mirror of
https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git
synced 2024-08-23 17:30:02 +00:00
![Linus Torvalds](/assets/img/avatar_default.png)
* Eager page splitting optimization for dirty logging, optionally allowing for a VM to avoid the cost of hugepage splitting in the stage-2 fault path. * Arm FF-A proxy for pKVM, allowing a pKVM host to safely interact with services that live in the Secure world. pKVM intervenes on FF-A calls to guarantee the host doesn't misuse memory donated to the hyp or a pKVM guest. * Support for running the split hypervisor with VHE enabled, known as 'hVHE' mode. This is extremely useful for testing the split hypervisor on VHE-only systems, and paves the way for new use cases that depend on having two TTBRs available at EL2. * Generalized framework for configurable ID registers from userspace. KVM/arm64 currently prevents arbitrary CPU feature set configuration from userspace, but the intent is to relax this limitation and allow userspace to select a feature set consistent with the CPU. * Enable the use of Branch Target Identification (FEAT_BTI) in the hypervisor. * Use a separate set of pointer authentication keys for the hypervisor when running in protected mode, as the host is untrusted at runtime. * Ensure timer IRQs are consistently released in the init failure paths. * Avoid trapping CTR_EL0 on systems with Enhanced Virtualization Traps (FEAT_EVT), as it is a register commonly read from userspace. * Erratum workaround for the upcoming AmpereOne part, which has broken hardware A/D state management. RISC-V: * Redirect AMO load/store misaligned traps to KVM guest * Trap-n-emulate AIA in-kernel irqchip for KVM guest * Svnapot support for KVM Guest s390: * New uvdevice secret API * CMM selftest and fixes * fix racy access to target CPU for diag 9c x86: * Fix missing/incorrect #GP checks on ENCLS * Use standard mmu_notifier hooks for handling APIC access page * Drop now unnecessary TR/TSS load after VM-Exit on AMD * Print more descriptive information about the status of SEV and SEV-ES during module load * Add a test for splitting and reconstituting hugepages during and after dirty logging * Add support for CPU pinning in demand paging test * Add support for AMD PerfMonV2, with a variety of cleanups and minor fixes included along the way * Add a "nx_huge_pages=never" option to effectively avoid creating NX hugepage recovery threads (because nx_huge_pages=off can be toggled at runtime) * Move handling of PAT out of MTRR code and dedup SVM+VMX code * Fix output of PIC poll command emulation when there's an interrupt * Add a maintainer's handbook to document KVM x86 processes, preferred coding style, testing expectations, etc. * Misc cleanups, fixes and comments Generic: * Miscellaneous bugfixes and cleanups Selftests: * Generate dependency files so that partial rebuilds work as expected -----BEGIN PGP SIGNATURE----- iQFIBAABCAAyFiEE8TM4V0tmI4mGbHaCv/vSX3jHroMFAmSgHrIUHHBib256aW5p QHJlZGhhdC5jb20ACgkQv/vSX3jHroORcAf+KkBlXwQMf+Q0Hy6Mfe0OtkKmh0Ae 6HJ6dsuMfOHhWv5kgukh+qvuGUGzHq+gpVKmZg2yP3h3cLHOLUAYMCDm+rjXyjsk F4DbnJLfxq43Pe9PHRKFxxSecRcRYCNox0GD5UYL4PLKcH0FyfQrV+HVBK+GI8L3 FDzUcyJkR12Lcj1qf++7fsbzfOshL0AJPmidQCoc6wkLJpUEr/nYUqlI1Kx3YNuQ LKmxFHS4l4/O/px3GKNDrLWDbrVlwciGIa3GZLS52PZdW3mAqT+cqcPcYK6SW71P m1vE80VbNELX5q3YSRoOXtedoZ3Pk97LEmz/xQAsJ/jri0Z5Syk0Ok0m/Q== =AMXp -----END PGP SIGNATURE----- Merge tag 'for-linus' of git://git.kernel.org/pub/scm/virt/kvm/kvm Pull kvm updates from Paolo Bonzini: "ARM64: - Eager page splitting optimization for dirty logging, optionally allowing for a VM to avoid the cost of hugepage splitting in the stage-2 fault path. - Arm FF-A proxy for pKVM, allowing a pKVM host to safely interact with services that live in the Secure world. pKVM intervenes on FF-A calls to guarantee the host doesn't misuse memory donated to the hyp or a pKVM guest. - Support for running the split hypervisor with VHE enabled, known as 'hVHE' mode. This is extremely useful for testing the split hypervisor on VHE-only systems, and paves the way for new use cases that depend on having two TTBRs available at EL2. - Generalized framework for configurable ID registers from userspace. KVM/arm64 currently prevents arbitrary CPU feature set configuration from userspace, but the intent is to relax this limitation and allow userspace to select a feature set consistent with the CPU. - Enable the use of Branch Target Identification (FEAT_BTI) in the hypervisor. - Use a separate set of pointer authentication keys for the hypervisor when running in protected mode, as the host is untrusted at runtime. - Ensure timer IRQs are consistently released in the init failure paths. - Avoid trapping CTR_EL0 on systems with Enhanced Virtualization Traps (FEAT_EVT), as it is a register commonly read from userspace. - Erratum workaround for the upcoming AmpereOne part, which has broken hardware A/D state management. RISC-V: - Redirect AMO load/store misaligned traps to KVM guest - Trap-n-emulate AIA in-kernel irqchip for KVM guest - Svnapot support for KVM Guest s390: - New uvdevice secret API - CMM selftest and fixes - fix racy access to target CPU for diag 9c x86: - Fix missing/incorrect #GP checks on ENCLS - Use standard mmu_notifier hooks for handling APIC access page - Drop now unnecessary TR/TSS load after VM-Exit on AMD - Print more descriptive information about the status of SEV and SEV-ES during module load - Add a test for splitting and reconstituting hugepages during and after dirty logging - Add support for CPU pinning in demand paging test - Add support for AMD PerfMonV2, with a variety of cleanups and minor fixes included along the way - Add a "nx_huge_pages=never" option to effectively avoid creating NX hugepage recovery threads (because nx_huge_pages=off can be toggled at runtime) - Move handling of PAT out of MTRR code and dedup SVM+VMX code - Fix output of PIC poll command emulation when there's an interrupt - Add a maintainer's handbook to document KVM x86 processes, preferred coding style, testing expectations, etc. - Misc cleanups, fixes and comments Generic: - Miscellaneous bugfixes and cleanups Selftests: - Generate dependency files so that partial rebuilds work as expected" * tag 'for-linus' of git://git.kernel.org/pub/scm/virt/kvm/kvm: (153 commits) Documentation/process: Add a maintainer handbook for KVM x86 Documentation/process: Add a label for the tip tree handbook's coding style KVM: arm64: Fix misuse of KVM_ARM_VCPU_POWER_OFF bit index RISC-V: KVM: Remove unneeded semicolon RISC-V: KVM: Allow Svnapot extension for Guest/VM riscv: kvm: define vcpu_sbi_ext_pmu in header RISC-V: KVM: Expose IMSIC registers as attributes of AIA irqchip RISC-V: KVM: Add in-kernel virtualization of AIA IMSIC RISC-V: KVM: Expose APLIC registers as attributes of AIA irqchip RISC-V: KVM: Add in-kernel emulation of AIA APLIC RISC-V: KVM: Implement device interface for AIA irqchip RISC-V: KVM: Skeletal in-kernel AIA irqchip support RISC-V: KVM: Set kvm_riscv_aia_nr_hgei to zero RISC-V: KVM: Add APLIC related defines RISC-V: KVM: Add IMSIC related defines RISC-V: KVM: Implement guest external interrupt line management KVM: x86: Remove PRIx* definitions as they are solely for user space s390/uv: Update query for secret-UVCs s390/uv: replace scnprintf with sysfs_emit s390/uvdevice: Add 'Lock Secret Store' UVC ...
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.. SPDX-License-Identifier: GPL-2.0
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The tip tree handbook
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=====================
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What is the tip tree?
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---------------------
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The tip tree is a collection of several subsystems and areas of
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development. The tip tree is both a direct development tree and a
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aggregation tree for several sub-maintainer trees. The tip tree gitweb URL
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is: https://git.kernel.org/pub/scm/linux/kernel/git/tip/tip.git
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The tip tree contains the following subsystems:
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- **x86 architecture**
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The x86 architecture development takes place in the tip tree except
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for the x86 KVM and XEN specific parts which are maintained in the
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corresponding subsystems and routed directly to mainline from
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there. It's still good practice to Cc the x86 maintainers on
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x86-specific KVM and XEN patches.
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Some x86 subsystems have their own maintainers in addition to the
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overall x86 maintainers. Please Cc the overall x86 maintainers on
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patches touching files in arch/x86 even when they are not called out
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by the MAINTAINER file.
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Note, that ``x86@kernel.org`` is not a mailing list. It is merely a
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mail alias which distributes mails to the x86 top-level maintainer
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team. Please always Cc the Linux Kernel mailing list (LKML)
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``linux-kernel@vger.kernel.org``, otherwise your mail ends up only in
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the private inboxes of the maintainers.
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- **Scheduler**
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Scheduler development takes place in the -tip tree, in the
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sched/core branch - with occasional sub-topic trees for
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work-in-progress patch-sets.
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- **Locking and atomics**
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Locking development (including atomics and other synchronization
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primitives that are connected to locking) takes place in the -tip
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tree, in the locking/core branch - with occasional sub-topic trees
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for work-in-progress patch-sets.
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- **Generic interrupt subsystem and interrupt chip drivers**:
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- interrupt core development happens in the irq/core branch
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- interrupt chip driver development also happens in the irq/core
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branch, but the patches are usually applied in a separate maintainer
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tree and then aggregated into irq/core
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- **Time, timers, timekeeping, NOHZ and related chip drivers**:
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- timekeeping, clocksource core, NTP and alarmtimer development
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happens in the timers/core branch, but patches are usually applied in
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a separate maintainer tree and then aggregated into timers/core
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- clocksource/event driver development happens in the timers/core
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branch, but patches are mostly applied in a separate maintainer tree
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and then aggregated into timers/core
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- **Performance counters core, architecture support and tooling**:
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- perf core and architecture support development happens in the
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perf/core branch
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- perf tooling development happens in the perf tools maintainer
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tree and is aggregated into the tip tree.
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- **CPU hotplug core**
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- **RAS core**
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Mostly x86-specific RAS patches are collected in the tip ras/core
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branch.
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- **EFI core**
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EFI development in the efi git tree. The collected patches are
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aggregated in the tip efi/core branch.
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- **RCU**
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RCU development happens in the linux-rcu tree. The resulting changes
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are aggregated into the tip core/rcu branch.
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- **Various core code components**:
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- debugobjects
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- objtool
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- random bits and pieces
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Patch submission notes
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----------------------
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Selecting the tree/branch
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^^^^^^^^^^^^^^^^^^^^^^^^^
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In general, development against the head of the tip tree master branch is
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fine, but for the subsystems which are maintained separately, have their
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own git tree and are only aggregated into the tip tree, development should
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take place against the relevant subsystem tree or branch.
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Bug fixes which target mainline should always be applicable against the
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mainline kernel tree. Potential conflicts against changes which are already
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queued in the tip tree are handled by the maintainers.
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Patch subject
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^^^^^^^^^^^^^
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The tip tree preferred format for patch subject prefixes is
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'subsys/component:', e.g. 'x86/apic:', 'x86/mm/fault:', 'sched/fair:',
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'genirq/core:'. Please do not use file names or complete file paths as
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prefix. 'git log path/to/file' should give you a reasonable hint in most
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cases.
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The condensed patch description in the subject line should start with a
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uppercase letter and should be written in imperative tone.
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Changelog
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^^^^^^^^^
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The general rules about changelogs in the :ref:`Submitting patches guide
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<describe_changes>`, apply.
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The tip tree maintainers set value on following these rules, especially on
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the request to write changelogs in imperative mood and not impersonating
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code or the execution of it. This is not just a whim of the
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maintainers. Changelogs written in abstract words are more precise and
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tend to be less confusing than those written in the form of novels.
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It's also useful to structure the changelog into several paragraphs and not
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lump everything together into a single one. A good structure is to explain
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the context, the problem and the solution in separate paragraphs and this
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order.
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Examples for illustration:
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Example 1::
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x86/intel_rdt/mbm: Fix MBM overflow handler during hot cpu
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When a CPU is dying, we cancel the worker and schedule a new worker on a
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different CPU on the same domain. But if the timer is already about to
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expire (say 0.99s) then we essentially double the interval.
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We modify the hot cpu handling to cancel the delayed work on the dying
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cpu and run the worker immediately on a different cpu in same domain. We
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donot flush the worker because the MBM overflow worker reschedules the
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worker on same CPU and scans the domain->cpu_mask to get the domain
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pointer.
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Improved version::
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x86/intel_rdt/mbm: Fix MBM overflow handler during CPU hotplug
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When a CPU is dying, the overflow worker is canceled and rescheduled on a
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different CPU in the same domain. But if the timer is already about to
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expire this essentially doubles the interval which might result in a non
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detected overflow.
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Cancel the overflow worker and reschedule it immediately on a different CPU
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in the same domain. The work could be flushed as well, but that would
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reschedule it on the same CPU.
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Example 2::
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time: POSIX CPU timers: Ensure that variable is initialized
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If cpu_timer_sample_group returns -EINVAL, it will not have written into
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*sample. Checking for cpu_timer_sample_group's return value precludes the
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potential use of an uninitialized value of now in the following block.
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Given an invalid clock_idx, the previous code could otherwise overwrite
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*oldval in an undefined manner. This is now prevented. We also exploit
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short-circuiting of && to sample the timer only if the result will
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actually be used to update *oldval.
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Improved version::
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posix-cpu-timers: Make set_process_cpu_timer() more robust
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Because the return value of cpu_timer_sample_group() is not checked,
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compilers and static checkers can legitimately warn about a potential use
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of the uninitialized variable 'now'. This is not a runtime issue as all
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call sites hand in valid clock ids.
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Also cpu_timer_sample_group() is invoked unconditionally even when the
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result is not used because *oldval is NULL.
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Make the invocation conditional and check the return value.
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Example 3::
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The entity can also be used for other purposes.
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Let's rename it to be more generic.
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Improved version::
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The entity can also be used for other purposes.
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Rename it to be more generic.
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For complex scenarios, especially race conditions and memory ordering
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issues, it is valuable to depict the scenario with a table which shows
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the parallelism and the temporal order of events. Here is an example::
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CPU0 CPU1
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free_irq(X) interrupt X
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spin_lock(desc->lock)
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wake irq thread()
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spin_unlock(desc->lock)
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spin_lock(desc->lock)
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remove action()
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shutdown_irq()
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release_resources() thread_handler()
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spin_unlock(desc->lock) access released resources.
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^^^^^^^^^^^^^^^^^^^^^^^^^
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synchronize_irq()
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Lockdep provides similar useful output to depict a possible deadlock
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scenario::
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CPU0 CPU1
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rtmutex_lock(&rcu->rt_mutex)
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spin_lock(&rcu->rt_mutex.wait_lock)
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local_irq_disable()
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spin_lock(&timer->it_lock)
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spin_lock(&rcu->mutex.wait_lock)
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--> Interrupt
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spin_lock(&timer->it_lock)
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Function references in changelogs
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^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
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When a function is mentioned in the changelog, either the text body or the
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subject line, please use the format 'function_name()'. Omitting the
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brackets after the function name can be ambiguous::
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Subject: subsys/component: Make reservation_count static
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reservation_count is only used in reservation_stats. Make it static.
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The variant with brackets is more precise::
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Subject: subsys/component: Make reservation_count() static
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reservation_count() is only called from reservation_stats(). Make it
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static.
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Backtraces in changelogs
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^^^^^^^^^^^^^^^^^^^^^^^^
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See :ref:`backtraces`.
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Ordering of commit tags
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^^^^^^^^^^^^^^^^^^^^^^^
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To have a uniform view of the commit tags, the tip maintainers use the
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following tag ordering scheme:
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- Fixes: 12char-SHA1 ("sub/sys: Original subject line")
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A Fixes tag should be added even for changes which do not need to be
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backported to stable kernels, i.e. when addressing a recently introduced
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issue which only affects tip or the current head of mainline. These tags
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are helpful to identify the original commit and are much more valuable
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than prominently mentioning the commit which introduced a problem in the
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text of the changelog itself because they can be automatically
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extracted.
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The following example illustrates the difference::
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Commit
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abcdef012345678 ("x86/xxx: Replace foo with bar")
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left an unused instance of variable foo around. Remove it.
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Signed-off-by: J.Dev <j.dev@mail>
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Please say instead::
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The recent replacement of foo with bar left an unused instance of
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variable foo around. Remove it.
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Fixes: abcdef012345678 ("x86/xxx: Replace foo with bar")
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Signed-off-by: J.Dev <j.dev@mail>
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The latter puts the information about the patch into the focus and
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amends it with the reference to the commit which introduced the issue
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rather than putting the focus on the original commit in the first place.
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- Reported-by: ``Reporter <reporter@mail>``
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- Originally-by: ``Original author <original-author@mail>``
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- Suggested-by: ``Suggester <suggester@mail>``
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- Co-developed-by: ``Co-author <co-author@mail>``
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Signed-off: ``Co-author <co-author@mail>``
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Note, that Co-developed-by and Signed-off-by of the co-author(s) must
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come in pairs.
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- Signed-off-by: ``Author <author@mail>``
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The first Signed-off-by (SOB) after the last Co-developed-by/SOB pair is the
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author SOB, i.e. the person flagged as author by git.
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- Signed-off-by: ``Patch handler <handler@mail>``
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SOBs after the author SOB are from people handling and transporting
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the patch, but were not involved in development. SOB chains should
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reflect the **real** route a patch took as it was propagated to us,
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with the first SOB entry signalling primary authorship of a single
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author. Acks should be given as Acked-by lines and review approvals
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as Reviewed-by lines.
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If the handler made modifications to the patch or the changelog, then
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this should be mentioned **after** the changelog text and **above**
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all commit tags in the following format::
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... changelog text ends.
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[ handler: Replaced foo by bar and updated changelog ]
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First-tag: .....
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Note the two empty new lines which separate the changelog text and the
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commit tags from that notice.
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If a patch is sent to the mailing list by a handler then the author has
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to be noted in the first line of the changelog with::
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From: Author <author@mail>
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Changelog text starts here....
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so the authorship is preserved. The 'From:' line has to be followed
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by a empty newline. If that 'From:' line is missing, then the patch
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would be attributed to the person who sent (transported, handled) it.
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The 'From:' line is automatically removed when the patch is applied
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and does not show up in the final git changelog. It merely affects
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the authorship information of the resulting Git commit.
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- Tested-by: ``Tester <tester@mail>``
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- Reviewed-by: ``Reviewer <reviewer@mail>``
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- Acked-by: ``Acker <acker@mail>``
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- Cc: ``cc-ed-person <person@mail>``
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If the patch should be backported to stable, then please add a '``Cc:
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stable@vger.kernel.org``' tag, but do not Cc stable when sending your
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mail.
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- Link: ``https://link/to/information``
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For referring to an email on LKML or other kernel mailing lists,
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please use the lore.kernel.org redirector URL::
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https://lore.kernel.org/r/email-message@id
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The kernel.org redirector is considered a stable URL, unlike other email
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archives.
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Maintainers will add a Link tag referencing the email of the patch
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submission when they apply a patch to the tip tree. This tag is useful
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for later reference and is also used for commit notifications.
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Please do not use combined tags, e.g. ``Reported-and-tested-by``, as
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they just complicate automated extraction of tags.
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Links to documentation
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^^^^^^^^^^^^^^^^^^^^^^
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Providing links to documentation in the changelog is a great help to later
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debugging and analysis. Unfortunately, URLs often break very quickly
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because companies restructure their websites frequently. Non-'volatile'
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exceptions include the Intel SDM and the AMD APM.
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|
|
|
Therefore, for 'volatile' documents, please create an entry in the kernel
|
|
bugzilla https://bugzilla.kernel.org and attach a copy of these documents
|
|
to the bugzilla entry. Finally, provide the URL of the bugzilla entry in
|
|
the changelog.
|
|
|
|
Patch resend or reminders
|
|
^^^^^^^^^^^^^^^^^^^^^^^^^
|
|
|
|
See :ref:`resend_reminders`.
|
|
|
|
Merge window
|
|
^^^^^^^^^^^^
|
|
|
|
Please do not expect large patch series to be handled during the merge
|
|
window or even during the week before. Such patches should be submitted in
|
|
mergeable state *at* *least* a week before the merge window opens.
|
|
Exceptions are made for bug fixes and *sometimes* for small standalone
|
|
drivers for new hardware or minimally invasive patches for hardware
|
|
enablement.
|
|
|
|
During the merge window, the maintainers instead focus on following the
|
|
upstream changes, fixing merge window fallout, collecting bug fixes, and
|
|
allowing themselves a breath. Please respect that.
|
|
|
|
The release candidate -rc1 is the starting point for new patches to be
|
|
applied which are targeted for the next merge window.
|
|
|
|
So called _urgent_ branches will be merged into mainline during the
|
|
stabilization phase of each release.
|
|
|
|
|
|
Git
|
|
^^^
|
|
|
|
The tip maintainers accept git pull requests from maintainers who provide
|
|
subsystem changes for aggregation in the tip tree.
|
|
|
|
Pull requests for new patch submissions are usually not accepted and do not
|
|
replace proper patch submission to the mailing list. The main reason for
|
|
this is that the review workflow is email based.
|
|
|
|
If you submit a larger patch series it is helpful to provide a git branch
|
|
in a private repository which allows interested people to easily pull the
|
|
series for testing. The usual way to offer this is a git URL in the cover
|
|
letter of the patch series.
|
|
|
|
Testing
|
|
^^^^^^^
|
|
|
|
Code should be tested before submitting to the tip maintainers. Anything
|
|
other than minor changes should be built, booted and tested with
|
|
comprehensive (and heavyweight) kernel debugging options enabled.
|
|
|
|
These debugging options can be found in kernel/configs/x86_debug.config
|
|
and can be added to an existing kernel config by running:
|
|
|
|
make x86_debug.config
|
|
|
|
Some of these options are x86-specific and can be left out when testing
|
|
on other architectures.
|
|
|
|
.. _maintainer-tip-coding-style:
|
|
|
|
Coding style notes
|
|
------------------
|
|
|
|
Comment style
|
|
^^^^^^^^^^^^^
|
|
|
|
Sentences in comments start with an uppercase letter.
|
|
|
|
Single line comments::
|
|
|
|
/* This is a single line comment */
|
|
|
|
Multi-line comments::
|
|
|
|
/*
|
|
* This is a properly formatted
|
|
* multi-line comment.
|
|
*
|
|
* Larger multi-line comments should be split into paragraphs.
|
|
*/
|
|
|
|
No tail comments:
|
|
|
|
Please refrain from using tail comments. Tail comments disturb the
|
|
reading flow in almost all contexts, but especially in code::
|
|
|
|
if (somecondition_is_true) /* Don't put a comment here */
|
|
dostuff(); /* Neither here */
|
|
|
|
seed = MAGIC_CONSTANT; /* Nor here */
|
|
|
|
Use freestanding comments instead::
|
|
|
|
/* This condition is not obvious without a comment */
|
|
if (somecondition_is_true) {
|
|
/* This really needs to be documented */
|
|
dostuff();
|
|
}
|
|
|
|
/* This magic initialization needs a comment. Maybe not? */
|
|
seed = MAGIC_CONSTANT;
|
|
|
|
Comment the important things:
|
|
|
|
Comments should be added where the operation is not obvious. Documenting
|
|
the obvious is just a distraction::
|
|
|
|
/* Decrement refcount and check for zero */
|
|
if (refcount_dec_and_test(&p->refcnt)) {
|
|
do;
|
|
lots;
|
|
of;
|
|
magic;
|
|
things;
|
|
}
|
|
|
|
Instead, comments should explain the non-obvious details and document
|
|
constraints::
|
|
|
|
if (refcount_dec_and_test(&p->refcnt)) {
|
|
/*
|
|
* Really good explanation why the magic things below
|
|
* need to be done, ordering and locking constraints,
|
|
* etc..
|
|
*/
|
|
do;
|
|
lots;
|
|
of;
|
|
magic;
|
|
/* Needs to be the last operation because ... */
|
|
things;
|
|
}
|
|
|
|
Function documentation comments:
|
|
|
|
To document functions and their arguments please use kernel-doc format
|
|
and not free form comments::
|
|
|
|
/**
|
|
* magic_function - Do lots of magic stuff
|
|
* @magic: Pointer to the magic data to operate on
|
|
* @offset: Offset in the data array of @magic
|
|
*
|
|
* Deep explanation of mysterious things done with @magic along
|
|
* with documentation of the return values.
|
|
*
|
|
* Note, that the argument descriptors above are arranged
|
|
* in a tabular fashion.
|
|
*/
|
|
|
|
This applies especially to globally visible functions and inline
|
|
functions in public header files. It might be overkill to use kernel-doc
|
|
format for every (static) function which needs a tiny explanation. The
|
|
usage of descriptive function names often replaces these tiny comments.
|
|
Apply common sense as always.
|
|
|
|
|
|
Documenting locking requirements
|
|
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
|
|
Documenting locking requirements is a good thing, but comments are not
|
|
necessarily the best choice. Instead of writing::
|
|
|
|
/* Caller must hold foo->lock */
|
|
void func(struct foo *foo)
|
|
{
|
|
...
|
|
}
|
|
|
|
Please use::
|
|
|
|
void func(struct foo *foo)
|
|
{
|
|
lockdep_assert_held(&foo->lock);
|
|
...
|
|
}
|
|
|
|
In PROVE_LOCKING kernels, lockdep_assert_held() emits a warning
|
|
if the caller doesn't hold the lock. Comments can't do that.
|
|
|
|
Bracket rules
|
|
^^^^^^^^^^^^^
|
|
|
|
Brackets should be omitted only if the statement which follows 'if', 'for',
|
|
'while' etc. is truly a single line::
|
|
|
|
if (foo)
|
|
do_something();
|
|
|
|
The following is not considered to be a single line statement even
|
|
though C does not require brackets::
|
|
|
|
for (i = 0; i < end; i++)
|
|
if (foo[i])
|
|
do_something(foo[i]);
|
|
|
|
Adding brackets around the outer loop enhances the reading flow::
|
|
|
|
for (i = 0; i < end; i++) {
|
|
if (foo[i])
|
|
do_something(foo[i]);
|
|
}
|
|
|
|
|
|
Variable declarations
|
|
^^^^^^^^^^^^^^^^^^^^^
|
|
|
|
The preferred ordering of variable declarations at the beginning of a
|
|
function is reverse fir tree order::
|
|
|
|
struct long_struct_name *descriptive_name;
|
|
unsigned long foo, bar;
|
|
unsigned int tmp;
|
|
int ret;
|
|
|
|
The above is faster to parse than the reverse ordering::
|
|
|
|
int ret;
|
|
unsigned int tmp;
|
|
unsigned long foo, bar;
|
|
struct long_struct_name *descriptive_name;
|
|
|
|
And even more so than random ordering::
|
|
|
|
unsigned long foo, bar;
|
|
int ret;
|
|
struct long_struct_name *descriptive_name;
|
|
unsigned int tmp;
|
|
|
|
Also please try to aggregate variables of the same type into a single
|
|
line. There is no point in wasting screen space::
|
|
|
|
unsigned long a;
|
|
unsigned long b;
|
|
unsigned long c;
|
|
unsigned long d;
|
|
|
|
It's really sufficient to do::
|
|
|
|
unsigned long a, b, c, d;
|
|
|
|
Please also refrain from introducing line splits in variable declarations::
|
|
|
|
struct long_struct_name *descriptive_name = container_of(bar,
|
|
struct long_struct_name,
|
|
member);
|
|
struct foobar foo;
|
|
|
|
It's way better to move the initialization to a separate line after the
|
|
declarations::
|
|
|
|
struct long_struct_name *descriptive_name;
|
|
struct foobar foo;
|
|
|
|
descriptive_name = container_of(bar, struct long_struct_name, member);
|
|
|
|
|
|
Variable types
|
|
^^^^^^^^^^^^^^
|
|
|
|
Please use the proper u8, u16, u32, u64 types for variables which are meant
|
|
to describe hardware or are used as arguments for functions which access
|
|
hardware. These types are clearly defining the bit width and avoid
|
|
truncation, expansion and 32/64-bit confusion.
|
|
|
|
u64 is also recommended in code which would become ambiguous for 32-bit
|
|
kernels when 'unsigned long' would be used instead. While in such
|
|
situations 'unsigned long long' could be used as well, u64 is shorter
|
|
and also clearly shows that the operation is required to be 64 bits wide
|
|
independent of the target CPU.
|
|
|
|
Please use 'unsigned int' instead of 'unsigned'.
|
|
|
|
|
|
Constants
|
|
^^^^^^^^^
|
|
|
|
Please do not use literal (hexa)decimal numbers in code or initializers.
|
|
Either use proper defines which have descriptive names or consider using
|
|
an enum.
|
|
|
|
|
|
Struct declarations and initializers
|
|
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
|
|
|
|
Struct declarations should align the struct member names in a tabular
|
|
fashion::
|
|
|
|
struct bar_order {
|
|
unsigned int guest_id;
|
|
int ordered_item;
|
|
struct menu *menu;
|
|
};
|
|
|
|
Please avoid documenting struct members within the declaration, because
|
|
this often results in strangely formatted comments and the struct members
|
|
become obfuscated::
|
|
|
|
struct bar_order {
|
|
unsigned int guest_id; /* Unique guest id */
|
|
int ordered_item;
|
|
/* Pointer to a menu instance which contains all the drinks */
|
|
struct menu *menu;
|
|
};
|
|
|
|
Instead, please consider using the kernel-doc format in a comment preceding
|
|
the struct declaration, which is easier to read and has the added advantage
|
|
of including the information in the kernel documentation, for example, as
|
|
follows::
|
|
|
|
|
|
/**
|
|
* struct bar_order - Description of a bar order
|
|
* @guest_id: Unique guest id
|
|
* @ordered_item: The item number from the menu
|
|
* @menu: Pointer to the menu from which the item
|
|
* was ordered
|
|
*
|
|
* Supplementary information for using the struct.
|
|
*
|
|
* Note, that the struct member descriptors above are arranged
|
|
* in a tabular fashion.
|
|
*/
|
|
struct bar_order {
|
|
unsigned int guest_id;
|
|
int ordered_item;
|
|
struct menu *menu;
|
|
};
|
|
|
|
Static struct initializers must use C99 initializers and should also be
|
|
aligned in a tabular fashion::
|
|
|
|
static struct foo statfoo = {
|
|
.a = 0,
|
|
.plain_integer = CONSTANT_DEFINE_OR_ENUM,
|
|
.bar = &statbar,
|
|
};
|
|
|
|
Note that while C99 syntax allows the omission of the final comma,
|
|
we recommend the use of a comma on the last line because it makes
|
|
reordering and addition of new lines easier, and makes such future
|
|
patches slightly easier to read as well.
|
|
|
|
Line breaks
|
|
^^^^^^^^^^^
|
|
|
|
Restricting line length to 80 characters makes deeply indented code hard to
|
|
read. Consider breaking out code into helper functions to avoid excessive
|
|
line breaking.
|
|
|
|
The 80 character rule is not a strict rule, so please use common sense when
|
|
breaking lines. Especially format strings should never be broken up.
|
|
|
|
When splitting function declarations or function calls, then please align
|
|
the first argument in the second line with the first argument in the first
|
|
line::
|
|
|
|
static int long_function_name(struct foobar *barfoo, unsigned int id,
|
|
unsigned int offset)
|
|
{
|
|
|
|
if (!id) {
|
|
ret = longer_function_name(barfoo, DEFAULT_BARFOO_ID,
|
|
offset);
|
|
...
|
|
|
|
Namespaces
|
|
^^^^^^^^^^
|
|
|
|
Function/variable namespaces improve readability and allow easy
|
|
grepping. These namespaces are string prefixes for globally visible
|
|
function and variable names, including inlines. These prefixes should
|
|
combine the subsystem and the component name such as 'x86_comp\_',
|
|
'sched\_', 'irq\_', and 'mutex\_'.
|
|
|
|
This also includes static file scope functions that are immediately put
|
|
into globally visible driver templates - it's useful for those symbols
|
|
to carry a good prefix as well, for backtrace readability.
|
|
|
|
Namespace prefixes may be omitted for local static functions and
|
|
variables. Truly local functions, only called by other local functions,
|
|
can have shorter descriptive names - our primary concern is greppability
|
|
and backtrace readability.
|
|
|
|
Please note that 'xxx_vendor\_' and 'vendor_xxx_` prefixes are not
|
|
helpful for static functions in vendor-specific files. After all, it
|
|
is already clear that the code is vendor-specific. In addition, vendor
|
|
names should only be for truly vendor-specific functionality.
|
|
|
|
As always apply common sense and aim for consistency and readability.
|
|
|
|
|
|
Commit notifications
|
|
--------------------
|
|
|
|
The tip tree is monitored by a bot for new commits. The bot sends an email
|
|
for each new commit to a dedicated mailing list
|
|
(``linux-tip-commits@vger.kernel.org``) and Cc's all people who are
|
|
mentioned in one of the commit tags. It uses the email message ID from the
|
|
Link tag at the end of the tag list to set the In-Reply-To email header so
|
|
the message is properly threaded with the patch submission email.
|
|
|
|
The tip maintainers and submaintainers try to reply to the submitter
|
|
when merging a patch, but they sometimes forget or it does not fit the
|
|
workflow of the moment. While the bot message is purely mechanical, it
|
|
also implies a 'Thank you! Applied.'.
|