Documentation/backports/hacking/todo

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The Linux kernel backports TODO list.

Contents

make localmodconfig support

The Linux kernel has make localmodconfig support, random users shouldn't be expected to know what modules they need, so in order to allow users to get only the drivers they need built we'd need something similar to make localmodconfig. There are a few ways to do this. The best way would be to get upstream a mapping of a kernel object of a device to list its respective Kconfig. We'd also need a map of Kconfig changes over time as the kernel advances so that if a user is on an older system their old kobject Kconfig could be mapped to a new one. This should require changes upstream.

Other simpler solutions are to rely on 'lspci -k' output and map this to respective device drivers but this solution would be PCI bus specific. We should review how the upstream make localmodconfig currently works and improve upon that to enable support for it on backports.

Who's working on this?

No one.

Module namespaces

Module namespace can consist of either adding prefixes to existing symbols or modifying the Linux kernel module data structure so that upon request for a symbol it's own namespace can be inspected for its requested namespace. The Linux kernel backports project embraces prefixing backported versions of symbols by prefixing backported versions of symbols with backports_. A macro LINUX_BACKPORT() was added to help with this. For example:

 #define crc8 LINUX_BACKPORT(crc8)

Andi Kleen introduced the modular structure modification version of module namespaces back in 2007 but Rusty Russell nacked these patches. Because of this we're left with remapping modules to their own namespaces without modifying the in-kernel module structure. It may be possible to somehow provide module namespaces without requiring modifications to the in-kernel module structure, but such mechanisms would end up being hacks. We need to evaluate if we can figure a clever way to support this that is not so error prone or if we want to respinning Andi's patches with the intent to help support kernel backporting.

Original motivation for module namespaces

Here's a brain dump from Andi about the original motivation behind module namespaces:

The original intent was to provide a cleaner export symbol API.

There are roughly two classes of exported symbols:

- Generally usable, well designed, interfaces intended to be used by multiple modules (e.g. functions for drivers to register themselves or library functions)

- Special purpose exports that are only really for a single module, but are not intended as a general interface. These interfaces are usually not really clean and reusable.

The idea was to mark the later special purpose exports with the name of the module that is supposed to them. They wouldn't be available to everybody else and wouldn't become part of the general kernel module API.

Motivations

At times Linux distributions may choose, for whatever support-nightmare reasons, to support two versions of a subsystem module and have two separate device drivers use a different version of that subsystem. The reason this is ill-advised is we stand to gain by having development done on the upstream and latest versions of each subsystem and drivers; that backports framework allows you to get that. An example helps to clarify here. Suppose a distribution wants to ship with an old version of mac80211 and have the iwlwifi driver use it, but for ath9k they'd want to ship the newer version of mac80211 and new version of ath9k. This cannot be supported unless module namespaces are created.

Another more reasonable motivation is to avoid regressions with features / symbols being updated only for backported drivers. Non-backported drivers will use the non-backported version of the routine. This should avoid regressions with non-backported drivers using these routines.

Who's working on this?

No one.

DKMS support

Someone seems to want add support for DKMS. Who was that? What benefits does this bring? Isn't DKMS for proprietary modules? If so we don't want this support. We don't want proprietary drivers using the Linux kernel backports framework.

Who's working on this ?

No one

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