Thanks for your reply.
uint32_t get_data_offset() {
return data.largest_data_off_in_tbl +
sizeof(__u8) + // encode struct_v
sizeof(__u8) + // encode compat_v
sizeof(__u32) + // encode len
sizeof(__u32); // data_bl len
}
1+1+4+4 = 10, mean that largest_data_off_in_tbl + 10
oid write(const coll_t& cid, const ghobject_t& oid, uint64_t off, uint64_t len,
> const bufferlist& write_data, uint32_t flags = 0) {
......
> assert(len == write_data.length());
> data.fadvise_flags = data.fadvise_flags | flags;
> if (write_data.length() > data.largest_data_len) {
> data.largest_data_len = write_data.length();
> data.largest_data_off = off;
> data.largest_data_off_in_data_bl = orig_len + sizeof(__u32); // we are about to
> }
> data.ops++;
> }
Mean that largest_data_off_in_tbl +10 +4
using debug info , I find that encoded buffer list , has 14 bytes before data. So I think "+10 +4" for encode.
I think data.largest_data_off_in_tbl has recorded data_bl_len using " sizeof(__u32); // data_bl len " ,
what's the diff between " data_bl len " and " orig_len + sizeof(__u32);"?
-----邮件原件-----
发件人: Gregory Farnum [mailto:gfarnum@xxxxxxxxxx]
发送时间: 2017年11月19日 18:34
收件人: liuhao 13701
抄送: ceph-devel
主题: Re: about memory alignment
On Tue, Nov 14, 2017 at 12:12 AM Liuhao <liu.haoA@xxxxxxx> wrote:
>
> HI, developers:
>
> data.largest_data_off_in_data_bl = orig_len + sizeof(__u32); // we
> are about to What 's mean of sizeof(__u32)? Why add sizeof(__u32)?
We're recording here the total size of the buffer used to transmit the data. Since the buffer includes a prefix of its own length, and that prefix is a __u32, we add that to the actual data size.
-Greg
>
>
> Detail:
> oid write(const coll_t& cid, const ghobject_t& oid, uint64_t off, uint64_t len,
> const bufferlist& write_data, uint32_t flags = 0) {
> uint32_t orig_len = data_bl.length();
> Op* _op = _get_next_op();
> _op->op = OP_WRITE;
> _op->cid = _get_coll_id(cid);
> _op->oid = _get_object_id(oid);
> _op->off = off;
> _op->len = len;
> ::encode(write_data, data_bl);
>
> assert(len == write_data.length());
> data.fadvise_flags = data.fadvise_flags | flags;
> if (write_data.length() > data.largest_data_len) {
> data.largest_data_len = write_data.length();
> data.largest_data_off = off;
> data.largest_data_off_in_data_bl = orig_len + sizeof(__u32); // we are about to
> }
> data.ops++;
> }
>
> Thanks
> --
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