This small series enables virtio-net device type in VDUSE.
With it, basic operation have been tested, both with
virtio-vdpa and vhost-vdpa using DPDK Vhost library series
adding VDUSE support [0] using split rings layout.
Control queue support (and so multiqueue) has also been
tested, but require a Kernel series from Jason Wang
relaxing control queue polling [1] to function reliably.
Other than that, we have identified a few gaps:
1. Reconnection:
a. VDUSE_VQ_GET_INFO ioctl() returns always 0 for avail
index, even after the virtqueue has already been
processed. Is that expected? I have tried instead to
get the driver's avail index directly from the avail
ring, but it does not seem reliable as I sometimes get
"id %u is not a head!\n" warnings. Also such solution
would not be possible with packed ring, as we need to
know the wrap counters values.
b. Missing IOCTLs: it would be handy to have new IOCTLs to
query Virtio device status, and retrieve the config
space set at VDUSE_CREATE_DEV time.
2. VDUSE application as non-root:
We need to run the VDUSE application as non-root. There
is some race between the time the UDEV rule is applied
and the time the device starts being used. Discussing
with Jason, he suggested we may have a VDUSE daemon run
as root that would create the VDUSE device, manages its
rights and then pass its file descriptor to the VDUSE
app. However, with current IOCTLs, it means the VDUSE
daemon would need to know several information that
belongs to the VDUSE app implementing the device such
as supported Virtio features, config space, etc...
If we go that route, maybe we should have a control
IOCTL to create the device which would just pass the
device type. Then another device IOCTL to perform the
initialization. Would that make sense?
3. Coredump:
In order to be able to perform post-mortem analysis, DPDK
Vhost library marks pages used for vrings and descriptors
buffers as MADV_DODUMP using madvise(). However with
VDUSE it fails with -EINVAL. My understanding is that we
set VM_DONTEXPAND flag to the VMAs and madvise's
MADV_DODUMP fails if it is present. I'm not sure to
understand why madvise would prevent MADV_DODUMP if
VM_DONTEXPAND is set. Any thoughts?
[0]: https://patchwork.dpdk.org/project/dpdk/list/?series=27594&state=%2A&archive=both
[1]: https://lore.kernel.org/lkml/CACGkMEtgrxN3PPwsDo4oOsnsSLJfEmBEZ0WvjGRr3whU+QasUg@xxxxxxxxxxxxxx/T/
Maxime Coquelin (2):
vduse: validate block features only with block devices
vduse: enable Virtio-net device type
drivers/vdpa/vdpa_user/vduse_dev.c | 11 +++++++----
1 file changed, 7 insertions(+), 4 deletions(-)
--
2.39.2
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