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From: Kent Overstreet on 4 Jul 2010 03:50
Most of what's here is going to have to be rewritten before it can be merged;
consider it more a rough idea as to what I'm trying to do. But the code here
does work, so I've been loathe to start on that until I can get some input
as to what a real solution will look like. I have some ideas, but this'll
likely involve some of the sketchier areas of the block layer...

Signed-off-by: Kent Overstreet <kent.overstreet(a)gmail.com>
---
block/blk-core.c | 10 +++++++---
fs/bio.c | 26 ++++++++++++++++++++++++++
include/linux/bio.h | 3 +++
include/linux/blkdev.h | 2 ++
include/linux/fs.h | 5 +++++
5 files changed, 43 insertions(+), 3 deletions(-)

diff --git a/block/blk-core.c b/block/blk-core.c
index f0640d7..4d54e9e 100644
--- a/block/blk-core.c
+++ b/block/blk-core.c
@@ -1428,11 +1428,11 @@ static inline int bio_check_eod(struct bio *bio, unsigned int nr_sectors)
* bi_sector for remaps as it sees fit. So the values of these fields
* should NOT be depended on after the call to generic_make_request.
*/
-static inline void __generic_make_request(struct bio *bio)
+inline void __generic_make_request(struct bio *bio)
{
struct request_queue *q;
sector_t old_sector;
- int ret, nr_sectors = bio_sectors(bio);
+ int ret = 1, nr_sectors = bio_sectors(bio);
dev_t old_dev;
int err = -EIO;

@@ -1505,7 +1505,10 @@ static inline void __generic_make_request(struct bio *bio)

trace_block_bio_queue(q, bio);

- ret = q->make_request_fn(q, bio);
+ if (bio->bi_bdev->bd_cache_fn)
+ ret = bio->bi_bdev->bd_cache_fn(q, bio);
+ if (ret)
+ ret = q->make_request_fn(q, bio);
} while (ret);

return;
@@ -1513,6 +1516,7 @@ static inline void __generic_make_request(struct bio *bio)
end_io:
bio_endio(bio, err);
}
+EXPORT_SYMBOL_GPL(__generic_make_request);

/*
* We only want one ->make_request_fn to be active at a time,
diff --git a/fs/bio.c b/fs/bio.c
index e7bf6ca..d86764f 100644
--- a/fs/bio.c
+++ b/fs/bio.c
@@ -257,6 +257,7 @@ void bio_init(struct bio *bio)
bio->bi_flags = 1 << BIO_UPTODATE;
bio->bi_comp_cpu = -1;
atomic_set(&bio->bi_cnt, 1);
+ atomic_set(&bio->bi_remaining, 1);
}
EXPORT_SYMBOL(bio_init);

@@ -1422,16 +1423,41 @@ EXPORT_SYMBOL(bio_flush_dcache_pages);
**/
void bio_endio(struct bio *bio, int error)
{
+ int old, new;
if (error)
clear_bit(BIO_UPTODATE, &bio->bi_flags);
else if (!test_bit(BIO_UPTODATE, &bio->bi_flags))
error = -EIO;

+ if (error) {
+ do {
+ old = new = atomic_read(&bio->bi_remaining);
+ if (!(new >> 16))
+ new += -error << 16;
+
+ } while (atomic_cmpxchg(&bio->bi_remaining, old, --new) != old);
+ } else {
+ new = atomic_sub_return(1, &bio->bi_remaining);
+ error = -(new >> 16);
+ }
+
+ if (new & ~(~0 << 16))
+ return;
+ atomic_set(&bio->bi_remaining, 0);
+
if (bio->bi_end_io)
bio->bi_end_io(bio, error);
}
EXPORT_SYMBOL(bio_endio);

+void bio_split_endio(struct bio *bio, int error)
+{
+ struct bio *p = bio->bi_private;
+ bio_put(bio);
+ bio_endio(p, error);
+}
+EXPORT_SYMBOL(bio_split_endio);
+
void bio_pair_release(struct bio_pair *bp)
{
if (atomic_dec_and_test(&bp->cnt)) {
diff --git a/include/linux/bio.h b/include/linux/bio.h
index 7fc5606..d9c84da 100644
--- a/include/linux/bio.h
+++ b/include/linux/bio.h
@@ -94,6 +94,8 @@ struct bio {

struct bio_vec *bi_io_vec; /* the actual vec list */

+ atomic_t bi_remaining; /* split count */
+
bio_end_io_t *bi_end_io;

void *bi_private;
@@ -364,6 +366,7 @@ extern void bio_put(struct bio *);
extern void bio_free(struct bio *, struct bio_set *);

extern void bio_endio(struct bio *, int);
+extern void bio_split_endio(struct bio *bio, int error);
struct request_queue;
extern int bio_phys_segments(struct request_queue *, struct bio *);

diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h
index 09a8402..8978c29 100644
--- a/include/linux/blkdev.h
+++ b/include/linux/blkdev.h
@@ -347,6 +347,7 @@ struct request_queue
make_request_fn *make_request_fn;
prep_rq_fn *prep_rq_fn;
unplug_fn *unplug_fn;
+ unplug_fn *cache_unplug_fn;
merge_bvec_fn *merge_bvec_fn;
prepare_flush_fn *prepare_flush_fn;
softirq_done_fn *softirq_done_fn;
@@ -772,6 +773,7 @@ static inline void rq_flush_dcache_pages(struct request *rq)
extern int blk_register_queue(struct gendisk *disk);
extern void blk_unregister_queue(struct gendisk *disk);
extern void register_disk(struct gendisk *dev);
+extern void __generic_make_request(struct bio *bio);
extern void generic_make_request(struct bio *bio);
extern void blk_rq_init(struct request_queue *q, struct request *rq);
extern void blk_put_request(struct request *);
diff --git a/include/linux/fs.h b/include/linux/fs.h
index 471e1ff..0c0a04e 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -514,6 +514,8 @@ enum positive_aop_returns {
struct page;
struct address_space;
struct writeback_control;
+struct bio;
+struct request_queue;

struct iov_iter {
const struct iovec *iov;
@@ -665,6 +667,9 @@ struct block_device {
int bd_invalidated;
struct gendisk * bd_disk;
struct list_head bd_list;
+
+ int (*bd_cache_fn)(struct request_queue *q, struct bio *bio);
+ char bd_cache_identifier;
/*
* Private data. You must have bd_claim'ed the block_device
* to use this. NOTE: bd_claim allows an owner to claim
--
1.7.0.4

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