librbd调用流程--读流程

==[x]== 代表说明符号
==== 代表关系符号

open流程

参见:

tgt bs_rbd.c

static tgtadm_err bs_rbd_init(struct scsi_lu *lu, char *bsopts)
static int bs_rbd_open(struct scsi_lu *lu, char *path, int *fd, uint64_t *size)

rados_create()|Vrados_conf_parse_env()|Vrados_conf_read_file()|Vrados_connect(rbd->cluster)|Vrados_ioctx_create()//librados.cc|-->librados::RadosClient::create_ioctx()//RadosClient.cc ...|Vrbd_open()

读流程(simpleMessenger为例)

参见：

tgt bs_rbd.c

static void bs_rbd_request(struct scsi_cmd *cmd)
“`
rbd_read() //librbd/librbd.cc
|
–>ImageRequestWQ::read() //ImageRequestWQ.cc
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–>ImageRequestWQ::aio_read()
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–>queue(new ImageReadRequest<>)
||ImageRequest<>::aio_read()

处理线程调用处理函数
ImageRequestWQ::process(ImageRequest *req)
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–>ImageRequest::send()//ImageRequest.cc
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–>ImageRequest::clip_request()
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V
ImageReadRequest::send_request()//[1]
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–>Striper::file_to_extents()//[2] osdc/striper.cc 数据分片 及计算 oid
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V
ObjectReadRequest::send()//ObjectRequest.cc [3]
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–>librados::IoCtx::aio_operate()//librados.cc
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–>librados::IoCtxImpl::aio_operate()//IoCtxImpl.cc
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–>Objecter::op_submit()//osdc/objecter.cc
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–>Objecter::_op_submit_with_budget()
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–>Objecter::_op_submit()
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–>Objecter::_send_op()
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–>PipeConnection::send_message()
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–>SimpleMessenger::_send_message(Message*, Connection*)
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–>SimpleMessenger::submit_message()
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–>Pipe::_send()
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–>out_q[m->get_priority()].push_back(m)
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V
cond.Signal()

[1]
AioCompletion *aio_comp = this->m_aio_comp;
//这个aio_comp是rbd_read的AioCompletion 由于之后是做分片请求的
//所以之后的read会被stripper成多个请求，每个请求又有各自的AioCompletion
//那么就需要分片的AioCompletion得到数据最终都要汇聚到aio_comp来得到一个rbd_read的完整返回

    -------------> AioCompletion <-------    |            ^        |             |    |            |    [stripper]        |[callback]      [cb]      |           [cb]    |            |        |             |    |            |        V             |AioCompletion ...AioCompletion ...AioCompletion                    ...aio_comp->set_request_count(request_count);...  auto req_comp = new io::ReadResult::C_SparseReadRequest<I>(    aio_comp);  ObjectReadRequest<I> *req = ObjectReadRequest<I>::create(    &image_ctx, extent.oid.name, extent.objectno, extent.offset,    extent.length, extent.buffer_extents, snap_id, true, req_comp,    m_op_flags);  req_comp->request = req;//<1>

理解io::ReadResult::C_SparseReadRequest//ReadResult.h
struct C_SparseReadRequest : public C_SparseReadRequestBase {
ObjectReadRequest *request;//<1>

C_SparseReadRequest(AioCompletion *aio_completion)  : C_SparseReadRequestBase(aio_completion) {}void finish(int r) override {//最终调用  C_SparseReadRequestBase::finish(request->get_extent_map(),                                  request->get_buffer_extents(),                                  request->get_offset(),                                  request->get_length(), request->data()//osd返回的读数据,                                  r);}

};

[2]
librados::IoCtxImpl::aio_operate_read():

Context *oncomplete = new C_aio_Complete(c);
…
Objecter::Op *objecter_op = objecter->prepare_read_op(oid, oloc,
*o, snap_seq, pbl, flags,
oncomplete, &c->objver);
//objecter_op->onfinish = oncomplete;

[3]
librados::AioCompletion *rados_completion =
util::create_rados_callback(this);//this 即 ObjectReadRequest
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–>template
librados::AioCompletion *create_rados_callback(T *obj)//librbd/Utils.h
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–>librados::Rados::aio_create_completion(obj, &detail::rados_callback, nullptr)//detail::rados_callback[3.1]
[3.1]
//librbd/Utils.h
template
void rados_callback(rados_completion_t c, void *arg) {//arg = ObjectReadRequest
reinterpret_cast