ceph關於multipart讀取資料的總結

通過計算rgwobjmanifest的obj_iterator中的各種偏移量來獲取下乙個multipart的location相關資訊，目的是通過location的object欄位來從ceph中按照長度讀取需要的obj

下面是乙個location的結構

location = else else {-----------------------------------------------當cur_stripe=0時，mannifest的location中object的組合以.cur_part_id_cur_stripe結尾

snprintf(buf, sizeof(buf), ".%d_%d", (int)cur_part_id, (int)cur_stripe);

oid += buf;

ns = shadow_ns;

正好反映了上述rados -p default.rgw.buckets.data ls的查詢結果。

讀取**功能在如下函式中，下面進行詳細分析：

int rgwrados::iterate_obj(rgwobjectctx& obj_ctx, rgw_obj& obj,

off_t ofs, off_t end,

uint64_t max_chunk_size,

int (*iterate_obj_cb)(rgw_obj&, off_t, off_t, off_t, bool, rgwobjstate *, void *),

void *arg)

if (astate->has_manifest) {

/* now get the relevant object stripe */

rgwobjmanifest::obj_iterator iter = astate->manifest.obj_find(ofs);

rgwobjmanifest::obj_iterator obj_end = astate->manifest.obj_end();

for (; iter != obj_end && ofs <= end; ++iter) {

off_t stripe_ofs = iter.get_stripe_ofs(); ---------------------------當前的切片偏移量，初值為0

off_t next_stripe_ofs = stripe_ofs + iter.get_stripe_size(); -----下乙個切片的偏移量，為退出while迴圈使用

while (ofs < next_stripe_ofs&& ofs <= end) {

read_obj = iter.get_location();--------------------- 返回location，其中包括的待讀取的object名字。

uint64_t read_len = min(len, iter.get_stripe_size() - (ofs - stripe_ofs));------------- 計算出了要讀取的長度。

read_ofs = iter.location_ofs() + (ofs - stripe_ofs);------------- 計算出了要讀取的起始偏移量。

if (read_len > max_chunk_size) {

read_len = max_chunk_size;

reading_from_head = (read_obj == obj);

r = iterate_obj_cb(read_obj, ofs, read_ofs, read_len, reading_from_head, astate, arg); ---- 開始讀取資料。

if (r < 0) {

return r;

len -= read_len;

ofs += read_len; ---- 累加讀取的長度