dm_io_async_bvec（）函数分析(三)
；异步操作调用async_io。
sync_io()函数如下：
[cpp]
static int sync_io(struct dm_io_client *client, unsigned int num_regions,
struct dm_io_region *where, int rw, struct dpages *dp,
unsigned long *error_bits)
{
struct io io;//将dm_io_request请求进一步封装
if (num_regions > 1 && (rw & RW_MASK) != WRITE) {//dm_io不能读多个io_region
WARN_ON(1);
return -EIO;
}
retry:
io.error_bits = 0;
io.eopnotsupp_bits = 0;
atomic_set(&io.count, 1); /* see dispatch_io() */
io.sleeper = current;
io.client = client;
dispatch_io(rw, num_regions, where, dp, &io, 1);
while (1) {
set_current_state(TASK_UNINTERRUPTIBLE);
if (!atomic_read(&io.count))
break;
io_schedule();
}
set_current_state(TASK_RUNNING);
if (io.eopnotsupp_bits && (rw & (1 << BIO_RW_BARRIER))) {
rw &= ~(1 << BIO_RW_BARRIER);
goto retry;
}
if (error_bits)
*error_bits = io.error_bits;
return io.error_bits -EIO : 0;
}
async_io()函数如下：
[cpp]
static int async_io(struct dm_io_client *client, unsigned int num_regions,
struct dm_io_region *where, int rw, struct dpages *dp,
io_notify_fn fn, void *context)
{
struct io *io;//之所以加入struct io，是为了将上面的dm_io_request重新封装，加入线程，以便io分发和处理
if (num_regions > 1 && (rw & RW_MASK) != WRITE) {//Dm-io can read from one io_region or write to one or more io_regions. Writes to multiple regions are specified by an array of io_region structures,dm_io不能读多个io_region
WARN_ON(1);
fn(1, context);
return -EIO;
}
io = mempool_alloc(client->pool, GFP_NOIO);
io->error_bits = 0;
io->eopnotsupp_bits = 0;
atomic_set(&io->count, 1); /* see dispatch_io() */
io->sleeper = NULL;
io->client = client;
io->callback = fn;
io->context = context;
dispatch_io(rw, num_regions, where, dp, io, 0);
return 0;
}