Linux NVMe feature and and quirk policy¶
This file explains the policy used to decide what is supported by the Linux NVMe driver and what is not.
NVM Express is an open collection of standards and information.
The Linux NVMe host driver in drivers/nvme/host/ supports devices implementing the NVM Express (NVMe) family of specifications, which currently consists of a number of documents:
- the NVMe Base specification
- various Command Set specifications (e.g. NVM Command Set)
- various Transport specifications (e.g. PCIe, Fibre Channel, RDMA, TCP)
- the NVMe Management Interface specification
See https://nvmexpress.org/developers/ for the NVMe specifications.
NVMe is a large suite of specifications, and contains features that are only useful or suitable for specific use-cases. It is important to note that Linux does not aim to implement every feature in the specification. Every additional feature implemented introduces more code, more maintenance and potentially more bugs. Hence there is an inherent tradeoff between functionality and maintainability of the NVMe host driver.
Any feature implemented in the Linux NVMe host driver must support the following requirements:
- The feature is specified in a release version of an official NVMe specification, or in a ratified Technical Proposal (TP) that is available on NVMe website. Or if it is not directly related to the on-wire protocol, does not contradict any of the NVMe specifications.
- Does not conflict with the Linux architecture, nor the design of the NVMe host driver.
- Has a clear, indisputable value-proposition and a wide consensus across the community.
Vendor specific extensions are generally not supported in the NVMe host driver.
It is strongly recommended to work with the Linux NVMe and block layer maintainers and get feedback on specification changes that are intended to be used by the Linux NVMe host driver in order to avoid conflict at a later stage.
Sometimes implementations of open standards fail to correctly implement parts of the standards. Linux uses identifier-based quirks to work around such implementation bugs. The intent of quirks is to deal with widely available hardware, usually consumer, which Linux users can’t use without these quirks. Typically these implementations are not or only superficially tested with Linux by the hardware manufacturer.
The Linux NVMe maintainers decide ad hoc whether to quirk implementations based on the impact of the problem to Linux users and how it impacts maintainability of the driver. In general quirks are a last resort, if no firmware updates or other workarounds are available from the vendor.
Quirks will not be added to the Linux kernel for hardware that isn’t available on the mass market. Hardware that fails qualification for enterprise Linux distributions, ChromeOS, Android or other consumers of the Linux kernel should be fixed before it is shipped instead of relying on Linux quirks.