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authorStefani Seibold <stefani@seibold.net>2009-12-21 14:37:26 -0800
committerLinus Torvalds <torvalds@linux-foundation.org>2009-12-22 14:17:55 -0800
commit45465487897a1c6d508b14b904dc5777f7ec7e04 (patch)
tree935c8dae68dc793ff2f795d57cf027531475cd53 /kernel
parent2ec91eec47f713e3d158ba5b28a24a85a2cf3650 (diff)
downloadvexpress-lsk-45465487897a1c6d508b14b904dc5777f7ec7e04.tar.gz
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>
Diffstat (limited to 'kernel')
-rw-r--r--kernel/kfifo.c65
1 files changed, 33 insertions, 32 deletions
diff --git a/kernel/kfifo.c b/kernel/kfifo.c
index 3765ff3c1bb..8da6bb9782b 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 @@ 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);
-
- ret = kfifo_init(buffer, size, gfp_mask, lock);
+ if (!buffer) {
+ _kfifo_init(fifo, 0, 0, NULL);
+ return -ENOMEM;
+ }
- if (IS_ERR(ret))
- kfree(buffer);
+ _kfifo_init(fifo, buffer, size, lock);
- 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);