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[functional-tests] recode the block cache in C

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This commit is contained in:
Joe Thornber 2017-09-07 15:36:32 +01:00
parent c70aad52e6
commit 7825380ffe
3 changed files with 1182 additions and 0 deletions
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897
functional-tests/bcache/bcache.c Normal file
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#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);
}
}
//----------------------------------------------------------------

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#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

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#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