[RFC][PATCH] dm-cache: block level disk cache target for device mapper
From: Eric Van Hensbergen
Date: Mon Nov 27 2006 - 13:27:11 EST
This is the first cut of a device-mapper target which provides a write-back
or write-through block cache. It is intended to be used in conjunction with
remote block devices such as iSCSI or ATA-over-Ethernet, particularly in
cluster situations.
In performance tests with iSCSI, gave peformance improvements of 2-10x that
of iSCSI alone when Postmark or Bonnie loads were applied from 8 clients to
a single server. Evidence suggests even greater differences on larger
clusters. A detailed performance analysis will be vailable shortly via a
technical report on IBM's CyberDigest.
This module was developed during an intership at IBM Research by
Ming Zhao. Please direct comments to both Ming and myself.
Signed-off-by: Eric Van Hensbergen <ericvh@xxxxxxxxx>
---
drivers/md/Kconfig | 6
drivers/md/Makefile | 1
drivers/md/dm-cache.c | 1465 +++++++++++++++++++++++++++++++++++++++++++++++++
3 files changed, 1472 insertions(+), 0 deletions(-)
diff --git a/drivers/md/Kconfig b/drivers/md/Kconfig
index c92c152..0f23a15 100644
--- a/drivers/md/Kconfig
+++ b/drivers/md/Kconfig
@@ -261,6 +261,12 @@ config DM_MULTIPATH_EMC
---help---
Multipath support for EMC CX/AX series hardware.
+config DM_CACHE
+ tristate "Cache target support (EXPERIMENTAL)"
+ depends on BLK_DEV_DM && EXPERIMENTAL
+ ---help---
+ Support for generic cache target for device-mapper.
+
endmenu
endif
diff --git a/drivers/md/Makefile b/drivers/md/Makefile
index 34957a6..49f7266 100644
--- a/drivers/md/Makefile
+++ b/drivers/md/Makefile
@@ -36,6 +36,7 @@ obj-$(CONFIG_DM_MULTIPATH_EMC) += dm-emc
obj-$(CONFIG_DM_SNAPSHOT) += dm-snapshot.o
obj-$(CONFIG_DM_MIRROR) += dm-mirror.o
obj-$(CONFIG_DM_ZERO) += dm-zero.o
+obj-$(CONFIG_DM_CACHE) += dm-cache.o
quiet_cmd_unroll = UNROLL $@
cmd_unroll = $(PERL) $(srctree)/$(src)/unroll.pl $(UNROLL) \
diff --git a/drivers/md/dm-cache.c b/drivers/md/dm-cache.c
new file mode 100755
index 0000000..209bae0
--- /dev/null
+++ b/drivers/md/dm-cache.c
@@ -0,0 +1,1465 @@
+/*
+ * dm-cache.c
+ * Device mapper target for block-level disk caching
+ *
+ * Copyright (C) International Business Machines Corp., 2006
+ * Author: Ming Zhao (mingzhao@xxxxxxx)
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; under version 2 of the License.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
+ *
+ */
+
+#include <asm/atomic.h>
+
+#include <linux/module.h>
+#include <linux/init.h>
+#include <linux/list.h>
+#include <linux/blkdev.h>
+#include <linux/bio.h>
+#include <linux/slab.h>
+#include <linux/hash.h>
+#include <linux/spinlock.h>
+#include <linux/workqueue.h>
+
+#include "dm.h"
+#include "dm-io.h"
+#include "dm-bio-list.h"
+#include "kcopyd.h"
+
+#define DMC_DEBUG 0
+
+#define DM_MSG_PREFIX "dm-cache"
+#define DMC_PREFIX "dm-cache: "
+
+#if DMC_DEBUG
+#define DPRINTK( s, arg... ) printk(DMC_PREFIX s "\n", ##arg)
+#else
+#define DPRINTK( s, arg... )
+#endif
+
+#define WRITE_THROUGH 0
+#define WRITE_BACK 1
+#define DEFAULT_WRITE_POLICY WRITE_BACK
+
+#define DMCACHE_COPY_PAGES 1024
+#define DEFAULT_CACHE_SIZE 65536
+#define DEFAULT_CACHE_ASSOC 1024
+#define DEFAULT_BLOCK_SIZE 8
+#define CONSECUTIVE_BLOCKS 128
+
+#define HASH 0
+#define UNIFORM 1
+#define DEFAULT_HASHFUNC UNIFORM
+
+/* states of a cache block */
+#define INVALID 0
+#define VALID 1 /* Valid */
+#define RESERVED 2 /* Allocated but data not in place yet */
+#define DIRTY 4 /* Locally modified */
+#define WRITEBACK 8 /* In the process of write back */
+
+/*
+ * cache: maps a cache range of a device.
+ */
+struct cache_c {
+ struct dm_dev *src_dev; /* Source device */
+ struct dm_dev *cache_dev; /* Cache device */
+ struct kcopyd_client *kcp_client; /* Kcopyd client for writing back data */
+
+ struct cacheblock *cache; /* Hash table for cache blocks */
+ sector_t size; /* Cache size */
+ unsigned int bits; /* Cache size in bits */
+ unsigned int assoc; /* Cache associativity */
+ unsigned int block_size; /* Cache block size */
+ unsigned int block_shift; /* Cache block size in bits */
+ unsigned int block_mask; /* Cache block mask */
+ unsigned int consecutive_shift; /* Consecutive blocks size in bits */
+ unsigned long counter; /* Logical timestamp of the cache's last access */
+ unsigned int write_policy; /* Cache write policy */
+ sector_t dirty_blocks; /* Number of dirty blocks */
+
+ spinlock_t lock; /* Lock to protect page allocation/deallocation */
+ struct page_list *pages; /* Pages for I/O */
+ unsigned int nr_pages; /* Number of pages */
+ unsigned int nr_free_pages; /* Number of free pages */
+ wait_queue_head_t destroyq; /* Wait queue for I/O completion */
+ atomic_t nr_jobs; /* Number of I/O jobs */
+ /* Stats */
+ unsigned long reads; /* Number of reads */
+ unsigned long writes; /* Number of writes */
+ unsigned long cache_hits; /* Number of cache hits */
+ unsigned long replace; /* Number of cache replacements */
+ unsigned long writeback; /* Number of blocks written back for replacements */
+};
+
+struct cacheblock { /* Cache block metadata structure (size: 28B) */
+ spinlock_t lock; /* Lock to protect operations on the bio list */
+ sector_t block; /* Sector number of the cached block */
+ unsigned short state; /* State of a block */
+ unsigned long counter; /* Logical timestamp of the block's last access */
+ struct bio_list bios; /* List of pending bios */
+};
+
+#if DMC_DEBUG
+/* Function for debugging; will be removed */
+static int hexdump(char *data, int data_len)
+{
+ int i, j;
+ char buf[1000];
+ char temp[10];
+
+ if (data == NULL) {
+ DPRINTK("null\n");
+ return -1;
+ }
+
+ for (i = 0; i < data_len; i++) {
+ j = sprintf(temp, "%x", data[i]);
+ if (j < 2) {
+ buf[(i % 16) * 3] = '0';
+ strcpy(buf + (i % 16) * 3 + 1, temp + j - 1);
+ } else
+ strcpy(buf + (i % 16) * 3, temp + j - 2);
+ strcpy(buf + (i % 16) * 3 + 2, " ");
+ if (i % 16 == 15)
+ DPRINTK("%s", buf);
+ }
+
+ if (i % 16 != 0)
+ DPRINTK("%s", buf);
+
+ return 1;
+}
+#endif /* DMC_DEBUG */
+
+/*
+ * Functions for allocating and deallocating pages used for async I/O
+ * Code is largely borrowed from kcopyd.c
+ */
+
+static struct page_list *alloc_pl(void)
+{
+ struct page_list *pl;
+
+ pl = kmalloc(sizeof(*pl), GFP_KERNEL);
+ if (!pl)
+ return NULL;
+
+ pl->page = alloc_page(GFP_KERNEL);
+ if (!pl->page) {
+ kfree(pl);
+ return NULL;
+ }
+
+ return pl;
+}
+
+static void free_pl(struct page_list *pl)
+{
+ __free_page(pl->page);
+ kfree(pl);
+}
+
+static void drop_pages(struct page_list *pl)
+{
+ struct page_list *next;
+
+ while (pl) {
+ next = pl->next;
+ free_pl(pl);
+ pl = next;
+ }
+}
+
+static int kcached_get_pages(struct cache_c *dmc, unsigned int nr,
+ struct page_list **pages)
+{
+ struct page_list *pl;
+
+ spin_lock(&dmc->lock);
+ if (dmc->nr_free_pages < nr) {
+ DPRINTK("No free pages: %u<%u", dmc->nr_free_pages, nr);
+ spin_unlock(&dmc->lock);
+ return -ENOMEM;
+ }
+
+ dmc->nr_free_pages -= nr;
+ for (*pages = pl = dmc->pages; --nr; pl = pl->next) ;
+
+ dmc->pages = pl->next;
+ pl->next = NULL;
+
+ spin_unlock(&dmc->lock);
+
+ return 0;
+}
+
+static void kcached_put_pages(struct cache_c *dmc, struct page_list *pl)
+{
+ struct page_list *cursor;
+
+ spin_lock(&dmc->lock);
+ for (cursor = pl; cursor->next; cursor = cursor->next)
+ dmc->nr_free_pages++;
+
+ dmc->nr_free_pages++;
+ cursor->next = dmc->pages;
+ dmc->pages = pl;
+
+// DPRINTK("Free pages %u", dmc->nr_free_pages);
+ spin_unlock(&dmc->lock);
+}
+
+static int alloc_bio_pages(struct cache_c *dmc, unsigned int nr)
+{
+ unsigned int i;
+ struct page_list *pl = NULL, *next;
+
+ for (i = 0; i < nr; i++) {
+ next = alloc_pl();
+ if (!next) {
+ if (pl)
+ drop_pages(pl);
+ return -ENOMEM;
+ }
+ next->next = pl;
+ pl = next;
+ }
+
+ kcached_put_pages(dmc, pl);
+ dmc->nr_pages += nr;
+
+ return 0;
+}
+
+static void free_bio_pages(struct cache_c *dmc)
+{
+ BUG_ON(dmc->nr_free_pages != dmc->nr_pages);
+ drop_pages(dmc->pages);
+ dmc->pages = NULL;
+ dmc->nr_free_pages = dmc->nr_pages = 0;
+}
+
+/*
+ * Functions and data structures for handling async I/O
+ * Code for queue handling is borrowed from kcopyd.c
+ */
+
+struct kcached_job {
+ struct list_head list;
+ struct cache_c *dmc;
+ struct bio *bio; /* Original bio */
+ struct io_region src;
+ struct io_region dest;
+ struct cacheblock *cacheblock;
+ int rw;
+ /*
+ * When the original bio is aligned with cache blocks,
+ * we need extra bvecs and pages for padding.
+ */
+ struct bio_vec *bvec;
+ unsigned int nr_pages;
+ struct page_list *pages;
+};
+
+static struct workqueue_struct *_kcached_wq;
+static struct work_struct _kcached_work;
+
+static inline void wake(void)
+{
+ queue_work(_kcached_wq, &_kcached_work);
+}
+
+#define MIN_JOBS 1024
+
+static kmem_cache_t *_job_cache;
+static mempool_t *_job_pool;
+
+static DEFINE_SPINLOCK(_job_lock);
+
+static LIST_HEAD(_complete_jobs);
+static LIST_HEAD(_io_jobs);
+static LIST_HEAD(_pages_jobs);
+
+static int jobs_init(void)
+{
+ _job_cache = kmem_cache_create("kcached-jobs",
+ sizeof(struct kcached_job),
+ __alignof__(struct kcached_job),
+ 0, NULL, NULL);
+ if (!_job_cache)
+ return -ENOMEM;
+
+ _job_pool = mempool_create(MIN_JOBS, mempool_alloc_slab,
+ mempool_free_slab, _job_cache);
+ if (!_job_pool) {
+ kmem_cache_destroy(_job_cache);
+ return -ENOMEM;
+ }
+
+ return 0;
+}
+
+static void jobs_exit(void)
+{
+ BUG_ON(!list_empty(&_complete_jobs));
+ BUG_ON(!list_empty(&_io_jobs));
+ BUG_ON(!list_empty(&_pages_jobs));
+
+ mempool_destroy(_job_pool);
+ kmem_cache_destroy(_job_cache);
+ _job_pool = NULL;
+ _job_cache = NULL;
+}
+
+/*
+ * Functions to push and pop a job onto the head of a given job
+ * list.
+ */
+static inline struct kcached_job *pop(struct list_head *jobs)
+{
+ struct kcached_job *job = NULL;
+ unsigned long flags;
+
+ spin_lock_irqsave(&_job_lock, flags);
+
+ if (!list_empty(jobs)) {
+ job = list_entry(jobs->next, struct kcached_job, list);
+ list_del(&job->list);
+ }
+ spin_unlock_irqrestore(&_job_lock, flags);
+
+ return job;
+}
+
+static inline void push(struct list_head *jobs, struct kcached_job *job)
+{
+ unsigned long flags;
+
+ spin_lock_irqsave(&_job_lock, flags);
+ list_add_tail(&job->list, jobs);
+ spin_unlock_irqrestore(&_job_lock, flags);
+}
+
+static void io_callback(unsigned long error, void *context)
+{
+ struct kcached_job *job = (struct kcached_job *)context;
+
+ if (error) {
+ /* TODO */
+ DPRINTK("io error");
+ }
+
+ if (job->rw == READ) {
+ job->rw = WRITE;
+ push(&_io_jobs, job);
+ } else
+ push(&_complete_jobs, job);
+ wake();
+}
+
+/*
+ * Read data from source device or write data to cache device, asynchronously
+ * (The most complicated function in the whole module, because the requested
+ * data may not align with the cache blocks and extra handling is required to
+ * pad a block or get the requested data from a block.)
+ */
+static int do_io(struct kcached_job *job)
+{
+ int r = 0, i, j;
+ struct bio *bio = job->bio;
+ struct cache_c *dmc = job->dmc;
+ unsigned int offset, head, tail, remaining, nr_vecs, idx = 0;
+ struct bio_vec *bvec;
+ struct page_list *pl;
+
+ offset = (unsigned int)(bio->bi_sector & dmc->block_mask);
+ head = to_bytes(offset);
+ tail = to_bytes(dmc->block_size) - bio->bi_size - head;
+
+// DPRINTK("do_io(%s): %llu(%llu->%llu,%llu), head:%u,tail:%u",
+// job->rw == READ ? "read" : "write",
+// bio->bi_sector, job->src.sector, job->dest.sector, job->src.count, head, tail);
+
+ if (job->rw == READ) { /* Read from source device */
+ if (bio_data_dir(bio) == READ) { /* The original request is a READ */
+ if (0 == job->nr_pages) { /* The request is aligned to cache block */
+ r = dm_io_async_bvec(1, &job->src, READ,
+ bio->bi_io_vec +
+ bio->bi_idx, io_callback,
+ job);
+ return r;
+ }
+
+ nr_vecs = bio->bi_vcnt - bio->bi_idx;
+ bvec =
+ kmalloc((nr_vecs + job->nr_pages) * sizeof(*bvec),
+ GFP_NOIO);
+ if (!bvec) {
+ DPRINTK("No memory");
+ return 1;
+ }
+
+ pl = job->pages;
+ i = 0;
+ while (head) {
+ bvec[i].bv_len =
+ min(head, (unsigned int)PAGE_SIZE);
+ bvec[i].bv_offset = 0;
+ bvec[i].bv_page = pl->page;
+ head -= bvec[i].bv_len;
+ pl = pl->next;
+ i++;
+ }
+
+ remaining = bio->bi_size;
+ j = bio->bi_idx;
+ while (remaining) {
+ bvec[i] = bio->bi_io_vec[j];
+ remaining -= bvec[i].bv_len;
+ i++;
+ j++;
+ }
+
+ while (tail) {
+ bvec[i].bv_len =
+ min(tail, (unsigned int)PAGE_SIZE);
+ bvec[i].bv_offset = 0;
+ bvec[i].bv_page = pl->page;
+ tail -= bvec[i].bv_len;
+ pl = pl->next;
+ i++;
+ }
+
+ job->bvec = bvec;
+ r = dm_io_async_bvec(1, &job->src, READ, job->bvec,
+ io_callback, job);
+ return r;
+ } else { /* The original request is a WRITE */
+ pl = job->pages;
+
+ if (head && tail) { /* Special case */
+ bvec =
+ kmalloc(job->nr_pages * sizeof(*bvec),
+ GFP_KERNEL);
+ if (!bvec) {
+ DPRINTK("No memory");
+ return 1;
+ }
+ for (i = 0; i < job->nr_pages; i++) {
+ bvec[i].bv_len = PAGE_SIZE;
+ bvec[i].bv_offset = 0;
+ bvec[i].bv_page = pl->page;
+ pl = pl->next;
+ }
+ job->bvec = bvec;
+ r = dm_io_async_bvec(1, &job->src, READ,
+ job->bvec, io_callback,
+ job);
+ return r;
+ }
+// DPRINTK("Create %u new bvecs", job->nr_pages + bio->bi_vcnt - bio->bi_idx);
+ bvec =
+ kmalloc((job->nr_pages + bio->bi_vcnt - bio->bi_idx)
+ * sizeof(*bvec), GFP_KERNEL);
+ if (!bvec) {
+ DPRINTK("No memory");
+ return 1;
+ }
+
+ i = 0;
+ while (head) {
+ bvec[i].bv_len =
+ min(head, (unsigned int)PAGE_SIZE);
+ bvec[i].bv_offset = 0;
+ bvec[i].bv_page = pl->page;
+ head -= bvec[i].bv_len;
+// DPRINTK("New bvec (len: %u, offset: %u, left: %u)", bvec[i].bv_len, bvec[i].bv_offset, head);
+ pl = pl->next;
+ i++;
+ }
+
+ remaining = bio->bi_size;
+ j = bio->bi_idx;
+ while (remaining) {
+ bvec[i] = bio->bi_io_vec[j];
+ remaining -= bvec[i].bv_len;
+// DPRINTK("Add bvec (len: %u, offset: %u, left: %u)", bvec[i].bv_len, bvec[i].bv_offset, remaining);
+ i++;
+ j++;
+ }
+
+ if (tail) {
+ idx = i;
+ bvec[i].bv_offset =
+ (to_bytes(offset) +
+ bio->bi_size) & (PAGE_SIZE - 1);
+ bvec[i].bv_len = PAGE_SIZE - bvec[i].bv_offset;
+ bvec[i].bv_page = pl->page;
+ tail -= bvec[i].bv_len;
+// DPRINTK("Added a bvec (offset: %u, len: %u, left: %u)", bvec[i].bv_offset, bvec[i].bv_len, tail);
+ pl = pl->next;
+ i++;
+ while (tail) {
+ bvec[i].bv_len = PAGE_SIZE;
+ bvec[i].bv_offset = 0;
+ bvec[i].bv_page = pl->page;
+// DPRINTK("Added a page (offset: %u, len: %u, left: %u)", bvec[i].bv_offset, bvec[i].bv_len, tail);
+ tail -= bvec[i].bv_len;
+ pl = pl->next;
+ i++;
+ }
+ }
+
+ job->bvec = bvec;
+// DPRINTK("idx: %u", idx);
+ r = dm_io_async_bvec(1, &job->src, READ,
+ job->bvec + idx, io_callback, job);
+ return r;
+ }
+ } else { /* job->rw == WRITE; Write to cache device */
+ if (0 == job->nr_pages) /* Original request is aligned with cache blocks */
+ r = dm_io_async_bvec(1, &job->dest, WRITE,
+ bio->bi_io_vec + bio->bi_idx,
+ io_callback, job);
+ else {
+ if (bio_data_dir(bio) == WRITE && head > 0 && tail > 0) { /* Special case */
+ DPRINTK("Special: %u %u %u", bio_data_dir(bio),
+ head, tail);
+ nr_vecs =
+ job->nr_pages + bio->bi_vcnt - bio->bi_idx;
+ if (offset
+ && (offset + bio->bi_size < PAGE_SIZE))
+ nr_vecs++;
+ DPRINTK("Create %u new vecs", nr_vecs);
+ bvec =
+ kmalloc(nr_vecs * sizeof(*bvec),
+ GFP_KERNEL);
+ if (!bvec) {
+ DPRINTK("No memory");
+ return 1;
+ }
+
+ i = 0;
+ while (head) {
+ bvec[i].bv_len =
+ min(head, job->bvec[i].bv_len);
+ bvec[i].bv_offset = 0;
+ bvec[i].bv_page = job->bvec[i].bv_page;
+ head -= bvec[i].bv_len;
+ DPRINTK
+ ("New bvec (len: %u, offset: %u, left: %u)",
+ bvec[i].bv_len, bvec[i].bv_offset,
+ head);
+ i++;
+ }
+ remaining = bio->bi_size;
+ j = bio->bi_idx;
+ while (remaining) {
+ bvec[i] = bio->bi_io_vec[j];
+ remaining -= bvec[i].bv_len;
+ DPRINTK
+ ("Add bvec (len: %u, offset: %u, left: %u)",
+ bvec[i].bv_len, bvec[i].bv_offset,
+ remaining);
+ i++;
+ j++;
+ }
+ j = (to_bytes(offset) +
+ bio->bi_size) / PAGE_SIZE;
+ bvec[i].bv_offset =
+ (to_bytes(offset) + bio->bi_size) -
+ j * PAGE_SIZE;
+ bvec[i].bv_len = PAGE_SIZE - bvec[i].bv_offset;
+ bvec[i].bv_page = job->bvec[j].bv_page;
+ tail -= bvec[i].bv_len;
+ DPRINTK
+ ("Added a bvec (offset: %u, len: %u, left: %u)",
+ bvec[i].bv_offset, bvec[i].bv_len, tail);
+ i++;
+ j++;
+ while (tail) {
+ bvec[i] = job->bvec[j];
+ DPRINTK
+ ("Added a page (offset: %u, len: %u, left: %u)",
+ bvec[i].bv_offset, bvec[i].bv_len,
+ tail);
+ tail -= bvec[i].bv_len;
+ i++;
+ j++;
+ }
+ kfree(job->bvec);
+ job->bvec = bvec;
+ }
+
+ r = dm_io_async_bvec(1, &job->dest, WRITE, job->bvec,
+ io_callback, job);
+ }
+ }
+
+ return r;
+}
+
+/*
+ * Flush the bios that are waiting for this cache insertion or write back
+ */
+static void flush_bios(struct cacheblock *cacheblock)
+{
+ struct bio *bio;
+ struct bio *n;
+
+ spin_lock(&cacheblock->lock);
+ bio = bio_list_get(&cacheblock->bios);
+ if (cacheblock->state & WRITEBACK) {
+ cacheblock->state = INVALID;
+ } else {
+ cacheblock->state |= VALID;
+ cacheblock->state &= ~RESERVED;
+ }
+ spin_unlock(&cacheblock->lock);
+
+ while (bio) {
+ n = bio->bi_next;
+ bio->bi_next = NULL;
+ DPRINTK("Flush bio: %llu->%llu (%u bytes)", cacheblock->block,
+ bio->bi_sector, bio->bi_size);
+ generic_make_request(bio);
+ bio = n;
+ }
+}
+
+static int do_complete(struct kcached_job *job)
+{
+ int r = 0;
+ struct bio *bio = job->bio;
+
+// DPRINTK("do_complete: %llu", bio->bi_sector);
+
+ bio_endio(bio, bio->bi_size, 0);
+
+ if (job->nr_pages > 0) {
+ kfree(job->bvec);
+ kcached_put_pages(job->dmc, job->pages);
+ }
+
+ flush_bios(job->cacheblock);
+ mempool_free(job, _job_pool);
+
+ if (atomic_dec_and_test(&job->dmc->nr_jobs))
+ wake_up(&job->dmc->destroyq);
+
+ return r;
+}
+
+static int do_pages(struct kcached_job *job)
+{
+ int r = 0;
+
+// DPRINTK("do_pages: %u", job->nr_pages);
+ r = kcached_get_pages(job->dmc, job->nr_pages, &job->pages);
+
+ if (r == -ENOMEM) /* can't complete now */
+ return 1;
+
+ /* this job is ready for io */
+ push(&_io_jobs, job);
+ return 0;
+}
+
+/*
+ * Run through a list for as long as possible. Returns the count
+ * of successful jobs.
+ */
+static int process_jobs(struct list_head *jobs,
+ int (*fn) (struct kcached_job *))
+{
+ struct kcached_job *job;
+ int r, count = 0;
+
+ while ((job = pop(jobs))) {
+ r = fn(job);
+
+ if (r < 0) {
+ /* error this rogue job; TODO */
+ DPRINTK("job processing error");
+ }
+
+ if (r > 0) {
+ /*
+ * We couldn't service this job ATM, so
+ * push this job back onto the list.
+ */
+ push(jobs, job);
+ break;
+ }
+
+ count++;
+ }
+
+ return count;
+}
+
+static void do_work(void *ignored)
+{
+ process_jobs(&_complete_jobs, do_complete);
+ process_jobs(&_pages_jobs, do_pages);
+ process_jobs(&_io_jobs, do_io);
+}
+
+static void queue_job(struct kcached_job *job)
+{
+ atomic_inc(&job->dmc->nr_jobs);
+ if (job->nr_pages > 0) /* Request pages */
+ push(&_pages_jobs, job);
+ else /* Go ahead to do I/O */
+ push(&_io_jobs, job);
+ wake();
+}
+
+static int kcached_init(struct cache_c *dmc)
+{
+ int r;
+
+ spin_lock_init(&dmc->lock);
+ dmc->pages = NULL;
+ dmc->nr_pages = dmc->nr_free_pages = 0;
+ r = alloc_bio_pages(dmc, DMCACHE_COPY_PAGES);
+ if (r) {
+ DMERR("Could not allocate bio pages");
+ return r;
+ }
+
+ r = dm_io_get(DMCACHE_COPY_PAGES);
+ if (r) {
+ DMERR("Could not resize dm io pool");
+ free_bio_pages(dmc);
+ return r;
+ }
+
+ init_waitqueue_head(&dmc->destroyq);
+ atomic_set(&dmc->nr_jobs, 0);
+
+ return 0;
+}
+
+/*
+ * Construct a cache mapping
+ */
+static int cache_ctr(struct dm_target *ti, unsigned int argc, char **argv)
+{
+ struct cache_c *dmc;
+ unsigned int consecutive_blocks;
+ sector_t localsize, i, order;
+ int r = -EINVAL;
+
+ if (argc < 2) {
+ ti->error = "dm-cache: Needs at least 2 arguments";
+ goto bad;
+ }
+
+ dmc = kmalloc(sizeof(*dmc), GFP_KERNEL);
+ if (dmc == NULL) {
+ ti->error = "dm-cache: Cannot allocate cache context";
+ r = ENOMEM;
+ goto bad;
+ }
+
+ r = dm_get_device(ti, argv[0], 0, ti->len,
+ dm_table_get_mode(ti->table), &dmc->src_dev);
+ if (r) {
+ ti->error = "dm-cache: Device lookup failed";
+ goto bad1;
+ }
+
+ r = dm_get_device(ti, argv[1], 0, 0,
+ dm_table_get_mode(ti->table), &dmc->cache_dev);
+ if (r) {
+ ti->error = "dm-cache: Device lookup failed";
+ goto bad2;
+ }
+
+ r = kcopyd_client_create(DMCACHE_COPY_PAGES, &dmc->kcp_client);
+ if (r) {
+ DMERR("Failed to initialize kcopyd client\n");
+ goto bad3;
+ }
+
+ r = kcached_init(dmc);
+ if (r) {
+ ti->error = "Could not create kcached";
+ goto bad4;
+ }
+
+ if (argc >= 3) {
+ if (sscanf(argv[2], "%u", &dmc->block_size) != 1) {
+ ti->error = "dm-cache: Invalid block size";
+ r = -EINVAL;
+ goto bad4;
+ }
+ } else
+ dmc->block_size = DEFAULT_BLOCK_SIZE;
+ if (!dmc->block_size || (dmc->block_size & (dmc->block_size - 1))) {
+ ti->error = "dm-cache: Invalid block size";
+ r = -EINVAL;
+ goto bad4;
+ }
+ ti->split_io = dmc->block_size;
+ dmc->block_shift = ffs(dmc->block_size) - 1;
+ dmc->block_mask = dmc->block_size - 1;
+
+ if (argc >= 4) {
+ if (sscanf(argv[3], "%llu", &dmc->size) != 1 || !dmc->size) {
+ ti->error = "dm-cache: Invalid cache size";
+ r = -EINVAL;
+ goto bad4;
+ }
+ } else
+ dmc->size = DEFAULT_CACHE_SIZE;
+ localsize = dmc->size;
+ dmc->bits = 0;
+ while (localsize > 1) {
+ if (localsize % 2) {
+ ti->error =
+ "dm-cache: Cache size must be a power of 2\n";
+ r = -EINVAL;
+ goto bad4;
+ }
+ localsize >>= 1;
+ dmc->bits++;
+ }
+
+ if (argc >= 5) {
+ if (sscanf(argv[4], "%u", &dmc->assoc) != 1 || !dmc->assoc) {
+ ti->error = "dm-cache: Invalid cache associativity";
+ r = -EINVAL;
+ goto bad4;
+ }
+ } else
+ dmc->assoc = DEFAULT_CACHE_ASSOC;
+ if (!dmc->assoc || (dmc->assoc & (dmc->assoc - 1))
+ || dmc->size < dmc->assoc) {
+ ti->error = "dm-cache: Invalid cache associativity";
+ r = -EINVAL;
+ goto bad4;
+ }
+ if (dmc->size * dmc->block_size >
+ dmc->cache_dev->bdev->bd_disk->capacity) {
+ DMERR
+ ("Requested cache size exeeds the cache device's capacity (%llu*%i>%llu)",
+ dmc->size, dmc->block_size,
+ dmc->cache_dev->bdev->bd_disk->capacity);
+ ti->error = "dm-cache: Invalid cache size";
+ r = -EINVAL;
+ goto bad4;
+ }
+// consecutive_blocks = dmc->assoc > CONSECUTIVE_BLOCKS ? dmc->assoc : CONSECUTIVE_BLOCKS;
+ consecutive_blocks = dmc->assoc;
+ dmc->consecutive_shift = ffs(consecutive_blocks) - 1;
+
+ order = dmc->size * sizeof(struct cacheblock);
+ localsize = dmc->size * dmc->block_size >> 11;
+ DMINFO("Going to allocate %lluKB (%uB per) mem for %llu-entry cache "
+ "(capacity: %lluMB, associativity: %u, block size: %u sectors)",
+ order >> 10, sizeof(struct cacheblock *), dmc->size, localsize,
+ dmc->assoc, dmc->block_size);
+ dmc->cache = (struct cacheblock *)vmalloc(order);
+ if (!dmc->cache) {
+ ti->error = "Unable to allocate memory";
+ r = -ENOMEM;
+ goto bad4;
+ }
+
+ /* Initialize the cache */
+ for (i = 0; i < dmc->size; i++) {
+ bio_list_init(&dmc->cache[i].bios);
+ dmc->cache[i].state = 0;
+ dmc->cache[i].counter = 0;
+ dmc->cache[i].block = 0;
+ spin_lock_init(&dmc->cache[i].lock);
+ }
+
+ dmc->counter = 0;
+ dmc->write_policy = DEFAULT_WRITE_POLICY;
+ dmc->dirty_blocks = 0;
+ dmc->reads = 0;
+ dmc->writes = 0;
+ dmc->cache_hits = 0;
+ dmc->replace = 0;
+ dmc->writeback = 0;
+
+ ti->private = dmc;
+ return 0;
+
+ bad4:
+ kcopyd_client_destroy(dmc->kcp_client);
+ bad3:
+ dm_put_device(ti, dmc->cache_dev);
+ bad2:
+ dm_put_device(ti, dmc->src_dev);
+ bad1:
+ kfree(dmc);
+ bad:
+ return r;
+}
+
+/*
+ * Functions for writing back dirty blocks
+ */
+
+static void copy_callback(int read_err, unsigned int write_err, void *context)
+{
+ struct cacheblock *cacheblock = (struct cacheblock *)context;
+
+ flush_bios(cacheblock);
+}
+
+static void copy_block(struct cache_c *dmc, struct io_region src,
+ struct io_region dest, struct cacheblock *cacheblock)
+{
+ DPRINTK("Copying: %llu:%llu->%llu:%llu",
+ src.sector, src.count * 512, dest.sector, dest.count * 512);
+ kcopyd_copy(dmc->kcp_client,
+ &src, 1, &dest, 0, copy_callback, cacheblock);
+}
+
+static void write_back(struct cache_c *dmc, sector_t index, unsigned int length)
+{
+ struct io_region src, dest;
+ struct cacheblock *cacheblock = &dmc->cache[index];
+ unsigned int i;
+
+ DPRINTK("Write back block %llu(%llu, %u)",
+ index, cacheblock->block, length);
+ src.bdev = dmc->cache_dev->bdev;
+ src.sector = index << dmc->block_shift;
+ src.count = dmc->block_size * length;
+ dest.bdev = dmc->src_dev->bdev;
+ dest.sector = cacheblock->block;
+ dest.count = dmc->block_size * length;
+
+ for (i = 0; i < length; i++)
+ dmc->cache[index + i].state |= WRITEBACK;
+ dmc->dirty_blocks -= length;
+ copy_block(dmc, src, dest, cacheblock);
+}
+
+static void cache_flush(struct cache_c *dmc)
+{
+ struct cacheblock *cache = dmc->cache;
+ sector_t i = 0;
+ unsigned int j;
+
+ DPRINTK("Starts flushing dirty blocks (%llu)", dmc->dirty_blocks);
+ while (i < dmc->size) {
+// DPRINTK("%llu: %u %llu", i, cache[i].state, cache[i].block);
+ j = 1;
+ if (cache[i].state & DIRTY) {
+ while ((i + j) < dmc->size
+ && (cache[i + j].state & DIRTY)
+ && (cache[i + j].block ==
+ cache[i].block + j * dmc->block_size)) {
+// DPRINTK("%llu %u %llu", i+j, cache[i+j].state, cache[i+j].block);
+ j++;
+ }
+ write_back(dmc, i, j);
+ }
+ i += j;
+ }
+}
+
+void kcached_client_destroy(struct cache_c *dmc)
+{
+ /* Wait for completion of all jobs submitted by this client. */
+ wait_event(dmc->destroyq, !atomic_read(&dmc->nr_jobs));
+
+ dm_io_put(dmc->nr_pages);
+ free_bio_pages(dmc);
+}
+
+/*
+ * Destroy the cache mapping
+ * TODO: store meta data persistently
+ */
+static void cache_dtr(struct dm_target *ti)
+{
+ struct cache_c *dmc = (struct cache_c *)ti->private;
+
+ if (dmc->dirty_blocks > 0)
+ cache_flush(dmc);
+
+ kcached_client_destroy(dmc);
+
+ kcopyd_client_destroy(dmc->kcp_client);
+
+ if (dmc->reads + dmc->writes > 0)
+ DMINFO
+ ("dm-cache stats: reads (%lu), writes (%lu), cache hits (%lu, 0.%lu), "
+ "replacement (%lu), write-backs (%lu)", dmc->reads,
+ dmc->writes, dmc->cache_hits,
+ dmc->cache_hits * 100 / (dmc->reads + dmc->writes),
+ dmc->replace, dmc->writeback);
+
+ vfree((void *)dmc->cache);
+
+ dm_put_device(ti, dmc->src_dev);
+ dm_put_device(ti, dmc->cache_dev);
+ kfree(dmc);
+}
+
+/*
+ * Basic hash function for the cache to map a block offset in the device to a block offset in the cache
+ * TODO: Hash consecutive device blocks to consecutive cache blocks in order to improve performance
+ */
+static unsigned long hash_block(struct cache_c *dmc, sector_t block)
+{
+ unsigned long set_number, value;
+
+ value =
+ (unsigned long)(block >>
+ (dmc->block_shift + dmc->consecutive_shift));
+ if (DEFAULT_HASHFUNC == HASH)
+ set_number = hash_long(value, dmc->bits) / dmc->assoc;
+ else if (DEFAULT_HASHFUNC == UNIFORM)
+ set_number =
+ value &
+ ((unsigned long)(dmc->size >> dmc->consecutive_shift) - 1);
+ DPRINTK("Hash: %llu(%lu)->%lu", block, value, set_number);
+ return set_number;
+}
+
+/*
+ * Reset the LRU counters (the cache's global counter and each cache block's counter)
+ * (This seems to be a naive implementaion. However, consider the rareness of the reset,
+ * it might more efficient that other more complex schemes.)
+ */
+static void cache_reset_counter(struct cache_c *dmc)
+{
+ sector_t i;
+ struct cacheblock *cache = dmc->cache;
+
+ DPRINTK("Reset LRU counters");
+ for (i = 0; i < dmc->size; i++)
+ cache[i].counter = 0;
+
+ dmc->counter = 0;
+}
+
+/*
+ * Lookup a block in the cache
+ *
+ * Return value:
+ * 1: cache hit (the index of the matched block is stored in *cache_block)
+ * 0: cache miss but block allocated for insertion (the index of the allocated frame is stored in *cache_block)
+ * -1: cache miss and no room for insertion
+ *
+ */
+static int cache_lookup(struct cache_c *dmc, sector_t block,
+ sector_t * cache_block)
+{
+ unsigned long set_number = hash_block(dmc, block);
+ sector_t index;
+ int i, res;
+ unsigned int cache_assoc = dmc->assoc;
+ struct cacheblock *cache = dmc->cache;
+ int invalid = -1, oldest = -1, oldest_clean = -1;
+ unsigned long counter = ULONG_MAX, clean_counter = ULONG_MAX;
+// int j = 0; char *log = kmalloc(1000, GFP_KERNEL);
+
+ index = set_number * cache_assoc;
+ for (i = 0; i < cache_assoc; i++, index++) {
+ if (cache[index].state & VALID || cache[index].state & RESERVED) {
+// if (j <= 1000 - sizeof(cacheblock) && i<10)
+// j += sprintf(log + j, "%llu,%llu,%i,%lu; ",
+// index, cache[index].block, cache[index].state, cache[index].counter);
+ if (cache[index].block == block) {
+ *cache_block = index;
+ if (dmc->counter == ULONG_MAX)
+ cache_reset_counter(dmc);
+ cache[index].counter = ++dmc->counter;
+ break;
+ } else {
+ /* Don't consider blocks that are in the middle of copying */
+ if (!(cache[index].state & RESERVED)
+ && !(cache[index].state & WRITEBACK)) {
+ if (!(cache[index].state & DIRTY)
+ && cache[index].counter <
+ clean_counter) {
+ clean_counter =
+ cache[index].counter;
+ oldest_clean = i;
+ }
+ if (cache[index].counter < counter) {
+ counter = cache[index].counter;
+ oldest = i;
+ }
+ }
+ }
+ } else {
+ if (invalid == -1)
+ invalid = i;
+ }
+ }
+// if (j > 0) DPRINTK("%s", log);
+ res = i < cache_assoc ? 1 : 0;
+ if (!res) {
+ if (invalid != -1)
+ *cache_block = set_number * cache_assoc + invalid;
+ else if (oldest_clean != -1)
+ *cache_block = set_number * cache_assoc + oldest_clean;
+ else if (oldest != -1) {
+ res = 2;
+ *cache_block = set_number * cache_assoc + oldest;
+ } else {
+ res = -1;
+ }
+ }
+
+ if (-1 == res)
+ DPRINTK("Cache lookup: Block %llu(%lu):%s", block, set_number,
+ "NO ROOM");
+ else
+ DPRINTK("Cache lookup: Block %llu(%lu):%llu(%s)",
+ block, set_number, *cache_block,
+ 1 == res ? "HIT" : (0 == res ? "MISS" : "WB NEEDED"));
+// kfree(log);
+ return res;
+}
+
+/*
+ * Insert a block into the cache (in the frame specified by cache_block)
+ */
+static int cache_insert(struct cache_c *dmc, sector_t block,
+ sector_t cache_block)
+{
+ struct cacheblock *cache = dmc->cache;
+
+ /*
+ * Mark the block as RESERVED because although it is allocated, the data are not in place
+ * until kcopyd finishes its job.
+ */
+ cache[cache_block].block = block;
+ cache[cache_block].state = RESERVED;
+ if (dmc->counter == ULONG_MAX)
+ cache_reset_counter(dmc);
+ cache[cache_block].counter = ++dmc->counter;
+
+ return 1;
+}
+
+/*
+ * Invalidate a block (specified by cache_block) in the cache
+ */
+static void cache_invalidate(struct cache_c *dmc, sector_t cache_block)
+{
+ struct cacheblock *cache = dmc->cache;
+
+ DPRINTK("Cache invalidate: Block %llu(%llu)", cache_block,
+ cache[cache_block].block);
+ cache[cache_block].state &= ~VALID;
+}
+
+static int cache_hit(struct cache_c *dmc, struct bio *bio, sector_t cache_block)
+{
+ unsigned int offset = (unsigned int)(bio->bi_sector & dmc->block_mask);
+ struct cacheblock *cache = dmc->cache;
+
+ dmc->cache_hits++;
+
+ if (bio_data_dir(bio) == READ) { /* READ hit */
+ bio->bi_bdev = dmc->cache_dev->bdev;
+ bio->bi_sector = (cache_block << dmc->block_shift) + offset;
+
+ spin_lock(&cache[cache_block].lock);
+ if (cache[cache_block].state & VALID) { /* Cache block is valid */
+ spin_unlock(&cache[cache_block].lock);
+ return 1;
+ }
+ /* Cache block is not ready yet */
+ DPRINTK("Add to bio list %s(%llu)",
+ dmc->cache_dev->name, bio->bi_sector);
+ bio_list_add(&cache[cache_block].bios, bio);
+ spin_unlock(&cache[cache_block].lock);
+ return 0;
+ } else { /* WRITE hit */
+ if (dmc->write_policy == WRITE_THROUGH) {
+ cache_invalidate(dmc, cache_block);
+ bio->bi_bdev = dmc->src_dev->bdev;
+ return 1;
+ }
+
+ /* Write delay */
+ if (!(cache[cache_block].state & DIRTY)) {
+ cache[cache_block].state |= DIRTY;
+ dmc->dirty_blocks++;
+ }
+
+ spin_lock(&cache[cache_block].lock);
+ if (cache[cache_block].state & WRITEBACK) { /* In the middle of write back */
+ /* Delay this write until the block is written back */
+ bio->bi_bdev = dmc->src_dev->bdev;
+ DPRINTK("Add to bio list %s(%llu)",
+ dmc->src_dev->name, bio->bi_sector);
+ bio_list_add(&cache[cache_block].bios, bio);
+ spin_unlock(&cache[cache_block].lock);
+ return 0;
+ }
+ if (cache[cache_block].state & RESERVED) { /* Cache block not ready yet */
+ bio->bi_bdev = dmc->cache_dev->bdev;
+ bio->bi_sector =
+ (cache_block << dmc->block_shift) + offset;
+ DPRINTK("Add to bio list %s(%llu)",
+ dmc->cache_dev->name, bio->bi_sector);
+ bio_list_add(&cache[cache_block].bios, bio);
+ spin_unlock(&cache[cache_block].lock);
+ return 0;
+ }
+ bio->bi_bdev = dmc->cache_dev->bdev;
+ bio->bi_sector = (cache_block << dmc->block_shift) + offset;
+ spin_unlock(&cache[cache_block].lock);
+ return 1;
+ }
+}
+
+static struct kcached_job *new_kcached_job(struct cache_c *dmc, struct bio *bio,
+ sector_t request_block,
+ sector_t cache_block)
+{
+ struct io_region src, dest;
+ struct kcached_job *job;
+
+ src.bdev = dmc->src_dev->bdev;
+ src.sector = request_block;
+ src.count = dmc->block_size;
+ dest.bdev = dmc->cache_dev->bdev;
+ dest.sector = cache_block << dmc->block_shift;
+ dest.count = src.count;
+
+ job = mempool_alloc(_job_pool, GFP_NOIO);
+ job->dmc = dmc;
+ job->bio = bio;
+ job->src = src;
+ job->dest = dest;
+ job->cacheblock = &dmc->cache[cache_block];
+
+ return job;
+}
+
+static int cache_read_miss(struct cache_c *dmc, struct bio *bio,
+ sector_t cache_block)
+{
+ struct cacheblock *cache = dmc->cache;
+ unsigned int offset, head, tail;
+ struct kcached_job *job;
+ sector_t request_block;
+
+ offset = (unsigned int)(bio->bi_sector & dmc->block_mask);
+ request_block = bio->bi_sector - offset;
+
+ if (cache[cache_block].state & VALID) {
+ DPRINTK("Replacing %llu->%llu", cache[cache_block].block,
+ request_block);
+ dmc->replace++;
+ } else
+ DPRINTK("Insert block %llu at empty frame %llu",
+ request_block, cache_block);
+
+ cache_insert(dmc, request_block, cache_block);
+
+ job = new_kcached_job(dmc, bio, request_block, cache_block);
+
+ head = to_bytes(offset);
+ tail = to_bytes(dmc->block_size) - bio->bi_size - head;
+
+ /* Requested block is aligned with a cache block */
+ if (0 == head && 0 == tail)
+ job->nr_pages = 0;
+ else /* Need new pages to store extra data */
+ job->nr_pages =
+ dm_div_up(head, PAGE_SIZE) + dm_div_up(tail, PAGE_SIZE);
+ job->rw = READ;
+// DPRINTK("Queue job for %llu (need %u pages)", bio->bi_sector, job->nr_pages);
+ queue_job(job);
+ return 0;
+}
+
+static int cache_write_miss(struct cache_c *dmc, struct bio *bio,
+ sector_t cache_block)
+{
+ struct cacheblock *cache = dmc->cache;
+ unsigned int offset, head, tail;
+ struct kcached_job *job;
+ sector_t request_block;
+
+ if (dmc->write_policy == WRITE_THROUGH) {
+ bio->bi_bdev = dmc->src_dev->bdev;
+ return 1;
+ }
+
+ offset = (unsigned int)(bio->bi_sector & dmc->block_mask);
+ request_block = bio->bi_sector - offset;
+
+ /* Write delay */
+ cache_insert(dmc, request_block, cache_block);
+ cache[cache_block].state |= DIRTY;
+ dmc->dirty_blocks++;
+
+ if (cache[cache_block].state & VALID) {
+ DPRINTK("Replacing %llu->%llu", cache[cache_block].block,
+ request_block);
+ dmc->replace++;
+ } else
+ DPRINTK("Insert block %llu at empty frame %llu",
+ request_block, cache_block);
+
+ job = new_kcached_job(dmc, bio, request_block, cache_block);
+
+ head = to_bytes(offset);
+ tail = to_bytes(dmc->block_size) - bio->bi_size - head;
+
+ if (0 == head && 0 == tail) { /* Requested block is aligned with a cache block */
+ job->nr_pages = 0;
+ job->rw = WRITE;
+ } else if (head && tail) { /* Special case: need to pad both head and tail */
+ job->nr_pages = dm_div_up(to_bytes(dmc->block_size), PAGE_SIZE);
+ job->rw = READ;
+ } else {
+ if (head) {
+ job->src.count = to_sector(head);
+ job->nr_pages = dm_div_up(head, PAGE_SIZE);
+ } else {
+ job->src.sector =
+ bio->bi_sector + to_sector(bio->bi_size);
+ job->src.count = to_sector(tail);
+ job->nr_pages = dm_div_up(tail, PAGE_SIZE);
+ }
+ job->rw = READ;
+ }
+
+// DPRINTK("Queue job for %llu (need %u pages)", bio->bi_sector, job->nr_pages);
+ queue_job(job);
+
+ return 0;
+}
+
+static int cache_miss(struct cache_c *dmc, struct bio *bio,
+ sector_t cache_block)
+{
+ if (bio_data_dir(bio) == READ)
+ return cache_read_miss(dmc, bio, cache_block);
+ else
+ return cache_write_miss(dmc, bio, cache_block);
+}
+
+static int cache_map(struct dm_target *ti, struct bio *bio,
+ union map_info *map_context)
+{
+ struct cache_c *dmc = (struct cache_c *)ti->private;
+ sector_t request_block, cache_block = 0, offset;
+ int res;
+
+ offset = bio->bi_sector & dmc->block_mask;
+ request_block = bio->bi_sector - offset;
+ DPRINTK("Got a %s for %llu ((%llu:%llu), %u bytes)",
+ bio_rw(bio) == WRITE ? "WRITE" : (bio_rw(bio) ==
+ READ ? "READ" : "READA"),
+ bio->bi_sector, request_block, offset, bio->bi_size);
+
+ if (bio_data_dir(bio) == READ)
+ dmc->reads++;
+ else
+ dmc->writes++;
+
+ res = cache_lookup(dmc, request_block, &cache_block);
+ if (1 == res) /* Cache hit; server request from cache */
+ return cache_hit(dmc, bio, cache_block);
+ else if (0 == res) /* Cache miss; replacement block is found */
+ return cache_miss(dmc, bio, cache_block);
+ else if (2 == res) { /* Cache set is dirty; initiate a write-back */
+ write_back(dmc, cache_block, 1);
+ dmc->writeback++;
+ }
+
+ /* Forward to source device */
+ bio->bi_bdev = dmc->src_dev->bdev;
+
+ return 1;
+}
+
+/* TODO */
+static int cache_status(struct dm_target *ti, status_type_t type,
+ char *result, unsigned int maxlen)
+{
+// struct cache_c *dmc = (struct cache_c *) ti->private;
+
+ switch (type) {
+ case STATUSTYPE_INFO:
+ result[0] = '\0';
+ break;
+ case STATUSTYPE_TABLE:
+ break;
+ }
+ return 0;
+}
+
+static struct target_type cache_target = {
+ .name = "cache",
+ .version = {1, 0, 1},
+ .module = THIS_MODULE,
+ .ctr = cache_ctr,
+ .dtr = cache_dtr,
+ .map = cache_map,
+ .status = cache_status,
+};
+
+int __init dm_cache_init(void)
+{
+ int r;
+
+ r = jobs_init();
+ if (r)
+ return r;
+
+ _kcached_wq = create_singlethread_workqueue("kcached");
+ if (!_kcached_wq) {
+ DMERR("couldn't start kcached");
+ return -ENOMEM;
+ }
+ INIT_WORK(&_kcached_work, do_work, NULL);
+
+ r = dm_register_target(&cache_target);
+ if (r < 0) {
+ DMERR("cache: register failed %d", r);
+ destroy_workqueue(_kcached_wq);
+ }
+
+ return r;
+}
+
+void dm_cache_exit(void)
+{
+ int r = dm_unregister_target(&cache_target);
+
+ if (r < 0)
+ DMERR("cache: unregister failed %d", r);
+
+ jobs_exit();
+ destroy_workqueue(_kcached_wq);
+}
+
+module_init(dm_cache_init);
+module_exit(dm_cache_exit);
+
+MODULE_DESCRIPTION(DM_NAME " cache target");
+MODULE_AUTHOR("Ming Zhao");
+MODULE_LICENSE("GPL");
--
1.4.1
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