A summary of 2.6.19 API changes

The 2.6.19 kernel cycle has brought the usual pile of changes visible to kernel developers. Here is a quick summary of the most significant API modifications in 2.6.19.

• The prototype for interrupt handler functions has changed. In short, the regs argument has been removed, since almost nobody used it. Any interrupt handler which needs the pre-interrupt register state can use get_irq_regs() to obtain it.

• The latency tracking infrastructure patch has been merged.

• The readv() and writev() methods in the file_operations structure have been removed in favor of aio_readv() and aio_writev() (whose prototypes have been changed). See this article for more information.

• The no_pfn() address space operation has been added.

• SRCU - a version of read-copy-update which allows read-side blocking - has been merged. See this article by Paul McKenney for lots of details.

• The CHECKSUM_HW value has long been used in the networking subsystem to support hardware checksumming. That value has been replaced with CHECKSUM_PARTIAL (intended for outgoing packets where the job must be completed by the hardware) and CHECKSUM_COMPLETE (for incoming packets which have been completely checksummed by the hardware).

• A number of memory management changes have been merged, including tracking of dirty pages in shared memory mappings, making the DMA32 and HIGHMEM zones optional, and an architecture-independent mechanism for tracking memory ranges (and the holes between them).

• The pud_page() and pgd_page() macros now return a struct page pointer, rather than a kernel virtual address. Code needing the latter should use pud_page_vaddr() or pgd_page_vaddr() instead.

• A number of driver core changes including experimental parallel device probing and some improvements to the suspend/resume process.

• There is now a notifier chain for out-of-memory situations; the idea here is to set up functions which might be able to free some memory when things get very tight.

• The semantics of the kmap() API have been changed a bit: on architectures with complicated memory coherence issues, kmap() and kunmap() are expected to manage coherency for the mapped pages, thus eliminating the need to explicitly flush pages from cache.

• PCI Express Advanced Error Reporting is now supported in the PCI layer.

• A number of changes have been made to the inode structure in an effort to make it smaller.

• Much improved suspend and resume support for the USB layer.

• A new set of functions has been added to allow USB drivers to quickly check the direction and transfer mode of an endpoint.

• A somewhat reduced version of Wireless Extensions version 21. Most of the original functionality has been removed with the idea that the wireless extensions will soon be superseded by something else.

• Vast numbers of annotations enabling the sparse utility to detect big/little endian errors.

• The flags field of struct request has been split into two new fields: cmd_type and cmd_flags. The former contains a value describing the type of request (filesystem request, sense, power management, etc.) while the latter has the flags which modify the way the command works (read/write, barriers, etc.).

• The block layer can be disabled entirely at kernel configuration time; this option can be useful in some embedded situations.

• The kernel now has a generic boolean type, called bool; it replaces a number of homebrewed boolean types found in various parts of the kernel.

• There is a new function for allocating a copy of a block of memory:

      void *kmemdup(const void *src, size_t len, gfp_t gfp);
  

  A number of allocate-then-copy code sequences have been updated to use kmemdup() instead.

As always, API changes are tracked on the LWN 2.6 API changes page.

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typedef _Bool  bool;