[Crash-utility] new printk ringbuffer interface

[John Ogness]

On 2020-04-23, HAGIO KAZUHITO(萩尾　一仁) <k-hagio-ab at nec.com> wrote:
>> Should all struct sizes and field offsets be exported? It
>> would look something like this:
>>
>>         VMCOREINFO_SYMBOL(prb);
>>
>>         VMCOREINFO_STRUCT_SIZE(printk_ringbuffer);
>>         VMCOREINFO_OFFSET(printk_ringbuffer, desc_ring);
>>         VMCOREINFO_OFFSET(printk_ringbuffer, text_data_ring);
>>         VMCOREINFO_OFFSET(printk_ringbuffer, dict_data_ring);
>>         VMCOREINFO_OFFSET(printk_ringbuffer, fail);
>>
>>         VMCOREINFO_STRUCT_SIZE(prb_desc_ring);
>>         VMCOREINFO_OFFSET(prb_desc_ring, count_bits);
>>         VMCOREINFO_OFFSET(prb_desc_ring, descs);
>>         VMCOREINFO_OFFSET(prb_desc_ring, head_id);
>>         VMCOREINFO_OFFSET(prb_desc_ring, tail_id);
>>
>>         VMCOREINFO_STRUCT_SIZE(prb_desc);
>>         VMCOREINFO_OFFSET(prb_desc, info);
>>         VMCOREINFO_OFFSET(prb_desc, state_var);
>>         VMCOREINFO_OFFSET(prb_desc, text_blk_lpos);
>>         VMCOREINFO_OFFSET(prb_desc, dict_blk_lpos);
>>
>>         VMCOREINFO_STRUCT_SIZE(prb_data_blk_lpos);
>>         VMCOREINFO_OFFSET(prb_data_blk_lpos, begin);
>>         VMCOREINFO_OFFSET(prb_data_blk_lpos, next);
>>
>>         VMCOREINFO_STRUCT_SIZE(printk_info);
>>         VMCOREINFO_OFFSET(printk_info, seq);
>>         VMCOREINFO_OFFSET(printk_info, ts_nsec);
>>         VMCOREINFO_OFFSET(printk_info, text_len);
>>         VMCOREINFO_OFFSET(printk_info, dict_len);
>>         VMCOREINFO_OFFSET(printk_info, caller_id);
>>
>>         VMCOREINFO_STRUCT_SIZE(prb_data_ring);
>>         VMCOREINFO_OFFSET(prb_data_ring, size_bits);
>>         VMCOREINFO_OFFSET(prb_data_ring, data);
>>         VMCOREINFO_OFFSET(prb_data_ring, head_id);
>>         VMCOREINFO_OFFSET(prb_data_ring, tail_id);
>
> If there is no efficient way, we will need all of the entries in
> VMCOREINFO.

It seems like a lot to export everything, but I don't have a problem
with it. If we decide to export everything (which I expect we will need
to do), then I would change my crash(8) implementation to also rely only
on the VMCOREINFO. I see no point in having some implementations using
debug data and other implementations using VMCOREINFO data, if
VMCOREINFO has everything that is needed.

John Ogness