[functional-tests] recode the block cache in C

functional-tests/bcache/bcache.c

@@ -0,0 +1,897 @@
+#define _GNU_SOURCE
+
+#include <assert.h>
+#include <errno.h>
+#include <fcntl.h>
+#include <sys/stat.h>
+#include <sys/types.h>
+#include <stdbool.h>
+#include <stdlib.h>
+#include <stdio.h>
+#include <stdint.h>
+#include <libaio.h>
+#include <unistd.h>
+#include <linux/fs.h>
+#include <sys/ioctl.h>
+
+#include "list.h"
+#include "bcache.h"
+
+//----------------------------------------------------------------
+
+static void warn(const char *msg)
+{
+	fprintf(stderr, "%s\n", msg);
+}
+
+// FIXME: raise a condition somehow?
+static void raise(const char *msg)
+{
+	warn(msg);
+	exit(1);
+}
+
+/*
+ * Assumes the list is not empty.
+ */
+static inline struct list_head *list_pop(struct list_head *head)
+{
+	struct list_head *l;
+
+	l = head->next;
+	list_del(l);
+	return l;
+}
+
+//----------------------------------------------------------------
+
+struct control_block {
+	struct list_head list;
+	void *context;
+	struct iocb cb;
+};
+
+struct cb_set {
+	struct list_head free;
+	struct list_head allocated;
+	struct control_block *vec;
+} control_block_set;
+
+static struct cb_set *cb_set_create(unsigned nr)
+{
+	int i;
+	struct cb_set *cbs = malloc(sizeof(*cbs));
+
+	if (!cbs)
+		return NULL;
+
+	cbs->vec = malloc(nr * sizeof(*cbs->vec));
+	if (!cbs->vec) {
+		free(cbs);
+		return NULL;
+	}
+
+	init_list_head(&cbs->free);
+	init_list_head(&cbs->allocated);
+
+	for (i = 0; i < nr; i++)
+		list_add(&cbs->vec[i].list, &cbs->free);
+
+	return cbs;
+}
+
+static void cb_set_destroy(struct cb_set *cbs)
+{
+	if (!list_empty(&cbs->allocated))
+		raise("async io still in flight");
+
+	free(cbs->vec);
+	free(cbs);
+}
+
+static struct control_block *cb_alloc(struct cb_set *cbs, void *context)
+{
+	struct control_block *cb;
+
+	if (list_empty(&cbs->free))
+		return NULL;
+
+	cb = container_of(list_pop(&cbs->free), struct control_block, list);
+	cb->context = context;
+	list_add(&cb->list, &cbs->allocated);
+
+	return cb;
+}
+
+static void cb_free(struct cb_set *cbs, struct control_block *cb)
+{
+	list_del(&cb->list);
+	list_add(&cb->list, &cbs->free);
+}
+
+static struct control_block *iocb_to_cb(struct iocb *icb)
+{
+	return container_of(icb, struct control_block, cb);
+}
+
+//----------------------------------------------------------------
+
+// FIXME: get from linux headers
+#define SECTOR_SHIFT 9
+#define PAGE_SIZE 4096
+
+enum dir {
+	DIR_READ,
+	DIR_WRITE
+};
+
+struct io_engine {
+	io_context_t aio_context;
+	struct cb_set *cbs;
+};
+
+static struct io_engine *engine_create(unsigned max_io)
+{
+	int r;
+	struct io_engine *e = malloc(sizeof(*e));
+
+	if (!e)
+		return NULL;
+
+	e->aio_context = 0;
+	r = io_setup(max_io, &e->aio_context);
+	if (r < 0) {
+		warn("io_setup failed");
+		return NULL;
+	}
+
+	e->cbs = cb_set_create(max_io);
+	if (!e->cbs) {
+		warn("couldn't create control block set");
+		free(e);
+		return NULL;
+	}
+
+	return e;
+}
+
+static void engine_destroy(struct io_engine *e)
+{
+	cb_set_destroy(e->cbs);
+	io_destroy(e->aio_context);
+	free(e);
+}
+
+static int engine_issue(struct io_engine *e, int fd, enum dir d,
+			sector_t sb, sector_t se, void *data, void *context)
+{
+	int r;
+	struct iocb *cb_array[1];
+	struct control_block *cb;
+
+	if (((uint64_t) data) & (PAGE_SIZE - 1))
+		return -1;
+
+	cb = cb_alloc(e->cbs, context);
+	if (!cb)
+		return false;
+
+	memset(&cb->cb, 0, sizeof(cb->cb));
+
+	cb->cb.aio_fildes = (int) fd;
+	cb->cb.u.c.buf = data;
+	cb->cb.u.c.offset = sb << SECTOR_SHIFT;
+	cb->cb.u.c.nbytes = (se - sb) << SECTOR_SHIFT;
+	cb->cb.aio_lio_opcode = (d == DIR_READ) ? IO_CMD_PREAD : IO_CMD_PWRITE;
+
+	cb_array[0] = &cb->cb;
+	r = io_submit(e->aio_context, 1, cb_array);
+	if (r < 0)
+		cb_free(e->cbs, cb);
+
+	return r;
+}
+
+#define MAX_IO 64
+typedef void complete_fn(void *context, int io_error);
+
+static int engine_wait(struct io_engine *e, struct timespec *ts, complete_fn fn)
+{
+	int i, r;
+	struct io_event event[MAX_IO];
+	struct control_block *cb;
+
+	memset(&event, 0, sizeof(event));
+	r = io_getevents(e->aio_context, 1, MAX_IO, event, ts);
+	if (r < 0) {
+		warn("io_getevents failed");
+		return r;
+	}
+
+	if (r == 0)
+		return 0;
+
+	for (i = 0; i < r; i++) {
+		struct io_event *ev = event + i;
+
+		cb = iocb_to_cb((struct iocb *) ev->obj);
+
+		if (ev->res == cb->cb.u.c.nbytes)
+			fn((void *) cb->context, 0);
+
+		else if ((int) ev->res < 0)
+			fn(cb->context, (int) ev->res);
+
+		else {
+			warn("short io");
+			fn(cb->context, -ENODATA);
+		}
+
+		cb_free(e->cbs, cb);
+	}
+
+	return -ENODATA;
+}
+
+//----------------------------------------------------------------
+#if 0
+struct timespec micro_to_ts(unsigned micro)
+{
+	struct timespec ts;
+	ts.tv_sec = micro / 1000000u;
+	ts.tv_nsec = (micro % 1000000) * 1000;
+	return ts;
+}
+
+static unsigned ts_to_micro(struct timespec const *ts)
+{
+	unsigned micro = ts->tv_sec * 1000000;
+	micro += ts->tv_nsec / 1000;
+	return micro;
+}
+#endif
+//----------------------------------------------------------------
+
+#define MIN_BLOCKS 16
+#define WRITEBACK_LOW_THRESHOLD_PERCENT 33
+#define WRITEBACK_HIGH_THRESHOLD_PERCENT 66
+
+//----------------------------------------------------------------
+
+static void *alloc_aligned(size_t len, size_t alignment)
+{
+	void *result = NULL;
+	int r = posix_memalign(&result, alignment, len);
+	if (r)
+		return NULL;
+
+	return result;
+}
+
+//----------------------------------------------------------------
+
+static bool test_flags(struct block *b, unsigned bits)
+{
+	return (b->flags & bits) != 0;
+}
+
+static void set_flags(struct block *b, unsigned bits)
+{
+	b->flags |= bits;
+}
+
+static void clear_flags(struct block *b, unsigned bits)
+{
+	b->flags &= ~bits;
+}
+
+//----------------------------------------------------------------
+
+enum block_flags {
+	BF_IO_PENDING = (1 << 0),
+	BF_DIRTY = (1 << 1),
+};
+
+struct bcache {
+	int fd;
+	sector_t block_sectors;
+	uint64_t nr_data_blocks;
+	uint64_t nr_cache_blocks;
+
+	struct io_engine *engine;
+
+	void *raw_data;
+	struct block *raw_blocks;
+
+	/*
+	 * Lists that categorise the blocks.
+	 */
+	unsigned nr_locked;
+	unsigned nr_dirty;
+	unsigned nr_io_pending;
+
+	struct list_head free;
+	struct list_head errored;
+	struct list_head dirty;
+	struct list_head clean;
+	struct list_head io_pending;
+
+	/*
+	 * Hash table.
+	 */
+	unsigned nr_buckets;
+	unsigned hash_mask;
+	struct list_head *buckets;
+
+	/*
+	 * Statistics
+	 */
+	unsigned read_hits;
+	unsigned read_misses;
+	unsigned write_zeroes;
+	unsigned write_hits;
+	unsigned write_misses;
+	unsigned prefetches;
+};
+
+//----------------------------------------------------------------
+
+/*  2^63 + 2^61 - 2^57 + 2^54 - 2^51 - 2^18 + 1 */
+#define GOLDEN_RATIO_PRIME_64 0x9e37fffffffc0001UL
+
+static unsigned hash(struct bcache *cache, uint64_t index)
+{
+	uint64_t h = index;
+	h *= GOLDEN_RATIO_PRIME_64;
+	return h & cache->hash_mask;
+}
+
+static struct block *hash_lookup(struct bcache *cache, uint64_t index)
+{
+	struct block *b;
+	unsigned h = hash(cache, index);
+
+	list_for_each_entry (b, cache->buckets + h, hash)
+		if (b->index == index)
+			return b;
+
+	return NULL;
+}
+
+static void hash_insert(struct block *b)
+{
+	unsigned h = hash(b->cache, b->index);
+	list_add(&b->hash, b->cache->buckets + h);
+}
+
+static void hash_remove(struct block *b)
+{
+	list_del(&b->hash);
+}
+
+/*
+ * Must return a power of 2.
+ */
+static unsigned calc_nr_buckets(unsigned nr_blocks)
+{
+	unsigned r = 8;
+	unsigned n = nr_blocks / 4;
+
+	if (n < 8)
+		n = 8;
+
+	while (r < n)
+		r <<= 1;
+
+	return r;
+}
+
+static int hash_table_init(struct bcache *cache, unsigned nr_entries)
+{
+	unsigned i;
+
+	cache->nr_buckets = calc_nr_buckets(nr_entries);
+	cache->hash_mask = cache->nr_buckets - 1;
+	cache->buckets = malloc(cache->nr_buckets * sizeof(*cache->buckets));
+	if (!cache->buckets)
+		return -ENOMEM;
+
+	for (i = 0; i < cache->nr_buckets; i++)
+		init_list_head(cache->buckets + i);
+
+	return 0;
+}
+
+static void hash_table_exit(struct bcache *cache)
+{
+	free(cache->buckets);
+}
+
+//----------------------------------------------------------------
+
+static int init_free_list(struct bcache *cache, unsigned count)
+{
+	unsigned i;
+	size_t block_size = cache->block_sectors << SECTOR_SHIFT;
+	unsigned char *data =
+		(unsigned char *) alloc_aligned(count * block_size, PAGE_SIZE);
+
+	/* Allocate the data for each block.  We page align the data. */
+	if (!data)
+		return -ENOMEM;
+
+	cache->raw_data = data;
+	cache->raw_blocks = malloc(count * sizeof(*cache->raw_blocks));
+
+	if (!cache->raw_blocks)
+		free(cache->raw_data);
+
+	for (i = 0; i < count; i++) {
+		struct block *b = cache->raw_blocks + i;
+		b->cache = cache;
+		b->data = data + (block_size * i);
+		list_add_tail(&b->list, &cache->free);
+	}
+
+	return 0;
+}
+
+static void exit_free_list(struct bcache *cache)
+{
+	free(cache->raw_data);
+	free(cache->raw_blocks);
+}
+
+static struct block *alloc_block(struct bcache *cache)
+{
+	struct block *b = container_of(list_pop(&cache->free), struct block, list);
+	return b;
+}
+
+/*----------------------------------------------------------------
+ * Clean/dirty list management.
+ * Always use these methods to ensure nr_dirty_ is correct.
+ *--------------------------------------------------------------*/
+
+static void unlink_block(struct block *b)
+{
+	if (test_flags(b, BF_DIRTY))
+		b->cache->nr_dirty--;
+
+	list_del(&b->list);
+}
+
+static void link_block(struct block *b)
+{
+	struct bcache *cache = b->cache;
+
+	if (test_flags(b, BF_DIRTY)) {
+		list_add_tail(&b->list, &cache->dirty);
+		cache->nr_dirty++;
+	} else
+		list_add_tail(&b->list, &cache->clean);
+}
+
+static void relink(struct block *b)
+{
+	unlink_block(b);
+	link_block(b);
+}
+
+/*----------------------------------------------------------------
+ * Low level IO handling
+ *
+ * We cannot have two concurrent writes on the same block.
+ * eg, background writeback, put with dirty, flush?
+ *
+ * To avoid this we introduce some restrictions:
+ *
+ * i)  A held block can never be written back.
+ * ii) You cannot get a block until writeback has completed.
+ *
+ *--------------------------------------------------------------*/
+
+/*
+ * |b->list| should be valid (either pointing to itself, on one of the other
+ * lists.
+ */
+static int issue_low_level(struct block *b, enum dir d)
+{
+	struct bcache *cache = b->cache;
+	sector_t sb = b->index * cache->block_sectors;
+	sector_t se = sb + cache->block_sectors;
+	set_flags(b, BF_IO_PENDING);
+
+	return engine_issue(cache->engine, cache->fd, d, sb, se, b->data, b);
+}
+
+static void issue_read(struct block *b)
+{
+	assert(!test_flags(b, BF_IO_PENDING));
+	issue_low_level(b, DIR_READ);
+}
+
+static void issue_write(struct block *b)
+{
+	assert(!test_flags(b, BF_IO_PENDING));
+	//b.v_->prepare(b.data_, b.index_);
+	issue_low_level(b, DIR_WRITE);
+}
+
+static void complete_io(void *context, int err)
+{
+	struct block *b = context;
+	struct bcache *cache = b->cache;
+
+	b->error = err;
+	clear_flags(b, BF_IO_PENDING);
+	cache->nr_io_pending--;
+
+	/*
+	 * b is on the io_pending list, so we don't want to use unlink_block.
+	 * Which would incorrectly adjust nr_dirty.
+	 */
+	list_del(&b->list);
+
+	if (b->error)
+		list_add_tail(&b->list, &cache->errored);
+
+	else {
+		clear_flags(b, BF_DIRTY);
+		link_block(b);
+	}
+}
+
+static int wait_io(struct bcache *cache)
+{
+	return engine_wait(cache->engine, NULL, complete_io);
+}
+
+/*----------------------------------------------------------------
+ * High level IO handling
+ *--------------------------------------------------------------*/
+
+static void wait_all(struct bcache *cache)
+{
+	while (!list_empty(&cache->io_pending))
+		wait_io(cache);
+}
+
+static void wait_specific(struct block *b)
+{
+	while (test_flags(b, BF_IO_PENDING))
+		wait_io(b->cache);
+}
+
+static unsigned writeback(struct bcache *cache, unsigned count)
+{
+	unsigned actual = 0;
+	struct block *b, *tmp;
+
+	list_for_each_entry_safe (b, tmp, &cache->dirty, list) {
+		if (actual == count)
+			break;
+
+		// We can't writeback anything that's still in use.
+		if (!b->ref_count) {
+			issue_write(b);
+			actual++;
+		}
+	}
+
+	return actual;
+}
+
+/*----------------------------------------------------------------
+ * High level allocation
+ *--------------------------------------------------------------*/
+
+static struct block *find_unused_clean_block(struct bcache *cache)
+{
+	struct block *b;
+
+	list_for_each_entry (b, &cache->clean, list) {
+		if (!b->ref_count) {
+			unlink_block(b);
+			hash_remove(b);
+			return b;
+		}
+	}
+
+	return NULL;
+}
+
+static struct block *new_block(struct bcache *cache, block_address index)
+{
+	struct block *b;
+
+	b = alloc_block(cache);
+	while (!b && cache->nr_locked < cache->nr_cache_blocks) {
+		b = find_unused_clean_block(cache);
+		if (!b) {
+			if (list_empty(&cache->io_pending))
+				writeback(cache, 16);
+			wait_io(cache);
+		}
+	}
+
+	if (b) {
+		init_list_head(&b->list);
+		init_list_head(&b->hash);
+		b->flags = 0;
+		b->index = index;
+		b->ref_count = 0;
+		b->error = 0;
+
+		hash_insert(b);
+	}
+
+	return b;
+}
+
+/*----------------------------------------------------------------
+ * Block reference counting
+ *--------------------------------------------------------------*/
+struct bcache *bcache_create(int fd, sector_t block_sectors, uint64_t on_disk_blocks,
+			     unsigned nr_cache_blocks)
+{
+	int r;
+	struct bcache *cache;
+
+	cache = malloc(sizeof(*cache));
+	if (!cache)
+		return NULL;
+
+	cache->fd = fd;
+	cache->block_sectors = block_sectors;
+	cache->nr_data_blocks = on_disk_blocks;
+	cache->nr_cache_blocks = nr_cache_blocks;
+
+	cache->engine = engine_create(nr_cache_blocks < 1024u ? nr_cache_blocks : 1024u);
+	if (!cache->engine) {
+		free(cache);
+		return NULL;
+	}
+
+	cache->nr_locked = 0;
+	cache->nr_dirty = 0;
+	cache->nr_io_pending = 0;
+
+	init_list_head(&cache->free);
+	init_list_head(&cache->errored);
+	init_list_head(&cache->dirty);
+	init_list_head(&cache->clean);
+	init_list_head(&cache->io_pending);
+
+	if (hash_table_init(cache, nr_cache_blocks)) {
+		engine_destroy(cache->engine);
+		free(cache);
+	}
+
+	cache->read_hits = 0;
+	cache->read_misses = 0;
+	cache->write_zeroes = 0;
+	cache->write_hits = 0;
+	cache->write_misses = 0;
+	cache->prefetches = 0;
+
+	r = init_free_list(cache, nr_cache_blocks);
+	if (r) {
+		engine_destroy(cache->engine);
+		hash_table_exit(cache);
+		free(cache);
+	}
+
+	return cache;
+}
+
+#define MD_BLOCK_SIZE 4096ull
+
+struct bcache *bcache_simple(const char *path, unsigned nr_cache_blocks)
+{
+	int r;
+	struct stat info;
+	struct bcache *cache;
+	int fd = open(path, O_DIRECT | O_EXCL | O_RDONLY);
+	uint64_t s;
+
+	if (fd < 0) {
+		raise("couldn't open cache file");
+		return NULL;
+	}
+
+	r = fstat(fd, &info);
+	if (r < 0) {
+		raise("couldn't stat cache file");
+		return NULL;
+	}
+
+	s = info.st_size;
+	cache = bcache_create(fd, MD_BLOCK_SIZE >> SECTOR_SHIFT, s / MD_BLOCK_SIZE, nr_cache_blocks);
+	if (!cache)
+		close(fd);
+
+	return cache;
+}
+
+void bcache_destroy(struct bcache *cache)
+{
+	if (cache->nr_locked)
+		warn("some blocks are still locked\n");
+
+	flush_cache(cache);
+	wait_all(cache);
+	exit_free_list(cache);
+	hash_table_exit(cache);
+	engine_destroy(cache->engine);
+	close(cache->fd);
+	free(cache);
+}
+
+// FIXME: we have to return an error code that can be turned into a Scheme
+// condition.
+static void check_index(struct bcache *cache, block_address index)
+{
+	if (index >= cache->nr_data_blocks)
+		raise("block out of bounds");
+}
+
+uint64_t get_nr_blocks(struct bcache *cache)
+{
+	return cache->nr_data_blocks;
+}
+
+uint64_t get_nr_locked(struct bcache *cache)
+{
+	return cache->nr_locked;
+}
+
+static void zero_block(struct block *b)
+{
+	b->cache->write_zeroes++;
+	memset(b->data, 0, b->cache->block_sectors << SECTOR_SHIFT);
+	set_flags(b, BF_DIRTY);
+}
+
+static void hit(struct block *b, unsigned flags)
+{
+	struct bcache *cache = b->cache;
+
+	if (flags & (GF_ZERO | GF_DIRTY))
+		cache->write_hits++;
+	else
+		cache->read_hits++;
+
+	relink(b);
+}
+
+static void miss(struct bcache *cache, unsigned flags)
+{
+	if (flags & (GF_ZERO | GF_DIRTY))
+		cache->write_misses++;
+	else
+		cache->read_misses++;
+}
+
+static struct block *lookup_or_read_block(struct bcache *cache,
+				  	  block_address index, unsigned flags)
+{
+	struct block *b = hash_lookup(cache, index);
+
+	if (b) {
+		// FIXME: this is insufficient.  We need to also catch a read
+		// lock of a write locked block.  Ref count needs to distinguish.
+		if (b->ref_count && (flags & (GF_DIRTY | GF_ZERO)))
+			raise("concurrent write lock attempt");
+
+		if (test_flags(b, BF_IO_PENDING)) {
+			miss(cache, flags);
+			wait_specific(b);
+
+		} else
+			hit(b, flags);
+
+		unlink_block(b);
+
+		if (flags & GF_ZERO)
+			zero_block(b);
+
+	} else {
+		miss(cache, flags);
+
+		b = new_block(cache, index);
+		if (b) {
+			if (flags & GF_ZERO)
+				zero_block(b);
+
+			else {
+				issue_read(b);
+				wait_specific(b);
+
+				// we know the block is clean and unerrored.
+				unlink_block(b);
+			}
+		}
+	}
+
+	if (b && !b->error) {
+		if (flags & (GF_DIRTY | GF_ZERO))
+			set_flags(b, BF_DIRTY);
+
+		link_block(b);
+		return b;
+	}
+
+	return NULL;
+}
+
+struct block *get_block(struct bcache *cache, block_address index, unsigned flags)
+{
+	check_index(cache, index);
+
+	struct block *b = lookup_or_read_block(cache, index, flags);
+	if (b) {
+		if (!b->ref_count)
+			cache->nr_locked++;
+		b->ref_count++;
+
+		return b;
+	}
+
+	raise("couldn't get block");
+	return NULL;
+}
+
+static void preemptive_writeback(struct bcache *cache)
+{
+	// FIXME: this ignores those blocks that are in the error state.  Track
+	// nr_clean instead?
+	unsigned nr_available = cache->nr_cache_blocks - (cache->nr_dirty - cache->nr_io_pending);
+	if (nr_available < (WRITEBACK_LOW_THRESHOLD_PERCENT * cache->nr_cache_blocks / 100))
+		writeback(cache, (WRITEBACK_HIGH_THRESHOLD_PERCENT * cache->nr_cache_blocks / 100) - nr_available);
+
+}
+
+void release_block(struct block *b)
+{
+	assert(b->ref_count);
+
+	b->ref_count--;
+	if (!b->ref_count)
+		b->cache->nr_locked--;
+
+	if (test_flags(b, BF_DIRTY))
+		preemptive_writeback(b->cache);
+}
+
+int flush_cache(struct bcache *cache)
+{
+	while (!list_empty(&cache->dirty)) {
+		struct block *b = container_of(list_pop(&cache->dirty), struct block, list);
+		if (b->ref_count || test_flags(b, BF_IO_PENDING))
+			// The superblock may well be still locked.
+			continue;
+
+		issue_write(b);
+	}
+
+	wait_all(cache);
+
+	return list_empty(&cache->errored) ? 0 : -EIO;
+}
+
+void prefetch_block(struct bcache *cache, block_address index)
+{
+	check_index(cache, index);
+	struct block *b = hash_lookup(cache, index);
+
+	if (!b) {
+		cache->prefetches++;
+
+		b = new_block(cache, index);
+		if (b)
+			issue_read(b);
+	}
+}
+
+//----------------------------------------------------------------

functional-tests/bcache/bcache.h

@@ -0,0 +1,69 @@
+#ifndef BCACHE_H
+#define BCACHE_H
+
+#include <stdint.h>
+
+/*----------------------------------------------------------------*/
+
+typedef uint64_t block_address;
+typedef uint64_t sector_t;
+
+struct block;
+struct bcache;
+
+// FIXME: allow the cache to be opened read only.
+struct bcache *bcache_create(int fd, sector_t block_size,
+			     uint64_t on_disk_blocks,
+			     unsigned nr_cache_blocks);
+
+/*
+ * A simpler way of creating a bcache that assumes 4k block size, and stats to
+ * get the file size.
+ */
+struct bcache *bcache_simple(const char *path, unsigned nr_cache_blocks);
+
+void bcache_destroy(struct bcache *cache);
+uint64_t get_nr_blocks(struct bcache *cache);
+uint64_t get_nr_locked(struct bcache *cache);
+
+int flush_cache(struct bcache *cache);
+
+struct bcache;
+
+struct block {
+	/* clients may only access these two fields */
+	void *data;
+	uint64_t index;
+
+	struct bcache *cache;
+	struct list_head list;
+	struct list_head hash;
+
+	unsigned flags;
+	unsigned ref_count;
+	int error;
+};
+
+enum get_flags {
+	/*
+	 * The block will be zeroed before get_block returns it.  This
+	 * potentially avoids a read if the block is not already in the cache.
+	 * GF_DIRTY is implicit.
+	 */
+	GF_ZERO = (1 << 0),
+
+	/*
+	 * Indicates the caller is intending to change the data in the block, a
+	 * writeback will occur after the block is released.
+	 */
+	GF_DIRTY = (1 << 1),
+};
+
+struct block *get_block(struct bcache *cache, block_address index, unsigned flags);
+void prefetch_block(struct bcache *cache, block_address index);
+
+void release_block(struct block *b);
+
+/*----------------------------------------------------------------*/
+
+#endif

functional-tests/bcache/list.h

@@ -0,0 +1,216 @@
+#ifndef LIB_BLOCK_CACHE_LIST_H
+#define LIB_BLOCK_CACHE_LIST_H
+
+#include <stddef.h>
+
+/*----------------------------------------------------------------*/
+
+/*
+ * Simple intrusive linked list code.  Lifted from Linux kernel.
+ */
+
+/**
+ * container_of - cast a member of a structure out to the containing structure
+ * @ptr:	the pointer to the member.
+ * @type:	the type of the container struct this is embedded in.
+ * @member:	the name of the member within the struct.
+ *
+ */
+#define container_of(ptr, type, member) ({			\
+	const typeof( ((type *)0)->member ) *__mptr = (ptr);	\
+	(type *)( (char *)__mptr - offsetof(type,member) );})
+
+struct list_head {
+	struct list_head *next, *prev;
+};
+
+static inline void init_list_head(struct list_head *list)
+{
+	list->next = list;
+	list->prev = list;
+}
+
+static inline void __list_add(struct list_head *new_,
+			      struct list_head *prev,
+			      struct list_head *next)
+{
+	next->prev = new_;
+	new_->next = next;
+	new_->prev = prev;
+	prev->next = new_;
+}
+
+/**
+ * list_add - add a new entry
+ * @new_: new entry to be added
+ * @head: list head to add it after
+ *
+ * Insert a new entry after the specified head.
+ * This is good for implementing stacks.
+ */
+static inline void list_add(struct list_head *new_, struct list_head *head)
+{
+	__list_add(new_, head, head->next);
+}
+
+
+/**
+ * list_add_tail - add a new entry
+ * @new_: new entry to be added
+ * @head: list head to add it before
+ *
+ * Insert a new entry before the specified head.
+ * This is useful for implementing queues.
+ */
+static inline void list_add_tail(struct list_head *new_, struct list_head *head)
+{
+	__list_add(new_, head->prev, head);
+}
+
+/*
+ * Delete a list entry by making the prev/next entries
+ * point to each other.
+ *
+ * This is only for internal list manipulation where we know
+ * the prev/next entries already!
+ */
+static inline void __list_del(struct list_head * prev, struct list_head * next)
+{
+	next->prev = prev;
+	prev->next = next;
+}
+
+/**
+ * list_del - deletes entry from list.
+ * @entry: the element to delete from the list.
+ * Note: list_empty() on entry does not return true after this, the entry is
+ * in an undefined state.
+ */
+static inline void __list_del_entry(struct list_head *entry)
+{
+	__list_del(entry->prev, entry->next);
+}
+
+static inline void list_del(struct list_head *entry)
+{
+	__list_del(entry->prev, entry->next);
+	entry->next = NULL;
+	entry->prev = NULL;
+}
+
+/**
+ * list_del_init - deletes entry from list and reinitialize it.
+ * @entry: the element to delete from the list.
+ */
+static inline void list_del_init(struct list_head *entry)
+{
+        __list_del_entry(entry);
+        init_list_head(entry);
+}
+
+/**
+ * list_move - delete from one list and add as another's head
+ * @list: the entry to move
+ * @head: the head that will precede our entry
+ */
+static inline void list_move(struct list_head *list, struct list_head *head)
+{
+	__list_del_entry(list);
+	list_add(list, head);
+}
+
+/**
+ * list_move_tail - delete from one list and add as another's tail
+ * @list: the entry to move
+ * @head: the head that will follow our entry
+ */
+static inline void list_move_tail(struct list_head *list,
+				  struct list_head *head)
+{
+	__list_del_entry(list);
+	list_add_tail(list, head);
+}
+
+/**
+ * list_empty - tests whether a list is empty
+ * @head: the list to test.
+ */
+static inline int list_empty(const struct list_head *head)
+{
+	return head->next == head;
+}
+
+/**
+ * list_entry - get the struct for this entry
+ * @ptr:	the &struct list_head pointer.
+ * @type:	the type of the struct this is embedded in.
+ * @member:	the name of the list_struct within the struct.
+ */
+#define list_entry(ptr, type, member) \
+	container_of(ptr, type, member)
+
+/**
+ * list_first_entry - get the first element from a list
+ * @ptr:	the list head to take the element from.
+ * @type:	the type of the struct this is embedded in.
+ * @member:	the name of the list_struct within the struct.
+ *
+ * Note, that list is expected to be not empty.
+ */
+#define list_first_entry(ptr, type, member) \
+	list_entry((ptr)->next, type, member)
+
+/**
+ * list_next_entry - get the next element in list
+ * @pos:	the type * to cursor
+ * @member:	the name of the list_struct within the struct.
+ */
+#define list_next_entry(pos, member) \
+	list_entry((pos)->member.next, typeof(*(pos)), member)
+
+/**
+ * list_for_each	-	iterate over a list
+ * @pos:	the &struct list_head to use as a loop cursor.
+ * @head:	the head for your list.
+ */
+#define list_for_each(pos, head) \
+	for (pos = (head)->next; pos != (head); pos = pos->next)
+
+/**
+ * list_for_each_safe - iterate over a list safe against removal of list entry
+ * @pos:	the &struct list_head to use as a loop cursor.
+ * @n:		another &struct list_head to use as temporary storage
+ * @head:	the head for your list.
+ */
+#define list_for_each_safe(pos, n, head) \
+	for (pos = (head)->next, n = pos->next; pos != (head); \
+		pos = n, n = pos->next)
+
+/**
+ * list_for_each_entry	-	iterate over list of given type
+ * @pos:	the type * to use as a loop cursor.
+ * @head:	the head for your list.
+ * @member:	the name of the list_struct within the struct.
+ */
+#define list_for_each_entry(pos, head, member)				\
+	for (pos = list_first_entry(head, typeof(*pos), member);	\
+	     &pos->member != (head);					\
+	     pos = list_next_entry(pos, member))
+
+/**
+ * list_for_each_entry_safe - iterate over list of given type safe against removal of list entry
+ * @pos:	the type * to use as a loop cursor.
+ * @n:		another type * to use as temporary storage
+ * @head:	the head for your list.
+ * @member:	the name of the list_struct within the struct.
+ */
+#define list_for_each_entry_safe(pos, n, head, member)			\
+	for (pos = list_first_entry(head, typeof(*pos), member),	\
+		n = list_next_entry(pos, member);			\
+	     &pos->member != (head); 					\
+	     pos = n, n = list_next_entry(n, member))
+
+
+/*----------------------------------------------------------------*/
+
+#endif