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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>
Linux kernel ============ The Linux kernel is the core of any Linux operating system. It manages hardware, system resources, and provides the fundamental services for all other software. Quick Start ----------- * Report a bug: See Documentation/admin-guide/reporting-issues.rst * Get the latest kernel: https://kernel.org * Build the kernel: See Documentation/admin-guide/quickly-build-trimmed-linux.rst * Join the community: https://lore.kernel.org/ Essential Documentation ----------------------- All users should be familiar with: * Building requirements: Documentation/process/changes.rst * Code of Conduct: Documentation/process/code-of-conduct.rst * License: See COPYING Documentation can be built with make htmldocs or viewed online at: https://www.kernel.org/doc/html/latest/ Who Are You? ============ Find your role below: * New Kernel Developer - Getting started with kernel development * Academic Researcher - Studying kernel internals and architecture * Security Expert - Hardening and vulnerability analysis * Backport/Maintenance Engineer - Maintaining stable kernels * System Administrator - Configuring and troubleshooting * Maintainer - Leading subsystems and reviewing patches * Hardware Vendor - Writing drivers for new hardware * Distribution Maintainer - Packaging kernels for distros * AI Coding Assistant - LLMs and AI-powered development tools For Specific Users ================== New Kernel Developer -------------------- Welcome! Start your kernel development journey here: * Getting Started: Documentation/process/development-process.rst * Your First Patch: Documentation/process/submitting-patches.rst * Coding Style: Documentation/process/coding-style.rst * Build System: Documentation/kbuild/index.rst * Development Tools: Documentation/dev-tools/index.rst * Kernel Hacking Guide: Documentation/kernel-hacking/hacking.rst * Core APIs: Documentation/core-api/index.rst Academic Researcher ------------------- Explore the kernel's architecture and internals: * Researcher Guidelines: Documentation/process/researcher-guidelines.rst * Memory Management: Documentation/mm/index.rst * Scheduler: Documentation/scheduler/index.rst * Networking Stack: Documentation/networking/index.rst * Filesystems: Documentation/filesystems/index.rst * RCU (Read-Copy Update): Documentation/RCU/index.rst * Locking Primitives: Documentation/locking/index.rst * Power Management: Documentation/power/index.rst Security Expert --------------- Security documentation and hardening guides: * Security Documentation: Documentation/security/index.rst * LSM Development: Documentation/security/lsm-development.rst * Self Protection: Documentation/security/self-protection.rst * Reporting Vulnerabilities: Documentation/process/security-bugs.rst * CVE Procedures: Documentation/process/cve.rst * Embargoed Hardware Issues: Documentation/process/embargoed-hardware-issues.rst * Security Features: Documentation/userspace-api/seccomp_filter.rst Backport/Maintenance Engineer ----------------------------- Maintain and stabilize kernel versions: * Stable Kernel Rules: Documentation/process/stable-kernel-rules.rst * Backporting Guide: Documentation/process/backporting.rst * Applying Patches: Documentation/process/applying-patches.rst * Subsystem Profile: Documentation/maintainer/maintainer-entry-profile.rst * Git for Maintainers: Documentation/maintainer/configure-git.rst System Administrator -------------------- Configure, tune, and troubleshoot Linux systems: * Admin Guide: Documentation/admin-guide/index.rst * Kernel Parameters: Documentation/admin-guide/kernel-parameters.rst * Sysctl Tuning: Documentation/admin-guide/sysctl/index.rst * Tracing/Debugging: Documentation/trace/index.rst * Performance Security: Documentation/admin-guide/perf-security.rst * Hardware Monitoring: Documentation/hwmon/index.rst Maintainer ---------- Lead kernel subsystems and manage contributions: * Maintainer Handbook: Documentation/maintainer/index.rst * Pull Requests: Documentation/maintainer/pull-requests.rst * Managing Patches: Documentation/maintainer/modifying-patches.rst * Rebasing and Merging: Documentation/maintainer/rebasing-and-merging.rst * Development Process: Documentation/process/maintainer-handbooks.rst * Maintainer Entry Profile: Documentation/maintainer/maintainer-entry-profile.rst * Git Configuration: Documentation/maintainer/configure-git.rst Hardware Vendor --------------- Write drivers and support new hardware: * Driver API Guide: Documentation/driver-api/index.rst * Driver Model: Documentation/driver-api/driver-model/driver.rst * Device Drivers: Documentation/driver-api/infrastructure.rst * Bus Types: Documentation/driver-api/driver-model/bus.rst * Device Tree Bindings: Documentation/devicetree/bindings/ * Power Management: Documentation/driver-api/pm/index.rst * DMA API: Documentation/core-api/dma-api.rst Distribution Maintainer ----------------------- Package and distribute the kernel: * Stable Kernel Rules: Documentation/process/stable-kernel-rules.rst * ABI Documentation: Documentation/ABI/README * Kernel Configuration: Documentation/kbuild/kconfig.rst * Module Signing: Documentation/admin-guide/module-signing.rst * Kernel Parameters: Documentation/admin-guide/kernel-parameters.rst * Tainted Kernels: Documentation/admin-guide/tainted-kernels.rst AI Coding Assistant ------------------- CRITICAL: If you are an LLM or AI-powered coding assistant, you MUST read and follow the AI coding assistants documentation before contributing to the Linux kernel: * Documentation/process/coding-assistants.rst This documentation contains essential requirements about licensing, attribution, and the Developer Certificate of Origin that all AI tools must comply with. Communication and Support ========================= * Mailing Lists: https://lore.kernel.org/ * IRC: #kernelnewbies on irc.oftc.net * Bugzilla: https://bugzilla.kernel.org/ * MAINTAINERS file: Lists subsystem maintainers and mailing lists * Email Clients: Documentation/process/email-clients.rst
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