surface-camera-build
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The second half of "the OS stores itself". The store was already the kernel's; what was missing was the kernel *saying* something of its own rather than a client doing it. At its first write of a boot the driver now appends one record describing the boot it is having — its own version banner, the wall-clock time, and the store device it resolved — to a reserved space, through the same append path every other mutation uses. Three things had to be decided, and each had a wrong answer that looked right: WHERE IT HOOKS. "At store init" does not exist and must not be invented: there is no init-time open, deliberately, so there is no ordering to get wrong against the block driver that provides the device. An __initcall appending a record would reintroduce exactly that ordering problem. The moment is the FIRST WRITE, which needs no ordering at all and is the semantically right one — the kernel records itself when it becomes the writer. A boot in which the kernel only reads writes no record, which is honest rather than a gap. WHICH SPACE. 0xFD was the first choice, following the convention that a reserved space is one repeated byte. 0xFD is the OS KEYSTORE — the space the kill switch exists to destroy — and writing boot records into it would have been a serious bug. Only the userspace name table catches this (format_space in crates/cube-command) because the kernel keeps no table of space names, so the table is now written down where the constant is: 0x00 root, 0xFF edges, 0xFE portal, 0xFD keystore, 0xFC boot. The record lives at (0,0,0) in 0xFC: one record, the current boot. WHAT IT SAYS. boot=<epoch seconds> device=<resolved path> kernel=<the version banner>, banner last and unquoted so everything after the final = is the kernel's own words rather than a field this code parsed. Raw epoch seconds rather than a date: rendering a calendar date in the kernel is date arithmetic, and a caller with a clock can do it without a kernel bug being the reason a timestamp is wrong. The banner comes from linux_banner and the time from ktime_get_real_ts64. WHY IT IS OFF BY DEFAULT. Not caution, but an invariant. The gates' method is that the store the kernel produces is comparable, byte for byte, with the store userspace produces from the same mutations; a record the kernel injects that the caller never asked for would turn those comparisons into non-comparisons. So it is cube_boot_record=1 on the kernel command line, parsed in C beside cube_store= for the reason that parameter is in C (this kernel's Rust cannot express a string parameter), and kernel/verify-boot-record.sh is the gate that turns it on. A failure to record is logged and never propagated: the record is worth having and is not a precondition for the caller's write. It is attempted once per boot rather than retried per write, because a store that will not take it will not take it later, and one warning is information where a stream of them is noise.
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 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 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