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Introduce USB4STREAM protocol and Linux implementation. This allows two
(or more) hosts to transfer data directly over Thunderbolt/USB4 cable
through a character device without need to go through the network stack.
Any application that supports read(2) and write(2) in some form should
be able to use the device without changes. The data is sent out to the
other side over a tunnel inside Thunderbolt/USB4 fabric. The character
device is called /dev/tbstreamX where X is the minor number starting
from 0.
All stream devices need to be configured first. This is done through
ConfigFS interface. There can be multiple streams at the same time (this
depends on number of DMA rings and available HopIDs) and a single stream
supports traffic in both directions. For example there could be an
application that uses one stream as control channel and another one as
bi-directional data channel.
A real use-case for this is to take a backup as a part of recovery
initramfs tooling (no need to setup networking or have ssh or similar
tooling as part of the initramfs). Say we want to backup the disk of
host1 to host2. First Thunderbolt/USB4 cable is connected between the
hosts (there can be devices in the middle too) then the receiving side
configures the stream:
host2 # mkdir /sys/kernel/config/thunderbolt/stream/0-1.0
host2 # mkdir /sys/kernel/config/thunderbolt/stream/0-1.0/backup
host2 # echo -1 > /sys/kernel/config/thunderbolt/stream/0-1.0/backup/in_hopid
host2 # echo -1 > /sys/kernel/config/thunderbolt/stream/0-1.0/backup/out_hopid
We use automatic HopID allocation (writing -1 to HopIDs) for simplicity.
From this point forward the /dev/tbstream0 can be used pretty much as
regular file:
host2 # dd if=/dev/tbstream0 of=/tmp/host1.nvme0n1.backup-$(date +%F) bs=256k
The host that is being backed up then configures the stream accordingly:
host1 # mkdir /sys/kernel/config/thunderbolt/stream/0-503.0
host1 # mkdir /sys/kernel/config/thunderbolt/stream/0-503.0/backup
Here we take advantage of the fact that host2 also announces the active
streams through XDomain properties so the name "backup" gives us the
HopIDs. It is also possible to configure them manually in the same way
we did for host2.
Then it is just a matter of copying the data over:
host1 # dd if=/dev/nvme0n1 of=/dev/tbstream0 bs=256k
Similarly it is possible to transfer parts of the filesystem. For
example copy contents of mydir over to the host2:
host2 # gunzip < /dev/tbstream0 | tar xf -
host1 # tar cf - mydir | gzip > /dev/tbstream0
Other end of the spectrum use-case is "borrowing" laptop (host1) camera
to desktop (host2):
host2 # gst-launch-1.0 filesrc location=/dev/tbstream0 ! jpegdec ! videoconvert ! \
autovideosink
host1 # gst-launch-1.0 v4l2src device=/dev/video0 ! video/x-raw,width=1920,height=1080 ! \
jpegenc quality=90 ! filesink location=/dev/tbstream0
Once the streams are no longer needed they can be removed:
host1 # cd /sys/kernel/config/thunderbolt/stream/
host1 # rmdir -p 0-503.0/backup
host2 # cd /sys/kernel/config/thunderbolt/stream
host2 # rmdir -p 0-1.0/backup
Co-developed-by: Alan Borzeszkowski <alan.borzeszkowski@linux.intel.com>
Signed-off-by: Alan Borzeszkowski <alan.borzeszkowski@linux.intel.com>
Signed-off-by: Mika Westerberg <mika.westerberg@linux.intel.com>
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