[dpdk-dev] [PATCH v6 00/11] bus: attach / detach API

Gaetan Rivet gaetan.rivet at 6wind.com
Tue Jun 27 18:11:07 CEST 2017

Following the work from Jan:

This patchset introduces the attach / detach API to rte_bus.
The rte_device structure is used as the generic device representation.

This API is implemented for the virtual bus.
The functions rte_eal_dev_attach and rte_eal_dev_detach are updated to
use this new interface.

-- v2

0. API rework

I would like to propose an evolution on the API developed by Jan.

The attach / detach rte_bus API is necessary to support the attach/detach
rte_dev API. Those are two different levels for one similar functionality.

Attach / detach does not allow true hotplugging, because the attach
function expects the devices operated upon to already exist within the
buses / sub-layers. This means that this API expects devices meta-datas
(bus-internal device representation and associated device information
read from the system) to be present upon attach. This part of the work
is done during scanning.

While it is best to avoid changing the public rte_dev API as it already
exists, nothing prevents this new rte_bus API from superseeding it.
It has been said during the previous release cycle that device hotplug
was a feature that interested users. True hotplug is not allowed by the
current attach / detach API. Worse, this API hinders the effort to bring
this new functionality by squatting its semantic field.

Thus, I propose to rename rte_bus attach / detach; plug / unplug. As it
is a superset of the attach / detach functionality, it can be used to
implement rte_dev attach / detach. Now is the right time to pivot to
this new feature.

This should help maintainers understanding the aim of this API and the
differences with the APIs higher-up, clarify the field and allow a new
functionality to be proposed.

The vdev bus is inherently supporting the new API, however it has been
made explicit. My implementation in the PCI bus in further patchset also
follows the rte_bus hotplug API instead of only attach / detach.

One remaining problem with the vdev bus is the rte_dev attach
implementation, which needs the rte_devargs rework to be properly fixed.

1. Additional evolutions in the patchset

The RTE_VERIFY on the find_device is too stringent I think and forces
all buses to implement a public device iterator. While it could be
argued that it would push for quicker support for the functionality, I
think it's possible that some buses are not interested at all in it and
should simply be ignored.

The bus devices iterator has been fixed.

The internal rte_device handle was not properly setup within the
net_ring PMD.

-- v3

The new API is now

typedef struct rte_device * (*rte_bus_plug_t)(struct rte_devargs *da);
typedef int (*rte_bus_unplug_t)(struct rte_device *dev);

So, plugging a device takes an rte_devargs as input and returns an rte_device.
While implementing related subsystems, I found that I usually needed
this rte_device handle upon a successful device plugging. This seems the
sensible and useful thing to do.
As such, on error NULL is returned and rte_errno is set by the bus.

Unplugging a device however now returns to the first version, which used
an rte_device. The explicit contract here is that if one has an
rte_device that has been obtained by calling bus->plug(), then this
handle can be used for bus->unplug().

Additionally, bus and device comparators now returns 0 on match,
following strcmp-like behavior.

-- v4

* rte_bus_find now takes a *start* parameter, that can be null.
  The bus search starts from this element if set.

* A few doc fixes.

* The rte_device field was fixed within the rte_ring PMD in a previous patch.
  This fix has been integrated by other means, it is not necessary anymore.

-- v5

* The commit
ethdev: use embedded rte_device to detach driver
  has been removed from this series to be sent separately.

* The PCI support for device access and hotplug is merged in this series
  instead of being proposed as a separate patchset.

* A few nitpicks to the code itself have been fixed.

* Some documentation has been reworked.

-- v6

* Fixed a bug in rte_eal_dev_attach with a wrong comparison callback used
  to find detached devices.

* Fixed coding style errors in PCI hotplug implementation.

* rte_bus find_device() method now takes a *start* parameter.

Gaetan Rivet (4):
  vdev: implement hotplug bus operation
  vdev: use standard bus registration function
  pci: implement find_device bus operation
  pci: implement hotplug bus operation

Jan Blunck (7):
  bus: add bus iterator to find a bus
  bus: add device iterator method
  bus: add helper to find which bus holds a device
  bus: add bus iterator to find a device
  bus: introduce hotplug functionality
  vdev: implement find_device bus operation
  dev: use new hotplug API in attach / detach

 lib/librte_eal/bsdapp/eal/rte_eal_version.map   |   3 +
 lib/librte_eal/common/eal_common_bus.c          |  64 ++++++++++++
 lib/librte_eal/common/eal_common_dev.c          |  92 ++++++++++++----
 lib/librte_eal/common/eal_common_pci.c          |  65 ++++++++++++
 lib/librte_eal/common/eal_common_vdev.c         |  73 ++++++++++---
 lib/librte_eal/common/include/rte_bus.h         | 133 ++++++++++++++++++++++++
 lib/librte_eal/common/include/rte_dev.h         |  21 ++++
 lib/librte_eal/common/include/rte_vdev.h        |   2 +
 lib/librte_eal/linuxapp/eal/rte_eal_version.map |   3 +
 9 files changed, 418 insertions(+), 38 deletions(-)


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