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SubjectRe: [RFC] Stacking bio support - patch 3/4 for 2.6.23.17 (stable)

From 1cb4c136df6a84b45d4e6bccbef159455b28e949 Mon Sep 17 00:00:00 2001
From: Alan D. Brunelle <alan.brunelle@hp.com>
Date: Fri, 14 Mar 2008 08:27:55 -0400
Subject: [PATCH] BIO stack


---
fs/bio.c | 64 +++++++++++++++++++++++++++++++++++++++++++++++++++
include/linux/bio.h | 14 ++++++++--
2 files changed, 75 insertions(+), 3 deletions(-)

diff --git a/fs/bio.c b/fs/bio.c
index 29cdd8b..d57f0f3 100644
--- a/fs/bio.c
+++ b/fs/bio.c
@@ -34,6 +34,63 @@ static struct kmem_cache *bio_slab __read_mostly;

#define BIOVEC_NR_POOLS 6

+/* Bio push/pop (C) 2008, Daniel Phillips <phillips@phunq.net> */
+
+#define BIOSTACK_ALIGN (1 << 2)
+#define BIOCHUNK_SIZE (1 << 7)
+#define BIOCHUNK_MAGIC (0xddc0ffee)
+#define BIOCHUNK_OVERHEAD (sizeof(struct biochunk) + sizeof(struct bioframe))
+#define BIOCHUNK_PAYLOAD (BIOCHUNK_SIZE - BIOCHUNK_OVERHEAD)
+
+struct biochunk { u32 magic; void *oldstack; char frames[]; };
+
+static struct kmem_cache *biospace __read_mostly;
+
+static struct biochunk *alloc_biochunk(void)
+{
+ return kmem_cache_alloc(biospace, __GFP_NOFAIL);
+}
+
+static void free_biochunk(struct biochunk *chunk)
+{
+ kmem_cache_free(biospace, chunk);
+}
+
+void *bio_push(struct bio *bio, unsigned size, bio_end_io_t *endio)
+{
+ struct bioframe *frame = bio->bi_stack;
+ size += sizeof(struct bioframe);
+ size += -size & (BIOSTACK_ALIGN - 1);
+ if (unlikely(size > frame->stacksize)) {
+ struct biochunk *chunk = alloc_biochunk();
+ bio_end_io_t *old = frame->endio;
+ BUG_ON(size > BIOCHUNK_PAYLOAD);
+ *chunk = (struct biochunk){ .oldstack = bio->bi_stack, .magic = BIOCHUNK_MAGIC };
+ frame = bio->bi_stack = chunk->frames;
+ *frame = (struct bioframe){ .stacksize = BIOCHUNK_PAYLOAD, .endio = old };
+ }
+ bio->bi_stack += size;
+ *(struct bioframe *)bio->bi_stack = (struct bioframe){
+ .stacksize = frame->stacksize - size,
+ .framesize = size, .endio = endio };
+ return frame->space;
+}
+EXPORT_SYMBOL_GPL(bio_push);
+
+void *bio_pop(struct bio *bio)
+{
+ struct bioframe *frame = bio->bi_stack;
+ if (unlikely(!frame->framesize)) {
+ struct biochunk *chunk = bio->bi_stack - sizeof(struct biochunk);
+ BUG_ON(chunk->magic != BIOCHUNK_MAGIC);
+ frame = bio->bi_stack = chunk->oldstack;
+ free_biochunk(chunk);
+ }
+ frame = bio->bi_stack -= frame->framesize;
+ return frame->space;
+}
+EXPORT_SYMBOL_GPL(bio_pop);
+
/*
* a small number of entries is fine, not going to be performance critical.
* basically we just need to survive
@@ -113,6 +170,9 @@ void bio_free(struct bio *bio, struct bio_set *bio_set)

BIO_BUG_ON(pool_idx >= BIOVEC_NR_POOLS);

+ if (!((struct bioframe *)bio->bi_stack)->framesize)
+ bio_pop(bio);
+
mempool_free(bio->bi_io_vec, bio_set->bvec_pools[pool_idx]);
mempool_free(bio, bio_set->bio_pool);
}
@@ -179,6 +239,8 @@ struct bio *bio_alloc_bioset(gfp_t gfp_mask, int nr_iovecs, struct bio_set *bs)
bio->bi_max_vecs = bvec_slabs[idx].nr_vecs;
}
bio->bi_io_vec = bvl;
+ bio->bi_stack = &bio->space;
+ bio->space.framesize = sizeof(struct bioframe);
}
out:
return bio;
@@ -1206,6 +1268,8 @@ static int __init init_bio(void)
if (!bio_split_pool)
panic("bio: can't create split pool\n");

+ biospace = kmem_cache_create("biospace", BIOCHUNK_SIZE, 0, SLAB_PANIC, NULL);
+
return 0;
}

diff --git a/include/linux/bio.h b/include/linux/bio.h
index 4c8d7a0..cca89d1 100644
--- a/include/linux/bio.h
+++ b/include/linux/bio.h
@@ -68,6 +68,11 @@ typedef int (bio_end_io_t) (struct bio *, unsigned int, int);
typedef void (bio_destructor_t) (struct bio *);

/*
+ * Support endio handler stacking with per-handler private workspace
+ */
+struct bioframe { u16 framesize, stacksize; bio_end_io_t *endio; char space[]; };
+
+/*
* main unit of I/O for the block layer and lower layers (ie drivers and
* stacking drivers)
*/
@@ -114,6 +119,8 @@ struct bio {
void *bi_private;

bio_destructor_t *bi_destructor; /* destructor */
+ void *bi_stack; /* endio stacking */
+ struct bioframe space;
};

/*
@@ -186,12 +193,12 @@ struct bio {

static inline void bio_set_endio(struct bio *bio, bio_end_io_t *endio)
{
- bio->bi_endio = endio;
+ ((struct bioframe *)bio->bi_stack)->endio = endio;
}

static inline bio_end_io_t *bio_get_endio(struct bio *bio)
{
- return bio->bi_endio;
+ return ((struct bioframe *)bio->bi_stack)->endio;
}

/*
@@ -295,7 +302,8 @@ extern struct bio *bio_alloc(gfp_t, int);
extern struct bio *bio_alloc_bioset(gfp_t, int, struct bio_set *);
extern void bio_put(struct bio *);
extern void bio_free(struct bio *, struct bio_set *);
-
+extern void *bio_push(struct bio *bio, unsigned size, bio_end_io_t *endio);
+extern void *bio_pop(struct bio *bio);
extern void bio_endio(struct bio *, unsigned int, int);
struct request_queue;
extern int bio_phys_segments(struct request_queue *, struct bio *);
--
1.5.2.5
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