linux-2.6.22中API的一些变化

主要参考：


主要是昨天在搞Hacking Linux Network Stack的时候，发现里面的代码，不能够在2.6.22下编译通过，并且提示找不到nh这个成员，我猜想一定是结构体发生了变化。查看/include/linux/skbuff.h发现没有了原先的联合h，nh和mac，
    union {
        struct tcphdr    *th;
        struct udphdr    *uh;
        struct icmphdr    *icmph;
        struct igmphdr    *igmph;
        struct iphdr    *ipiph;
        struct ipv6hdr    *ipv6h;
        unsigned char    *raw;
    } h;

    union {
        struct iphdr    *iph;
        struct ipv6hdr    *ipv6h;
        struct arphdr    *arph;
        unsigned char    *raw;
    } nh;

    union {
          unsigned char     *raw;
    } mac;
换成了   
    sk_buff_data_t        transport_header;
    sk_buff_data_t        network_header;
    sk_buff_data_t        mac_header;

本身我并不是很支持联合的使用，即使它能够节省内存，但是实际运行时候还是有一定的时空开销的。
这一改变将会导致很多程序不能够在2.6.22下使用，比如VMWare；几乎所有的网卡驱动需要打patch。
感觉从2.6.18之后的变化比较大，看Kernel还是选择2.6.18比较合适。
另外，ktime替换掉了jiffies，这也算是网络部分改变比较大的一个地方了。

2.6.22 (July 8, 2007)

• The mac80211 (formerly "Devicescape") wireless stack has been merged, creating a whole new API for the creation of wireless drivers, especially those requiring software MAC support.

• The eth_type_trans() function now sets the skb->dev field, consistent with how similar functions for other link types operate. As a result, many Ethernet drivers have been changed to remove the (now) redundant assignment.

• The header fields in the sk_buff structure have been renamed and are no longer unions. Networking code and drivers can now just use skb->transport_header, skb->network_header, and skb->skb_mac_header. There are new functions for finding specific headers within packets: tcp_hdr(), udp_hdr(), ipip_hdr(), and ipipv6_hdr().

• Also in the networking area: the packet scheduler has been reworked to use ktime values rather than jiffies.

• The i2c layer has seen significant new changes meant to make i2c drivers look more like drivers for other buses. There are, for example, new probe() and remove() methods for notifying devices when i2c peripherals come and go. Since i2c is not a self-describing bus, the support code still needs help to know where i2c devices might be; for many classes of device, this information can be had from the system BIOS.

• The crypto API has a new set of functions for use with asynchronous block ciphers. There is also a new cryptd kernel thread which can run any synchronous cipher in an asynchronous mode.

• The subsystem structure has been removed from the Linux device model; there never really was any need for it. Most code which was expecting a struct subsystem argument has been changed to use the relevant kset instead.

• There is a new version of the in-kernel rpcbind (portmapper) client which supports versions 2-4 of the rpcbind protocol. The portmapper API has changed as a result.

• Numerous changes to the paravirt_ops methods have been made. Additionally, paravirt_ops is no longer a GPL-only export.

• There is a new memory function:

      void *krealloc(const void *p, size_t new_size, gfp_t flags);
  

  As one would expect, it changes the size of the allocated memory, moving it if need be.

• The has been merged as an experimental (for now) alternative to the slab code. The SLUB API generally matches slab, but the handling of zero-length allocations somewhat.

• A new macro has been added to make the creation of slab caches easier:

      struct kmem_cache KMEM_CACHE(struct-type, flags);
  

  The result is the creation of a cache holding objects of the given struct_type, named after that type, and with the additional slab flags (if any).

• The SLAB_DEBUG_INITIAL flag has been removed, along with the associated SLAB_CTOR_VERIFY flag passed to constructors. The result is a set of changes which ripples through quite a few source files. The unused SLAB_CTOR_ATOMIC flag is also gone.

• The SuperH architecture has working kgdb support again.

• The ia64 architecture has a new tool which will inject machine check errors into a running system. Not recommended for production machines.

• The has been merged. There is also a new macro for initializing workqueue entries (INIT_DELAYED_WORK_DEFERRABLE()) which causes the job to be queued in a deferrable manner.

• The old SA_* interrupt flags have not been removed as originally scheduled, but their use will now generate warnings at compile time.

• There is a new list_first_entry() macro which, surprisingly, gets the first entry from a list.

• The atomic64_t and local_t types are now fully supported on a wider set of architectures.

• Workqueues have been reworked again. There is a new function:

      void cancel_work_sync(struct work_struct *work);
  

  This function tries to cancel a single workqueue entry, be it on the shared (keventd) or a private workqueue. Meanwhile run_scheduled_work() has been removed.