• Stefani Seibold's avatar
    kfifo: move struct kfifo in place · 45465487
    Stefani Seibold authored
    This is a new generic kernel FIFO implementation.
    
    The current kernel fifo API is not very widely used, because it has to
    many constrains.  Only 17 files in the current 2.6.31-rc5 used it.
    FIFO's are like list's a very basic thing and a kfifo API which handles
    the most use case would save a lot of development time and memory
    resources.
    
    I think this are the reasons why kfifo is not in use:
    
     - The API is to simple, important functions are missing
     - A fifo can be only allocated dynamically
     - There is a requirement of a spinlock whether you need it or not
     - There is no support for data records inside a fifo
    
    So I decided to extend the kfifo in a more generic way without blowing up
    the API to much.  The new API has the following benefits:
    
     - Generic usage: For kernel internal use and/or device driver.
     - Provide an API for the most use case.
     - Slim API: The whole API provides 25 functions.
     - Linux style habit.
     - DECLARE_KFIFO, DEFINE_KFIFO and INIT_KFIFO Macros
     - Direct copy_to_user from the fifo and copy_from_user into the fifo.
     - The kfifo itself is an in place member of the using data structure, this save an
       indirection access and does not waste the kernel allocator.
     - Lockless access: if only one reader and one writer is active on the fifo,
       which is the common use case, no additional locking is necessary.
     - Remove spinlock - give the user the freedom of choice what kind of locking to use if
       one is required.
     - Ability to handle records. Three type of records are supported:
       - Variable length records between 0-255 bytes, with a record size
         field of 1 bytes.
       - Variable length records between 0-65535 bytes, with a record size
         field of 2 bytes.
       - Fixed size records, which no record size field.
     - Preserve memory resource.
     - Performance!
     - Easy to use!
    
    This patch:
    
    Since most users want to have the kfifo as part of another object,
    reorganize the code to allow including struct kfifo in another data
    structure.  This requires changing the kfifo_alloc and kfifo_init
    prototypes so that we pass an existing kfifo pointer into them.  This
    patch changes the implementation and all existing users.
    
    [akpm@linux-foundation.org: fix warning]
    Signed-off-by: default avatarStefani Seibold <stefani@seibold.net>
    Acked-by: default avatarGreg Kroah-Hartman <gregkh@suse.de>
    Acked-by: default avatarMauro Carvalho Chehab <mchehab@redhat.com>
    Acked-by: default avatarAndi Kleen <ak@linux.intel.com>
    Acked-by: default avatarArnd Bergmann <arnd@arndb.de>
    Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
    Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
    45465487
fhci-sched.c 23.5 KB