kfifo: move struct kfifo in place

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: Stefani Seibold <stefani@seibold.net>
Acked-by: Greg Kroah-Hartman <gregkh@suse.de>
Acked-by: Mauro Carvalho Chehab <mchehab@redhat.com>
Acked-by: Andi Kleen <ak@linux.intel.com>
Acked-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

kernel/kfifo.c

@@ -1,6 +1,7 @@
 /*
- * A simple kernel FIFO implementation.
+ * A generic kernel FIFO implementation.
  *
+ * Copyright (C) 2009 Stefani Seibold <stefani@seibold.net>
  * Copyright (C) 2004 Stelian Pop <stelian@popies.net>
  *
  * This program is free software; you can redistribute it and/or modify
@@ -26,49 +27,51 @@
 #include <linux/kfifo.h>
 #include <linux/log2.h>
 
+static void _kfifo_init(struct kfifo *fifo, unsigned char *buffer,
+		unsigned int size, spinlock_t *lock)
+{
+	fifo->buffer = buffer;
+	fifo->size = size;
+	fifo->lock = lock;
+
+	kfifo_reset(fifo);
+}
+
 /**
- * kfifo_init - allocates a new FIFO using a preallocated buffer
+ * kfifo_init - initialize a FIFO using a preallocated buffer
+ * @fifo: the fifo to assign the buffer
  * @buffer: the preallocated buffer to be used.
  * @size: the size of the internal buffer, this have to be a power of 2.
- * @gfp_mask: get_free_pages mask, passed to kmalloc()
  * @lock: the lock to be used to protect the fifo buffer
  *
- * Do NOT pass the kfifo to kfifo_free() after use! Simply free the
- * &struct kfifo with kfree().
  */
-struct kfifo *kfifo_init(unsigned char *buffer, unsigned int size,
-			 gfp_t gfp_mask, spinlock_t *lock)
+void kfifo_init(struct kfifo *fifo, unsigned char *buffer, unsigned int size,
+			spinlock_t *lock)
 {
-	struct kfifo *fifo;
-
 	/* size must be a power of 2 */
 	BUG_ON(!is_power_of_2(size));
 
-	fifo = kmalloc(sizeof(struct kfifo), gfp_mask);
-	if (!fifo)
-		return ERR_PTR(-ENOMEM);
-
-	fifo->buffer = buffer;
-	fifo->size = size;
-	fifo->in = fifo->out = 0;
-	fifo->lock = lock;
-
-	return fifo;
+	_kfifo_init(fifo, buffer, size, lock);
 }
 EXPORT_SYMBOL(kfifo_init);
 
 /**
- * kfifo_alloc - allocates a new FIFO and its internal buffer
- * @size: the size of the internal buffer to be allocated.
+ * kfifo_alloc - allocates a new FIFO internal buffer
+ * @fifo: the fifo to assign then new buffer
+ * @size: the size of the buffer to be allocated, this have to be a power of 2.
  * @gfp_mask: get_free_pages mask, passed to kmalloc()
  * @lock: the lock to be used to protect the fifo buffer
  *
+ * This function dynamically allocates a new fifo internal buffer
+ *
  * The size will be rounded-up to a power of 2.
+ * The buffer will be release with kfifo_free().
+ * Return 0 if no error, otherwise the an error code
  */
-struct kfifo *kfifo_alloc(unsigned int size, gfp_t gfp_mask, spinlock_t *lock)
+int kfifo_alloc(struct kfifo *fifo, unsigned int size, gfp_t gfp_mask,
+			spinlock_t *lock)
 {
 	unsigned char *buffer;
-	struct kfifo *ret;
 
 	/*
 	 * round up to the next power of 2, since our 'let the indices
@@ -80,26 +83,24 @@ struct kfifo *kfifo_alloc(unsigned int size, gfp_t gfp_mask, spinlock_t *lock)
 	}
 
 	buffer = kmalloc(size, gfp_mask);
-	if (!buffer)
-		return ERR_PTR(-ENOMEM);
+	if (!buffer) {
+		_kfifo_init(fifo, 0, 0, NULL);
+		return -ENOMEM;
+	}
 
-	ret = kfifo_init(buffer, size, gfp_mask, lock);
+	_kfifo_init(fifo, buffer, size, lock);
 
-	if (IS_ERR(ret))
-		kfree(buffer);
-
-	return ret;
+	return 0;
 }
 EXPORT_SYMBOL(kfifo_alloc);
 
 /**
- * kfifo_free - frees the FIFO
+ * kfifo_free - frees the FIFO internal buffer
  * @fifo: the fifo to be freed.
  */
 void kfifo_free(struct kfifo *fifo)
 {
 	kfree(fifo->buffer);
-	kfree(fifo);
 }
 EXPORT_SYMBOL(kfifo_free);