A summary of 2.6.15 API changes

The 2.6.15 kernel is out. The following is a summary of changes to the internal kernel API found in this release, with an emphasis on changes visible to driver writers. This information will be folded into the LWN 2.6 API changes page shortly.

• The nested class device patch was merged, allowing class_device structures to have other class_devices as parents. This patch is a hack to make the input subsystem work with sysfs. This code will change again in the future; see Greg Kroah-Hartman's article for more information on what is planned.

• The prototypes for the driver model class "interface" methods add() and remove() have changed; there is now a new parameter pointing to the relevant interface structure.

• A new platform_driver structure has been added to describe drivers for devices built into the core "platform."

• The prototypes for the suspend() and resume() methods in struct device_driver have changed. They are also only called once per event, rather than three times as in previous kernels.

• Two new fields have been added to the device_pm_info which control how drivers should act on hardware-created wakeup events; see this article for details.

• There is a notification mechanism which lets interested modules know when a USB device is added to (or removed from) the system. This system is used by some core code; drivers do not normally need to hook in to it.

• The gfp_t type is now used throughout the kernel. If you have a function which takes memory allocation flags, it should probably be using this type.

• Code using reader/writer semaphores can now use rwsem_is_locked() to test the (read) state of the semaphore without blocking.

• The new vmalloc_node() function allocates memory on a specific NUMA node.

• The "reserved" bit for memory pages has, for all practical purposes, been removed.

• vm_insert_page() has been added to make it easier for drivers to remap RAM into user space VMAs.

• There is a new kthread_stop_sem() function which can be used to stop a kernel thread which might be currently blocked on a specific semaphore.

• RapidIO bus support has been merged into the mainline.

• The netlink connector mechanism makes netlink code easier to write. Independently, a type-safe netlink interface has been added and is used in parts of the networking subsystem.

• These kernel symbols have been unexported and are no longer available to modules: clear_page_dirty_for_io, console_unblank, cpu_core_id hugetlb_total_pages, idle_cpu, nr_swap_pages, phys_proc_id, reprogram_timer, swapper_space, sysctl_overcommit_memory, sysctl_overcommit_ratio, sysctl_max_map_count, total_swap_pages, user_get_super, uts_sem, vm_acct_memory, and vm_committed_space.

• Version 1 of the Video4Linux API is now officially scheduled for removal in July, 2006.

• The owner field has been removed from the pci_driver structure.

• A number of SCSI subsystem typedefs (Scsi_Device, Scsi_Pointer, and Scsi_Host_Template) have been removed.

• The DMA32 memory zone has been added to the x86-64 architecture; its purpose is to make it easy to allocate memory below the 4GB barrier (with the new GFP_DMA32 flag).

• A call to rcu_barrier() will block the calling process until all current RCU callbacks have completed.

As can be seen from this list, the kernel API continues to evolve. The claims of certain well-known maintainers notwithstanding, it doesn't look like things will slow down much anytime soon.

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