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>
diff --git a/kernel/kfifo.c b/kernel/kfifo.c
index 3765ff3..8da6bb9 100644
--- a/kernel/kfifo.c
+++ b/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 @@
}
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);