the virtio-vhost-user code to a separate driver looks strange for me.
What is the purpose?
Exporting a lot of vhost internal structures will lead to a frequent API/ABI
breakages and will slow down accepting changes to releases in general.
It looks inconsistent to have 'trans_af_unix.c' in 'lib/librte_vhost/' and
'trans_virtio_vhost_user.c' in 'drivers/virtio_vhost_user/' because these
files should be similar in provided functionality, hence, should be located
in similar places.
>
> 5. made use of the virtio PCI capabilities for the additional device
> resources (doorbells, shared memory). This required changes in
> virtio_pci.c and trans_virtio_vhost_user.c.
>
> 6. [minor] changed some commit headlines to comply with
> check-git-log.sh.
>
> Please, have a look and let me know about your thoughts. Any
> reviews/pointers/suggestions are welcome.
>
> Best regards,
> Nikos
>
> [1] http://mails.dpdk.org/archives/dev/2018-January/088155.html
>
>
> Nikos Dragazis (23):
> vhost: introduce vhost transport operations structure
> vhost: move socket management code
> vhost: move socket fd and un sockaddr
> vhost: move vhost-user connection
> vhost: move vhost-user reconnection
> vhost: move vhost-user fdset
> vhost: propagate vhost transport operations
> vhost: use a single structure for the device state
> vhost: extract socket I/O into transport
> vhost: move slave request fd and lock
> vhost: move mmap/munmap
> vhost: move setup of the log memory region
> vhost: remove main fd parameter from msg handlers
> vhost: move postcopy live migration code
> vhost: support registering additional vhost-user transports
> drivers/virtio_vhost_user: add virtio PCI framework
> drivers: add virtio-vhost-user transport
> drivers/virtio_vhost_user: use additional device resources
> vhost: add flag for choosing vhost-user transport
> net/vhost: add virtio-vhost-user support
> mk: link apps with virtio-vhost-user driver
> config: add option for the virtio-vhost-user transport
> usertools: add virtio-vhost-user devices to dpdk-devbind.py
>
> Stefan Hajnoczi (5):
> vhost: allocate per-socket transport state
> vhost: move start server/client calls
> vhost: add index field in vhost virtqueues
> examples/vhost_scsi: add --socket-file argument
> examples/vhost_scsi: add virtio-vhost-user support
>
> config/common_base | 6 +
> config/common_linux | 1 +
> drivers/Makefile | 5 +
> drivers/net/vhost/rte_eth_vhost.c | 13 +
> drivers/virtio_vhost_user/Makefile | 27 +
> .../rte_virtio_vhost_user_version.map | 4 +
> .../virtio_vhost_user/trans_virtio_vhost_user.c | 1077 +++++++++++++++++++
> drivers/virtio_vhost_user/virtio_pci.c | 520 ++++++++++
> drivers/virtio_vhost_user/virtio_pci.h | 289 ++++++
> drivers/virtio_vhost_user/virtio_vhost_user.h | 18 +
> drivers/virtio_vhost_user/virtqueue.h | 181 ++++
> examples/vhost_scsi/vhost_scsi.c | 103 +-
> lib/librte_vhost/Makefile | 4 +-
> lib/librte_vhost/rte_vhost.h | 1 +
> lib/librte_vhost/rte_vhost_version.map | 11 +
> lib/librte_vhost/socket.c | 685 +-----------
> lib/librte_vhost/trans_af_unix.c | 1094 ++++++++++++++++++++
> lib/librte_vhost/vhost.c | 22 +-
> lib/librte_vhost/vhost.h | 298 +++++-
> lib/librte_vhost/vhost_user.c | 474 ++-------
> lib/librte_vhost/vhost_user.h | 10 +-
> mk/rte.app.mk | 6 +
> usertools/dpdk-devbind.py | 7 +
> 23 files changed, 3764 insertions(+), 1092 deletions(-)
> create mode 100644 drivers/virtio_vhost_user/Makefile
> create mode 100644 drivers/virtio_vhost_user/rte_virtio_vhost_user_version.map
> create mode 100644 drivers/virtio_vhost_user/trans_virtio_vhost_user.c
> create mode 100644 drivers/virtio_vhost_user/virtio_pci.c
> create mode 100644 drivers/virtio_vhost_user/virtio_pci.h
> create mode 100644 drivers/virtio_vhost_user/virtio_vhost_user.h
> create mode 100644 drivers/virtio_vhost_user/virtqueue.h
> create mode 100644 lib/librte_vhost/trans_af_unix.c
>
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